Effect of the Resistance Exercise on Elementary School Students’ Physical Fitness
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Physical activity programs using components of resistance have the potential to improve health in school children. The purpose of this study was to examine the effect of a school-based resistance exercise program on physical fitness in elementary school students.
The sample was 256 children (mean age = 8.3 ± 2.5 years; 119 girls) from kindergarten to 5th grade. Participants performed a 10-min resistance exercise 2–3 times in each school day. Physical fitness outcomes were assessed using President’s Physical Fitness Challenge test. Measures were collected at baseline and at a 6-month post-test time point. A 2 × 2 doubly MANOVA was employed to examine the effect of sex and time.
The multivariate model was statistically significant with a main time effect (Wilks’ λ = 0.19, F = 290.9, P < 0.001). Follow-univariate tests found significant differences between time-points on flex arm hang (P = 0.033), shuttle run (P < 0.001), and 1-mile run/walk times (P < 0.001).
A 6-month resistance exercise program improved upper body strength and cardiorespiratory endurance in elementary school aged children. The use of resistance exercise intervention during school day can be effectively used to promote physical fitness and ultimately improve the health of children.
KeywordsResistance exercise Children Physical fitness
The prevalence of childhood and adolescence obesity has been dramatically increasing during the past three decades in the US . It was estimated that 20% of the American children and adolescents aged 6–19 years were obese . The overweight and obesity among these young populations could persist into adulthood , lead to low physical fitness level, thus present a higher risk to develop chronic diseases (e.g., diabetes mellitus, hypertension, and cardiovascular disease) [24, 30, 33]. Numerous studies and agencies have confirmed the importance of physical fitness, and its positive relationship with well-being among all types of population [1, 18, 39]. Therefore, an optimal development of young children’s physical fitness is of significant importance for their overall health condition.
School is an appropriate setting where young people can improve their health and well-being . It has been well documented that school-age children’s physical fitness (i.e., cardiorespiratory endurance, muscular fitness, flexibility, and body composition) benefits from various types of school-based physical activity programs, such as classroom-based active video game , comprehensive school physical activity program , physical education curriculum . Specifically, Fu et al.  reported that, after participating an 18-week active video game program in their classroom, a group of 6th grade school children improved cardiorespiratory endurance relative to the comparison group who did not play the active video game. Brusseau et al.  reported that the elementary school students from low-income families improved cardiorespiratory endurance and body composition after participating in a 2-year comprehensive school physical activity program. In addition, some school-based physical education programs, such as SPARK, also demonstrated a positive influence on elementary and middle school student’s cardiorespiratory endurance and body composition.
U.S. Centers for Disease Control and Prevention (CDC) recommends resistance exercise for at least 3 days per week as part of 60 or more minutes physical activity participation in children and adolescents. According to the literature, resistance exercise is safe and effective improving muscular strength and endurance while decreasing the severity and incidence of sport injuries . Resistance exercise can be also implemented with other health-related fitness activities in school physical education curriculum . However, limited studies have investigated the effect of school-based resistance exercise or strength exercise programs on fitness physical in children or investigated the specific resistance exercises in influencing fitness components in young population. Among the limited available studies, Eather et al’s research  suggested significant improvements in physical fitness levels in a sample of aged 15–16 year-old adolescents who participated in an 8-week school-based CrossFit program. Previous studies also reported that school-based resistance exercise programs, employing free weights, weight machines, resistance elastic bands, body weight, medicine ball, and circuit training, have demonstrated positive impacts on fitness levels in adolescents [11, 25, 29]. Nevertheless, none of the available studies has employed a school-based resistance exercise that targets multiple components of physical fitness for elementary school children. Therefore, the aim of this study was to investigate the effect of resistance exercise on physical fitness in elementary school children. It was hypothesized that children’s physical fitness level would improve as a result of resistance exercise participation and that possible gender differences would display among the study outcomes.
A convenience sample of 256 kindergarten through 5th grade children (mean age = 8.3 ± 2.5 years; 119 girls, 137 boys) were recruited from an urban elementary school located in the Western US. The school recruited has 350–400 students with grades K-5. The school mandated 150 min of weekly physical education and a daily 30 min recess. The specific inclusion criteria for this study were children who were (1) enrolled in the public elementary school; (2) aged 6–11 years; (3) without a diagnosed physical or mental disability according to school records; and (4) able to provide parental consent and child assent. Inclusion eligibility was obtained from school records and the demographic information survey. Written assent was obtained from the children and consent was obtained from the parents prior to data collection. The University of Nevada, Reno Institutional Review Board approved the study protocols.
Participants’ physical fitness level was assessed by the President’s Physical Fitness Challenge test . The test assesses physical fitness across 5 components with 5 subtests, which consists of the 1-mile walk/run, 1-min bent-knee curl-ups, pull-ups/flexed arm hang, sit and reach/V-sit reach, and 30-foot shuttle-run.
