Attending After-School Physical Activity Club 2 Days a Week Attenuated an Increase in Percentage Body Fat and a Decrease in Fitness Among Adolescent Girls at Risk for Obesity

Abstract

Purpose:

To evaluate the effect of a 17-week intervention, including an after-school physical activity (PA) club 3 d/wk, on moderate-to-vigorous physical activity (MVPA), body mass index (BMI) z score, percentage body fat (%BF), and cardiorespiratory fitness (CRF) among fifth to eighth grade girls having a BMI z score ≥0, and explore whether intervention outcomes varied by club attendance (1 vs 2 vs 3 d/wk).

Design:

Secondary analysis of data from a group randomized controlled trial (N = 1519, 10- to 15-year-old girls: n = 753 intervention; n = 766 control).

Setting:

Twenty-four Midwestern US schools (n = 12 intervention; n = 12 control).

Sample:

Subsample (n = 1194 girls) from trial’s intervention (n = 593 girls) and control (n = 601 girls) groups having BMI z scores ≥0.

Measures:

Moderate-to-vigorous physical activity (min/h), BMI z score, %BF, and CRF ( ${\dot{V} O}_{2max}$ : mL/kg/min) were estimated at baseline and postintervention.

Analysis:

Linear mixed-effect models.

Results:

Intervention group gained less %BF (B = −0.35, P = .016), and their CRF decreased less (B = 0.22, P = .010) than the control. Marginally significant findings showed girls attending the club an average of 1 d/wk had greater increases in %BF (B = 0.33, P = .087) and MVPA (B = 0.20, P = .083) and a greater decrease in CRF (B = −0.20, P = .061) than girls attending 3 d/wk. No differences occurred between girls who attended 2 versus 3 d/wk for any outcomes.

Conclusions:

The intervention attenuated an increase in %BF and a decrease in CRF among girls at risk for obesity from baseline to postintervention. Offering the after-school PA club 2 d/wk may be adequate for achieving outcomes.

Keywords

female body mass index exercise intervention attendance

Purpose

Adolescents in the upper healthy weight range (body mass index [BMI] ≥50th percentile) are at risk for becoming overweight or obese¹ (BMI ≥85th to <95th percentile; BMI ≥95th percentile, respectively).² The average BMI z score of healthy weight adolescents having ≥2 cardiometabolic risk factors is −0.1,³ which is close to having a BMI at the 50th percentile (equivalent to BMI z score = 0). This information underscores the need to include at-risk healthy weight adolescents, as well as those who are overweight or obese, in interventions.

Despite the importance, no study was found that examined the effect of a physical activity (PA) intervention on improving PA or reducing health risk factors among adolescents having a BMI z score ≥0. Many studies testing PA interventions did not report PA session attendance, even though low session attendance can mask true effectiveness of an intervention.⁴ To contribute toward filling these gaps, this study’s 2-fold purpose was to (1) evaluate the effect of a 17-week PA intervention on increasing moderate-to-vigorous physical activity (MVPA) and improving BMI z score, percentage body fat (%BF), and cardiorespiratory fitness (CRF) among fifth-eighth grade girls having a BMI z score ≥0, and (2) explore whether intervention outcomes varied by after-school PA club attendance (1 vs 2 vs 3 d/wk).

Methods

Design and Sample

A secondary analysis of data from a group randomized controlled trial (RCT) was conducted (N = 1519 10- to 15-year-old girls: n = 753 in the intervention group; n = 766 in control group). Twenty-four US schools were randomly assigned to intervention (n = 12) or control (n = 12; usual activities) conditions. The intervention included an after-school PA program 3 d/wk. Approval to conduct the trial was received from the university institutional review board. Parents and girls signed consent and assent forms, respectively, and completed an eligibility screening tool.⁵ This study included a subsample of 1194 girls with BMI z scores ≥0 (n = 593 in the intervention group; n = 601 in the control group).

Measures

Girls’ demographic information was collected at baseline. Data on BMI, BMI z score, %BF, CRF, and MVPA were obtained from both groups at baseline and postintervention (immediately after the 17-week intervention had ended).

