Physical Fitness in Children during Growth: Associations with Body Composition, Physical Activity, and Cognitive Skills

Abstract

Fostering childhood physical activity and fitness levels could have important implications for public health, given growing concerns about high obesity rates, the amount of time spent being sedentary and not getting enough physical activity already at early childhood. World Health Organization states that from 1975 to 2016, the prevalence of children and adolescents with overweight or obesity increased more than four-fold from 4% to 18% globally. Obesity prevention is critical in controlling obesity-related noncommunicable diseases, psychological, and social problems, as well as inferior academic achievement mediated by others attitude and diminished executive cognitive function. A decline of physical activity from early childhood into middle childhood and further to adolescence has been reported. Accompanying health risks from low activity and high sedentariness are comparable to those arising from obesity, and the impact extends into adulthood. Wide range of physical, mental, and cognitive health benefits related to high physical fitness levels in children have been reported. This chapter aims to summarize current evidence clarifying whether higher physical activity is associated with higher physical fitness, and whether higher physical fitness predicts healthier body composition and better cognitive functions in children.

1. Introduction

Physical fitness, as the capacity to perform physical activity, determines a full range of physiological and psychological qualities [1]. Besides an epidemic of obesity, accumulating evidence suggests that young children spend excessive time being sedentary, and they frequently fail to achieve physical activity guidelines [2]. While excessive sedentary time has been linked with a number of health concerns [3], wide range of physical, mental, and cognitive health benefits related to the engagement in physical activity and greater physical fitness in children have been reported, including improved motor and cognitive development [1], higher academic performance [1] and bone mineral density [1], better cardiometabolic health indicators [1, 4, 5], greater psychological well-being [1, 6], and health-related quality of life [1, 7], as well as prevention of overweight/obesity [1, 4, 8] and psychological ill-being [1, 6].

Regarding many health benefits arising from being fit, it is important to monitor physical fitness parameters during growth and maturation in children. Cardiorespiratory fitness represents the overall capacity of the cardiovascular and respiratory systems and the ability to perform prolonged strenuous exercise [1]. Peak oxygen consumption (V̇O₂peak), the highest rate at which oxygen can be consumed during exercise, is widely recognized as the best single measure of young people’s cardiorespiratory condition [9]. In epidemiological studies involving children and adolescents, cardiorespiratory fitness is most frequently assessed by 20 m shuttle run test or modified versions of that [1, 10, 11, 12, 13, 14]. Higher cardiorespiratory fitness is beneficially associated with multiple health indicators among children [15]. On the other hand, low levels of cardiorespiratory fitness at young age have been attributed to a higher risk of developing cardiovascular disease risk in adulthood [16].

Speed/agility fitness includes the ability to move the body or its parts as fast as possible (speed) and the ability to move quickly and change direction while maintaining control and balance (agility) [1]. The 30 m sprint test and the 4 × 10 m shuttle run test are widely used tests for assessing speed and/or agility at young age [10, 11, 12, 13, 14]. Several other tests such as 10 × 5 m shuttle run and 20–100 m dash have also been proposed [1, 17, 18, 19, 20]. Better performance in 4 × 10 m shuttle run test has been associated with lower fatness [12] and stronger bones [21] at young age.

Balance denotes the ability to maintain equilibrium while stationary (static balance) or moving (dynamic balance) [20]. The one-leg stance test is widely used to assess static balance [10, 11, 20] and for dynamic balance assessment, lower quarter Y balance test [22] or balance beam [23] is applied. A well-developed postural control system is a prerequisite to manage successfully with daily (e.g., climbing stairs) and or recreational/sports-related (e.g., fundamental movement skills such as kicking, jumping, or advanced skills, such as balancing on a beam) activities [22, 24]. Deficits in postural control because of ongoing growth and maturation processes of the postural control system [25] might be responsible for the high prevalence of sustaining a fall, particularly in children [26]. Furthermore, postural control deficit is a risk factor for musculoskeletal injuries [27, 28].

