Impact Of A 9-month School-based Physical Activity Intervention On Bone Development Among Sedentary Adolescent Females

Abstract

PURPOSE Increased levels of peak bone mass have been associated with a decreased risk of osteoporotic fracture later in life. The present study evaluated the effects of a school-based physical activity intervention on bone mass development among sedentary, unfit, postmenarcheal adolescent females. METHODS Adolescents (mean age = 15.04 +/- .79 years) of mixed ethnicity (57% Caucasian) were assigned to an intervention (n = 63) or comparison (n = 59) group based on school attended. The 9-month intervention consisted of supervised in-class physical activity (4 days/week for 40 min), health education, and internet-based self-monitoring. The comparison group participated in assessments only. Bone mineral content (BMC) and bone mass density (BMD) for the whole body, left leg, left arm, spine, hip, and femoral neck were assessed via dual x-ray absorptiometer (DEXA) at baseline, 4 months, and 9 months. Calcium consumption (mg/kcal) and fat body mass at baseline were measured through a 3-day diet record and DEXA, respectively. Data were analyzed using one-way ANCOVAs of the change scores, controlling for body fat and calcium consumption at baseline. RESULTS Although trends were consistent with a beneficial impact of the physical activity intervention on BMC for the spine (+2.6% vs. −0.3%), hip (+1.7% vs. −1.4%), and femoral neck (+2.3% vs. −1.7%) between baseline and 4 months, the effects were not strong enough to reach statistical significance. Between 4 and 9 months, improvements in BMC for the left leg (+2.5% vs. − 1.2%) and left arm (+2.7% vs. −2.1%) were significantly greater in the intervention group as compared to the comparison group (ps < .05). CONCLUSIONS Small increases of bone mineral content at specific structural sites can be detected among sedentary, postmenarcheal adolescent females participating in a school-based intervention that increases physical activity.