Skip Navigation LinksHome > Fall 2011 - Volume 23 - Issue 3 > Health-Related Fitness in Children and Adolescents
Pediatric Physical Therapy:
doi: 10.1097/PEP.0b013e318227b3fc
Special Communication

Health-Related Fitness in Children and Adolescents

Ganley, Kathleen J. PT, PhD, C/NDT; Paterno, Mark V. PT, PhD, MBA, SCS, ATC; Miles, Cindy PT, MEd, PCS, C/NDT; Stout, Jean PT, MS; Brawner, Lorrie PT, MHS; Girolami, Gay PT, MS, C/NDT; Warren, Meghan PT, MPH, PhD

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Author Information

Department of Physical Therapy and Athletic Training, Northern Arizona University (Drs Ganley and Warren), Flagstaff, Arizona; Sports Medicine Biodynamics Center, Division of Occupational and Physical Therapy, Cincinnati Children's Hospital Medical Center (Dr Paterno), Cincinnati, Ohio; Cindy Miles and Associates (Ms Miles), Whitehall, Pennsylvania; Center for Gait and Motion Analysis, Gillette Children's Specialty Healthcare (Ms Stout), St. Paul, Minnesota; Ashland Community Hospital (Ms Brawner), Ashland, Oregon; Department of Kinesiology and Nutrition, University of Illinois at Chicago (Ms Girolami), Chicago, Illinois.

Correspondence: Kathleen J. Ganley, PT, PhD, PO Box 15105, Flagstaff, AZ 86011 (Kathleen.ganley@nau.edu).

The authors declare no conflict of interest.

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Abstract

Purpose: The American Physical Therapy Association Section on Pediatrics developed a task force to summarize fitness guidelines for children and adolescents. The purposes of this article were to review components, measurement methods, and consequences of physical fitness, and to summarize evidence-based activity recommendations for youth.

Summary of Key Points: Health-related fitness is comprised of body composition, flexibility, cardiorespiratory endurance, and muscular strength and endurance. Each of these components is reviewed in terms of definition, assessment, normative values, and recommendations.

Conclusions: The task force supports the guidelines of the US Department of Health and Human Services, which state that to promote overall health and wellness, youth should participate in 60 minutes or more of physical activity every day.

Recommendations for Clinical Practice: Physical therapists should apply research relevant to health-related fitness when treating youth. Promoting fitness, health, and wellness in our communities is a responsibility all therapists should assume.

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INTRODUCTION

The American Physical Therapy Association (APTA) Section on Pediatrics developed a task force to identify and summarize physical fitness guidelines for children (6–11 years old) and adolescents (12–19 years old) that could be used when (a) designing or implementing treatment programs, (b) applying research, and (c) establishing community-based fitness programs. The primary purposes of this article were to review components of fitness, measurement methods, and health-related consequences of fitness, and to summarize evidence-based recommendations for physical activity in children and adolescents. In addition, this article should serve as a “call to arms” to all physical therapists (PTs) who are or will be assuming the rights and responsibilities associated with being service providers for health, fitness, and wellness.

For the purposes of this article operational definitions, which have been described in detail by Caspersen et al1 and the American College of Sports Medicine,2 were used. “Physical fitness” refers to a set of attributes that people have or achieve that relates to the ability to perform physical activity; “physical activity” refers to any body movement produced by skeletal muscles that results in energy expenditure; “exercise” refers to physical activity that is planned, structured, repetitive, and purposive in the sense that improvement or maintenance of one or more components of physical fitness is an objective.

Physical fitness can be described in terms of skill-related and health-related fitness. Skill-related fitness is associated with motor skill performance or sport; the components of skill-related fitness include speed, agility, balance, coordination, power, and reaction time.2 The focus of this article was health-related fitness, which has the following components: body composition, flexibility, cardiorespiratory endurance, and muscular strength and endurance.2,3 As implied by the name, health-related fitness is an important component of overall health. Children who are unfit are at increased risk for cardiovascular4,5 and metabolic disease.6 Risk factors for these conditions continue from childhood into adulthood.710 Furthermore, fitness in children may be important for bone health11,12 and academic performance.1315 Current tests to measure fitness in youths are presented in Table 1. Each component of health-related fitness is reviewed below including definitions, assessments, published normative values, and recommendations for a healthy level of fitness.

