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. Author manuscript; available in PMC: 2014 Oct 9.
Published in final edited form as: J Physic Educ Sport Manag. 2011 Jul;2(3):32–36.

An after-school exercise program improves fitness, and body composition in elementary school children

Aaron L Carrel 1, Julie Logue 3, Heidi Deininger 3, R Randall Clark 2, Vanessa Curtis 1, Paul Montague, Sharon Baldwin 3
PMCID: PMC4190056  NIHMSID: NIHMS481511  PMID: 25309803

Abstract

Reduced cardiovascular fitness (CVF) is a risk factor for obesity and cardiovascular disease. It has previously shown that a school-based fitness curriculum can improve CVF, and other health indicators in middle school aged children. Whether an afterschool program improves CVF and other health markers in elementary-school children is unresolved. The objective of this study was therefore to determine whether an on-site afterschool-based fitness program improves body composition, cardiovascular fitness level, in elementary school children. 80 elementary school children were evaluated in a “fitness-oriented” afterschool program managed by the local YMCA. Children underwent evaluation of cardiovascular fitness by maximal VO2 treadmill testing and body composition by dual x-ray absorptiometry (DXA), at baseline (prior to the school-year) and again at end of the school year. Findings revealed that, at baseline, children had a mean age of 8.8 years, BMI of 18.7± 3, with a maximal VO2 of 40.03 ± 7.6 ml/kg/min, and percent body fat of 28.7 ± 7%. After a 9-month intervention, children maximal VO2 increased to 44.8 ± 7.5 ml/kg/min (p=0.04) and percent body fat decreased to 25.8 ± 6.2% (p=0.033). The study concluded that on-site afterschool programming focusing on fitness improved body composition and cardiovascular fitness, in elementary school children. Combined with prior studies, these data demonstrate that afterschool-based fitness curricula can benefit both obese and non-obese children. It was therefore recommended that, partnerships with schools to promote fitness even outside of school time should be a part of a school approach to improving children’s health.

Keywords: schools, obesity, poor fitness, children

Introduction

Poor physical fitness as well as obesity are risk factors for type 2 diabetes mellitus (T2DM), and cardiovascular disease (Katzmarzyk PT et al., 2001), (Must A and Strauss RS, 1999), (Freedman DS et al., 1987). In adults, poor cardiovascular fitness (CVF) is a risk factor for illness, independent of obesity.(Blair SN et al., 2001) Given the multiple factors contributing to the current epidemic of childhood obesity, an effective strategy for the prevention and treatment of childhood obesity must be pervasive and collaborative in its scope. One attractive venue for such a collaborative effort is the school setting, even outside of formal school hours.

While obesity increases the risk of illness and other cardiovascular diseases, (Dietz WH, 1998b), it has been demonstrated in adults that fitness level is a stronger predictor of mortality than obesity.(Lee CD et al., 1999) It is thought that the beneficial effect of fitness training reflects the combined effects of increased lean mass and reduced fat mass in adults (Sinha R et al., 2002) (Kelley DE and Goodpaster BH, 1999), and children. (Eliakim A et al., 2001; Travers SH et al., 1998) We have shown that, in obese children, both CVF, as measured by maximal VO2, and body fat were highly significant independent predictors of insulin sensitivity and health. (Allen DB et al., 2007) Thus efforts to improve health in children should include a focus on increasing physical activity, in addition to encouraging healthy eating for health promotion. (Dietz WH, 1998a)

We have previously reported that a school-based intervention for obese children was effective at improving CVF, and decreasing percent body fat and fasting insulin.(Carrel AL et al., 2005) However, whether these beneficial changes would also occur in non-obese children is unclear. Most adults do not achieve the Surgeon General’s recommendations for moderate physical activity. (United States Department of Health and Human Services, 2000) Thus, childhood has been identified as a critical period for nurturing lifetime physical activity behavior, and school physical education as a vehicle to promote active lifestyles. (United States Department of Health and Human Services, 2000) We hypothesized that beneficial changes could also occur in non-obese children from a school-based program.

