The best indicator of cardiorespiratory or aerobic fitness is

Abstract

Cardiorespiratory fitness (CRF) refers to the capacity of the circulatory and respiratory systems to supply oxygen to skeletal muscle mitochondria for energy production needed during physical activity. CRF is an important marker of physical and mental health and academic achievement in youth. However, only 40% of US youth are currently believed to have healthy CRF. In this statement, we review the physiological principles that determine CRF, the tools that are available to assess CRF, the modifiable and nonmodifiable factors influencing CRF, the association of CRF with markers of health in otherwise healthy youth, and the temporal trends in CRF both in the United States and internationally. Development of a cost-effective CRF measurement process that could readily be incorporated into office visits and in field settings to screen all youth periodically could help identify those at increased risk.

Cardiorespiratory fitness (CRF) refers to the capacity of the circulatory and respiratory systems to supply oxygen to skeletal muscle mitochondria for energy production needed during physical activity.1,2 Low or unhealthy CRF is a strong, independent predictor of cardiovascular disease (CVD) and all-cause mortality in adults.1 In youth, CRF is a predictor of a number of health indicators, including cardiometabolic health,3,4 premature CVD,5 academic achievement,6 and mental health.4,7 Unfortunately, only 40% of 12- to 15-year-olds in United States currently are believed to have healthy CRF.8 In addition, over the past 6 decades, CRF has declined, both in the United States and internationally.9–11 Although the reasons for this decline are not well understood, an increase in obesity, increased sedentary time, decreased levels of moderate to vigorous physical activity, and social and economic changes may have contributed.9,11

Although CRF is assessed at times in certain youth such as those with congenital heart disease, asthma, and cystic fibrosis, assessment of CRF has a broader range of applications. CRF is an objective measure of health that can be tracked over time and compared across populations.1,9 Whereas self-reported physical activity levels can be unreliable12 and provide only a snapshot of behavior, assessments of CRF provide a more robust measure of cardiovascular health. Consistent with this sentiment, a recent American Heart Association statement suggests that CRF be assigned as a vital sign because it has the power to predict mortality in adults similar to traditionally assessed risk factors such as tobacco use, type 2 diabetes mellitus, hypertension, and hypercholesterolemia.1

The central focus of this statement is to raise clinicians’ awareness of the importance of CRF in predicting current and future health in otherwise healthy youth, knowing that CRF measurements provide an objective measure of health as opposed to physical activity recall, which is the current practice. An explicit purpose of this statement is to explore valid, low-cost alternatives to traditional cardiopulmonary exercise tests (CPETs) to assess CRF in otherwise healthy youth in office settings with limited space that can be performed by personnel not formally trained in exercise physiology. This statement reviews current knowledge related to the association between CRF and health outcomes in youth, describes the added value of CRF to improve risk prediction, and highlights gaps for future research with the following areas addressed:

1. Physiological considerations

2. Various tests that can be used to assess CRF in the field and office settings

3. Key modifiable and nonmodifiable factors influencing CRF, including the effect of interventions

4. The impact of CRF on cardiovascular, cerebrovascular, cognitive, and mental health

5. Temporal trends in CRF in youth nationally and internationally

6. Knowledge gaps and suggestions for future research

This statement does not discuss special risk groups of youth such as those with unpalliated/palliated congenital heart disease.13 Physical activity guidelines for youth are covered in detail in other documents14; discussion of these guidelines is limited. The focus of this statement is primarily to examine CRF in otherwise able and healthy, disease-free youth.

Health-Related Fitness and Associated Physiological Changes

Although this statement focuses on CRF, this is only 1 of 4 distinct health-related fitness components. CRF, also known as cardiorespiratory endurance, cardiovascular fitness, aerobic capacity, and aerobic fitness, among others, refers to the capacity of the circulatory and respiratory systems to supply oxygen to skeletal muscle mitochondria for energy production during physical activity.15 A second component, muscular fitness, is the ability of the body to exert maximal force against an external resistance (ie, muscular strength) or repeatedly under submaximal loads (ie, local muscular endurance). Third, flexibility refers to an individual’s range of motion around a joint or group of joints. Flexibility is important for preventing musculoskeletal injury, maintaining functional independence, and performing sports and activities of daily living. The fourth component, body composition, is the relative proportion of total body mass composed of fat, fat-free tissue, and total body water.

Table 1 includes a summary of physical activity intensity categories for youth 8 to 18 years of age that are based on heart rate, maximum oxygen uptake, perceived exertion, and metabolic equivalent (MET).20–23 Energy expenditure often is quantified as METs, with 1 MET equal to 3.5 mL O2·kg−1·min−1 (oxygen consumed).22 Energy expenditure ranges from low levels used during sedentary activities (1–2 METs) to the considerable levels required during sprint interval training (9–20 METs).22 Compared with adults, energy expended is typically higher in youth, leading to an underestimation of energy expenditure if adult reference values are used. Therefore, Table 1 includes age- and sex-appropriate MET values associated with activity of varying intensity.20–23

Intensity Category	Description	Example Activities	Measures (mean values for 8–18 y of age)
Sedentary	Waking behavior typically performed in a sitting, reclining, or lying posture	Sitting or reclining while watching television, playing video games, driving, reading, and fishing	<1.5 METs <40% HRmax<20% HRR <20% max RPE: <8
Light	Light aerobic activity that does not cause a noticeable increase in breathing and can be sustained for at least 60 min	Domestic or occupational tasks such as washing dishes, ironing, working at a desk, or performing office duties	1.5–4 METs 40%–63% HRmax20%–39% HRR 20%–45% max RPE: 8–11
Moderate	Aerobic activity that can be sustained while maintaining a conversation uninterrupted	Gentle swimming, social tennis, and golf	4–6 METs 64%–76% HRmax40%–59% HRR 46%–63% max RPE: 12–13
Vigorous	Aerobic activity during which a conversation cannot be maintained; an intensity that may last up to 30 min	Jogging, aerobics, fast bicycling, resistance training, competitive sports	6–9 METs 77%–95% HRmax60%–89% HRR 64%–90% max RPE: 14–17
Near maximal to maximal	Activity that typically cannot be sustained for >10 min	Sprinting, periods of competitive team sport activity	≥ 9 METs ≥ 96% HRmax≥ 90% HRR ≥ 91% max RPE: ≥18

Physiological Changes

Exercise-induced improvements in CRF may be explained by structural and functional adaptations leading to a better oxygen transport system24 such as increased blood volume, myocardial contractility, ventricular compliance, and angiogenesis,25 all of which lead to an increased cardiac output.26,27 This was illustrated by Rowland and colleagues,27 who found that the cardiac index (cardiac output divided by body surface area) was significantly greater in trained youth cyclists compared with their nontrained peers. On the other hand, there appears to be little difference in maximal oxygen extraction between trained and untrained youth,28,29 and findings have been equivocal as to whether exercise-induced improvements in stroke volume result from increases in cardiac dimensions.30

Although the two are often conflated, physical activity and CRF are distinct but related concepts. Physical activity is voluntary movement produced by skeletal muscles that results in energy expenditure.2 Exercise and training refer to a subset of physical activity in which the goal is to improve performance, health, or both.2 CRF can reflect an individual’s past physical activity and reflect the ability to be physically active (an individual with greater CRF has more capacity for aerobic physical activity), forming a virtuous cycle of an active-fit lifestyle. Thus, physical activity is a behavior (will do), whereas CRF represents an individual’s capacity (can do) to perform certain types of aerobic physical activity.

Key Points

1. Exercise-induced improvements in CRF are caused by structural and functional adaptations in the oxygen transport system.

2. Physical activity, exercise, and CRF are associated but distinct concepts.

How to Measure CRF in Youth

CRF can be measured or estimated with a variety of tests and protocols. The tests used to measure CRF that require maximal effort are referred to as maximal exercise tests. Maximal exercise tests often but not always are performed in the office setting and usually measure cardiometabolic parameters such as inspiratory and expiratory gases, blood pressure, heart rate, and the electric activity of the heart. Tests that do not require maximal effort are referred to as submaximal exercise tests. Submaximal exercise tests often estimate CRF with the use of equations or nomograms that have been validated against CRF measurements obtained directly during a maximal exercise test. Submaximal tests can be used when a maximal test cannot be performed for safety, setting, or cost reasons. Although submaximal tests are easier to perform, there are often large measurement errors; thus, estimated CRF comparisons are fraught with inaccuracies. However, these tests may be useful for identifying and following up those with low/unhealthy CRF. Table 2 summarizes key information on some of the commonly used tests to measure or estimate CRF.

	Description	Ability to Assess CRF†	Limitations	Suggestions for Clinical Practice
CPET (gas analyzed)	Participants exercise with incrementally increasing difficulty/workload with measured via respiratory gases	+++	Sophisticated equipment needed	Gold standard for measurement of
20mSRT (not gas analysed; field based)	Participants run/walk between 2 points on a floor in sync with audio signals with incrementally increasing frequency	++	Need 20 m of open space	Modified protocols are available for office populations
Run tests (eg, 1.5 miles/2400 m; field based)	Participants run a given distance as quickly as possible	++	Dependent on motivation and body size	Often used in school settings
Step test (office or field based)	Participants step up and down on a block of a given height; each stage is associated with an increased step rate	+	Validity not well established	Portable; test can be performed in small spaces
Walk tests (office based; eg, 6MWT)	Participants instructed to walk as far as possible in 6 min	+/−	Poor validity in healthy populations	Useful for populations with low exercise capacity
Questionnaires	Questionnaire to assess fitness level	+/−	Large error in estimation of	Used mainly for population research

The measurement and reporting of CRF depend on various factors: the test used and its protocol, whether CRF is measured or estimated, whether CRF measures are reported as absolute values versus indexed to body size, and participant motivation.31 The reader is referred to CRF normative measures that are test and protocol specific.32–34

For each test described below, it is assumed that participants are able-bodied youth without impairment and that maximal effort is given. Although modifications can certainly be made for many of these tests for youth with physical or cognitive impairments, we do not discuss them in that context because the primary purpose of this statement is to address CRF in healthy youth.

Table 3 lists terms commonly used to describe CRF measures.

Term	Unit
peak (peak oxygen uptake)	L/min
max (maximal oxygen uptake)	L/min
peak (scaled to body weight)	mL·kg−1·min−1
max (scaled to body weight)	mL·kg−1·min−1
No. of 20mSRT laps or stages completed	n
Work	W (absolute or scaled)

Gas-Analyzed Tests

Graded CPETs

According to the Fick principle, oxygen uptake (

The highest oxygen uptake attained during graded exercise to volitional exhaustion (

Reporting norms for

Although CPETs provide a wealth of data, clinicians should be aware of limitations, including the limited ability to perform this test in settings other than the office or hospital. The test requires expensive equipment and well-trained staff, which are not always available. The metabolic cart requires meticulous maintenance and calibration. Another limitation is that most CPET parameters are measured breath by breath, with a range of options to analyze the data and to filter the noise in the data. This can introduce differences between laboratories and equipment, which makes comparisons among participants and studies difficult. Finally, the pattern of activity performed during the CPET may not reflect the types of physical activities in which youth are commonly engaged.