Muscular fitness is the ability to perform work against a resistance [1]. Maximal (isometric and dynamic) strength, explosive strength, endurance strength, and isokinetic strength have been proposed for the prime health-related muscular fitness components [1]. The handgrip test is one of the most frequently applied tests for investigating muscular fitness in epidemiological studies [1, 10, 11, 12, 13, 14, 29]. Handgrip strength correlates positively with body mass index (BMI) and fat-free mass, meanwhile, handgrip strength associates inversely with body fat percentage in children [30]. Accordingly, grip strength serves as an indicator of muscle mass and healthy body composition. Handgrip strength-to-BMI ratio in children aged 5–10 yrs was positively related to different physical fitness parameters such as absolute handgrip strength, vertical jump, V̇O₂peak, and 20 m shuttle run test results [31], suggesting that strong grip expresses general fitness of a young person. There are inconsistent findings about the associations between grip strength and cardiometabolic risk factors. Some studies have shown that higher handgrip strength at young age is associated with lower cardiometabolic risk [29]. Meanwhile Rioux et al. [32] reported inverse association between handgrip strength and cardiometabolic risk score specifically in girls, but not in boys. But it has been also stated that handgrip strength is not suitable as a predictor for cardiometabolic risk factors in children of both sexes [33].

Among jump tests, standing long jump test has been widely used in young population for assessing explosive strength [1, 10, 11, 12, 13, 14]. Since standing long jump test is strongly correlated with other lower- and upper-limb muscular strength tests, it is regarded as a general index of muscular fitness in youth [34].

Among fitness tests, greater isometric muscle strength of the abdomen and back in youth predict lower levels of cardiovascular disease risk factors in young adulthood independently of cardiorespiratory fitness, adiposity, and other sociodemographic and lifestyle factors [35].

The true global burden of mental illness has only recently been understood [36]. Worldwide, about 15% of children and adolescents experience a mental disorder [37]. There is some confidence from experimental and observational studies that physical activity has mental health effects at young age [6, 38]. Current research concerning physical fitness and mental health in childhood is limited, with some evidence for positive mental health benefits from higher physical fitness. LaVigne et al. [39] demonstrated that physical fitness [a composite score of bent-knee sit-ups, sit-and-reach, flexed arm hang (girls only), pull-ups (boys only), and long jump, endurance run, shuttle run, and sprints] was associated with a range of psychological well-being indicators for both boys and girls.

In conclusion, all domains of physical fitness are significant indicators of health status at young age [1, 6, 21, 29, 35]. Thus, it is relevant to work on maintaining and developing sufficient physical fitness in children in order to contribute to their health and well-being [40].

2. Methodology

Scientific articles containing data on the associations between physical fitness, body composition, physical activity, and cognitive skills in children published up to May 2023 were included. The searches were conducted in electronic databases [(PubMed, CINAHL, and Education Resources Information Center (ERIC)]. Eligibility criteria were the following: (1) cross-sectional and longitudinal studies, reviews, systematic reviews, and meta-analyses (design criterion), (2) articles published in scientific journals, book chapters, books, conference proceedings, and theses (publish criterion), (3) children and adolescents aged up to 19 yrs (participant criterion), and (4) articles published in English and German (language criterion). No time limits were set. The papers were screened by two researchers independently, to come to a first selection (after reading title/abstract), and then to second selection (after reading full text) of relevant papers. A total of 2709 studies were identified through the databases searches, and 70 were included into this review.