Table 1
Table 1
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BODY COMPOSITION

Body composition refers to the relative amount of fat versus fat-free body mass.2 A healthier body composition in childhood and adolescence is associated with a healthier cardiovascular profile later in life and with a lower risk of death.5 Eisenmann6 explains that body composition (fatness) is more strongly related to adverse health conditions (eg, metabolic syndrome) than is overall fitness, as determined by maximal oxygen uptake (VO2max), in children. Healthy ranges of body fat percentages are 10% to 25% for boys and 17% to 32% for girls.19

Body composition changes with chronological age, growth, and maturation, and may not be accurately determined simply by measuring body mass. There are several technologically sophisticated tools/methods that can be used to measure body composition with varying degrees of accuracy. These methods, including magnetic resonance imaging, computerized tomography, dual-energy x-ray absorptiometry,2023 bioelectrical impedence,24,25 and air displacement plethysmography,26 involve expensive equipment and/or exposure to radiation. The principles, strengths, and limitations of each of these methods have been reviewed.2729 Of these sophisticated methods, dual-energy x-ray absorptiometry is considered the gold standard for validation studies of body composition and other research because of its balance of accuracy, cost efficiency, and safety.30,31 In the following paragraphs, calculation of body mass index (BMI) and measures of waist circumference and skinfolds are described in detail as these are reasonable estimates of body composition and are more readily available to clinicians.32

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Body Mass Index

Body mass index is often used as a proxy for body composition.33 It is calculated by dividing the child's body mass (kg) by height (m) squared. A percentile value is determined by comparing the measured BMI to sex- and age-normed tables.34 Median data (50th percentile) from these tables were averaged across months to approximate normative values by year of age. These data are reported in Table 2.

Table 2
Table 2
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In general, BMI declines during infancy and early childhood, reaches a nadir at about 5 to 7 years, and then increases through the remainder of childhood and adolescence. Generally, youth with a BMI between the 5th and 85th percentile when matched for sex and age are considered to be in a healthy range. A child or adolescent may be considered underweight, overweight, or obese if his/her BMI falls below the 5th percentile, between the 85th and 95th percentiles, or above the 95th percentile, respectively.37 Children and adolescents who have high BMIs are likely to have multiple cardiovascular risk factors and a high risk for adult obesity.38 According to data from The National Health and Nutrition Examination Survey 2007–2008, almost 17% of children and adolescents, 2 to 19 years of age are considered obese and almost 32% are overweight.39

Measures to calculate BMI are safe, simple, and inexpensive.32 However, the use of BMI to estimate body composition is not without limitations.40 Because it is only based on height and weight, BMI does not discriminate between lean mass and fat mass, nor does it indicate fat distribution. Two other anthropometric measures that provide information about relative proportions of body fat and fat distribution are skinfold thickness and waist circumference.

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Skinfold Thickness

Measurements of skinfold thickness at specific sites can be used to estimate proportions of fat mass, or adiposity, in children and adolescents32,35,41; hence, more specific information about the amount and distribution of fat can be obtained from skinfold measurements than from BMI. So, whereas BMI and skinfold measurements are each used to estimate body composition, they are independent of each other. This was illustrated, especially in the upper extremes of BMI distribution, in a study by Olds,42 which demonstrated that median skinfold thicknesses for children considered overweight or obese on the basis of BMI cutoffs do not correlate with skinfold percentiles across age.

Common sites for skinfold measurements include the tissue over the triceps and subscapularis muscles.35 However, some protocols also include measurements over the abdomen43 or calf musculature.16 A thorough discussion on the measurement of skinfold thickness at various sites has been provided by Durnin et al.44 Typically, the average of 2 or 3 measurements at each site is determined and regression equations are used to estimate the percentage of body fat.45,46 For example, for girls 8 to 18 years of age the following equation was recommended by Slaughter et al46:

Equation (Uncited)
Equation (Uncited)
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Centile standards35 can then be used for assessment. Median tricep and subscapular skinfold values35 by age are presented in Table 2. Although skinfold measurements can estimate body fat with reasonable accuracy (95%–97%),47 caliper selection and intra- and interobserver errors are concerns.48

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Waist Circumference

Waist circumference is easy to determine and is a reasonable indicator of central adiposity for children and adolescents.49,50 In children51,52 and adolescents51,53 central adiposity, independent of total adiposity, is associated with hyperlipidemia, cardiovascular disease risk factors, and type II diabetes. Garnett et al54 reported that children with an increased central adiposity at the age of 8 years were 4 times as likely to have cardiovascular disease risk clustering in adolescence as were children with a smaller waist circumference.

Age, sex, and ethnicity-specific waist circumference percentiles have been compiled for children and adolescents.55,36 Age and sex-specific median values, averaged for year of age, are reported in Table 2. For preschool-aged children, waist circumference cutoffs that can be used to discriminate central adiposity range from 53 cm at 3 years to 57 cm at 5 years.56

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Recommendations Regarding Body Composition

Current physical activity guidelines for youth recommend 60 minutes or more of daily physical activity.57 Work by Wittmeier et al,58 which established an association between 60 minutes per day of physical activity with an energy expenditure of 8 or more kcal/kg/d and acceptable levels of BMI and percent body fat in children, substantiates this recommendation. Tudor-Locke et al59 estimated daily step counts necessary for children to maintain a healthy body composition; 12,000 and 15,000 steps per day were recommended for 6- to 12-year-old girls and boys, respectively.