Non–Gas-Analyzed Tests

Field-Based Tests

The 20-m Shuttle Run Test

For the reasons stated above, alternative tests for measuring CRF in youth have been developed.42,43 One such test is the 20-m shuttle run test (20mSRT) developed by Léger et al.44,45 The 20mSRT and its variants are now the most widely used tests to estimate CRF in youth in the world.46

Several different names are used for the 20mSRT: beep test, progressive aerobic cardiovascular endurance run test, and multistage fitness test. However, the protocols are very similar. Typically, youth are instructed to run at an increasing standardized pace (starting at ≈5 mph [8 km/h], increasing in 0.3-mph [0.5-km/h] increments each minute), noting the number of laps or stages during which they can keep up with the pace, which can then be compared with results from a reference population.9

The 20mSRT has been studied in both sexes and in a range of ethnicities and ages.32,47 According to a systematic review, the 20mSRT is a valid estimate of CRF compared with CPET-measured CRF.48 In this review of 73 studies addressing the criterion-related validity of field-based fitness tests in children and adolescents, there was strong evidence that the 20mSRT had moderate to high validity against CPETs to estimate CRF. Because the 20mSRT can be administered in group settings such as schools, it is efficient for testing large cohorts of youth simultaneously and thus is feasible for population-based CRF surveillance. However, as is true for all CRF tests, it is influenced by motivation and performance. If estimated

In the United States, the 20mSRT is commonly used as a component in the FITNESSGRAM.16 The FITNESSGRAM is a group of tests used to assess various forms of fitness in school-aged youth. In addition to the 20mSRT, the FITNESSGRAM measures body mass index (BMI), abdominal strength, trunk extensor strength, upper-body strength, and flexibility. The results are classified into various fitness zones.16 All 50 states in the United States currently use the FITNESSGRAM to assess >22 million students each year.34

Run Tests

In run tests, the participant is given a set distance (eg, 1.5 miles or 2400 m) or time (eg, 12 minutes) and instructed to complete the run in as short an amount of time as possible or to cover the greatest possible distance, respectively. Mayorga-Vega et al50 recently performed a meta-analysis to determine which distance or time was most appropriate to use in youth. Of the various distances and times used, they found that the highest correlation to CPET-measured

Office-Based Tests

The text below describes some of the commonly used tests that are suitable for use in office settings, but this list is by no means exhaustive.

Ebbeling Test (Single-Stage Treadmill Walking Test)

This test is performed on a treadmill with a 5% graded incline. Heart rate is measured after 4 minutes and is combined with speed, age, and sex to estimate CRF.51 Nemeth et al52 evaluated the Ebbeling test in 130 youth 11 to 14 years of age who were overweight and concluded that the CRF estimate was within 10% of the

Åstrand-Rhyming Test

This test is performed with a cycle ergometer and is often used in Europe. This test is typically performed over 6 minutes with a constant load (or single stage) aimed at producing a heart rate between 125 and 170 bpm. The heart rate and workload are used to estimate

Physical Work Capacity Corresponding to a Heart Rate of 170 bpm

This test has been used since the 1960s. It is administered with a cycle ergometer and typically conducted with three 3-minute stages or three 4-minute stages of increasing workload. Work (Watts) is measured once the heart rate reaches 170 bpm. This capacity test was moderately well correlated with measured

6-Minute Walk Test

This is the most commonly administered walk test and measures the distance walked in 6 minutes.56 The 6-minute walk test is easy to administer, and international guidelines have been established,57,58 along with test-specific reference standards.59 However, the 6-minute walk test is less useful in healthy youth to estimate CRF. The 6-minute walk test shows a relatively poor correlation with

Step Tests (Queen’s College or Harvard Step Tests)

Step tests are another category of tests that use stepping up on and down from a bench in an effort to engage larger muscle mass. One of the first such protocols described in children (Harvard Step Test) involved stepping up on a 12-in bench at a rate of 24 steps per minute for a duration of 3 minutes with heart rates collected after exercise.62 Recently, Hayes et al63 reported the validity of a step test in elementary school children and showed that the step test, along with sex and BMI, significantly predicted

Questionnaires

Some youth are unable to complete fitness testing for various reasons (body size, maturity limitations, etc), so methods to estimate CRF without objective testing have been evaluated. Questionnaires may offer the least burdensome method for examining CRF in youth. However, questionnaires are currently used for epidemiological studies, not for estimating CRF in individuals.

The International Fitness Scale (IFIS) is 1 option.65,66 It consists of 5 questions that use a 5-point Likert scale on general physical fitness, CRF, muscular strength, speed/agility, and flexibility. The IFIS is designed to measure CRF in populations and can be completed in ≈5 minutes. Ortega et al65 reported that in 3059 youth 12 to 18 years of age, the IFIS was linearly related to CRF (milliliters per kilogram per minute) as estimated by the 20mSRT with an odds for having a healthy CRF based on FITNESSGRAM thresholds of 7.3 (95% CI, 4.0–13.5) for those reporting very good CRF on the IFIS questionnaire. However, its usefulness at the individual level is not established.65 It should also be noted that the correlation between the IFIS and FITNESSGRAM compares surrogates with surrogates and does not use measured

Key Points

1. The most accurate measure of CRF in youth is gas-analyzed (measured)

   
   peak obtained during a graded CPET, but this testing cannot be universally performed.

2. Graded tests such as the 20mSRT provide the best alternative to CPET in a field setting.

3. Step tests may be a good alternative to CPET when space and resources are limited.

4. In general, tests that require more effort are preferred to tests that primarily measure function such as walk tests.

5. Estimated

   
   peak can be misleading and needs to be reconciled with other factors such as the protocol and testing used and participant motivation/effort.

6. Questionnaires may provide insightful information for epidemiological purposes but are considered the least accurate method for assessing CRF.

Factors Affecting CRF in Youth

Studies have investigated the relationship between CRF and various nonmodifiable and modifiable factors, including genetics,67 age, sex,68 race/ethnicity,69 physical activity and dietary patterns,70,71 obesity,72,73 sedentary time,74 built environment,75 and socioeconomics.76,77 These topics are discussed below.

Nonmodifiable

Genetics

In adults, it has been noted that an individual’s response to physical training varies widely, with some people markedly increasing their CRF (responders) and some having only a minimal increase in CRF (nonresponders).78,79 One study suggested that nearly 50% of an individual’s response to training is inherited.67,80 Furthermore, the variance in response to aerobic training was 2.5 times higher between families than within families.80 However, none of the nearly 300 000 single nucleotide polymorphisms studied have been found to be associated with exercise-induced changes in

Age and Sex

As youth age, there is an increase in CRF as measured by

Race/Ethnicity

In adults,

Prematurity

Using data from Northern Ireland Young Hearts Study, investigators found that compared with those born at full term, those born even slightly early, between 37 and 38 weeks’ gestation, had a 57% higher risk of having low CRF (milliliters per kilogram per minute) at 12, 15, and 22 years of age.95 These effects were not related to decreased physical activity.95,96 In a meta-analysis, participants born prematurely had ≈13% lower CRF than those born at term.97 The mechanism is not clear but may be related to smaller lung volumes.

Modifiable

Habitual Physical Activity and Exercise Training

It is generally assumed that physically active youth have higher CRF. However, the strength of the association between habitual physical activity and CRF in youth is small to moderate,98 with most of the benefits accruing only with sustained vigorous physical activity.98–100 A number of factors may explain the lack of a strong association between physical activity and CRF in youth. First, CRF has an incompletely defined but clear hereditary component. Second, habitual physical activity levels in youth rarely achieve the vigorous intensity or duration necessary to improve CRF. Finally, challenges in the accurate assessment of both physical activity and CRF may mask the relationship.

Using an objective measure of physical activity, Gutin et al101 found that CRF (milliliters per kilogram per minute) in youth had a stronger relationship with the time spent in vigorous physical activity than with the time spent in moderate- or light-intensity physical activities. In general, training programs of various intensities can improve

The importance of high levels of moderate to vigorous physical activity is illustrated best by studies of high-intensity interval training (HIIT). Evidence is growing that HIIT may be effective in improving youths’ CRF. HIIT is typically considered to be exercise that is characterized by alternating intermittent bursts of vigorous activity with periods of rest or low-intensity activity. Studies have demonstrated that small amounts of vigorous, maximal to near-maximal activity can induce improvements in youths’

Although the impact of physical activity on CRF is variable, even small improvements in CRF with increases in physical activity resulted in major health benefits in adults.1 In fact, it is well established that moving from the lowest quintile CRF to the next-lowest quintile group is associated with the most striking health benefits in adults.1 No studies to date have measured the impact of physical activity in youth with low baseline CRF, but this is a critical health question to answer because they potentially stand to benefit most from intervention.

Sedentary Time

The time spent sedentary makes up as much as 75% of a 15-year-old’s waking hours and increased from 7 to 8.2 h/d from 2003 to 2016 in adolescents in England and the United States.105,106 A recent American Heart Association statement on sedentary time in adults107 noted several meta-analyses suggesting a strong relationship between sedentary time and all-cause death. In a recent meta-analysis in adults, the negative effects of high levels of sedentary time were reduced with, but not eliminated by, high levels of moderate to vigorous physical activity.108

The relationship between sedentary time and CRF in youth is unclear. Studies have demonstrated both the presence74,109,110 and absence111,112 of a relationship. In a large study of 11- to 13-year-old girls, objectively measured physical activity improved CRF (milliliter per fat-free mass per minute), but there was no relationship between CRF and objectively measured sedentary time.113 In another study, CRF was associated with objectively measured sedentary time independently of time spent in moderate to vigorous physical activity.74 The authors of a recent meta-analysis examining the cross-sectional association between total sedentary time and CRF in children and adolescents (n=4499 participants) found conflicting results. There was a significant association in children (r=−0.06, P=0.037), whereas no association was found in adolescents (r=0.02, P=0.7).114

Obesity

Youth with obesity who are less physically active exhibit lower

Diet

An overall healthy dietary quality score was associated with better CRF in the Coronary Artery Risk Development in Young Adults study in all race-sex groups of youth studied except blacks.71 A dietary pattern specifically rich in fruits and vegetables was associated with healthy CRF in New Zealand and European youth.119,120 The nutritional contributions to CRF are rooted in mitochondrial energetics, which are fundamental to skeletal muscle oxidative capacity and efficiency and therefore to CRF.121

As defined at the beginning of this statement, CRF reflects the integrated ability to transport oxygen from the atmosphere to the mitochondria to perform physical work. A signature feature of mitochondria is their ability to proliferate or, conversely, to be degraded in response to nutritional and extracellular environmental stimuli. Exercise training and dietary patterns rich in omega 3 fatty acids and polyphenols are the principal external influences known to promote mitochondrial bioenergetic pathways.122 Several specific essential fatty acids and polyphenolics, including those from cocoa, apples, beets, pomegranates, grapes, olives, and cruciferous vegetables, have been shown to increase mitochondrial biogenesis and to improve mitochondrial function.123 Nitrate, an inorganic ion abundant in fruits and vegetables, can also be converted in the mammalian mouth and gut to bioactive nitric oxide, further reducing the oxygen cost of exercise.124

Social, Economic, and Environmental Factors

Disparities in CRF may be socioeconomically driven, with rates of both poor nutrition and physical inactivity greatest among urban youth.125 In addition, the effects of the environment on lifestyle and CRF may be mediated through various levels of physical activity resulting from the built environment. Gahche et al8 did not find a difference in socioeconomic status and CRF (submaximal, gas-analyzed CRF measured in milliliters per kilogram per minute), but other studies have found that poor socioeconomic status is associated with low CRF (measured with the 20mSRT) in youth.77

A recent study identified a strong negative association between country-level CRF and income inequality. In countries with a wide income gap between rich and poor residents, youth had poorer CRF.93 In a review, the same authors reported that countries with a widening economic gap between rich and poor residents had less favorable CRF trends (ie, large declines).9 Although these assessments of income inequality may not be stringent, these data provide some proof of concept that there are social and economic determinants of CRF.126

Figure 1 summarizes key influencers of CRF and outcomes influenced by CRF.