2.1 Associations of physical fitness and body composition in children

Henriksson et al. [12] demonstrated that speed-agility fitness, cardiorespiratory fitness, and lower-limbs muscular strength at 4.5 yrs were negatively associated with fat mass index and body fat percentage at 5.5 yrs. Meanwhile, higher handgrip strength at 4.5 yrs was associated with higher BMI and fat-free mass index 1 year later. Body composition in this study was assessed by air-displacement plethysmography [12]. In another longitudinal study by Martins et al. [41], children in grade 1 (at 6 yrs) were followed through grade 5 (at 10 yrs). The results from 1-mile run/walk test were not associated with BMI changes, but gross motor coordination was inversely associated with changes in BMI [41]. Findings in children aged 4.6–11 yrs relate baseline V̇O₂peak inversely to increasing (over a 3- to 5-yr period) adiposity after adjustments for age, maturity, ethnicity, initial fat mass, and increase in lean tissue mass (assessed by dual-energy X-ray absorptiometry, DEXA) [42]. Additionally, cardiorespiratory fitness seemed to be more important than absolute energy expenditure in the development of obesity [42]. Children at 7–10 yrs with cardiorespiratory fitness of the lowest tertile had a 5.5–6-fold greater chance of having overweight and obesity, as well as metabolic syndrome at 14–17 yrs than the children having better cardiorespiratory fitness levels after controlling for BMI percentile, blood pressure, and cholesterol levels [43]. In children aged 6–12 yrs (on average 8.8 yrs), BMI, parental obesity, and low performance in 20 m shuttle run were the main predictors of the 2-yr tracking of body fatness, and cardiorespiratory fitness level at baseline was a predictor of high waist circumference after 2 yrs [44].

Hruby et al. [45] followed over 1–4 yrs a large sample of 2793 children, who were at baseline 1st to 7th graders. They were classified as “fit” or “underfit” according to age- and sex-specific norms in five fitness domains. It was concluded that schoolchildren with overweight who achieve or maintain physical fitness are more likely to achieve healthy weight, and healthy-weight children who maintain fitness are more likely to maintain healthy weight [45]. This is in accordance with a study, where children aged 10–17 yrs (on average 13 yrs) with abdominal obesity had 8.5 and 6.5 increased odds of low handgrip-to-BMI ratio compared to children with normal waist circumference, both in boys and girls, respectively [46].

Freitas et al. [47] observed children on average for 7.2 yrs starting at age 8 yrs, showing that the variance in adiposity was explained to a small extent by physical fitness. More specifically, for girls, Flamingo balance at 8 and 12 yrs was a predictor of body fatness at 15 and 19 yrs (2–8%). Flexed arm hang at 8 yrs predicted waist circumference at 15 yrs by 8%. The association of flexed arm hang was negative. In boys, about 2–4% of the variance in BMI, waist circumference, and sum of skinfolds at 15 yrs was explained by the sit-ups at 8 yrs [47]. After controlling for fatness indicators, the sit-ups were negatively associated with adult fatness. Other fitness items (strength and endurance) become predictors of future fatness at later age periods. Overall, Flamingo balance and flexed arm hang were the most stable predictors of body fatness in childhood, adolescence, and young adulthood. Yet, the signal of the regression coefficients for Flamingo balance was positive in the age intervals 8–15 and 16–23 yrs but negative in the age interval of 12–19 yrs [47].