Body composition is determined by the balance, or imbalance, of caloric intake and energy expenditure. A thorough review of dietary considerations and recommendations are beyond the scope of this article, and readers are referred to nutrition guidelines published by the American Dietetic Association.60 Briefly, it is recommended that children and adolescents follow the US Department of Health and Human Services' Dietary Guidelines for Healthy Eating.61 The guidelines recommend consumption of fruits and vegetables, whole grains, low-fat and nonfat dairy products, beans, fish, and lean meat, and limited intake of saturated and trans fat, cholesterol, and foods with added sugar or salt. Furthermore, drinking water versus beverages with added sugars, such as soft drinks, fruit juice drinks, and sports drinks, is highly recommended.

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FLEXIBILITY

Flexibility refers to the ability to move a joint through its complete range of motion.2 Flexibility is joint specific, and the extensibility of muscle, as well as that of neighboring noncontractile tissues (eg, joint capsule, ligaments, and tendons) affects the flexibility of a joint. Evidence to quantify the relationship between flexibility and health is lacking.5

Measuring flexibility, or available motion, at an individual joint generally involves the use of a goniometer, an inclinometer, or a tape measure.2 However, measuring all anatomical joints of an extremity or of the body is not a practical method of estimating or determining overall flexibility. Therefore, flexibility screenings and field tests often include a single measurement thought to represent general flexibility. The most commonly used measure is the sit and reach test,6267 which is a composite assessment of gastrocnemius, hamstring, buttock, lumbar, thoracic, and scapular flexibility.68 The modified sit and reach68 and the back saver sit and reach tests69 are alternatives for assessing flexibility; however, their use may be limited as normative data have not been published.

For a sit and reach test,2,3 a specially constructed box is used. The box is 30 cm high, and the top panel has a measuring scale with 23 cm aligning with the static foot position. The participant sits without shoes, with legs about shoulder width apart, and knees extended. The soles of the feet are placed against the box; the participant then slowly reaches forward as far as possible with both hands (relatively symmetrically) along the top of the box. After 3 practice trials, the participant holds the fourth reach for 2 to 3 seconds while that distance is recorded to the nearest centimeter.

The v-sit and reach3 is a modification of the sit and reach test that does not require a box. For this test, a straight line extending approximately 60 cm is marked on the floor as the baseline. A measuring line, approximately 120 cm long, is drawn perpendicular to the midpoint of the baseline extending 2 feet on each side and marked off in centimeter intervals. The point where the baseline and measuring line intersect is the “0” point. The participant sits without shoes, with legs about shoulder width apart and knees extended with the measuring line between the legs and the soles of feet placed immediately behind the baseline. With one hand on top of the other, palms down, the participant places them on the measuring line and slowly reaches forward as far as possible, keeping fingers on the measuring line. After 3 practice trials, the participant holds the fourth reach for 2 to 3 seconds while that distance is recorded to the nearest centimeter, with positive scores representing reaches beyond baseline and negative scores representing reaches behind baseline.

The President's Council on Fitness reports sit and reach and v-sit and reach scores and percentiles for girls and boys 5 to 17 years of age based on the 1985 National School Population Fitness Survey.3 The values were validated in 1998 through comparison with a large nationwide sample collected in 1994. Median, normative values are provided in Table 3. In general, maximal distances reached increased with age and reach scores of girls slightly exceeded those of boys. At the 50th percentile, sit and reach scores ranged from 26 to 34 cm in boys and from 27 to 35 cm in girls, with 23 cm corresponding to the position of the feet. However, visual inspection suggests that the pattern may be sex-specific. In girls, the distance reached tended to increase with age until about 15 years of age, and values plateaued or declined from 15 to 17 years of age. In boys, the distance reached appeared relatively stable from 5 to 12 years of age and increased from 12 to 17 years of age.

Table 3
Table 3
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Specific guidelines regarding flexibility have not been identified. However, it is generally accepted that static, versus ballistic, stretching performed several times per week can maintain or increase flexibility.70

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CARDIORESPIRATORY ENDURANCE

Cardiorespiratory endurance, the focus of this section, is one of the health-related physical fitness components.2 Because children and adolescents are not frequently diagnosed with cardiovascular and metabolic diseases, much of the work has examined risk factor profiles to reduce disease risk with age. Observational studies have shown that physically active children and adolescents have higher high-density lipoproteins,7172 lower triglycerides,72,73 lower low-density lipoproteins,74 lower BMI,71,72,75 lower estimates for body fat,72,73,76 improved insulin sensitivity,73,74,76,77 and lower systolic blood pressure.78 Some of these findings were independent of body fat and BMI.73,76 When a measure of cardiorespiratory endurance was examined, favorable associations were found between aerobic fitness and high-density lipoproteins, systolic blood pressure, diastolic blood pressure,79 BMI, measures of body fat,75 and arterial stiffness80; this finding was independent of body weight. A positive association was also found between cardiorespiratory endurance and measures of insulin sensitivity,77,79 although this relationship is stronger in boys than in girls.77

Cardiorespiratory endurance is the ability of the cardiovascular and pulmonary systems to deliver oxygen to the tissues appropriate to the level of activity.2 Maximal oxygen uptake is the criterion measure for cardiorespiratory endurance, and measures the highest rate of oxygen consumed by the skeletal muscle during exercise. It is expressed either as liters of oxygen per minute (absolute) or relative to body weight (milliliters of oxygen per kilogram body weight per minute [mL/kg/min]).