Demographics

Data were collected on age, race, Hispanic ethnicity status, race, academic grade, enrollment in school’s free or reduced-price lunch program, and participation in sports or PA classes/lessons. Each girl completed the Pubertal Development Scale. Response choices for body hair and breast development ranged from not yet started (1) to development completed (4). Girls reported whether menstruation started (4) or not (1). A summed score of 2, 3, or >3 without menstruation indicated pre-, early, or middle puberty, respectively. A summed score of ≤7 or 8 with menstruation indicated late puberty or postpuberty, respectively.⁶

Body mass index, BMI z-score, and %BF

A Shorr Board (Weigh and Measure, LLC, Olney, Maryland) was used to measure height to the nearest 0.1 cm. Weight to the nearest 0.1 kg and %BF to the nearest 0.1% were assessed with a foot-to-foot bioelectric impedance scale (Tanita Corporation, Tokyo, Japan). Both BMI (weight [kg]/height [m²]) and BMI z score were estimated.²

Cardiorespiratory fitness

The Progressive Aerobic Cardiovascular Endurance Run (15- or 20-m shuttle run test)⁷ was used Each girl’s number of completed laps was converted to the mile equivalent for estimating ${\dot{V} O}_{2max}$ (ml/kg/min).⁸

Moderate-to-vigorous physical activity (minutes/hour)

Each girl wore an ActiGraph GT3X-plus accelerometer (www.theactigraph.com) for 7 days. Physical activity intensities were estimated based on acceleration count cut points: moderate (574-1002 counts/15 seconds) and vigorous (≥1003 counts/15 seconds).⁸

Data Analysis

Data analyses were performed in SAS 9.4 and R 3.2.4. Multiple imputations (n = 20) were performed to handle missing data.⁹ Baseline demographics, BMI z score, and MVPA were included in the imputation model. Descriptive statistics were used to describe variables. Linear mixed-effect models were applied to examine intervention effects on BMI z score, %BF, CRF, and MVPA after adjusting for age, ethnicity, race, socioeconomic status (SES), puberty stage, study year, and baseline outcome. Because girls were nested within schools, school was treated as a random effect in the model. Cohen d was calculated to describe effect size: 0.2 small effect size, 0.5 medium effect size, and 0.8 strong effect size.¹⁰ To examine the effect of after-school club attendance on intervention outcomes among intervention girls, linear mixed-effect models were used by controlling for age, ethnicity, race, SES, and pubertal stage. Based on the intraclass correlation (ICC) obtained from the baseline data, post hoc study power analyses showed that the minimum identified effect size (Cohen d) for 80% power was 0.24 (ICC = 0.02), 0.27 (ICC = 0.03), 0.34 (ICC = 0.06), and 0.38 (ICC = 0.08) for BMI z score, %BF, CRF, and MVPA, respectively.

Results

Demographics

Girls’ mean age was 12.07 years. About 61.3% were black, 78.6% were of low SES, 25.6% were overweight, and 40.0% were obese. The control group had more black girls (64.7% vs 57.8%, P = .015) and a higher obesity rate (43.8% vs 36.3%, P = .017) than the intervention group (Supplement Table 1).

Intervention Effect on Outcomes

Overall, intervention girls gained less %BF (B = −0.35, P = .016), and their CRF decreased less (B = 0.22, P = .010) than the control girls (Supplement Table 2). From baseline to postintervention, intervention girls had an increase of 0.32% in %BF and a decrease of 0.33 in CRF, while control girls had an increase of 0.62% and a decrease of 0.54, respectively (Table 1). The %BF model explained about 92.8% of the variance in %BF, and the CRF model explained about 94.4% of the variance in CRF. No significant differences occurred in postintervention BMI z score (B = −0.02, P = .232) or MVPA (B = −0.07, P = .332).

Table 1.

Study Outcomes by Group and Time (N = 1194).