Figure 1. Cardiorespiratory fitness (CRF) in youth: key influencers and effects. Relationship between CRF in youth and variables.

Key Points

1. Hereditary factors are known to influence CRF, but specific genes that explain these differences have not yet been elucidated.

2. Racial/ethnic differences in CRF seem to be related to extrinsic factors such as lifestyle, other CVD risk factors, and socioeconomic status.

3. Age, sex, and vigorous physical activity are the most influential determinants of CRF in youth. The influence of modifiable factors on CRF is likely mediated by duration, frequency, and intensity of physical activity.

4. There is little evidence to suggest that sedentary behavior is related to CRF in youth once adjusted for objectively measured physical activity.

5. Nutrient modulation of CRF may be mediated by mitochondria number and function.

Implications of CRF for Health Outcomes

CRF and Health Outcomes in Adults

Numerous large studies have established that in adults low CRF is associated with greater risk for all-cause mortality, CVD events, and cancer mortality independently from, and perhaps more strongly than, traditional risk factors.1,127,128 A nonlinear pattern whereby the largest benefit occurs between the least fit and next-least fit groups underscores the potential benefits of even modestly increasing CRF in the most sedentary individuals,1 but there are no studies in youth in this regard. Apart from mortality, low CRF in adults is also associated with greater risks for congestive heart failure, stroke, type 2 diabetes mellitus, some cancers, and neuropsychological disturbances (eg, dementia, anxiety, and depression).1,127,129 Most important, improvements in CRF over time are associated with reduced mortality and morbidity.129,130

CRF Tracking

In light of these well-documented benefits of optimal CRF in adults, the degree of CRF tracking from childhood to adulthood is of interest. Several studies have found that the degree to which CRF tracks into adulthood varies by methodology (eg, measured or estimated

Childhood CRF and Health Outcomes

Longitudinal data on the relationship between CRF in youth and CVD end points have come primarily from studies following up male military recruits. These studies have collectively demonstrated inverse associations between CRF (Watts per kilogram) in youth and all-cause mortality (hazard ratio [HR], 0.49 [95% CI, 0.47–0.51] for highest versus lowest quintile of CRF),135 CRF and myocardial infarction (HR, 0.82 [95% CI, 0.80–0.85] per 1-SD higher CRF),5 CRF (Watts) and stroke (HR, 0.84 [95% CI, 0.81–0.88] per 1-SD higher CRF),136 CRF (Watts per kilogram) and heart failure (HR, 1.60 [95% CI, 1.44–1.77] for low versus high CRF),137 and CRF (Watts) and disability (HR, 1.85 [95% CI, 1.71–2.00] for low versus high CRF).138

Childhood CRF has also been associated with cardiometabolic risks and a variety of more proximal health outcomes.139 In a study of 154 youth followed up for 24 years, improvement in CRF was associated with lower arterial stiffness (for each unit increase in measured CRF adjusted for body weight, carotid compliance was higher [P=0.04], even after adjustment for several risk factors).140 Cross-sectional and short-term longitudinal studies have also shown an inverse relationship of childhood CRF with adiposity,116,141,142 waist circumference,143 blood pressure,144 insulin resistance, nonalcoholic fatty liver disease,145,146 and a clustered cardiometabolic risk score.139 Furthermore, in a systematic review and meta-analysis, low CRF was significantly associated with the development of pediatric metabolic syndrome.147 In the only prospective study included in this meta-analysis, youth with metabolic syndrome had an odds ratio of 6.1 (95% CI, 1.2–60.3) for having had low CRF (milliliters per kilogram per minute) 7 years earlier.148

Given these associations, several studies have developed criterion-referenced CRF cut points to help identify youth with high cardiometabolic risk.149 These studies attempt to define CRF thresholds in youth to help providers identify those with the highest risk of cardiometabolic disease. In a meta-analysis combining 7 published criterion-referenced standards on 9280 youth 8 to 19 years of age from 14 countries, CRF <35 mL·kg−1·min−1 for girls and 42 mL·kg−1·min−1 for boys identified youth with a higher likelihood of adverse cardiometabolic risk factors (eg, insulin resistance, dyslipidemia, adiposity, high blood pressure) with odds ratios of 5.7 (95% CI, 4.8–6.7) for girls and 3.6 (3.0–4.3) for boys.150 For ease of interpretation, 20mSRT stages that achieve these CRF cut points for boys and girls of different ages also have been published.150

CRF and Lung Function

In a population-based study with cross-sectional and longitudinal components, each 1-SD higher CRF was associated with 2% to 3% greater predicted value of both forced expiratory volume in the first second and forced vital capacity among individuals 9 through 38 years of age. Moreover, improvements in CRF during youth were associated with better lung volumes.151 However, these improvements were not necessarily related to any measures of change in physical activity or interventions undertaken during the course of the longitudinal follow up.

Childhood CRF: Cognitive and Mental Health Outcomes

CRF has been associated with a range of cognitive and academic outcomes in youth. Academic achievement generally has been found to be positively associated with CRF, although most studies have used a cross-sectional design.3,6,152 Among longitudinal studies, maintaining a healthy CRF or improving CRF over time has been associated with better academic achievement.152–154 For example, in a recent large longitudinal study of ≈400 000 Taiwanese junior high school students followed up for 3 years, there was a dose-dependent, positive association between number of years with high CRF (top age- and sex-specific quartile versus bottom 3 quartiles of CRF for all 3 years) and standardized test scores in the third year, with between-group differences up to 0.3 SD for math and science after adjustment for sex, BMI, and urbanization.155 Although effect sizes have varied across studies, even small effect sizes could be impactful at the population level.

High CRF may improve school achievement through improving cognitive abilities or psychological factors.6 Higher CRF has been associated with better attention allocation and cognition modulation (as assessed by task performance and event-related brain potentials) and more efficient neural activation in the prefrontal and parietal cortices (as assessed by functional magnetic resonance imaging).156 In a randomized trial involving a physical activity intervention in 8-year-olds, neural efficiency increased in direct proportion to the increase in CRF.157 In another intervention, youth receiving structured physical activity had an increase both in performance on cognitive tests and in

Furthermore, better childhood CRF has been associated with a lower incidence of mental disorders (mood disorders, psychosis, or suicidality)159 and improved self-worth160,161 and life satisfaction.162,163 In fact, in an exercise intervention study in children, effects on mental health outcomes were more strongly related to improvements in CRF than to changes in body composition.161 These mental health effects are thought to be related to structural brain changes and changes in brain signaling (eg, serotonin).

Key Points

1. A linear inverse relationship exists between CRF during the youth years and all-cause mortality, as well as CVD across the life span.

2. In youth, a protective inverse association has been demonstrated between CRF and multiple conditions that compound cardiovascular risk, including but not limited to metabolic syndrome, type 2 diabetes mellitus, nonalcoholic fatty liver disease, and mental health disorders.

3. CRF is also positively associated with cognitive function, self-worth, and life satisfaction in youth.

Epidemiology of CRF in Youth: Temporal Trends

Both in the United States and internationally, CRF in youth is thought to have declined over the past 40 years.8–10 Globally, a decline in CRF in youth has been noted since the 1960s.11 Armstrong et al103 reported a small but downward trend in the gas-analyzed

United States

In a nationally representative sample in the United States, only 42% of 12- to 15-year olds had healthy CRF (milliliters per kilogram per minute) in 2012 (Figure 2).8 The percentage of boys who had healthy CRF decreased significantly from 65% in 1999 to 2000 to 50% in 2012. For girls, the percentage decreased over the same time period, although not as substantially, from 41% to 34%.8 In addition, 54% of normal-weight youth had healthy CRF, whereas only 30% of youth who were overweight (BMI ≥85th percentile for age and sex) and 20% of youth with obesity (BMI ≥95th percentile for age and sex) had healthy CRF. This percentage did not differ by race and Hispanic origin or ratio of family income to poverty.8 Others have reported declines in mean CRF of 0.9 mL·kg−1·min−1 per decade between 1995 and 2013 in 166 900 US youth 9 to 17 years of age.9

Figure 2. Percentage of youth 12 to 15 years of age who had healthy cardiorespiratory fitness by sex and survey period: United States, 1999 to 2004 and 2012.8 NHANES indicates National Health and Nutrition Examination Survey; and NNYFS, NHANES National Youth Fitness Survey.

Internationally

CRF declined by >7% from 1981 to 2014 in a recent analysis of 137 studies that reported 20mSRT data on youth 9 to 17 years of age.9 Temporal trends were estimated at the country-sex-age level for 19 high-income and upper-middle-income countries. CRF (milliliters per kilogram per minute) trends varied over time and across countries. Moderate CRF declines were seen in earlier years; these declines then slowed and have been stable since 2000.9 However, not all data suggest that there has been a decrease. In Greece, with the use of a measure of CRF based on the 20mSRT, there was an increase in CRF in both sexes from the cohorts evaluated in 1992 to 1993 and 2006 to 2007.164 It should be noted that these CRF estimates based on the 20mSRT, which are only moderately correlated with

A significant percent of the reported decline in CRF (milliliters per kilogram per minute) may be attributable to the increasing prevalence of obesity.9 Caution should be used in the interpretation of associations between

Key Points

1. One-half of boys and two-thirds of girls 12 to 15 years of age do not have healthy CRF.

2. Only 1 in 5 youth with obesity has healthy CRF.

Gaps and Limitations

1. Although several tests beyond CPETs are currently available to measure CRF in office and field settings in youth, there is a pressing need for standardization of testing protocols, uniform interpretation of tests, and data harmonization. Tests such as the step test may be a suitable alternative to CPETs in the office setting but need further study.

2. Stronger clinic-community partnerships to share results or to easily access CRF assessments performed at different settings would be meaningful in providing a customized counseling and intervention.

3. Research is needed to further determine which interventions improve CRF in youth, including youth with obesity or low CRF. We need more research to determine thresholds at which intervention is needed.

4. There is a need for continued collection of data to assess the impact of CRF in youth on CVD outcomes because currently longitudinal data are limited.

5. Furthermore, research should aim to determine the reasons for the reported decline in CRF in youth in order to develop strategies to reverse this trend.

Conclusions

Healthy CRF is positively associated with cardiovascular health, academic achievement, and mental well-being in youth. Accurately and reliably measured CRF may identify youth who would benefit from lifestyle interventions but may be missed by subjective physical activity recall, anthropometric measures, or CVD risk factor testing, which are current standards of care.

Although accurate assessment of CRF in youth has traditionally relied on CPETs, less resource-intensive tests, in particular the 20mSRT in the field setting, are useful. Office-based CRF testing that can be performed by providers with little or no formal training in exercise physiology and low-cost equipment is also superior to physical activity recall. With future research, a practical, widely applicable test to estimate CRF in office settings may become a reality and an essential part of health assessment in all youth during office visits.

Every child will benefit from a CRF estimate as part of a yearly physical. Repeated bursts of vigorous physical activity, including HIIT, improve youth CRF. Public health measures and school policies that support lifestyle improvements to improve CRF in individuals and populations are expected to result in substantial health and cognitive benefits.

Footnotes

https://www.ahajournals.org/journal/circ

The findings and conclusions in this report are those of the authors and do not necessarily represent the official positions of the American Heart Association or the Centers for Disease Control and Prevention.