Maximal oxygen uptake is assessed in a laboratory during a progressive exercise test using a treadmill or cycle ergometer while oxygen uptake and carbon dioxide output are measured; the point at which oxygen uptake does not increase in response to increasing workload (plateau in oxygen uptake) is considered maximal oxygen consumption or VO2max. Many studies have measured VO2max in children and adolescents; a review of these studies is published.81 Exercise testing for clinical health/fitness purposes is generally not indicated for children or adolescents unless there is a health concern.2

Differences in VO2max (both absolute and relative to body weight) between boys and girls are generally similar at young ages (eg, 1.8 ± 0.2 L/min for both girls and boys at the age of 10 years). As children age, absolute VO2max increases in boys to a greater extent than in girls (2.3 ± 0.5 L/min vs 2.7 ± 0.5 L/min for girls and boys, respectively at 16 years of age).82 When examining VO2max relative to body weight, boys remain fairly consistent throughout adolescence whereas girls experience a decline82,83 due to an increase in body mass during that time. In a study of 235 adolescents (102 boys and 133 girls), VO2max remained fairly consistent at 59 mL/kg/min in boys, but girls showed a gradual decrease, from about 50 mL/kg/min at the age of 12 years to 45 mL/kg/min at the age of 17 years.83

In a majority of children, there is an absence of the oxygen uptake plateau84; normally a criterion measure for a maximal test. Therefore, it may be more appropriate to define the highest oxygen uptake (VO2) during a test to voluntary exhaustion as VO2peak rather than VO2max.84,85 In addition, maximal exercise testing in most children may not be indicated. The American College of Sports Medicine states, “Exercise testing for clinical or health/fitness purpose is generally not indicated for children or adolescents unless there is a health concern,”2 and this opinion is shared by the American Heart Association.86

A measure of cardiorespiratory endurance may be useful to track progress in an exercise program. Field testing can be employed for this purpose to estimate VO2peak87 and is often more cost efficient and can be completed outside a laboratory. The most common measures among youth in the field are distance runs, and the 1-mile run/walk is the most common of these.88 This test requires youth to complete the mile distance as quickly as possible, running is expected, although walking is allowed. The 1-mile run/walk test is a component of several youth fitness tests, including The President's Challenge Health Fitness Test.3 Alternatively, time-based tests such as the shuttle test are used in several fitness batteries.3,89 Age and sex-specific normative values for the 1-mile run and shuttle test are presented in Table 3 based on The President's Challenge Health and Physical Fitness Tests.3 These values signify the levels at which youth would receive The National Physical Fitness Award, which demonstrates a basic, yet challenging, level of physical fitness. FITNESSGRAM (Human Kinetics, Champaign, IL) normative values have also been published.16 Several studies have also assessed the use of the 20-m shuttle test as a field test for cardiorespiratory endurance. Castro-Piñero et al90 published a review of the psychometric properties of the shuttle test and have concluded the test is a valid and acceptable field measure for children and adolescents.

A physical activity or exercise program is recommended for all children and adolescents. Aerobic exercise has been shown to improve cardiorespiratory endurance or fitness by 5% to 15% in youth.57 In a review of 22 studies assessing the dose of aerobic exercise to attain improvements in fitness, it was concluded that an intensity greater than 80% of maximal heart rate, a frequency of 3 to 4 days per week, a duration of 30 to 60 minutes per session, and a length of 1 to 3 months resulted in improvements in cardiorespiratory fitness.84 Current physical activity guidelines for youth published by the US Department of Health and Human Services recommend 60 minutes (1 hr) or more of age-appropriate physical activity daily, and that most of this time should be spent doing aerobic exercise.57

An exercise prescription should consider 4 parameters: mode (type), intensity, frequency, and duration.2 Mode or type refers to the specific exercises or activity completed. Intensity is related to the effort or amount of work (energy expenditure) required to complete the activity. Frequency indicates the number of exercise sessions in a given period of time, and duration is the length of the activity.