Encouraging additional exercise in children can be promoted or obstructed in varying environments.(Epstein LH et al., 1994; Knowler WC et al., 1995; Owens S and Gutin B, 1999) The most successful programs are those that incorporate activity into the child’s lifestyle, as a part of the family and school environment.(Gutin B et al., 2002),(Tuomilehto J et al., 2001),(Sallis JF et al., 1997) Gutin et al. have successfully designed school-based programs that promote physical activity and monitor changes in fitness, as well as metabolic parameters including lipid profiles. (Gutin B et al., 2002) Jamner demonstrated that a school-based intervention in adolescent females can increase physical activity and prevent a decline in cardiovascular fitness. (Jamner MS et al., 2004) Some school-based nutrition and exercise interventions such as “Planet Health” have been successful at reducing BMI and triceps skinfold thickness among female students (Gortmaker SL et al., 1999; Robinson TN, 1999) while others (for example, the “Pathways” project) have fallen short of their goals in Native American schools.(Caballero B et al., 2003) Our study differs from previous interventions by focusing upon fitness and body composition, rather than weight or BMI, in both “non-obese” and obese children. By incorporating the intervention into the school environment, based upon the social-ecological model of public health, we believe we have a greater chance for success at incorporating health changes.

MATERIALS AND METHODS

Ninety-five children participating in an afterschool program were invited for participation in this study. Ninety children agreed to be evaluated for “baseline testing” at the University of Wisconsin Exercise Science Laboratory (ESL). Eighty children completed both baseline and post-intervention testing; only subjects who completed both testing sessions were included for analysis. The same investigators completed all testing, during a single visit. The procedures were approved by the University Human Subjects Committee, and informed written consent was obtained from both the parent and child prior to initiating the testing protocol. Testing included baseline body composition by DEXA, and cardiovascular fitness by maximal VO2 testing assessment prior to beginning the program. Height was measured on a wall-mounted stadiometer to the nearest 0.1 cm. Weight was measured on a calibrated beam balance platform scale to the nearest 0.1 kg. Based upon these, body mass index (BMI) was calculated.

Percent body fat and fat free mass (FFM) were measured by DXA. Whole body scans were performed using the Norland XR-36 whole body bone densitometer (Norland Corporation, Ft. Atkinson, Wisconsin USA) and tissue masses were analyzed using software version 3.7.4/2.1.0. Subjects wore only workout shorts and a t-shirt for the scan procedure, methods described previously.(Clark RR et al., 2004) Each scan session was preceded by a calibration routine using multiple quality control phantoms that simulate soft tissue and bone. Percent body fat and lean body mass (LBM) were measured by dual-energy x-ray absorptiometry (DXA). Whole body scans were performed using the Norland XR-36 whole body bone densitometer (Norland Corporation, Ft. Atkinson, Wisconsin USA) and tissue masses were analyzed using software version 3.7.4/2.1.0. The XR-36 x-ray tube operates at 100 kV and uses dynamic samarium filtration (K-edge at 46.8 keV) to produce energy peaks at maximum of 40 and 80 keV. Dual NaI detectors measure the attenuated x-ray using a pixel size of 6.5 x 13.0 mm and a scan speed of 260mm/sec. Subjects removed metal objects or clothing containing metal components and wore only workout shorts and a t-shirt for the scan procedure, methods described previously. Each scan session was preceded by a calibration routine using multiple quality control phantoms that simulate soft tissue and bone. Based on 18 scans of 6 subjects using the XR-36 whole body procedures the total body coefficients of variation (CV) are as follows: soft tissue mass 0.2%, total body mass 0.2%, lean body mass 1.0%, fat mass 2.5%, percent fat 2.4% and total BMC 0.9%.

Children underwent measurement of maximal oxygen consumption (VO2max) performed by open circuit spirometry using a progressive treadmill walking protocol to volitional fatigue using a Medical Graphics CPX-D (St. Paul, MN). Requirements to assure subjects reached their maximal oxygen consumption by this protocol included at least two of the following three criteria: 1) Maximal heart rate>200 beats per min; 2)respiratory exchange ratio (VCO2/VO2) >1.0; and 3) a plateau in oxygen consumption. All subjects reached their maximal oxygen consumption according to the above criteria.