The American Heart Association makes every effort to avoid any actual or potential conflicts of interest that may arise as a result of an outside relationship or a personal, professional, or business interest of a member of the writing panel. Specifically, all members of the writing group are required to complete and submit a Disclosure Questionnaire showing all such relationships that might be perceived as real or potential conflicts of interest.

This statement was approved by the American Heart Association Science Advisory and Coordinating Committee on April 23, 2020, and the American Heart Association Executive Committee on May 5, 2020. A copy of the document is available at https://professional.heart.org/statements by using either “Search for Guidelines & Statements” or the “Browse by Topic” area. To purchase additional reprints, call 215-356-2721 or email Meredith.[email protected]com.

The American Heart Association requests that this document be cited as follows: Raghuveer G, Hartz J, Lubans DR, Takken T, Wiltz JL, Mietus-Snyder M, Perak AM, Baker-Smith C, Pietris N, Edwards NM; on behalf of the American Heart Association Young Hearts Athero, Hypertension and Obesity in the Young Committee of the Council on Lifelong Congenital Heart Disease and Heart Health in the Young. Cardiorespiratory fitness in youth: an important marker of health: a scientific statement from the American Heart Association. Circulation. 2020;142:e101–e118. doi: 10.1161/CIR.0000000000000866

The expert peer review of AHA-commissioned documents (eg, scientific statements, clinical practice guidelines, systematic reviews) is conducted by the AHA Office of Science Operations. For more on AHA statements and guidelines development, visit https://professional.heart.org/statements. Select the “Guidelines & Statements” drop-down menu, then click “Publication Development.”

Permissions: Multiple copies, modification, alteration, enhancement, and/or distribution of this document are not permitted without the express permission of the American Heart Association. Instructions for obtaining permission are located at https://www.heart.org/permissions. A link to the “Copyright Permissions Request Form” appears in the second paragraph (https://www.heart.org/en/about-us/statements-and-policies/copyright-request-form).