The recommended mode of aerobic exercise includes activities requiring rhythmic movement of the large muscles (eg, running, hopping, skipping, swimming, dancing, and bicycling).57 The short bursts of activities in which many children participate (eg, tag) may not technically be considered aerobic activities, but are included in the recommendations for aerobic exercise. The mode of activity should also be age-appropriate with more play activities for younger age groups that focus of developmental milestones. As children age, activities may be more structured and include fewer brief burst-type activities.57

With respect to intensity, the current exercise guidelines recommend a combination of moderate- and vigorous-intensity aerobic physical activities or only vigorous-intensity aerobic physical activities.57 It is not recommended that youth perform only moderate-intensity activity because of the greater improvement in cardiorespiratory endurance with vigorous-intensity activities.84 Although exercise testing can be used to prescribe intensity using a percentage of heart rate or VO2max/peak, the current guidelines use either an absolute or a relative intensity scale.57 Absolute intensity is determined by the amount of energy expended during the activity, without taking into account a person's cardiorespiratory fitness, and is measured with metabolic equivalents (METs).91 A MET corresponds to the ratio of work metabolic rate to the resting metabolic rate. Resting metabolic rate is defined as 1 MET or 3.5 mLO2/kg/min. Activities between 3.0 and 5.9 METs are considered moderate and more than 6.0 METs, vigorous. Relative intensity, on the contrary, describes a person's effort relative to fitness using a scale of 0 to 10, where 0 corresponds to sitting and the hardest effort possible is 10. Moderate-intensity activity is considered 5 or 6 of 10, and is characterized by youths feeling their heart beating faster than normal and breathing harder than normal. Vigorous-intensity activity is considered to be 7 or 8 with a feeling of the heart beating much faster than normal and breathing much harder than normal. Categorizing intensity in either of these ways allows children and adolescents to monitor their own intensity, and does not require additional equipment or supervision.

Current guidelines recommend daily exercise and state, “most of the 60 or more minutes a day should be....aerobic physical activity.”57 Although 2 days per week has been shown to increase VO2peak in children,92 gains in VO2peak among children and adolescents were higher with increased frequency of activity.84 The evidence for the duration of the exercise is not as clear, but 30 to 60 minutes of exercise has been shown to result in improvements in VO2peak.84 One hour daily allows time for aerobic exercise, but also time to meet the other recommendations for muscle and bone strengthening exercises. Although the evidence is not sufficient for a consistent conclusion on parameters of aerobic exercise in children and adolescents, for overall health it appears that the total amount of physical activity is more important than any one parameter (frequency, intensity, or duration).57

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STRENGTH

Muscular strength (“maximum force application”88) and muscular endurance (“repeated, high resistance muscle contractions”88) are components of health-related physical fitness.2 Muscular fitness has been shown to have an inverse association with clustered metabolic risk factors, independent of cardiorespiratory endurance.93 Although conclusions are limited due to methodologic limitations of the studies, several articles have reported evidence for some potential health-related benefits of strength training in children and adolescents. Resistance training has not been found to result in meaningful or statistical long-term differences in body composition (eg, weight, limb circumference, skinfolds),94 but some short-term favorable effects were found.9597 Resistance training has also been shown to provide some protection against loss of fat-free mass during weight loss in obese children.98 The majority of studies have not shown strong results for specific resistance training protocols to favorably affect metabolic health,99 but evidence indicates that insulin sensitivity was improved in 22 boys who were overweight after 16 weeks of resistance training that remained after adjusting for changes in body composition.100 The benefits of resistance training on estimates of bone strength are not consistent, but significant changes in femoral neck bone mineral density were found after 15 months of 3 times weekly resistance training in 46 adolescent girls compared with a control group (n = 21).101 The lack of methodologically strong and consistent evidence, however, should not halt efforts to engage children and adolescents in strength training, because individual studies show benefit, and more rigorously designed studies are ongoing. Readers are referred to a more detailed review by Faigenbaum and Myer102 on specific program design for pediatric resistance training.

Historically, participation in resistance (or strength) training programs by children and adolescents was thought to carry significant risks of injury and was not routinely recommended.103 Concerns were related to injury to epiphyseal plates altering growth and development.104106 Most evidence shows that many of the reported injuries were related to improper training, excessive weight, and/or lack of adult supervision.106,107 With proper supervision and exercise prescription, strength training results in minimal risk to children and adolescents.94,108 In addition, it was thought that children could not improve muscular strength through resistance training because of a lack of circulating androgens.109 Evidence has shown that youth are able to improve muscular strength with resistance training,94,110112 and the relative magnitude of improvement is similar between youth and adults, as well as between girls and boys.112 These strength gains appear to be related to resistance training, and not only to growth and maturation, as strength gains associated with resistance training were not maintained during a period of detraining.94

Recent evidence suggests that resistance training in children and adolescents can not only be safe when certain important guiding principles are followed, but can also result in positive outcomes.94,113 Several organizations, including the National Strength and Conditioning Association,107 the American College of Sports Medicine,2 and the American Academy of Pediatrics,114 advocate for resistance training for children and adolescents within certain guidelines (see later).