Study Design

Once baseline testing was completed, children were enrolled into an afterschool fitness oriented program for 9 months (the entire school year). This (after-school fitness) program was designed to focus on lifelong fitness, and make fitness fun and achievable and maximize the amount of movement during the afterschool time. At the end of the school year, post-treatment assessment of all study outcomes was obtained. The study was designed so that each participant served as his/her own control.

Afterschool Fitness Curriculum

The frequency of the fitness-oriented program was 2 times every week, as part of a 2 hour after-school session. The recommended target for time spent in moderate to vigorous physical activity was greater than 30 min, and most programs were 40 min. All activities took place at the school, after the normal school day. The curriculum was modified to encourage student participation. Competitive games were de-emphasized and replaced with lifestyle-focused activities (walking, games, station-based activities, snowshoeing). All students participated in “structured or teacher-led” activity, and the goal of the activity was predominately cardiovascular fitness. The games and activities were specifically designed to minimize down time. A consistent warm-up plan brought students into movement participation led by YMCA fitness instructors. The activities encouraged physical fitness and fun, and full group participation.

Statistical analyses

Categorical variables were summarized using frequencies and percentages. All continuous variables were summarized and reported in terms of means ± standard deviations (SD). Changes from baseline were evaluated using a paired t-test or the non-parametric Wilcoxon Signed Rank test, if data were not normally distributed. All p-values were two-sided, and p<0.05 was used to indicate statistical significance. Statistical analyses were performed using SAS software version 8.2 (SAS Institute, Cary, NC, USA).

RESULTS

Ninety-five children from the program were randomly recruited to perform baseline and end of the school years evaluations. Ninety children performed baseline testing. However, due to student dropout, only 80 subjects completed both pre- and post-measures. For the purposes of program analyses, only subjects who completed both pre- and post-procedures were included. YMCA staff reported that many families reported “dropping” from the program due to economic difficulties in the area, rather than a reflection on the YMCA programming. Students were considered to have met the curriculum criteria if they attended at least 75% of classes.

Anthropometrics and Body Composition

Patient characteristics are presented in Table 1 as mean ± SD. At baseline, the mean age of the study participants was 8.8±0.5 years (range 7–10), and 53% of the subjects were female. The mean body mass index (BMI) was 18.7± 3. In this fitness oriented class there was a decrease in BMI z-score (−0.14 ± 0.33, p= 0.022), and an increase in muscle mass (2281.9± 1882.7 grams, p < after completion of the 9-month intervention, reflecting the duration of the entire school year (Table 2).

Table 1.

Baseline demographics (mean ± SD).

Total (n=80)
Age (years) 8.8 ±0.8
BMI 18.7±3.4
VO2max (ml/kg/min) 40.03 ± 7.6
%Body Fat 28.7±6.6
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Table 2.

Change from baseline evaluation.

Mean ± SD P value
BMI −0.03 ± 0.33 0.52
Muscle mass (grams) 1558 ± 483 <0.001
Percent body fat −3.0 ± 1.3% 0.03
VO2max (ml/kg/min) 4.77 ± 2.34 0.04
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Cardiovascular Fitness

After 9 months of the fitness intervention, the after-school intervention group showed significant improvements in cardiovascular fitness [VO2 max] when compared to baseline measurements (+4.8±4.3 ml/kg/min, p=0.04). These changes reflect the duration of the entire school year, without the summer vacation. These changes are greater than seen during the course of normal changes without fitness intervention during the course of the 9-month school year.

DISCUSSION

It is generally acknowledged that change in health behavior is facilitated when interventions focus on both the individual and the environment, and for children one of the most important environments is the school.(Swinburn B et al., 1999) This study evaluated the effect of an on-site afterschool based fitness program for elementary school children. These results demonstrate that body composition, cardiovascular fitness (VO2), were favorably changed in elementary-aged children who participated in an after-school program with a YMCA fitness curriculum. Even this small change in the amount of physical activity (5 sessions every 2 weeks) showed beneficial health effects. Similar benefits have been shown following lifestyle improvements in adults. These data are important as a recent meta-analysis and review showed that there was limited evidence that after-school programs can improve physical activity levels and other health-related aspects, and called for additional studies. (Beets MW et al., 2009; Beets MW et al., 2010) These changes to the environment such as after-school opportunities for physical activity, are one example of how small environmental changes can provide population level (school-wide) changes, and how these changes can be sustained.