References

• 1. Ross R, Blair SN, Arena R, Church TS, Després JP, Franklin BA, Haskell WL, Kaminsky LA, Levine BD, Lavie CJ, et al.; on behalf of the American Heart Association Physical Activity Committee of the Council on Lifestyle and Cardiometabolic Health; Council on Clinical Cardiology; Council on Epidemiology and Prevention; Council on Cardiovascular and Stroke Nursing; Council on Functional Genomics and Translational Biology; Stroke Council. Importance of assessing cardiorespiratory fitness in clinical practice: a case for fitness as a clinical vital sign: a scientific statement from the American Heart Association.Circulation. 2016; 134:e653–e699. doi: 10.1161/CIR.0000000000000461LinkGoogle Scholar
• 2. Caspersen CJ, Powell KE, Christenson GM. Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research.Public Health Rep. 1985; 100:126–131.MedlineGoogle Scholar
• 3. Lang JJ, Belanger K, Poitras V, Janssen I, Tomkinson GR, Tremblay MS. Systematic review of the relationship between 20m shuttle run performance and health indicators among children and youth.J Sci Med Sport. 2018; 21:383–397. doi: 10.1016/j.jsams.2017.08.002CrossrefMedlineGoogle Scholar
• 4. Ortega FB, Ruiz JR, Castillo MJ, Sjöström M. Physical fitness in childhood and adolescence: a powerful marker of health.Int J Obes (Lond). 2008; 32:1–11. doi: 10.1038/sj.ijo.0803774CrossrefMedlineGoogle Scholar
• 5. Högström G, Nordström A, Nordström P. High aerobic fitness in late adolescence is associated with a reduced risk of myocardial infarction later in life: a nationwide cohort study in men.Eur Heart J. 2014; 35:3133–3140. doi: 10.1093/eurheartj/eht527CrossrefMedlineGoogle Scholar
• 6. Santana CCA, Azevedo LB, Cattuzzo MT, Hill JO, Andrade LP, Prado WL. Physical fitness and academic performance in youth: a systematic review.Scand J Med Sci Sports. 2017; 27:579–603. doi: 10.1111/sms.12773CrossrefMedlineGoogle Scholar
• 7. Lubans D, Richards J, Hillman C, Faulkner G, Beauchamp M, Nilsson M, Kelly P, Smith J, Raine L, Biddle S. Physical activity for cognitive and mental health in youth: a systematic review of mechanisms.Pediatrics. 2016; 138:e2161642. doi: 10.1542/peds.2016-1642CrossrefGoogle Scholar
• 8. Gahche J, Fakhouri T, Carroll DD, Burt VL, Wang CY, Fulton JE. Cardiorespiratory fitness levels among U.S. youth aged 12–15 years: United States, 1999–2004 and 2012.NCHS Data Brief. 2014:1–8.MedlineGoogle Scholar
• 9. Tomkinson GR, Lang JJ, Tremblay MS. Temporal trends in the cardiorespiratory fitness of children and adolescents representing 19 high-income and upper middle-income countries between 1981 and 2014.Br J Sports Med. 2019; 53:478–486. doi: 10.1136/bjsports-2017-097982CrossrefMedlineGoogle Scholar
• 10. Moraes Ferrari GL, Bracco MM, Matsudo VK, Fisberg M. Cardiorespiratory fitness and nutritional status of schoolchildren: 30-year evolution.J Pediatr (Rio J). 2013; 89:366–373. doi: 10.1016/j.jped.2012.12.006CrossrefMedlineGoogle Scholar
• 11. Tomkinson GR, Olds TS. Secular changes in pediatric aerobic fitness test performance: the global picture.Med Sport Sci. 2007; 50:46–66. doi: 10.1159/000101075CrossrefMedlineGoogle Scholar
• 12. Prince SA, Adamo KB, Hamel ME, Hardt J, Connor Gorber S, Tremblay M. A comparison of direct versus self-report measures for assessing physical activity in adults: a systematic review.Int J Behav Nutr Phys Act. 2008; 5:56. doi: 10.1186/1479-5868-5-56CrossrefMedlineGoogle Scholar
• 13. Longmuir PE, Brothers JA, de Ferranti SD, Hayman LL, Van Hare GF, Matherne GP, Davis CK, Joy EA, McCrindle BW; on behalf of the American Heart Association Atherosclerosis, Hypertension and Obesity in Youth Committee of the Council on Cardiovascular Disease in the Young. Promotion of physical activity for children and adults with congenital heart disease: a scientific statement from the American Heart Association.Circulation. 2013; 127:2147–2159. doi: 10.1161/CIR.0b013e318293688fLinkGoogle Scholar
• 14. 2018Physical Activity Guidelines Advisory Committee. 2018 Physical Activity Guidelines Advisory Committee Scientific Report.Washington, DC:US Department of Health and Human Services; 2018.Google Scholar
• 15. Institute of Medicine. Fitness Measures and Health Outcomes in Youth. Washington, DC: National Academies Press; 2012.Google Scholar
• 16. Welk GJ, De Saint-Maurice Maduro PF, Laurson KR, Brown DD. Field evaluation of the new FITNESSGRAM® criterion-referenced standards.Am J Prev Med. 2011; 41(suppl 2):S131–S142. doi: 10.1016/j.amepre.2011.07.011CrossrefMedlineGoogle Scholar
• 17. Borg G. Borg’s Perceived Exertion and Pain Scales. Champaign, IL: Human Kinetics; 1998.Google Scholar
• 18. Tremblay MS, Aubert S, Barnes JD, Saunders TJ, Carson V, Latimer-Cheung AE, Chastin SFM, Altenburg TM, Chinapaw MJM. Sedentary Behavior Research Network (SBRN): terminology consensus project process and outcome.Ing J Behav Nutr Phys Act. 2017; 14:75. doi: 10.1186/s12966-017-0525-8CrossrefMedlineGoogle Scholar
• 19. Ainsworth BE, Haskell WL, Whitt MC, Irwin ML, Swartz AM, Strath SJ, O’Brien WL, Bassett DR, Schmitz KH, Emplaincourt PO, et al.. Compendium of physical activities: an update of activity codes and MET intensities.Med Sci Sports Exerc. 2000; 32(suppl):S498–S504. doi: 10.1097/00005768-200009001-00009CrossrefMedlineGoogle Scholar
• 20. Pollock ML, Gaesser GA, Butcher JD, Després J-P, Dishman RK, Franklin BA, Garber CE. ACSM Position Stand: the recommended quantity and quality of exercise for developing and maintaining cardiorespiratory and muscular fitness, and flexibility in healthy adults.Med Sci Sports Exerc. 1998; 30:975–991. doi: 10.1097/00005768-199806000-00032MedlineGoogle Scholar
• 21. Eather N, Ridley K, Leahy A. Physiological health benefits of physical activity for young people.Brusseau T, Fairclough S, Lubans DR, eds. In: The Routledge Handbook of Physical Activity for Youth. Oxon, UK: Routledge; 2020:103–120.Google Scholar
• 22. Norton K, Norton L, Sadgrove D. Position statement on physical activity and exercise intensity terminology.J Sci Med Sport. 2010; 13:496–502. doi: 10.1016/j.jsams.2009.09.008CrossrefMedlineGoogle Scholar
• 23. Butte NF, Watson KB, Ridley K, Zakeri IF, McMurray RG, Pfeiffer KA, Crouter SE, Herrmann SD, Bassett DR, Long A, et al.. A youth compendium of physical activities: activity codes and metabolic intensities.Med Sci Sports Exerc. 2018; 50:246–256. doi: 10.1249/MSS.0000000000001430CrossrefMedlineGoogle Scholar
• 24. Malina RM, Bouchard C, Bar-Or O. Growth, Maturation, and Physical Activity. Champaign, IL: Human Kinetics; 2004.CrossrefGoogle Scholar
• 25. McArdle WD, Katch FI, Katch VI. Exercise Physiology: Energy, Nutrition and Human Performance. Baltimore, MA: Lippincott Williams & Wilkins; 2015.Google Scholar
• 26. Armstrong N, Barker AR. Endurance training and elite young athletes.Med Sport Sci. 2011; 56:59–83. doi: 10.1159/000320633CrossrefMedlineGoogle Scholar
• 27. Rowland T, Unnithan V, Fernhall B, Baynard T, Lange C. Left ventricular response to dynamic exercise in young cyclists.Med Sci Sports Exerc. 2002; 34:637–642. doi: 10.1097/00005768-200204000-00012MedlineGoogle Scholar
• 28. Nottin S, Vinet A, Stecken F, N’Guyen LD, Ounissi F, Lecoq AM, Obert P. Central and peripheral cardiovascular adaptations to exercise in endurance-trained children.Acta Physiol Scand. 2002; 175:85–92. doi: 10.1046/j.1365-201X.2002.00975.xCrossrefMedlineGoogle Scholar
• 29. Rowland T, Wehnert M, Miller K. Cardiac responses to exercise in competitive child cyclists.Med Sci Sports Exerc. 2000; 32:747–752. doi: 10.1097/00005768-200004000-00005CrossrefMedlineGoogle Scholar
• 30. Rowland TW, Unnithan VB, MacFarlane NG, Gibson NG, Paton JY. Clinical manifestations of the “athlete’s heart” in prepubertal male runners.Int J Sports Med. 1994; 15:515–519. doi: 10.1055/s-2007-1021097CrossrefMedlineGoogle Scholar
• 31. Tomkinson GR, Léger LA, Olds TS, Cazorla G. Secular trends in the performance of children and adolescents (1980-2000): an analysis of 55 studies of the 20m shuttle run test in 11 countries.Sports Med. 2003; 33:285–300. doi: 10.2165/00007256-200333040-00003CrossrefMedlineGoogle Scholar
• 32. Tomkinson GR, Lang JJ, Tremblay MS, Dale M, LeBlanc AG, Belanger K, Ortega FB, Léger L. International normative 20 m shuttle run values from 1 142 026 children and youth representing 50 countries.Br J Sports Med. 2017; 51:1545–1554. doi: 10.1136/bjsports-2016-095987CrossrefMedlineGoogle Scholar
• 33. Takken T, Mylius CF, Paap D, Broeders W, Hulzebos HJ, Van Brussel M, Bongers BC. Reference values for cardiopulmonary exercise testing in healthy subjects: an updated systematic review.Expert Rev Cardiovasc Ther. 2019; 17:413–426. doi: 10.1080/14779072.2019.1627874CrossrefMedlineGoogle Scholar
• 34. Plowman SA, Meredith MD. FITNESSGRAM/ACTIVITYGRAM Reference Guide. 4th ed. Dallas, TX: The Cooper Institute; 2013.Google Scholar
• 35. Fick A. Ueber die Messung des Blutquantums in den Herzventrikeln. Wurzburg: Sitx der Physik-Med Ges; 1870.Google Scholar
• 36. Shephard RJ, Allen C, Benade AJ, Davies CT, Di Prampero PE, Hedman R, Merriman JE, Myhre K, Simmons R. The maximum oxygen intake: an international reference standard of cardiorespiratory fitness.Bull World Health Organ. 1968; 38:757–764.MedlineGoogle Scholar
• 37. Wold B, Hendry L. Social and environmental factors associated with physical activity in young people.Biddle S, Sallis J, Cavill N, eds. In: Young People and Health-Enhancing Physical Activity: Evidence and Implications. London, UK: Health Education Authority; 1998:119–132.Google Scholar
• 38. Rowland TW. Does peak VO2 reflect VO2max in children? Evidence from supramaximal testing.Med Sci Sports Exerc. 1993; 25:689–693.CrossrefMedlineGoogle Scholar
• 39. Armstrong N, Welsman J, Winsley R. Is peak VO2 a maximal index of children’s aerobic fitness?Int J Sports Med. 1996; 17:356–359. doi: 10.1055/s-2007-972860CrossrefMedlineGoogle Scholar
• 40. Hansen D, Marinus N, Remans M, Courtois I, Cools F, Calsius J, Massa G, Takken T. Exercise tolerance in obese vs. lean adolescents: a systematic review and meta-analysis.Obes Rev. 2014; 15:894–904. doi: 10.1111/obr.12202CrossrefMedlineGoogle Scholar
• 41. Werneck AO, Conde J, Coelho-E-Silva MJ, Pereira A, Costa DC, Martinho D, Duarte JP, Valente-Dos-Santos J, Fernandes RA, Batista MB, et al.. Allometric scaling of aerobic fitness outputs in school-aged pubertal girls.BMC Pediatr. 2019; 19:96. doi: 10.1186/s12887-019-1462-2CrossrefMedlineGoogle Scholar
• 42. Cooper DM. Rethinking exercise testing in children: a challenge.Am J Respir Crit Care Med. 1995; 152(4 Pt 1):1154–1157. doi: 10.1164/ajrccm.152.4.7551363CrossrefMedlineGoogle Scholar
• 43. Batista MB, Romanzini CLP, Castro-Piñero J, Ronque ERV. Validity of field tests to estimate cardiorespiratory fitness in children and adolescents: a systematic review.Rev Paul Pediatr. 2017; 35:222–233. doi: 10.1590/1984-0462/;2017;35;2;00002CrossrefMedlineGoogle Scholar
• 44. Léger LA, Mercier D, Gadoury C, Lambert J. The multistage 20 metre shuttle run test for aerobic fitness.J Sports Sci. 1988; 6:93–101. doi: 10.1080/02640418808729800CrossrefMedlineGoogle Scholar
• 45. Léger L, Lambert J, Goulet A, Rowan C, Dinelle Y. Aerobic capacity of 6 to 17-year-old Quebecois: 20 meter shuttle run test with 1 minute stages [in French].Can J Appl Sport Sci. 1984; 9:64–69.MedlineGoogle Scholar
