Abstract
BackgroundLack of regular physical activity and consequent sub-optimal bone mass acquisition in youth has been implicated as a primary cause of adult-onset osteoporosis. IMPACT was a behavioral theory-based 1 1/2 year randomized controlled field study aimed at increasing bone accretion in middle school girls. The objective of this study was to determine the intervention effects of the IMPACT program upon key physical and sedentary activity endpoints among schools that participated in the IMPACT study. Endpoints examined included weight bearing physical activity (WBPA); moderate to vigorous physical activity (MVPA); vigorous physical activity (VPA); MET (metabolic equivalent) – weighted WBPA and MVPA; sedentary activity; before/after-school physical activity; and weekend physical activity.MethodsPrimary data analysis using a pretest-posttest control group design was conducted utilizing mixed model analysis of covariance. Data gathered from the IMPACT cohort from 2000–2002 were analyzed to determine baseline versus follow-up differences in activity endpoints. Confounders investigated included ethnicity, body mass index, menarcheal status, participation in 7th grade PE/athletics, friend/familial support and neighborhood safety.ResultsFollow-up means were higher for participating intervention schools relative to control schools for all physical activity variables but were statistically significant only for the following variables: daily minutes of vigorous physical activity (mean difference between Intervention (I) and Control (C) = 6.00↑ minutes, 95% CI = 5.82–6.18, p = 0.05), daily after school activity minutes (mean difference between I and C = 8.95↑ minutes, 95% CI = 8.69–9.21, p = 0.04), and daily weekend activity minutes (mean difference between I and C = 19.00↑ minutes, 95% CI = 18.40–19.60, p = 0.05). The intervention significantly reduced duration of student daily TV/Video watching (mean difference between I and C = 12.11↓ minutes, 95% CI = 11.74–12.48, p = 0.05) and total daily sedentary activity minutes (mean difference between I and C = 16.99↓ minutes, 95% CI = 16.49–17.50, p = 0.04).ConclusionA well designed and implemented school based health and physical activity intervention can result in a positive influence upon increasing physical activity levels and decreasing sedentary activity. Future interventions should consider a more structured intervention component to obtain significant changes in WBPA.
Highlights
Lack of regular physical activity and consequent sub-optimal bone mass acquisition in youth has been implicated as a primary cause of adult-onset osteoporosis
The purpose of this paper is to briefly describe the physical activity component of IMPACT and to report major results with respect to changes obtained in levels of weight-bearing physical activity (WBPA), moderate to vigorous physical activity (MVPA), vigorous physical activity (VPA), sedentary activities, before/after-school activities and weekend activities among students from schools that participated in the IMPACT intervention
Twelve schools had initially been recruited for the study and they remained in the study throughout the 1 1/2 year intervention period; results from process evaluation indicated that one of the intervention schools did not complete any of the IMPACT curriculum lessons during the first year, and no health education lessons were observed during process evaluation and quality control visits
Summary
Lack of regular physical activity and consequent sub-optimal bone mass acquisition in youth has been implicated as a primary cause of adult-onset osteoporosis. The World Health Organization has defined osteoporosis as a bone mineral density value more than 2.5 standard deviations below the mean for normal young White women [4]. Based on this definition, an estimated 10 million individuals over age 50 in the United States presently have osteoporosis and an additional 33.6 million individuals over age 50 have low bone mass or "osteopenia" of the hip. It has been suggested that one of the primary means of preventing osteoporosis is to affect modifying factors (such as diet and physical activity) that influence bone density so that peak bone mass is achieved during the first twenty years of life [2,8,10]
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