Despite evidence of the association between CVF and IR in children (Allen DB et al., 2007), questions remain whether targeting “healthy” levels of CVF can be identified and how such standards for fitness should influence public health policy. (Ruiz JR et al., 2007) It is important to note that the most significant changes noted in our program, specifically changes in CVF (as measured by maximal O2 consumption during treadmill testing to voluntary exhaustion), have not routinely been measured in most previous programs. Thus, the reporting of weight or BMI in some studies, compared to fitness or body composition is truly comparing very different variables. Further, given the expected and desired normal growth of middle-school children, we specifically did not use weightas a primary endpoint of this intervention. We acknowledge that there are many ways of evaluating health and fitness, including maximal VO2 testing, body composition, BMI z-scores (percentiles corrected for age and gender) and insulin sensitivity. In this and prior studies, we have demonstrated improved BMI z-score and insulin sensitivity in spite of an increase in total body fat. While this study did not measure fasting blood levels of glucose or insulin, which would be necessary for assessment of insulin resistance, other studies have shown strong correlations between fitness and insulin resitance in children (Allen DB et al, 2007). Thus, there is growing evidence that physical activity and fitness, as well as fatness, are each individually important in affecting health in children.

While it has previously been shown that aerobic exercise is useful and effective as a treatment strategy for insulin resistance (Katzmarzyk PT et al., 2003), it is important to consider what changes in fitness levels would normally be expected for children. This is especially true in our study, which has no formal control group, and each subject acts as his/her own control. In a longitudinal study of fitness in 8–10 year olds, data suggests that fitness levels tend to remain constant without formal intervention, but that children with obese parents tend to have less physical activity and lower fitness levels.(Treuth MS et al., 2004) (Baranowski T et al., 1992) In children and adolescents, percent body fat and visceral adipose tissue are also positively correlated with IR (Kang H-S et al., 2002), an independent predictor of stroke, cancer, coronary artery disease, hypertension and T2DM in adulthood (Sinha R et al., 2002; Yip J et al., 1998). Our group has previously shown that CVF is a stronger predictor of fasting insulin levels than fatness in overweight middle school children.(Allen DB et al., 2007)

Limitations of this study include the lack of a formal control group, and the relatively small sample size. Without a control group, we acknowledge that there may be confounding factors playing a role in these data that are unrecognized. This project focused on increasing physical activity and no dietary intervention or outcomes were measured.

As childhood obesity is predictive of adult obesity, (Dietz WH, 1998b) it is important to develop and evaluate interventions that begin during childhood. This study demonstrates that it is feasible to achieve changes in physical activity sufficient to favorably affect fitness level and percent body fat in children. These findings can provide encouragement to public health researchers and school personnel that increase in physical activity have tangible benefits, and should encourage the development of fitness-emphasis after-school and physical education programs. Optimally, an effective public health approach would also promote increased physical activity outside of school and throughout the summer months,(Carrel AL et al., 2007) as physical activity recommendations cannot be met through physical education classes alone. These type of changes are effective since they alter the environment in which children already participate. The social-ecological model of public health states that children exist in many “layers” of their environment including the school and community environment. By having opportunities to increase physical activity “built in” to the environment, we have a greater likelihood of sustaining these changes.

Conclusions

School based fitness programs can significantly improve cardiovascular fitness levels, and body composition in young children. These findings suggest that modifications of school physical education curricula and after-school programs toward a fitness emphasis may be an effective vehicle for increasing physical activity and improving cardiovascular health for all children.

Acknowledgments

Supported by the Carol M White Physical Education Programming Grant

We thank the YMCA of Dane County staff and the administration and students of YMCA after-school programs. Funding for this evaluation came from the Carol M. White, Department of Education Physical Education Programming (PEP) Grant, Q215F070128.

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