• 46. Tomkinson GR, Lang JJ, Blanchard J, Léger LA, Tremblay MS. The 20-m shuttle run: assessment and interpretation of data in relation to youth aerobic fitness and health.Pediatr Exerc Sci. 2019; 31:152–163. doi: 10.1123/pes.2018-0179CrossrefMedlineGoogle Scholar
• 47. Ruiz JR, Silva G, Oliveira N, Ribeiro JC, Oliveira JF, Mota J. Criterion-related validity of the 20-m shuttle run test in youths aged 13-19 years.J Sports Sci. 2009; 27:899–906. doi: 10.1080/02640410902902835CrossrefMedlineGoogle Scholar
• 48. Castro-Piñero J, Artero EG, España-Romero V, Ortega FB, Sjöström M, Suni J, Ruiz JR. Criterion-related validity of field-based fitness tests in youth: a systematic review.Br J Sports Med. 2010; 44:934–943. doi: 10.1136/bjsm.2009.058321CrossrefMedlineGoogle Scholar
• 49. Mayorga-Vega D, Bocanegra-Parrilla R, Ornelas M, Viciana J. Criterion-related validity of the distance- and time-based walk/run field tests for estimating cardiorespiratory fitness: a systematic review and meta-analysis.PLoS One. 2016; 11:e0151671. doi: 10.1371/journal.pone.0151671CrossrefMedlineGoogle Scholar
• 50. Mayorga-Vega D, Aguilar-Soto P, Viciana J. Criterion-related validity of the 20-m shuttle run test for estimating cardiorespiratory fitness: a meta-analysis.J Sports Sci Med. 2015; 14:536–547.MedlineGoogle Scholar
• 51. Ebbeling CB, Ward A, Puleo EM, Widrick J, Rippe JM. Development of a single-stage submaximal treadmill walking test.Med Sci Sports Exerc. 1991; 23:966–973.CrossrefMedlineGoogle Scholar
• 52. Nemeth BA, Carrel AL, Eickhoff J, Clark RR, Peterson SE, Allen DB. Submaximal treadmill test predicts VO2max in overweight children.J Pediatr. 2009; 154:677–681. doi: 10.1016/j.jpeds.2008.11.032CrossrefMedlineGoogle Scholar
• 53. Astrand PO, Ryhming I. A nomogram for calculation of aerobic capacity (physical fitness) from pulse rate during sub-maximal work.J Appl Physiol. 1954; 7:218–221. doi: 10.1152/jappl.1954.7.2.218CrossrefMedlineGoogle Scholar
• 54. Woynarowska B. The validity of indirect estimations of maximal oxygen uptake in children 11–12 years of age.Eur J Appl Physiol Occup Physiol. 1980; 43:19–23. doi: 10.1007/BF00421351CrossrefMedlineGoogle Scholar
• 55. Bland J, Pfeiffer K, Eisenmann JC. The PWC170: comparison of different stage lengths in 11-16 year olds.Eur J Appl Physiol. 2012; 112:1955–1961. doi: 10.1007/s00421-011-2157-zCrossrefMedlineGoogle Scholar
• 56. Bartels B, de Groot JF, Terwee CB. The six-minute walk test in chronic pediatric conditions: a systematic review of measurement properties.Phys Ther. 2013; 93:529–541. doi: 10.2522/ptj.20120210CrossrefMedlineGoogle Scholar
• 57. Holland AE, Spruit MA, Troosters T, Puhan MA, Pepin V, Saey D, McCormack MC, Carlin BW, Sciurba FC, Pitta F, et al.. An official European Respiratory Society/American Thoracic Society technical standard: field walking tests in chronic respiratory disease.Eur Respir J. 2014; 44:1428–1446. doi: 10.1183/09031936.00150314CrossrefMedlineGoogle Scholar
• 58. ATS Committee on Proficiency Standards for Clinical Pulmonary Function Laboratories. ATS statement: guidelines for the six-minute walk test.Am J Respir Crit Care Med. 2002; 166:111–117. doi: 10.1164/ajrccm.166.1.at1102CrossrefMedlineGoogle Scholar
• 59. Mylius CF, Paap D, Takken T. Reference value for the 6-minute walk test in children and adolescents: a systematic review.Expert Rev Respir Med. 2016; 10:1335–1352. doi: 10.1080/17476348.2016.1258305CrossrefMedlineGoogle Scholar
• 60. Lammers AE, Diller GP, Odendaal D, Tailor S, Derrick G, Haworth SG. Comparison of 6-min walk test distance and cardiopulmonary exercise test performance in children with pulmonary hypertension.Arch Dis Child. 2011; 96:141–147. doi: 10.1136/adc.2009.169904CrossrefMedlineGoogle Scholar
• 61. Takken T. Six-minute walk test is a poor predictor of maximum oxygen uptake in children.Acta Paediatr. 2010; 99:958;author reply 959. doi: 10.1111/j.1651-2227.2010.01750.xCrossrefMedlineGoogle Scholar
• 62. Kasch FW. A comparison of the exercise tolerance of post-rheumatic and normal boys.J Assoc Phys Mental Rehabil. 1961; 15:35–40.Google Scholar
• 63. Hayes RM, Maldonado D, Gossett T, Shepherd T, Mehta SP, Flesher SL. Developing and validating a step test of aerobic fitness among elementary school children.Physiother Can. 2019; 71:187–194. doi: 10.3138/ptc.2017-44.ppCrossrefMedlineGoogle Scholar
• 64. Francis K, Feinstein R. A simple height-specific and rate-specific step test for children.South Med J. 1991; 84:169–174. doi: 10.1097/00007611-199102000-00005CrossrefMedlineGoogle Scholar
• 65. Ortega FB, Ruiz JR, España-Romero V, Vicente-Rodriguez G, Martínez-Gómez D, Manios Y, Béghin L, Molnar D, Widhalm K, Moreno LA, et al.; HELENA Study Group. The International Fitness Scale (IFIS): usefulness of self-reported fitness in youth.Int J Epidemiol. 2011; 40:701–711. doi: 10.1093/ije/dyr039CrossrefMedlineGoogle Scholar
• 66. Ramírez-Vélez R, Cruz-Salazar SM, Martínez M, Cadore EL, Alonso-Martinez AM, Correa-Bautista JE, Izquierdo M, Ortega FB, García-Hermoso A. Construct validity and test-retest reliability of the International Fitness Scale (IFIS) in Colombian children and adolescents aged 9-17.9 years: the FUPRECOL study.PeerJ. 2017; 5:e3351. doi: 10.7717/peerj.3351CrossrefMedlineGoogle Scholar
• 67. Sarzynski MA, Ghosh S, Bouchard C. Genomic and transcriptomic predictors of response levels to endurance exercise training.J Physiol. 2017; 595:2931–2939. doi: 10.1113/JP272559CrossrefMedlineGoogle Scholar
• 68. Pfeiffer KA, Dowda M, Dishman RK, Sirard JR, Pate RR. Physical fitness and performance: cardiorespiratory fitness in girls–change from middle to high school.Med Sci Sports Exerc. 2007; 39:2234–2241. doi: 10.1249/mss.0b013e318156aa60CrossrefMedlineGoogle Scholar
• 69. Howard EN, Frierson GM, Willis BL, Haskell WL, Powell-Wiley TM, Defina LF. The impact of race and higher socioeconomic status on cardiorespiratory fitness.Med Sci Sports Exerc. 2013; 45:2286–2291. doi: 10.1249/MSS.0b013e31829c2f4fCrossrefMedlineGoogle Scholar
• 70. Júdice PB, Silva AM, Berria J, Petroski EL, Ekelund U, Sardinha LB. Sedentary patterns, physical activity and health-related physical fitness in youth: a cross-sectional study.Int J Behav Nutr Phys Act. 2017; 14:25. doi: 10.1186/s12966-017-0481-3CrossrefMedlineGoogle Scholar
• 71. Shikany JM, Jacobs DR, Lewis CE, Steffen LM, Sternfeld B, Carnethon MR, Richman JS. Associations between food groups, dietary patterns, and cardiorespiratory fitness in the Coronary Artery Risk Development in Young Adults study.Am J Clin Nutr. 2013; 98:1402–1409. doi: 10.3945/ajcn.113.058826CrossrefMedlineGoogle Scholar
• 72. Mendelson M, Michallet AS, Tonini J, Favre-Juvin A, Guinot M, Wuyam B, Flore P. Low cardiorespiratory fitness is partially linked to ventilatory factors in obese adolescents.Pediatr Exerc Sci. 2016; 28:87–97. doi: 10.1123/pes.2013-0151CrossrefMedlineGoogle Scholar
• 73. Ortega FB, Ruiz JR, Labayen I, Martínez-Gómez D, Vicente-Rodriguez G, Cuenca-García M, Gracia-Marco L, Manios Y, Beghin L, Molnar D, et al.; HELENA Project Group. Health inequalities in urban adolescents: role of physical activity, diet, and genetics.Pediatrics. 2014; 133:e884–e895. doi: 10.1542/peds.2013-1665CrossrefMedlineGoogle Scholar
• 74. Santos R, Mota J, Okely AD, Pratt M, Moreira C, Coelho-e-Silva MJ, Vale S, Sardinha LB. The independent associations of sedentary behaviour and physical activity on cardiorespiratory fitness.Br J Sports Med. 2014; 48:1508–1512. doi: 10.1136/bjsports-2012-091610CrossrefMedlineGoogle Scholar
• 75. Hoehner CM, Handy SL, Yan Y, Blair SN, Berrigan D. Association between neighborhood walkability, cardiorespiratory fitness and body-mass index.Soc Sci Med. 2011; 73:1707–1716. doi: 10.1016/j.socscimed.2011.09.032CrossrefMedlineGoogle Scholar
• 76. Ombrellaro KJ, Perumal N, Zeiher J, Hoebel J, Ittermann T, Ewert R, Dörr M, Keil T, Mensink GBM, Finger JD. Socioeconomic correlates and determinants of cardiorespiratory fitness in the general adult population: a systematic review and meta-analysis.Sports Med Open. 2018; 4:25. doi: 10.1186/s40798-018-0137-0CrossrefMedlineGoogle Scholar
• 77. Bai Y, Saint-Maurice PF, Welk GJ, Allums-Featherston K, Candelaria N. Explaining disparities in youth aerobic fitness and body mass index: relative impact of socioeconomic and minority status.J Sch Health. 2016; 86:787–793. doi: 10.1111/josh.12434CrossrefMedlineGoogle Scholar
• 78. Bouchard C, Rankinen T, Timmons JA. Genomics and genetics in the biology of adaptation to exercise.Compr Physiol. 2011; 1:1603–1648. doi: 10.1002/cphy.c100059CrossrefMedlineGoogle Scholar
• 79. Williams CJ, Williams MG, Eynon N, Ashton KJ, Little JP, Wisloff U, Coombes JS. Genes to predict VO2max trainability: a systematic review.BMC Genomics. 2017; 18(suppl 8):831. doi: 10.1186/s12864-017-4192-6CrossrefMedlineGoogle Scholar
• 80. Bouchard C, An P, Rice T, Skinner JS, Wilmore JH, Gagnon J, Pérusse L, Leon AS, Rao DC. Familial aggregation of VO(2max) response to exercise training: results from the HERITAGE Family Study.J Appl Physiol (1985). 1999; 87:1003–1008. doi: 10.1152/jappl.1999.87.3.1003CrossrefMedlineGoogle Scholar
• 81. Bouchard C, Sarzynski MA, Rice TK, Kraus WE, Church TS, Sung YJ, Rao DC, Rankinen T. Genomic predictors of the maximal O2 uptake response to standardized exercise training programs.J Appl Physiol (1985). 2011; 110:1160–1170. doi: 10.1152/japplphysiol.00973.2010CrossrefMedlineGoogle Scholar
• 82. Venezia AC, Roth SM. Recent research in the genetics of exercise training adaptation.Med Sport Sci. 2016; 61:29–40. doi: 10.1159/000445239CrossrefMedlineGoogle Scholar
• 83. Rankinen T, Fuku N, Wolfarth B, Wang G, Sarzynski MA, Alexeev DG, Ahmetov II, Boulay MR, Cieszczyk P, Eynon N, et al.. No evidence of a common DNA variant profile specific to world class endurance athletes.PLoS One. 2016; 11:e0147330. doi: 10.1371/journal.pone.0147330CrossrefMedlineGoogle Scholar
• 84. Armstrong N, Welsman J. Development of peak oxygen uptake from 11-16 years determined using both treadmill and cycle ergometry.Eur J Appl Physiol. 2019; 119:801–812. doi: 10.1007/s00421-019-04071-3CrossrefMedlineGoogle Scholar
• 85. Catley MJ, Tomkinson GR. Normative health-related fitness values for children: analysis of 85347 test results on 9-17-year-old Australians since 1985.Br J Sports Med. 2013; 47:98–108. doi: 10.1136/bjsports-2011-090218CrossrefMedlineGoogle Scholar
• 86. Ortega FB, Artero EG, Ruiz JR, España-Romero V, Jiménez-Pavón D, Vicente-Rodriguez G, Moreno LA, Manios Y, Béghin L, Ottevaere C, et al.; HELENA Study. Physical fitness levels among European adolescents: the HELENA study.Br J Sports Med. 2011; 45:20–29. doi: 10.1136/bjsm.2009.062679CrossrefMedlineGoogle Scholar
• 87. Winsley RJ, Fulford J, Roberts AC, Welsman JR, Armstrong N. Sex difference in peak oxygen uptake in prepubertal children.J Sci Med Sport. 2009; 12:647–651. doi: 10.1016/j.jsams.2008.05.006CrossrefMedlineGoogle Scholar
• 88. Tarnopolsky MA, Rennie CD, Robertshaw HA, Fedak-Tarnopolsky SN, Devries MC, Hamadeh MJ. Influence of endurance exercise training and sex on intramyocellular lipid and mitochondrial ultrastructure, substrate use, and mitochondrial enzyme activity.Am J Physiol Regul Integr Comp Physiol. 2007; 292:R1271–R1278. doi: 10.1152/ajpregu.00472.2006CrossrefMedlineGoogle Scholar