Because of the time constraints of the physical education class, only a select number of testing items were employed in the current study. The 1-mile walk/run was used to measure the cardiorespiratory endurance, participants in this study were encouraged to cover the 1-mile distance as quickly (minutes and seconds) as possible, walking may be interspersed with running during the test. The shuttle-run test was used to measure the speed and agility, and participants ran back and forth in-between two parallel lines 30 feet apart, score was recorded to the nearest tenth of a second. 1-min Bent-knee curl-ups test was used to measure abdominal strength/endurance, participants were lying down with knees flexed, arms were crossed with hands placed on opposite shoulders and elbows held close to chest. On the signal, participant raised the trunk, curling up to touch the outside of forearms and elbows to thighs and then lowering the back to the floor so that the scapula touched the floor, for one curl-up. Score was recorded in the repetition of the curl-up within 1 min. Flexed-arm hang was employed to assess children’s upper body strength/endurance by maintaining flexed-arm hang position as long as possible, participant’s chest must be held close to the bar with legs hanging straight. Timing is stopped when participant’s chin touched or fell below the bar. Sit-and-reach was used to measure flexibility of children’s lower back and hamstrings. During the test, participant’s legs must remain straight, soles of feet against box, and fingertips of both hands must reach evenly along measuring line. Each participant had three practice reaches, the fourth reach was held while the distance was recorded to the nearest centimeter. These items were chosen because they represent important fitness often utilized in physical activity and sports settings. At the onset of testing administration, those who taking the test had a chance to review the correct techniques and protocols for each test.
This study employed a repeated measures design. All the participants in the current study attended the resistance exercise program for an entire school year (Fall and Spring semesters) with the support from their school administrative and classroom teachers. The intervention length was 6 months and all fitness outcome variables were measured twice at baseline and at a 6-month post-test time-point.
The intervention in this study was a 10-min resistance exercise program designed for children and young youths. In this study, the resistance exercise intervention was incorporated into the regular school routine. In each school day (Monday–Friday) during the interventional period, children participated 2–3 10-min resistance exercise sessions during their recess in classrooms or outside playground, supervised by classroom teachers. Each 10-min resistance exercise session included various types of strength exercises and cross-fit activities that aim to train the major muscle groups (including the chest, shoulders, back, arms, legs, abdomen, and lower back), such as burpees, squat jumps, push-ups, step-ups, planks, superman, running relay, crab walks, etc. The class conducted the same activity at the same time, 1–2 sets per exercise, with 6–15 repetitions in each set, and took approximately 1–3 min rest between sets.
Assessment of physical fitness occurred at baseline, 1–2 weeks prior to commencement of the intervention at the beginning of the spring semester; and at a 6-month follow-up, 1–2 weeks prior to the end of the fall semester of the school year. The same testing protocol was used at both testing time points. Children attended the tests and completed the anthropometric survey with class as the unit (class size ranged from 19 to 25) in their physical education classes during the first two school weeks. For each physical fitness test, the research assistant demonstrated the protocol to the participants prior to collecting data and then scored the item based on the procedures described in President’s Physical Fitness Challenge test manual. All scoring was coded live during each participant’s physical education class. One member of the research team collected 1-mile walk/run, shuttle run information and one member collected curl-up, sit and reach, and flexed arm hang information so as to maintain testing consistency.
Each member of the research team was trained for several weeks prior to the start of data collection using a sample of children from a different school. Training involved testing elementary school-aged children on the President’s Physical Fitness Challenge test protocols during their physical education class. Each member of the research team practiced and collected all the physical fitness test items. All the classroom teachers were provided with the resistance exercise program manual, which included the description of all the resistance exercise and cross-fit activities that designed by the research team.
The data in the present study was analyzed with the following four steps: (1) all dependent variables were initially checked for normal distribution using k-density plots and screened outliers using box-plots and z scores (with a ± 3.0 z cutoff). (2) Descriptive statistics (means and standard deviations) were calculated for each dependent variable within each sex and time point. (3) A 2 × 2 doubly Multivariate Analysis of Variance (MANOVA) test was employed to examine the effect of sex (male, female) and time (pre-test, post-test) on curl-up repetitions, back-saver sit and reach distance, flexed arm hang time, shuttle run time, and 1-mile run/walk time. Specifically, analysis of the sex × time interaction included examining the sex × time F-statistic and P value within the MANOVA model in addition to the examination of univariate F-statistics, P values, and line graphs if multivariate statistical significance was observed. (4) If any statistically significant multivariate main effects were found using Wilks’ Lambda, follow-up univariate mixed design 2 × 2 analysis of variance (ANOVA) tests were conducted. ANOVA tests effect sizes were quantified using partial eta-squared (η2). Effects of interest included the time main effect and the sex × time interaction. Cohen’s delta (d) determined the effect size and practical significance of each pairwise comparison. Effect sizes were classified as small if d ≤ 0.2, medium if d = 0.5, and large if d ≥ 0.8 . All analyses assumed an initial alpha level of P ≤ 0.05 and were carried out using STATA 15.0 statistical software program (College Station, TX).