Koutedakis et al. [48] demonstrated that in children at 12.3 yrs, 20 m shuttle run test predicted lower body fat percentage (assessed by skinfolds) 2 years later after controlling for age, sex, maturation status, physical activity, cardiorespiratory fitness, and energy intake at follow-up. Twisk et al. [49] reported that baseline neuromotor fitness index including measurements of muscle strength, flexibility, speed, and coordination at 13 yrs was negatively related to sum of skinfolds at 27 yrs. In addition, among children aged 13–16 yrs, V̇O₂peak predominantly predicted lower sum of skinfolds both in boys and girls, and smaller waist circumference in girls, but not waist-to-height ratio at 32 yrs [49]. By contrast, Barnekow-Bergkvist et al. [50] found that better performance in 9-min run at 16 yrs was associated with greater odds of high BMI in males at the age 34 yrs. Higher bench press (male) and two-hand lift (female) results at 16 yrs were associated with greater risk of high BMI at age 34. The associations for waist-to-hip ratio were less clear. The number of sit-ups predicted neither BMI nor waist-to-hip ratio [50]. In turn, Janz et al. [51] found that changes in V̇O₂peak and handgrip strength from childhood (mean age 10.5 yrs) to adolescence at 5-yr follow-up were negatively related to fat mass (assessed by bioelectrical impedance) and waist circumference after controlling for age and sex, with even stronger associations after adding fat-free mass and sexual maturation as confounding factors. Changes in cardiorespiratory fitness and muscular strength explained 15% of the variability in 5-yr adiposity and 15% variability in the 5-yr abdominal adiposity [51]. In a study by Hasselstrøm et al. [52] children aged 15–19 yrs were observed again 8 yrs later, reporting that higher or increased V̇O₂peak (in both sexes) and composite of strength parameters (the sum of maximal isometric contractions of trunk flexors and extensors and elbow flexors and knee extensors) (in males) were related to lower body fat percentage (sum of skinfolds) at follow-up after adjustments for age [52]. These findings are strongly supported by a study with long follow-up for 22 yrs, where a five-factor composite, physical test was used to assess the physical fitness level. It was found out that high-school students with low fitness levels were more likely to be overweight in adulthood vs. those with high fitness levels. The interpretation of outcomes is limited since potential confounding effects were not controlled [53]. The long-lasting contribution from better cardiorespiratory fitness in maintaining healthier body composition was confirmed by Kvaavik et al. [54], who observed that higher V̇O₂peak levels at 11–15 yrs (on average 13 yrs) may provide protection against later obesity (assessed by BMI and triceps skinfold thickness), although the effects diminished over time, disappearing at 40 yrs. Controlling for educational attainment of both the parent and the study member had little impact on these associations [54]. Correspondingly, Boreham et al. [55] showed modest inverse associations between the number of laps in 20 m shuttle run at 12 and 15 yrs with sum of skinfolds at 22.5 yrs in both sexes [55]. Similarly, low fitness, such as running speed, arm pull, standing high jump, and V̇O₂peak during adolescence predicted lower fatness during early adulthood, after controlling for baseline physical activity and fatness (sum of skinfolds) [56]. In accordance, overweight/obese boys aged 8–13 yrs with greater V̇O₂peak levels had a lower increase in total body fat mass (assessed by DEXA) at 15 yrs after adjustments for changes in Tanner stage, age, and fat-free mass. A total of 15% higher V̇O₂peak at baseline resulted in a 1.38 kg lower fat mass gain over 4 years [57]. Likewise, adolescents categorized as low-fit based on the composite physical fitness test score demonstrated higher BMI compared with fit peers within 3-yrs follow-up period [58]. Meanwhile, Kim et al. [59] observed that in a large sample consisting of children from kindergarten to eighth grade not all physical fitness items uniformly predicted further fatness in childhood. They identified that the associations between abdominal strength, upper body strength, flexibility, and agility test outcomes (pass vs. fail) and incidence of overweight 1 year later were attenuated after controlling for baseline BMI status, except for the endurance run in girls [59]. To the contrary to findings by Kim et al. [59], Grøntved et al. [35] demonstrated longitudinally that greater strength fitness predicted lower fatness. More precisely, greater isometric muscle strength of the abdomen and back in youth was inversely associated with lower BMI levels 12 yrs later in multivariable adjusted analyses including fitness [35].

To summarize, most research demonstrates healthy longitudinal associations between physical fitness and fatness indicators in childhood and adolescence, with some positive impact reaching even into adulthood. Yet, there is some variation in the results, including heterogeneity within physical fitness domains and gender groups. Also, there is a deficiency of studies exploring the relationships between physical fitness and fat-free mass in preschool-aged children. Therefore, further investigations are warranted to clarify the associations between muscular fitness and body composition in childhood.

2.2 Associations of physical activity, sedentary time and physical fitness in children

Physical activity is a major modifiable determinant for increasing physical fitness [23]. At early age (4–6 yrs) only vigorous physical activity, but not moderate or total physical activity, was related to the improvement in 20 m shuttle run test, agility in obstacle course, and dynamic balance on balance beam after 9 months by controlling for sociocultural confounding factors [23]. Similarly, findings in children aged 9–15 yrs (on average 12.2 yrs) indicate that light and moderate physical activity were not associated with V̇O₂peak at 2-yr follow-up, but baseline vigorous physical activity had a positive dose–response association with cardiorespiratory fitness 2 years later after adjustment for age, sex, diet quality, accelerometer wear time, other intensities of physical activity, and baseline value of V̇O₂peak [60].

