A School-Based Exercise Intervention Elicits Substantial Bone Health Benefits: A 2-Year Randomized Controlled Trial in Girls Kerry J. MacKelvie, PhD*; Karim M. Khan, MD, PhD‡§; Moira A. Petit, PhD§; Patricia A. Janssen, PhD¶; and Heather A. McKay, PhD§ ABSTRACT. Objective. Childhood weight-bearing physical activity is recognized as an important determi- nant of peak bone mass, and physical activity interven- tion may represent a feasible strategy for primary pre- vention of osteoporosis. Previous school-based exercise interventions have all been of <10 months in duration. We implemented a high-impact, circuit-based, jumping intervention (10 minutes, 3 times a week) over 2 school years and compared changes in bone mineral content (BMC) over 20 months (2 school years) in 9.9  0.6-year- old intervention girls (N  32) and controls (10.3  0.4 years, N  43). Methods. We measured BMC for the total body, lum- bar spine, proximal femur (and femoral neck and tro- chanteric subregions), and lean and fat mass by dual- energy radiograph absorptiometry (Hologic QDR 4500), and height, sitting height, leg length, and weight at base- line and 20 months. We assessed Tanner stage, general physical activity, and calcium intake by questionnaire. Results. Girls were Tanner breast stage 1 to 3 at base- line. There were no significant differences in baseline or 20-month change in body size or composition, average physical activity, or calcium intake between groups. There were substantially greater gains in lumbar spine (41.7% vs 38.0%) and femoral neck (24.8% vs 20.2%) BMC in interven- tion than in control girls (P < .05, analysis of covariance; covariates were baseline BMC and height, change in height, physical activity, and final Tanner stage). Conclusion. Three brief sessions of high-impact exer- cise per week implemented over 2 consecutive years within the elementary school curriculum elicited a sub- stantial bone mineral accrual advantage in pubertal girls. Pediatrics 2003;112:e447–e452. URL: http://www.pediatrics. org/cgi/content/full/112/6/e447; girls, bone health, bone min- eral content, exercise, intervention. ABBREVIATIONS. LS, lumbar spine; FN, femoral neck; PE, phys- ical education; BMC, bone mineral content; BA, bone area; TB, total body; PF, proximal femur; TR, trochanteric. T he World Health Organization reports that lack of physical activity is a major underlying cause of death, disease, and disability and at- tributes 2 million deaths annually to physical inac- tivity. 1 The health costs of chronic diseases associ- ated with physical inactivity are nearly $1 trillion annually in the United States. 2 There is considerable evidence that strongly links physical inactivity to the increasing prevalence of osteoporosis. 3 The costs of osteoporosis and related fracture continue to escalate and currently exceed $6 billion/year in the United States 2 and are of considerable concern worldwide. 4 It is increasingly accepted that the roots of adult osteoporosis are cultivated in childhood, 5–7 and the World Health Organization agrees that the debate around noncommunicable diseases must be redi- rected toward prevention. 1 A recent editorial argued strongly that, of all modifiable lifestyle factors that influence bone, exercise during growth has the great- est capacity to reduce the public health burden of osteoporosis-related fractures. 5 The author called for safe, effective, relatively simple, and inexpensive programs of activity in childhood to reduce the bur- den of adult osteoporosis. 5 We previously reported a 1% to 3% bone-mass ad- vantage at the lumbar spine (LS) and femoral neck (FN) in children who completed simple yet diverse weight- bearing exercise programs for 10 to 20 minutes, 3 times per week. 8 –11 These programs were instructed by class- room, not physical education (PE) specialist, teachers. Others have reported similar findings with more in- tense school programs 12–15 and repetitive school-based box-jumping programs. 16 However, all previous pro- spective trials of exercise interventions have been com- pleted in 1 academic year (10 months). The question of whether reported short-term benefits continue to accrue with participation over a longer term has not been addressed. Thus, we assessed bone outcomes (bone mineral content [BMC] and bone area [BA]) in girls who completed a 20-month, school-based exercise pro- gram during regular elementary school PE. We hy- pothesized that, over 20 months, girls in intervention schools would accrue more BMC and increase BA more than controls. If this proved to be the case, it would have substantial implications for the content of school PE classes. MATERIALS AND METHODS We have detailed our procedures in previous reports. 8 –10,17 All measurements took place at the University of British Columbia From the *Endocrinology and Diabetes Unit, British Columbia Children’s Hospital and Food, Nutrition and Health, ‡School of Human Kinetics, §Faculty of Medicine, and ¶Department of Health Care and Epidemiology, University of British Columbia, Vancouver, BC, Canada; and Department of Health Evaluation Sciences, Pennsylvania State University College of Medicine, Hershey, Pennsylvania. Received for publication May 30, 2003; accepted Aug 25, 2003. Address correspondence to Heather A. McKay, PhD, Department of Ortho- pedics, Vancouver General Hospital Research Pavilion, 5th Floor, 828 W 10th Ave, Vancouver, BC, Canada V5Z 1L8. E-mail: mckayh@interchange. ubc.ca PEDIATRICS (ISSN 0031 4005). 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