• 89. Swift DL, Johannsen NM, Earnest CP, Newton RL, McGee JE, Church TS. Cardiorespiratory fitness and exercise training in African Americans.Prog Cardiovasc Dis. 2017; 60:96–102. doi: 10.1016/j.pcad.2017.06.001CrossrefMedlineGoogle Scholar
• 90. Ong KC, Loo CM, Ong YY, Chan SP, Earnest A, Saw SM. Predictive values for cardiopulmonary exercise testing in sedentary Chinese adults.Respirology. 2002; 7:225–231. doi: 10.1046/j.1440-1843.2002.00393.xCrossrefMedlineGoogle Scholar
• 91. Pandey A, Park BD, Ayers C, Das SR, Lakoski S, Matulevicius S, de Lemos JA, Berry JD. Determinants of racial/ethnic differences in cardiorespiratory fitness (from the Dallas Heart Study).Am J Cardiol. 2016; 118:499–503. doi: 10.1016/j.amjcard.2016.05.043CrossrefMedlineGoogle Scholar
• 92. Shaibi GQ, Ball GD, Goran MI. Aerobic fitness among Caucasian, African-American, and Latino youth.Ethn Dis. 2006; 16:120–125.MedlineGoogle Scholar
• 93. Lang JJ, Tremblay MS, Léger L, Olds T, Tomkinson GR. International variability in 20 m shuttle run performance in children and youth: who are the fittest from a 50-country comparison? A systematic literature review with pooling of aggregate results.Br J Sports Med. 2018; 52:276. doi: 10.1136/bjsports-2016-096224CrossrefMedlineGoogle Scholar
• 94. Bansal N, Mahadin DR, Smith R, French M, Karpawich PP, Aggarwal S. Comparative cardiorespiratory fitness in children: racial disparity may begin early in childhood.Pediatr Cardiol. 2019; 40:1183–1189. doi: 10.1007/s00246-019-02129-9CrossrefMedlineGoogle Scholar
• 95. Ferreira I, Gbatu PT, Boreham CA. Gestational age and cardiorespiratory fitness in individuals born at term: a life course study.J Am Heart Assoc. 2017; 6:e006467. doi: 10.1161/JAHA.117.006467LinkGoogle Scholar
• 96. Welsh L, Kirkby J, Lum S, Odendaal D, Marlow N, Derrick G, Stocks J; EPICure Study Group. The EPICure study: maximal exercise and physical activity in school children born extremely preterm.Thorax. 2010; 65:165–172. doi: 10.1136/thx.2008.107474CrossrefMedlineGoogle Scholar
• 97. Edwards MO, Kotecha SJ, Lowe J, Watkins WJ, Henderson AJ, Kotecha S. Effect of preterm birth on exercise capacity: a systematic review and meta-analysis.Pediatr Pulmonol. 2015; 50:293–301. doi: 10.1002/ppul.23117CrossrefMedlineGoogle Scholar
• 98. Ruiz JR, Rizzo NS, Hurtig-Wennlöf A, Ortega FB, Wärnberg J, Sjöström M. Relations of total physical activity and intensity to fitness and fatness in children: the European Youth Heart Study.Am J Clin Nutr. 2006; 84:299–303. doi: 10.1093/ajcn/84.1.299CrossrefMedlineGoogle Scholar
• 99. Gralla MH, McDonald SM, Breneman C, Beets MW, Moore JB. Associations of objectively measured vigorous physical activity with body composition, cardiorespiratory fitness, and cardiometabolic health in youth: a review.Am J Lifestyle Med. 2019; 13:61–97. doi: 10.1177/1559827615624417CrossrefMedlineGoogle Scholar
• 100. Hussey J, Bell C, Bennett K, O’Dwyer J, Gormley J. Relationship between the intensity of physical activity, inactivity, cardiorespiratory fitness and body composition in 7-10-year-old Dublin children.Br J Sports Med. 2007; 41:311–316. doi: 10.1136/bjsm.2006.032045CrossrefMedlineGoogle Scholar
• 101. Gutin B, Yin Z, Humphries MC, Barbeau P. Relations of moderate and vigorous physical activity to fitness and fatness in adolescents.Am J Clin Nutr. 2005; 81:746–750. doi: 10.1093/ajcn/81.4.746CrossrefMedlineGoogle Scholar
• 102. Baquet G, van Praagh E, Berthoin S. Endurance training and aerobic fitness in young people.Sports Med. 2003; 33:1127–1143. doi: 10.2165/00007256-200333150-00004CrossrefMedlineGoogle Scholar
• 103. Armstrong N, Tomkinson G, Ekelund U. Aerobic fitness and its relationship to sport, exercise training and habitual physical activity during youth.Br J Sports Med. 2011; 45:849–858. doi: 10.1136/bjsports-2011-090200CrossrefMedlineGoogle Scholar
• 104. Costigan SA, Eather N, Plotnikoff RC, Taaffe DR, Lubans DR. High-intensity interval training for improving health-related fitness in adolescents: a systematic review and meta-analysis.Br J Sports Med. 2015; 49:1253–1261. doi: 10.1136/bjsports-2014-094490CrossrefMedlineGoogle Scholar
• 105. Janssen X, Mann KD, Basterfield L, Parkinson KN, Pearce MS, Reilly JK, Adamson AJ, Reilly JJ. Development of sedentary behavior across childhood and adolescence: longitudinal analysis of the Gateshead Millennium Study.Int J Behav Nutr Phys Act. 2016; 13:88. doi: 10.1186/s12966-016-0413-7CrossrefMedlineGoogle Scholar
• 106. Yang L, Cao C, Kantor ED, Nguyen LH, Zheng X, Park Y, Giovannucci EL, Matthews CE, Colditz GA, Cao Y. Trends in sedentary behavior among the US population, 2001-2016.JAMA. 2019; 321:1587–1597. doi: 10.1001/jama.2019.3636CrossrefMedlineGoogle Scholar
• 107. Young DR, Hivert MF, Alhassan S, Camhi SM, Ferguson JF, Katzmarzyk PT, Lewis CE, Owen N, Perry CK, Siddique J, et al.; on behalf of the Physical Activity Committee of the Council on Lifestyle and Cardiometabolic Health; Council on Clinical Cardiology; Council on Epidemiology and Prevention; Council on Functional Genomics and Translational Biology; and Stroke Council. Sedentary behavior and cardiovascular morbidity and mortality: a science advisory from the American Heart Association.Circulation. 2016; 134:e262–e279. doi: 10.1161/CIR.0000000000000440LinkGoogle Scholar
• 108. Ekelund U, Steene-Johannessen J, Brown WJ, Fagerland MW, Owen N, Powell KE. Does physical activity attenuate, or even eliminate, the detrimental association of sitting time with mortality? A harmonised meta-analysis of data from more than 1 million men and women.Lancet. 2016; 388:1302–1310. doi: 10.1016/S0140-6736(16)30370-1CrossrefMedlineGoogle Scholar
• 109. Aggio D, Ogunleye AA, Voss C, Sandercock GR. Temporal relationships between screen-time and physical activity with cardiorespiratory fitness in English schoolchildren: a 2-year longitudinal study.Prev Med. 2012; 55:37–39. doi: 10.1016/j.ypmed.2012.04.012CrossrefMedlineGoogle Scholar
• 110. Martinez-Gomez D, Ortega FB, Ruiz JR, Vicente-Rodriguez G, Veiga OL, Widhalm K, Manios Y, Béghin L, Valtueña J, Kafatos A, et al.; HELENA Study Group. Excessive sedentary time and low cardiorespiratory fitness in European adolescents: the HELENA study.Arch Dis Child. 2011; 96:240–246. doi: 10.1136/adc.2010.187161CrossrefMedlineGoogle Scholar
• 111. Grund A, Krause H, Siewers M, Rieckert H, Müller MJ. Is TV viewing an index of physical activity and fitness in overweight and normal weight children?Public Health Nutr. 2001; 4:1245–1251. doi: 10.1079/phn2001178CrossrefMedlineGoogle Scholar
• 112. Hardy LL, Dobbins TA, Denney-Wilson EA, Okely AD, Booth ML. Sedentariness, small-screen recreation, and fitness in youth.Am J Prev Med. 2009; 36:120–125. doi: 10.1016/j.amepre.2008.09.034CrossrefMedlineGoogle Scholar
• 113. Denton SJ, Trenell MI, Plötz T, Savory LA, Bailey DP, Kerr CJ. Cardiorespiratory fitness is associated with hard and light intensity physical activity but not time spent sedentary in 10-14 year old schoolchildren: the HAPPY study.PLoS One. 2013; 8:e61073. doi: 10.1371/journal.pone.0061073CrossrefMedlineGoogle Scholar
• 114. Cliff DP, Hesketh KD, Vella SA, Hinkley T, Tsiros MD, Ridgers ND, Carver A, Veitch J, Parrish AM, Hardy LL, et al.. Objectively measured sedentary behaviour and health and development in children and adolescents: systematic review and meta-analysis.Obes Rev. 2016; 17:330–344. doi: 10.1111/obr.12371CrossrefMedlineGoogle Scholar
• 115. Pate RR, Wang CY, Dowda M, Farrell SW, O’Neill JR. Cardiorespiratory fitness levels among US youth 12 to 19 years of age: findings from the 1999-2002 National Health and Nutrition Examination Survey.Arch Pediatr Adolesc Med. 2006; 160:1005–1012. doi: 10.1001/archpedi.160.10.1005CrossrefMedlineGoogle Scholar
• 116. Byrd-Williams CE, Shaibi GQ, Sun P, Lane CJ, Ventura EE, Davis JN, Kelly LA, Goran MI. Cardiorespiratory fitness predicts changes in adiposity in overweight Hispanic boys.Obesity (Silver Spring). 2008; 16:1072–1077. doi: 10.1038/oby.2008.16CrossrefMedlineGoogle Scholar
• 117. Schnurr TM, Gjesing AP, Sandholt CH, Jonsson A, Mahendran Y, Have CT, Ekstrøm CT, Bjerregaard AL, Brage S, Witte DR, et al.. Genetic correlation between body fat percentage and cardiorespiratory fitness suggests common genetic etiology.PLoS One. 2016; 11:e0166738. doi: 10.1371/journal.pone.0166738CrossrefMedlineGoogle Scholar
• 118. Browning MG, Bean MK, Wickham EP, Stern M, Evans RK. Cardiometabolic and fitness improvements in obese girls who either gained or lost weight during treatment.J Pediatr. 2015; 166:1364–1369. doi: 10.1016/j.jpeds.2015.03.011CrossrefMedlineGoogle Scholar
• 119. Howe AS, Skidmore PM, Parnell WR, Wong JE, Lubransky AC, Black KE. Cardiorespiratory fitness is positively associated with a healthy dietary pattern in New Zealand adolescents.Public Health Nutr. 2016; 19:1279–1287. doi: 10.1017/S1368980015002566CrossrefMedlineGoogle Scholar
• 120. Zaqout M, Vyncke K, Moreno LA, De Miguel-Etayo P, Lauria F, Molnar D, Lissner L, Hunsberger M, Veidebaum T, Tornaritis M, et al.. Determinant factors of physical fitness in European children.Int J Public Health. 2016; 61:573–582. doi: 10.1007/s00038-016-0811-2CrossrefMedlineGoogle Scholar
• 121. Gonzalez-Freire M, Scalzo P, D’Agostino J, Moore ZA, Diaz-Ruiz A, Fabbri E, Zane A, Chen B, Becker KG, Lehrmann E, et al.. Skeletal muscle ex vivo mitochondrial respiration parallels decline in vivo oxidative capacity, cardiorespiratory fitness, and muscle strength: the Baltimore Longitudinal Study of Aging.Aging Cell. 2018; 17:e12725. doi: 10.1111/acel.12725CrossrefGoogle Scholar
• 122. Delille HK, Alves R, Schrader M. Biogenesis of peroxisomes and mitochondria: linked by division.Histochem Cell Biol. 2009; 131:441–446. doi: 10.1007/s00418-009-0561-9CrossrefMedlineGoogle Scholar
• 123. Treviño-Saldaña N, García-Rivas G. Regulation of sirtuin-mediated protein deacetylation by cardioprotective phytochemicals.Oxid Med Cell Longev. 2017; 2017:1750306. doi: 10.1155/2017/1750306CrossrefMedlineGoogle Scholar
• 124. Larsen FJ, Schiffer TA, Borniquel S, Sahlin K, Ekblom B, Lundberg JO, Weitzberg E. Dietary inorganic nitrate improves mitochondrial efficiency in humans.Cell Metab. 2011; 13:149–159. doi: 10.1016/j.cmet.2011.01.004CrossrefMedlineGoogle Scholar
• 125. Albarwani S, Al-Hashmi K, Al-Abri M, Jaju D, Hassan MO. Effects of overweight and leisure-time activities on aerobic fitness in urban and rural adolescents.Metab Syndr Relat Disord. 2009; 7:369–374. doi: 10.1089/met.2008.0052CrossrefMedlineGoogle Scholar
• 126. Blackorby C, Donaldson D. A theoretical treatment of indices of absolute inequality.Int Econ Rev. 1980; 21:107–136.CrossrefGoogle Scholar
• 127. Kodama S, Saito K, Tanaka S, Maki M, Yachi Y, Asumi M, Sugawara A, Totsuka K, Shimano H, Ohashi Y, et al.. Cardiorespiratory fitness as a quantitative predictor of all-cause mortality and cardiovascular events in healthy men and women: a meta-analysis.JAMA. 2009; 301:2024–2035. doi: 10.1001/jama.2009.681CrossrefMedlineGoogle Scholar