At the same time, a study by Leppänen et al. [13] showed that both greater moderate and vigorous physical activity at 4–5 yrs were associated with higher cardiorespiratory fitness in 20 m shuttle run test, lower-limbs muscular strength and speed-agility fitness 1 year later after adjustment for age, sex, sedentary time and accelerometer wear time. Substituting 5 min/day of sedentary time, light or moderate physical activity with vigorous physical activity at 4–5 yrs was associated with higher upper- and lower-limbs muscular strength at 1-yr follow-up [13].

Associations between parent-reported physical activity (h/wk) at 4.5 yrs and fitness composite score (including predicted V̇O₂peak, grip strength, vertical jump, sit-and-reach, and the inverse of waist circumference) at 3-yr follow-up were positive, and relations of baseline physical activity and follow-up V̇O₂peak approached significance (p = 0.051) after controlling for follow-up age, sex, and household income [61]. No significant associations of sedentary time, physical activity, change in sedentary time, or change in physical activity with any of the follow-up composite or single fitness measures existed, with the only exception for sedentary time at 4.5 yrs, that negatively predicted follow-up handgrip strength after controlling for follow-up age, sex, household income, and BMI. No sex interactions were observed [61].

Day et al. [62] have investigated the longitudinal associations between organized sports activity (h/wk) and core strength parameters in young females. The authors observed that premenarcheal organized physical activity participation was a significant predictor of sit-up performance at both premenarcheal and post-menarcheal assessments after accounting for maturity, body size, and baseline values. However, participation in organized sports over a two-year circum-menarcheal period was not a strong independent predictor of strength outcomes at the postmenarcheal assessment [62].

A study in adolescents with long follow-up period reported that leisure time sports activity in females and participation in organized sports in both sexes at the age of 15–18 yrs were related to greater probability of having higher V̇O₂peak level 18 yrs later [50]. On the contrary, in adolescents aged 15–19 yrs, increased physical activity (h/wk) was not associated with higher or increased V̇O₂peak at 8-yr follow-up neither in males nor females by controlling for age [52].

To summarize, there is a major shortage of studies investigating the longitudinal relationships between physical activity, sedentary time, and physical fitness in childhood. Studies using questionnaires for assessment of physical activity show mixed results, meanwhile, objectively measured physical activity data reveal that a higher amount of moderate and/or intensive type of activities in childhood is a predictor of better physical fitness at later age. Differences in objective and self-reported outcomes might come from the aspect that questionnaires assessing physical activity did not collect information about its intensity, rather the frequency and duration. It is suggested that the intensity of physical activity may be a stronger predictor of physical fitness than the duration or frequency [61].

2.3 Associations of physical fitness and cognitive skills in children

Higher physical fitness is a capacity that enables easier access to and greater engagement in activities within the physical domain. Greater engagement in physical activities, in turn, provides greater opportunity to engage in problem-solving, experience multiple perspectives, support formation of meaningful relationships, and employ social skills that require impulse control and other cognitive abilities [39].

A study on the relations between physical fitness and cognitive functioning in children at early age (4–6 yrs) shows that more laps in 20 m shuttle run test and motor skills (agility and dynamic balance) predicted superior spatial working memory and/or attention at baseline, whereas 9 months later some of the positive associations between initial physical fitness measures and cognitive functions were preserved to some extent [63]. At follow-up, cardiorespiratory fitness predicted still better attention in unadjusted analysis and the relations between dynamic balance (steps on the beam) and spatial working memory turned significant after controlling for confounding factors such as age, sex, BMI, migration status, parental education, native language, linguistic region, and baseline cognitive performance. At the same time, the cross-sectional beneficial relations of agility (obstacle course) and cognition disappeared at follow-up in adjusted model [63].

Preadolescents with high cardiorespiratory fitness level on 20 m shuttle run test exhibited superior performance in a visual discrimination task [64] and performed more accurately the tasks involving inhibition compared to children in the low fitness group, whereas no group differences were observed for reaction time [65].