Descriptive statistics within sex groups at baseline (Mean ± SD)
Girls (n = 135)
Boys (n = 119)
Shuttle run (s)
13.73 ± 1.45*
13.09 ± 1.33
One-mile/run walk (min)
16.10 ± 3.71*
14.20 ± 4.02
44.07 ± 46.69
47.69 ± 42.41
Flex arm hang (s)
14.23 ± 10.55
15.48 ± 12.33
23.22 ± 9.48*
20.55 ± 8.63
Physical fitness test scores across time-points (Mean ± SD)
Shuttle run (s)
13.30 ± 1.50
12.65 ± 1.74*
One-mile/run walk (min)
15.15 ± 4.01
12.81 ± 2.90*
45.00 ± 44.21
45.16 ± 34.45
Flex arm hang (s)
14.92 ± 11.25
16.84 ± 14.20*
22.41 ± 9.49
26.79 ± 8.28*
The purpose of this study was to examine the effect of a 6-month school-based resistance exercise program on physical fitness among elementary school students. The results demonstrated significant effects of this intervention on shuttle run, 1-mile run/walk, flexed-arm hang and the sit-and-reach. In another word, children in this study improved their cardiorespiratory endurance, upper body strength and flexibility after participating in the resistance exercise over 6 months. Particularly, girls improved more from baseline to the post-test time-point compared to boys on cardiorespiratory endurance. These results suggest that resistance exercise is an effective strategy to increase physical fitness level in children.
Although limited research investigated the effect of resistance exercise on prepubescent children, a positive relationship between resistance exercise and physical fitness has been shown in the existing literature [14, 20, 26]. For instance, Marta et al.  reported a combined resistance and endurance exercise significantly increased 10–11 years old participants’ performance of vertical jump, standing long jump, 3000-m run, running speed, and level of VO2max through an 8-week training. The results of the current study echoed the literature and revealed improvements on children’s muscular strength and power. One of the plausible reasons for the improvement may relate to the length of training. The present study implemented a 6-month intervention providing daily resistance exercise to the prepubescent participants. Previous research indicated that children and adolescents could increase their muscle strength beyond natural development if sufficient duration, intensity, volume, and longer training period were provided in the training [3, 13]. The research concluded that 6–8 weeks of training might elicit measurable changes on individual’s neuromuscular, metabolic, and physiological conditions. Similar results were also found in overweight and obese children with the training length, intensity, and volume [27, 34]. A 10-week high-intensity strength training program resulted in a significant increase on children’s knee extensor/flexor peak torque (60°/180°) even though no muscle hypertrophy was caused . These studies suggested that long-term interventions with a greater number of training sessions per week might benefit strength gains.
Another prominent result of the present study is that children significantly increased their upper body strength/endurance as reflected by the improvement of the flex arm hang test. This significant result is in line with the pediatric resistance literature and may come from the differences in training frequencies and volume [6, 12]. Faigenbaum et al.  compared the effects of training frequency on strength gain among prepubescent children and revealed that training twice per week resulted in more favorable changes in upper body strength as compared to training once per week only. During childhood, there is a gradual increase in height and weight, yet the legs grow at a faster rate than the trunk . This developmental lag in upper body maturation may impact the functional development of muscle tissue . In this current study, participants completed a 6-month school-based resistance exercise that provided a high training frequency (≥ 10 times/week). It is known that smaller muscles of the upper body produce smaller gains (as compared to the lower body), but this high frequency training program may have promoted strength gains of the young participants. McLester et al.  reported that more frequent training programs (e.g. 2–3 times/week) and higher volume training programs (e.g. 3 sets of 10–15 repetitions per exercise with a moderate load) resulted in greater gains in upper body strength than less frequent and lower volume training programs among adults. These results suggest that a higher frequency may enhance the upper body strength of children. More studies on the dynamics of upper body strength development in children are needed in the future.