• 128. Imboden MT, Harber MP, Whaley MH, Finch WH, Bishop DL, Kaminsky LA. Cardiorespiratory fitness and mortality in healthy men and women.J Am Coll Cardiol. 2018; 72:2283–2292. doi: 10.1016/j.jacc.2018.08.2166CrossrefMedlineGoogle Scholar
• 129. Benjamin EJ, Muntner P, Alonso A, Bittencourt MS, Callaway CW, Carson AP, Chamberlain AM, Chang AR, Cheng S, Das SR, et al.; on behalf of the American Heart Association Council on Epidemiology and Prevention Statistics Committee and Stroke Statistics Subcommittee. Heart disease and stroke statistics–2019 update: a report from the American Heart Association [published correction appears in Circulation. 2020;141:e33].Circulation. 2019; 139:e56–e528. doi: 10.1161/CIR.0000000000000659LinkGoogle Scholar
• 130. Ehrman JK, Brawner CA, Al-Mallah MH, Qureshi WT, Blaha MJ, Keteyian SJ. Cardiorespiratory fitness change and mortality risk among black and white patients: Henry Ford Exercise Testing (FIT) Project.Am J Med. 2017; 130:1177–1183. doi: 10.1016/j.amjmed.2017.02.036CrossrefMedlineGoogle Scholar
• 131. Sorić M, Jembrek Gostović M, Gostović M, Hočevar M, Mišigoj-Duraković M. Tracking of BMI, fatness and cardiorespiratory fitness from adolescence to middle adulthood: the Zagreb Growth and Development Longitudinal Study.Ann Hum Biol. 2014; 41:238–243. doi: 10.3109/03014460.2013.851739CrossrefMedlineGoogle Scholar
• 132. Van Oort C, Jackowski SA, Eisenmann JC, Sherar LB, Bailey DA, Mirwald R, Baxter-Jones AD. Tracking of aerobic fitness from adolescence to mid-adulthood.Ann Hum Biol. 2013; 40:547–553. doi: 10.3109/03014460.2013.817606CrossrefMedlineGoogle Scholar
• 133. Trudeau F, Shephard RJ, Arsenault F, Laurencelle L. Tracking of physical fitness from childhood to adulthood.Can J Appl Physiol. 2003; 28:257–271. doi: 10.1139/h03-020CrossrefMedlineGoogle Scholar
• 134. Campbell PT, Katzmarzyk PT, Malina RM, Rao DC, Pérusse L, Bouchard C. Prediction of physical activity and physical work capacity (PWC150) in young adulthood from childhood and adolescence with consideration of parental measures.Am J Hum Biol. 2001; 13:190–196. doi: 10.1002/1520-6300(200102/03)13:2<190::AID-AJHB1028>3.0.CO;2-NCrossrefMedlineGoogle Scholar
• 135. Högström G, Nordström A, Nordström P. Aerobic fitness in late adolescence and the risk of early death: a prospective cohort study of 1.3 million Swedish men.Int J Epidemiol. 2016; 45:1159–1168. doi: 10.1093/ije/dyv321CrossrefMedlineGoogle Scholar
• 136. Högström G, Nordström A, Eriksson M, Nordström P. Risk factors assessed in adolescence and the later risk of stroke in men: a 33-year follow-up study.Cerebrovasc Dis. 2015; 39:63–71. doi: 10.1159/000369960CrossrefMedlineGoogle Scholar
• 137. Lindgren M, Åberg M, Schaufelberger M, Åberg D, Schiöler L, Torén K, Rosengren A. Cardiorespiratory fitness and muscle strength in late adolescence and long-term risk of early heart failure in Swedish men.Eur J Prev Cardiol. 2017; 24:876–884. doi: 10.1177/2047487317689974CrossrefMedlineGoogle Scholar
• 138. Rabiee R, Agardh E, Kjellberg K, Falkstedt D. Low cardiorespiratory fitness in young adulthood and future risk of disability pension: a follow-up study until 59 years of age in Swedish men.J Epidemiol Community Health. 2015; 69:266–271. doi: 10.1136/jech-2014-204851CrossrefMedlineGoogle Scholar
• 139. Agbaje AO, Haapala EA, Lintu N, Viitasalo A, Barker AR, Takken T, Tompuri T, Lindi V, Lakka TA. Peak oxygen uptake cut-points to identify children at increased cardiometabolic risk: the PANIC study.Scand J Med Sci Sports. 2019; 29:16–24. doi: 10.1111/sms.13307CrossrefMedlineGoogle Scholar
• 140. Ferreira I, Twisk JW, Stehouwer CD, van Mechelen W, Kemper HC. Longitudinal changes in V̇O2max: associations with carotid IMT and arterial stiffness.Med Sci Sports Exerc. 2003; 35:1670–1678. doi: 10.1249/01.MSS.0000089247.37563.4BCrossrefMedlineGoogle Scholar
• 141. Johnson MS, Figueroa-Colon R, Herd SL, Fields DA, Sun M, Hunter GR, Goran MI. Aerobic fitness, not energy expenditure, influences subsequent increase in adiposity in black and white children.Pediatrics. 2000; 106:E50. doi: 10.1542/peds.106.4.e50CrossrefMedlineGoogle Scholar
• 142. Koutedakis Y, Bouziotas C, Flouris AD, Nelson PN. Longitudinal modeling of adiposity in periadolescent Greek schoolchildren.Med Sci Sports Exerc. 2005; 37:2070–2074. doi: 10.1249/01.mss.0000178099.80388.15CrossrefMedlineGoogle Scholar
• 143. Sigal RJ, Alberga AS, Goldfield GS, Prud’homme D, Hadjiyannakis S, Gougeon R, Phillips P, Tulloch H, Malcolm J, Doucette S, et al.. Effects of aerobic training, resistance training, or both on percentage body fat and cardiometabolic risk markers in obese adolescents: the healthy eating aerobic and resistance training in youth randomized clinical trial.JAMA Pediatr. 2014; 168:1006–1014. doi: 10.1001/jamapediatrics.2014.1392CrossrefMedlineGoogle Scholar
• 144. Agostinis-Sobrinho C, Ruiz JR, Moreira C, Abreu S, Lopes L, Oliveira-Santos J, Mota J, Santos R. Cardiorespiratory fitness and blood pressure: a longitudinal analysis.J Pediatr. 2018; 192:130–135. doi: 10.1016/j.jpeds.2017.09.055CrossrefMedlineGoogle Scholar
• 145. Kelishadi R, Cook SR, Amra B, Adibi A. Factors associated with insulin resistance and non-alcoholic fatty liver disease among youths.Atherosclerosis. 2009; 204:538–543. doi: 10.1016/j.atherosclerosis.2008.09.034CrossrefMedlineGoogle Scholar
• 146. Schmidt MD, Magnussen CG, Rees E, Dwyer T, Venn AJ. Childhood fitness reduces the long-term cardiometabolic risks associated with childhood obesity.Int J Obes (Lond). 2016; 40:1134–1140. doi: 10.1038/ijo.2016.61CrossrefMedlineGoogle Scholar
• 147. Oliveira RG, Guedes DP. Physical activity, sedentary behavior, cardiorespiratory fitness and metabolic syndrome in adolescents: systematic review and meta-analysis of observational evidence.PLoS One. 2016; 11:e0168503. doi: 10.1371/journal.pone.0168503CrossrefMedlineGoogle Scholar
• 148. McMurray RG, Bangdiwala SI, Harrell JS, Amorim LD. Adolescents with metabolic syndrome have a history of low aerobic fitness and physical activity levels.Dyn Med. 2008; 7:5. doi: 10.1186/1476-5918-7-5CrossrefMedlineGoogle Scholar
• 149. Lang JJ, Tremblay MS, Ortega FB, Ruiz JR, Tomkinson GR. Review of criterion-referenced standards for cardiorespiratory fitness: what percentage of 1 142 026 international children and youth are apparently healthy?Br J Sports Med. 2019; 53:953–958. doi: 10.1136/bjsports-2016-096955CrossrefMedlineGoogle Scholar
• 150. Ruiz JR, Cavero-Redondo I, Ortega FB, Welk GJ, Andersen LB, Martinez-Vizcaino V. Cardiorespiratory fitness cut points to avoid cardiovascular disease risk in children and adolescents; what level of fitness should raise a red flag? A systematic review and meta-analysis.Br J Sports Med. 2016; 50:1451–1458. doi: 10.1136/bjsports-2015-095903CrossrefMedlineGoogle Scholar
• 151. Hancox RJ, Rasmussen F. Does physical fitness enhance lung function in children and young adults?Eur Respir J. 2018; 51:1701374. doi: 10.1183/13993003.01374-2017CrossrefMedlineGoogle Scholar
• 152. Marques A, Santos DA, Hillman CH, Sardinha LB. How does academic achievement relate to cardiorespiratory fitness, self-reported physical activity and objectively reported physical activity: a systematic review in children and adolescents aged 6-18 years.Br J Sports Med. 2018; 52:1039. doi: 10.1136/bjsports-2016-097361CrossrefMedlineGoogle Scholar
• 153. Sardinha LB, Marques A, Minderico C, Palmeira A, Martins S, Santos DA, Ekelund U. Longitudinal relationship between cardiorespiratory fitness and academic achievement.Med Sci Sports Exerc. 2016; 48:839–844. doi: 10.1249/MSS.0000000000000830CrossrefMedlineGoogle Scholar
• 154. Wittberg RA, Northrup KL, Cottrell LA. Children’s aerobic fitness and academic achievement: a longitudinal examination of students during their fifth and seventh grade years.Am J Public Health. 2012; 102:2303–2307. doi: 10.2105/AJPH.2011.300515CrossrefMedlineGoogle Scholar
• 155. Hsieh SS, Tsai JR, Chang SH, Ho JY, Chen JF, Chen PH, Sung YT, Hung TM. The subject-dependent, cumulative, and recency association of aerobic fitness with academic performance in Taiwanese junior high school students.BMC Pediatr. 2019; 19:25. doi: 10.1186/s12887-018-1384-4CrossrefMedlineGoogle Scholar
• 156. Haapala EA. Cardiorespiratory fitness and motor skills in relation to cognition and academic performance in children: a review.J Hum Kinet. 2013; 36:55–68. doi: 10.2478/hukin-2013-0006CrossrefMedlineGoogle Scholar
• 157. Drollette ES, Pontifex MB, Raine LB, Scudder MR, Moore RD, Kao SC, Westfall DR, Wu CT, Kamijo K, Castelli DM, et al.. Effects of the FITKids physical activity randomized controlled trial on conflict monitoring in youth.Psychophysiology. 2018; 55:10.1111/psyp.13017. doi: 10.1111/psyp.13017CrossrefGoogle Scholar
• 158. Hillman CH, Pontifex MB, Castelli DM, Khan NA, Raine LB, Scudder MR, Drollette ES, Moore RD, Wu CT, Kamijo K. Effects of the FITKids randomized controlled trial on executive control and brain function.Pediatrics. 2014; 134:e1063–e1071. doi: 10.1542/peds.2013-3219CrossrefMedlineGoogle Scholar
• 159. Tacchi MJ, Heggelund J, Scott J. Predictive validity of objective measures of physical fitness for the new onset of mental disorders in adolescents and young adults.Early Interv Psychiatry. 2019; 13:1310–1318. doi: 10.1111/eip.12783CrossrefMedlineGoogle Scholar
• 160. Reddon H, Meyre D, Cairney J. Physical activity and global self-worth in a longitudinal study of children.Med Sci Sports Exerc. 2017; 49:1606–1613. doi: 10.1249/MSS.0000000000001275CrossrefMedlineGoogle Scholar
• 161. Goldfield GS, Adamo KB, Rutherford J, Murray M. The effects of aerobic exercise on psychosocial functioning of adolescents who are overweight or obese.J Pediatr Psychol. 2012; 37:1136–1147. doi: 10.1093/jpepsy/jss084CrossrefMedlineGoogle Scholar
• 162. Padilla-Moledo C, Castro-Piñero J, Ortega FB, Mora J, Márquez S, Sjöström M, Ruiz JR. Positive health, cardiorespiratory fitness and fatness in children and adolescents.Eur J Public Health. 2012; 22:52–56. doi: 10.1093/eurpub/ckr005CrossrefMedlineGoogle Scholar
• 163. Rodriguez-Ayllon M, Cadenas-Sanchez C, Esteban-Cornejo I, Migueles JH, Mora-Gonzalez J, Henriksson P, Martín-Matillas M, Mena-Molina A, Molina-García P, Estévez-López F, et al.. Physical fitness and psychological health in overweight/obese children: a cross-sectional study from the ActiveBrains project.J Sci Med Sport. 2018; 21:179–184. doi: 10.1016/j.jsams.2017.09.019CrossrefMedlineGoogle Scholar
• 164. Smpokos EA, Linardakis M, Papadaki A, Lionis C, Kafatos A. Secular trends in fitness, moderate-to-vigorous physical activity, and TV-viewing among first grade school children of Crete, Greece between 1992/93 and 2006/07.J Sci Med Sport. 2012; 15:129–135. doi: 10.1016/j.jsams.2011.08.006CrossrefMedlineGoogle Scholar
• 165. Dyrstad SM, Aandstad A, Hallén J. Aerobic fitness in young Norwegian men: a comparison between 1980 and 2002.Scand J Med Sci Sports. 2005; 15:298–303. doi: 10.1111/j.1600-0838.2005.00432.xCrossrefMedlineGoogle Scholar
• 166. Andersen LB, Froberg K, Kristensen PL, Moller NC, Resaland GK,Anderssen SA. Secular trends in physical fitness in Danish adolescents.Scand J Med Sci Sports. 2010; 20:757–763. doi: 10.1111/j.1600-0838.2009.00936.xCrossrefMedlineGoogle Scholar