At adolescence (on average 14 yrs) positive indirect associations of motor skills (the sum of the performance in a 5-leaps test and a tennis ball throwing-catching combination test) and muscular fitness with mathematics performance were mediated by visuospatial working memory once adjusted for age, sex, pubertal stage, body fat percentage, learning difficulties, and mother’s education. Meantime, 20 m shuttle run performance was positively associated with mathematics achievement, but the authors did not detect indirect path through cognition [66].

A study with 2-yr-follow-up indicated that boys aged 6–9 yrs, who were in the lowest third of motor competence score at baseline had worse nonverbal reasoning test score over the 2-yr follow-up than boys whose initial motor performance score was in the middle and uppermost thirds after adjusting for age and study group [17]. Secondly, it was found that a lower motor competence score, a shorter 50 m shuttle run test duration and a larger number of cubes moved in the Box and Block Test at 6–9 yrs were associated with smaller increase in the nonverbal reasoning test score during 2-yr follow-up in boys after adjustment for age and study group. None of these associations remained significant after further adjustment for baseline cognitive test (Raven’s Colored Progressive Matrices) score. Thus, the associations were largely explained by baseline cognitive abilities. Accordingly, cognition at baseline may predominantly predict later cognitive functioning compared to changes in motor fitness and cardiorespiratory fitness in childhood. As a proof, a negative relationship between cardiorespiratory fitness (maximal workload on cycle ergometer/fat-free mass) at baseline and cognitive skills 2 years later disappeared after controlling for cognition at baseline. In addition, cardiorespiratory fitness was not associated with cognition in boys, and cardiorespiratory fitness and motor competence were not related to cognition in girls. As well the changes in motor competence or cardiorespiratory fitness were not associated with changes in cognition in children at follow-up [17].

Cross-sectional data imply that V̇O₂peak at 7–9 yrs was positively associated with inhibitory control, though not with working memory [67]. At the same time, Skog et al. [68] found that most of cardiorespiratory fitness indicators were related to better cognitive functions such as working memory accuracy and/or visual learning in children at 16–19 yrs after adjustments for age and sex. Inconsistent with Pindus et al. [67], V̇O₂peak among higher-fit adolescents was related to better flexible modulation of cognitive control processes to meet task demands than in lower-fit ones [69].

There is also longitudinal evidence about the beneficial association between V̇O₂peak at 9-10 yrs and cognitive control. Children with higher levels of cardiorespiratory fitness demonstrated increased accuracy on a modified compatible and incompatible flanker task both at initial and 1-y follow-up test sessions, coupled with a superior ability to flexibly allocate strategies during task conditions that required different amounts of cognitive control, compared to less fit children. More fit children also gained a speed benefit at follow-up testing. These findings are supported by the structural data from magnetic resonance imaging as bilateral putamen volumes of the dorsal striatum and globus pallidus volumes predicted flanker performance at initial and follow-up testing one year later [70].

To summarize, the research reveals predominantly beneficiary associations between different physical fitness items and cognitive functions in children. However, considering some inconsistency in the results [17, 63, 65, 66] and the limited number of longitudinal studies [17, 63, 70] the conclusions regarding the causality and duration of the positive effects of fitness on children’s cognition cannot be firmly drawn.

3. Conclusions

Given current evidence in children, we can conclude the existence of healthy longitudinal relations between physical fitness and fatness of some positive associations reaching into adulthood. With regards to the limited number of longitudinal studies, the associations between objectively measured physical activity and physical fitness in children are partially supported, favoring activities of moderate and/or vigorous intensity. At present, the association between sedentary behavior and physical fitness remains unclear. Better physical fitness mostly predicts superior cognitive development in children, though, there is need for clarification considering scarcity of longitudinal research, short-follow-up periods, and partially mixed results.

Therefore, continued research on physical fitness and activity, body composition, and cognition in children should be supported. Future research should apply more precise methods over BMI or waist circumference, such as DEXA, air-displacement plethysmography, bioelectrical impedance analysis, and skinfold thicknesses, in accurately assessing body composition; objective assessment of physical activity should be encouraged to precisely capture information of its intensity. Evaluating cohorts with greater variability in activity level and body composition and as soon as at the earliest stages of life should help to corroborate current findings. More studies are needed to better understand whether the associations differ in male and female, given that this could have implications for future policy recommendations.