Although muscular strength and muscular endurance are separate concepts with different physiological bases, testing often combines them into a single measure called muscular strength/endurance. Because measures of muscular strength/endurance are specific to a particular muscle group, testing ideally should encompass each muscle group of interest. Despite the known importance of specificity in muscle group testing, little has been published concerning muscle-specific testing protocols, especially for children and adolescents without neuromuscular disease.

In the laboratory or clinic, muscle strength is typically measured using an isometric or isokinetic dynamometer, or isotonic 1 repetition maximum (1 RM).88,115 Regardless of the testing method, strength is measured by a maximal force exerted against an external object. Muscle endurance can be measured using the same instruments with isometric endurance signified by the longest sustained contraction at a force corresponding to a percentage of isometric strength; isokinetic endurance can be measured by using a set cadence and determining when torque decreases beyond a prespecified percentage of maximum isokinetic strength; and isotonic endurance can be measured by the maximum number of isotonic contractions against a percentage of 1 RM.88

Isotonic 1 RM testing methods have not been used frequently in children and adolescents because of the presumption that high-intensity lifts may lead to unfavorable structural changes.103 Studies that have used isotonic 1 RM testing, however, have reported no injuries when used in carefully designed protocols (eg, warm-up, close supervision, critically selected tests).110,116119 Test-retest reliability of 1 RM testing in a laboratory has been reported to be high in a cohort of children.120 Isotonic 1 RM has been reported to be quite variable in children. Milliken et al119 reported leg press 1 RM ranged from 75% to 363% of body weight and chest press 1 RM from 25% to 103% of body weight in a sample of 90 children aged 6 to 13 years. Therefore, it may be useful to examine 1 RM values relative to body weight or mass. To our knowledge, no normative values for 1 RM have been published for children or adolescents. Because of the time-consuming nature of 1 RM testing and lingering concerns about its safety with children, prediction equations have been developed to estimate 1 RM using submaximal loads, although most have used athletic or resistance-trained adolescent cohorts and may not be applicable to the general population of youth. Robertson et al121 included 70 girls and boys and used a rate of perceived exertion scale (Children's OMNI Resistance Exercise Scale) to estimate 1 RM for bicep curls and knee extension. The prediction equations estimated 1 RM moderately well (R2 for boys: 0.79 and 0.76 for bicep curls and knee extension, respectively; and girls: 0.76 and 0.79 for bicep curls and knee extension, respectively) in a sample of youth 10 to 14 years old. This may provide some categorization of isotonic muscular strength for children and adolescents.

Isometric reference values have been published from a cohort of 270 children 4 to 16 years old, who were healthy.122 These researchers used a hand-held dynamometer and tested 11 muscle groups (neck flexors, shoulder abductors, elbow flexors and extensors, wrist extensors, 3-point grip, hip flexors and abductors, knee flexors and extensors, and foot dorsiflexors) in boys and girls. Reference values were influenced by weight, age, and sex. The authors concluded that these values can be used to quantify muscle weakness or to evaluate the possible effects of disease or therapy in children.

The National Isometric Muscle Strength Consortium developed prediction equations of normal isometric strength that can be used to determine strength deficits in 10 different muscle groups.123 Unfortunately, the sample comprised men and women between 18 and 80 years old and the authors caution against using the equations for populations other than adults. A similar tool in children would be valuable.

The most complete reference values for muscle strength in children and adolescents have been published using isokinetic testing methods. Wiggin et al115 tested quadriceps and hamstring strength at 3 speeds in 3587 children aged 6 to 13 years. Age- and sex-specific normative values were determined for each speed and muscle, again with height explaining the majority of the variance in strength among the participants.

Although maximal strength testing as described earlier can be used to assess strength changes resulting from a resistance training program in children and adolescents, these tests are labor- and time-intensive, and cannot be completed practically in a group setting. The testing protocols often require equipment that is not readily available; require testing multiple muscle groups; and require several measures to obtain the most accurate result. For example, a protocol used for children and adolescents required on average 7 trials for upper body and 11 trials for the lower body to reach 1 RM with 2 minutes between each trial.118 Therefore, field-based measures may have more clinical applicability for strength assessment. Significant and moderate correlations have been reported between 1 RM isotonic strength testing and common field measures (eg, handgrip and long jump).119 Many youth fitness tests include subtests that combine strength and endurance; examples include the curl-up test and modified pull-up test or push-up test. Information on the measurement properties of each of these tests can be found in an excellent review by Plowman.124 A pull-up or flexed arm test could also be used, but these tests require youths to overcome body weight to complete the test.125

The curl-up test is measured with knees bent and feet on the floor unanchored. The youth is asked to perform as many curl-ups as possible, curling to 45°. The test is performed to a set cadence and continues until the youth is unable to continue or is unable to maintain the set pace. This test has been reported to have moderate to good reliability (0.6 and 0.9)126 and good face validity127; little is known about the validity compared with a reference standard of muscle strength and muscle endurance. A modified pull-up test is performed by having the youth lie in a supine position and grasp a bar above the body. With the feet on the floor and legs straight, the youth pulls up as many times as possible, lifting the buttocks off the floor and bringing the chin above the bar. Reliability was measured in 62 youth aged 10 to 13 years and was found to be excellent (intraclass correlation coefficient = 0.95–0.99).128 In addition, the test was able to be used to correctly classify youths on passing standards using normative values over 2 trials.