The results of the present study indicated that resistance exercise enhanced cardiovascular fitness, with the improvements of their performance on 1-mile walk/run test. Limited research examined the reason for the positive relationship between resistance exercise and cardiovascular benefits in children and youth, with some documented in the adult resistance exercise literature [2, 6, 36]. For example, during resistance exercise heart rate (HR) is significantly increased . Steele et al.  highlighted that individual’s cardiac output, which directly impacts oxygen delivery, increases when performing resistance exercise with a higher intensity. Resistance exercise is associated with an increase in systolic blood pressure and the increase can be a stimulus to alter the left ventricular size, which should enhance pumping mechanics, total heart volume, and maximum cardiac output . Beyond these findings, another possible factor interpreting the cardiovascular gains may be the growth in type IIα fibers . However, it is difficult to explain the gains in pre-puberty children, since their resistance training induced adaptations are mainly neurological meaning increased motor unit recruitment and coordination .
Another significant finding of the present study is that girls had higher improvement in both shuttle-run and 1-mile run than boys (Figs. 1, 2). Girls demonstrated significant higher improvement in cardiorespiratory endurance and speed/agility as compared to boys from baseline to post-test time points even though there is only a small to medium sized effect (low eta-squared shuttle-run: η2 = 0.016 and 1-mile run/walk: η2 = 0.029). Limited literature on this subject made us speculate that the results may be associated with the relatively low initial VO2max level among girls. Research showed that VO2max may increase in young subjects following RT when their initial relative VO2max is lower than 40 mL/kg/min. Two studies have demonstrated that VO2max increased 9% and 6%, respectively, after RT when initial VO2max was about 39 mL/kg/min in both studies . Since girls had a significant lower initial level of VO2max than boys did, it may be easier to have significant improvements for girls compared to boys. Hu et al.  reported that VO2max tended to increase by approximately 8% following 10 weeks of RT (initial VO2max was 36 mL/kg/min). Unfortunately, there is no study investigating the dose-response relationship between initial VO2max and the increase in VO2max following traditional resistance exercise; therefore, future research is needed.
A number of limitations of this study must be considered before any findings can be determined. The major limitation of this study was that there was no control group to compare with the resistance exercise group. Since there was no control group, the internal validity of the results would be attenuated. There are a variety of other factors that may weaken the internal validity, which could have been exacerbated due to the single-group research design, including history, maturation, regression toward the mean, selection of the testing protocols. For instance, influences from outside of the study protocol, such as physical activity participations during after school hours or in the home setting, might have increased children’s physical fitness levels in this study. It has been reported that children could accumulate a substantially level of physical activity outside of the school day  and at home . The participants in this study may have also physically matured over the 6-month intervention period, especially the older cohorts, which may have affected the results. However, because 6-month period is a relatively short time period, the odds of significant maturation effects were small. In addition, it was determined that the dependent variable scores were approximately Gaussian, which attenuates confounding effects due to the regression toward the mean. Although the children were blinded from scores at the baseline time point, greater familiarity with the testing rules and protocols may have confounded the results. In addition, President’s Physical Fitness Challenge test, the fitness testing battery employed in this study, was outdated and replaced by the Presidential Youth Fitness Program and Fitness Gram since 2012. Finally, the participants were recruited from an urban school from the Western region of the United States, therefore the external validity of the results is questionable if generalized to other regions or using cohorts with different ethnic and socioeconomic representation.
In conclusion, the 6-month school-based resistance exercise significantly improved physical fitness among elementary school-aged children, although the magnitude of the effects was weak to moderate. In particular, girls demonstrated higher improvement in cardiorespiratory endurance than boys did. The improved measurements may attenuate health risk as this cohort of children track through adolescence and into adulthood. Despite the potential benefits of this program, its sustainability over longer periods of time is questionable.
Implications for School Health
This study supports the positive impact of school-based resistance training on elementary school-aged children’s physical fitness over time, specifically on their cardiorespiratory endurance, upper body strength and flexibility. In addition, a stronger improvement in cardiorespiratory endurance was observed on girls. Given the increasing prevalence of overweight and obesity in children, it is important to understand and utilize the school-based resistance training interventions, in order to interpret the existing physical activity behaviors and the impacts on relevant health outcomes. Moreover, the findings of this study would arise a greater awareness of physical activity, particularly the child-friendly resistance training program. The findings of the present study can also be used to support and inform school and community-based interventions aiming to employ multicomponent physical activity modification to promote physical activity participation, and thus improve the health conditions of school children. Policymakers, especially on elementary school campuses, should seek school-based interventions aiming to encourage children’s physical activity participation. Public health practitioners and professionals should work closely with community and school administrative to enforce physical education policies that could efficiently promote the proportion of resistance training component in their physical education lesson plans. Further research should focus on elucidating which type of resistance training has the greatest influence on children’s health fitness.
The authors would like to thank the school students and teachers who participated in this study, and the graduate assistants who aided in the data collection process.
Compliance with Ethical Standards
The University of Nevada, Reno Institutional Review Board approved the study protocols.
In this study, written assent was obtained from the children and consent was obtained from the parents prior to data collection.
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