Study Outcome	Intervention (n = 593)		Control (n = 601)		Unadjusted Effect Size Cohen d ^a
Study Outcome	Baseline, M (SD)	Postintervention, M (SD)	Baseline, M (SD)	Postintervention, M (SD)	Unadjusted Effect Size Cohen d ^a
BMI z score	1.30 (0.74)	1.30 (0.74)	1.42 (0.73)	1.44 (0.73)	−0.03
1 d/wk (n = 290)	1.30 (0.72)	1.31 (0.73)			0.04
2 d/wk (n = 147)	1.35 (0.73)	1.37 (0.70)			0.05
3 d/wk (n = 156)	1.25 ((0.79)	1.23 (0.79)			-
%BF	32.40 (8.37)	32.72 (8.30)	33.48 (8.24)	34.10 (8.14)	−0.04
1 d/wk	32.40 (7.98)	32.96 (7.90)			0.07
2 d/wk	32.81 (8.39)	33.07 (8.20)			0.03
3 d/wk	31.93 (9.01)	31.90 (9.02)			-
CRF	36.74 (4.85)	36.41 (4.94)	36.17 (4.73)	35.63 (4.83)	0.04
1 d/wk	36.70 (4.58)	36.24 (4.71)			−0.06
2 d/wk	36.54 (4.81)	36.32 (4.87)			−0.01
3 d/wk	37.04 (5.34)	36.86 (5.37)			-
MVPA	2.99 (1.33)	3.19 (1.49)	2.87 (1.30)	3.20 (1.48)	−0.09
1 d/wk	3.08 (1.38)	3.36 (1.56)			0.10
2 d/wk	3.10 (1.40)	3.22 (1.58)			−0.02
3 d/wk	2.71 (1.10)	2.86 (1.18)			-

Abbreviations: %BF, percentage body fat; BMI, body mass index; CRF, cardiorespiratory fitness; MVPA, moderate-to-vigorous physical activity; SD, standard deviation

^a Positive effect size indicates intervention or 1 d/wk or 2 d/wk group had a higher mean change than control or 3 d/wk group.

After-School PA Club Attendance Effect on Outcomes

Girls attending the after-school club 1 d/wk had greater increases in %BF (B = 0.33, P = .087) and MVPA (B = 0.20, P = .083) and a greater decrease in CRF (B = −0.20, P = .061) than girls attending club 3 d/wk (Table 2). No significant differences occurred between girls who attended 2 versus 3 d/wk for any outcomes.

Table 2.

Attendance Effect Results From Linear Mixed-Effect Models (n = 593).

Variable	BMI z Score			%BF			CRF			MVPA
Variable	Estimate	SE	P Value	Estimate	SE	P Value	Estimate	SE	P Value	Estimate	SE	P Value
Intercept	−0.13	0.12	.31	2.13	1.13	.087	1.83	0.77	.037	1.73	0.72	.035
Age	0	0	.173	−0.01	0.01	.245	−0.01	0	.215	0	0	.400
Hispanic (Ref: no)	0.02	0.02	.466	−0.09	0.22	.665	0.02	0.12	.855	−0.15	0.13	.249
Black (Ref: no)	−0.02	0.02	.353	0.02	0.17	.922	0.09	0.10	.351	−0.06	0.11	.564
Low SES (Ref: no)	0.02	0.02	.365	0.27	0.20	.193	0.05	0.12	.679	0.15	0.12	.223
Puberty stage (Ref: early stage)	−0.01	0.02	.585	0.49	0.18	.008	0.07	0.10	.481	−0.03	−0.11	.794
Attendance (Ref: 3 days)
1 day	0	0.02	.819	0.33	0.19	.087	−0.20	0.11	.061	0.20	0.12	.083
2 days	0.02	0.02	.286	0.24	0.21	.261	−0.11	0.12	.342	0.16	0.13	.220

Abbreviations: %BF, percentage body fat; BMI, body mass index; CRF, cardiorespiratory fitness; MVPA, moderate-to-vigorous physical activity; SE, standard error; SES, socioeconomic status.