Finally, the push-up test is completed by starting in a regular push-up position and by completing as many push-ups as possible using a set cadence. The test stops when the participant stops or rests, or is unable to maintain correct body position or push-up form. Like the modified pull-up test, the push-up test showed excellent test-retest reliability (intraclass correlation coefficient = 0.94–0.99) as well as an ability to reliably distinguish between those participants who “passed” and “failed” using normative values (κ = 0.94 for girls and boys as well as for the combined sample).128 Interestingly, the researchers found that the 2 tests—modified pull-up and push-up tests—did not classify the participants similarly when comparing with passing standards from the FITNESSGRAM normative values. Therefore, the completion of both tests may be appropriate to describe strength and endurance relative to other children and adolescents.

These field-based tests are common methods used to assess muscular strength and endurance in several youth fitness batteries.3,16 Criterion values for different levels of fitness are available for these youth fitness batteries. The median values for The President's Physical Fitness Test3 are displayed in Table 3, which signify the levels at which youth receive The National Physical Fitness Award. FITNESSGRAM normative values have also been published.16

Recently, research has been conducted to examine alternative field tests for muscular strength. The standing long jump was found to have the strongest association (R2 = 0.829–0.864) with other lower body field muscular strength tests (eg, vertical jump), and with upper body (eg, push-ups) field muscular strength tests (R2 = 0.694–0.851) in 94 youths aged 6 to 17 years.129 The authors concluded that this test could be used as a general index of upper and lower body muscular fitness in youth, although additional studies in varied populations would be useful to fully understand the test's clinical applicability.

Current physical activity guidelines include muscle-strengthening activities for all youth. The guideline states, “As part of their 60 or more minutes of daily physical activity, children and adolescents should include muscle-strengthening physical activity on at least 3 days of the week.”57 Similar to aerobic exercise, a muscle-strengthening exercise prescription should include mode, intensity (volume), and frequency.

The choice of an exercise (mode) is dependent on the age of the youth, as well as preference for the activity. It is important that the activity adheres to the principle of overload; that is, the muscles must be worked at a level above normal daily activities.2 The muscle-strengthening activities can include unstructured activities as part of play (eg, climbing trees, tug-of-war), or more structured activities (eg, lifting weights, resistance bands). Regardless of the specific exercise selected, multiple- and single-joint exercises should be included as well as exercises that work muscles both concentrically and eccentrically.107

The current exercise guidelines do not include detailed recommendations on the intensity/volume of the muscle-strengthening activities. Intensity usually refers to the amount of resistance for a specific exercise. Conversely, volume refers to the total amount of work performed in an exercise session. The National Strength and Conditioning Association has explicit recommendations regarding intensity/volume as well as frequency107 that are summarized in Table 4. Intensity is reported in percentage of 1 RM. If maximal testing is not completed, an intensity of 10 to 15 RM may be used initially, progressing to 6 to 10 RM. Alternatively, prediction equations from submaximal loads may be used.121 Volume is recommended to allow lighter loads initially to ensure proper technique is used, and volume may be modified for specific exercises.107

Table 4
Table 4
Image Tools

Three times weekly is the recommended frequency in the current physical activity guidelines,57 and the recommended frequency from The National Strength and Conditioning Association.107 Both of the guidelines also recommend muscle strengthening (resistance training or muscle-strengthening activities) on nonconsecutive days to minimize injury risk.

Several additional considerations are recommended for a safe resistance-training program. Before participation, any signs or symptoms suggestive of any conditions that would contraindicate participation in resistance training should be considered; children and adolescents should be cleared by a health care professional, but in general this is not mandatory.107,130 Currently, a minimum age requirement for participation in resistance training has not been published. According to The National Strength and Conditioning Association, in general, if a child is ready for participation in sports (7–8 years), then resistance training is appropriate.107 Children and adolescents should be supervised with resistance training and should be instructed in proper form with no/light loads before progressing to heavier weights. Previous reports of injury during resistance training in children were often related to a lack of supervision resulting in traumatic injury, or poor technique resulting in overuse injury.94,106,108 Finally, adequate warm up and cool down should be conducted before and after participation. Evidence regarding the effectiveness of stretching to reduce activity- or exercise-related injuries is inconsistent.131135 More detailed youth resistance-training guidelines for repetition velocity, choice and order of exercise, and progression are beyond the scope of this review; readers are referred to excellent summaries.102,107