Discussion

The null findings for BMI z score are consistent with those of 3 other group RCTs including adolescent girls.^11
-13 Two of these studies included a measure of %BF, but in contrast to the current study, no significant differences occurred between the intervention and control groups.^12,13 Consistent with this study’s findings, no PA differences emerged between the control and intervention groups in 2 prior group RCTs with adolescent girls.^14,15

Although the effect size was small, the significant, positive finding for CRF contrasted with results of 2 prior group RCTs. One included an intervention for eighth grade boys and girls who received pedometers,¹⁶ and the other involved an intervention for third to eighth grade boys and girls who received PA strategies.¹⁷ Researchers conducting the trials concluded that their intervention might not have been intense enough to result in group differences in CRF.

The current study’s findings that girls attending the after-school PA club an average of 3 d/wk versus 1 d/wk gained less %BF and decreased CRF suggest that 1 d/wk may not be sufficient. The finding that girls who attended the after-school PA club 3 d/wk had lower MVPA at postintervention than those who attended 1 d/wk may have occurred because the former group lost their after-school opportunity to engage in PA when the club ended, whereas the latter group had more after-school time for other activities, some of which may have included PA, that continued beyond the intervention period.

Limitation

Findings may not be generalizable to boys. The potential for bias exists when comparing girls based on the number of days/week that they attended the PA club because girls were not randomized to attendance frequencies and the sample size might not be adequate for sufficient power. Therefore, differences in observed outcomes may be due to other confounding factors and not necessarily due to additional attendance days.

Conclusions

Offering an after-school PA club 2 d/wk may be adequate for achieving outcomes.

SO WHAT?

What is already known on this topic?

Adolescents having a BMI z score ≥0 are at risk for adverse health outcomes.

What does this article add?

A PA intervention can attenuate an increase in %BF and a decrease in CRF among girls at risk for obesity; however, it has no effect on BMI z score and MVPA at postintervention. Girls attending the after-school club (offered 3 d/wk) an average of 1 d/wk had greater increases in %BF and MVPA and a greater decrease in CRF than girls attending club 3 d/wk. No differences in outcomes occurred between girls who attended 2 versus 3 d/wk.

What are the implications for health promotion practice or research?

An intervention focusing on PA alone may not be sufficient for reducing at-risk adolescent girls’ BMI. Strategies to help girls achieve adequate MVPA after an intervention ends are needed. To be feasible for girls to attend, offering an after-school PA club 2 d/wk may warrant consideration.

Supplemental Material

Supplemental Material, sj-pdf-1-ahp-10.1177_0890117120915679 - Attending After-School Physical Activity Club 2 Days a Week Attenuated an Increase in Percentage Body Fat and a Decrease in Fitness Among Adolescent Girls at Risk for Obesity

Supplemental Material, sj-pdf-1-ahp-10.1177_0890117120915679 for Attending After-School Physical Activity Club 2 Days a Week Attenuated an Increase in Percentage Body Fat and a Decrease in Fitness Among Adolescent Girls at Risk for Obesity by Lorraine B. Robbins, Jiying Ling and Fujun Wen in American Journal of Health Promotion

Footnotes

Authors’ Note

L.B.R. designed the study and its objectives and procured funding. As principal investigator, she supervised the study activities and was responsible for the acquisition of data. She also wrote the initial draft of the manuscript. J.L. and F.W. analyzed the data and wrote the analysis and results sections. L.B.R., J.L., and F.W. interpreted the data. J.L. and F.W. critically reviewed and edited the manuscript. L.B.R., J.L., and F.W. approved the final version to be published.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The study was funded by a grant from the National Heart, Lung, and Blood Institute at the National Institutes of Health (R01HL109101); PI: L. B. Robbins. The contents are solely the responsibility of the authors and do not necessarily represent the official views of NIH.

ORCID iDs

Lorraine B. Robbins, PhD, RN, FNP-BC, FAAN

Jiying Ling, PhD, RN

Supplemental Material

Supplemental material for this article is available online.

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