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DISCUSSION

This article reviewed definitions of fitness, components of, and measurement methods for health-related fitness, available normative values, and consequences of poor health-related fitness. The challenge to this task force by the Board of Directors of the Pediatric Section of the APTA was to determine fitness guidelines. As such, and as an overall conclusion of the article, the task force supports the guidelines of the US Department of Health and Human Services,57 which state that to promote overall health and wellness, children and adolescents should participate in 60 minutes or more of physical activity every day. Most of the 1 hour or more a day should be either moderate- or vigorous-intensity aerobic physical activity. As part of their daily physical activity, children and adolescents should participate in vigorous-intensity activity and muscle-strengthening and bone-strengthening activities on at least 3 days per week. These overall guidelines primarily address cardiorespiratory function and strength. With respect to body composition, a BMI below the 85th percentile is recommended and can generally be attained through a balance of energy intake and expenditure.34 Although age-specific, population-based normative values are available for waist circumference and skinfold measurements,55,36 guidelines specific to children and adolescents have yet to be published. The relationship between flexibility and overall health is weak to nonexistent,5 and no specific guidelines or recommendations for flexibility could be identified.

To get the recommended amount of activity, youths may participate in competitive or noncompetitive play, such as bike riding, dancing, swimming, or skating. Several studies have shown that children whose parents are physically active tend to be more active themselves.57 Therefore, parents can be encouraged to plan family activities that include play and exercise. Finally, children and adolescents often must choose whether to fill free time with active or sedentary behaviors. A general recommendation is to limit a child's screen time, which includes time spent watching television, playing video games, and leisure-time computer use, to less than 2 hours per day.57

A full review of interventions aimed to improve health-related fitness is beyond the scope of this article and is a suggested topic for a subsequent review. Furthermore, the information presented in this article is largely related to a “nonclinical” population, one that is not often part of a PT's practice. Physical fitness is often compromised in children with developmental disabilities,17,18,136 and physical activity is known to provide health benefits for this population.137 Research in the areas of fitness testing and interventions for children with disabilities is emerging,138141 yet further work in this area is needed. A review of literature related to fitness in children with developmental disabilities is another excellent topic and would be a valuable contribution to the literature.137 For a review of information specific to fitness in children with cerebral palsy and secondary conditions associated with inactivity, the reader is referred to an article by Fowler et al.18

This article raises 2 primary questions. The first is “How should PTs use the information regarding health-related fitness and activity guidelines presented in this article?” The authors of this article feel that the answer to this question is 2-fold and that PTs should (1) advocate for physical activity opportunities for children and (2) provide fitness, health promotion, wellness, and risk-reduction interventions on both individual and community levels.

In 2010, the National Association for Sport and Physical Education and the American Heart Association reported on the status of physical education in the United States.142 According to this report, mandates for physical education range across states from requiring no physical education to requiring up to 250 minutes per week. The average across states (130–160 min/wk) equates to less than 50% of the recommended amount of physical activity for children. Hence, the need for additional physical activity in children's homes and communities is evident. Physical therapists should educate children, parents, teachers, and community leaders about the benefits of activity and lifelong fitness and advocate for increased physical activity opportunities within their communities.

The following represents APTA's vision for the role of PT in fitness and primary prevention: “Intervention, prevention, and the promotion of health, wellness, and fitness are vital parts of the practice of PTs. As clinicians, physical therapists are well positioned to provide services as members of primary care teams.”143

Hence, the second primary question raised by this article shall be addressed: Are PTs prepared to fulfill this vision of APTA? According to Rea et al144 PTs reported high self-efficacy in promoting physical activity with patients. However, of the 179 accredited PT education programs in the United States that listed both the prerequisites and physical therapy curriculum online, only 89 programs required exercise physiology, or exercise science, as a prerequisite or a course within the physical therapy curriculum. Although the authors recognize that these numbers may not accurately represent those programs that embed exercise physiology, testing, and prescription in other courses within the PT curriculum, it appears unlikely that entry-level programs are preparing clinicians to realize the vision of APTA.

Although the task force was initially charged with generating fitness guidelines for all children, meeting that charge is a bit premature. This article summarizes a wealth of research on health-related fitness, but comparable studies for children with disability are lacking. Further research is necessary before guidelines for fitness that are generalizable to children with disabilities can be proposed.

In summary, PTs should routinely apply research relevant to health-related fitness when treating children and adolescents. Promoting activity, fitness, health, and wellness in our communities is a responsibility all therapists should assume. To provide high-quality services, enhanced education in exercise physiology, public health, and health promotion may be necessary.

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adolescent; child; guidelines; exercise; health; pediatrics; physical activity; physical fitness; physical therapy

© 2011 Lippincott Williams & Wilkins, Inc.

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