Eight Months of Twice Weekly Ten Minute Jumping Activity for PE Warm Up Improves Bone in Adolescent Boys and Girls: the POWER PE Study

Abstract

High intensity skeletal loading during growth may be an effective strategy to maximise bone accrual and reduce fracture risk in old age. Preventing Osteoporosis With Exercise Routines in Physical Education (POWER PE) was an 8-month randomised controlled school-based exercise intervention designed to apply known principles of effective bone loading to practical opportunities to improve life long musculoskeletal outcomes. We replaced regular warm up activities with jumping in the twice-weekly PE classes of early high school students to observe the effect on bone accrual in adolescent boys and girls. A total of 99 adolescents (46M:53F, 13.8 ? 0.4 years) volunteered to participate in the yearlong study. Most were classified as Tanner IV (53%). Intervention group subjects performed ten minutes of supervised jumping activity in place of regular PE warm up activities. Control subjects performed regular PE warm-up activities directed by their teacher. Anthropometrics, Tanner staging, peak height velocity, muscle strength and power, flexibility, and bone mass (DXA and QUS) were measured at baseline and follow-up. Geometric properties (such as FN cross-sectional moment of inertia and LS index of bone strength) were estimated from DXA measures. Physical activity and dietary calcium were determined by questionnaire. There were no differences in any measured variable between control and intervention groups at baseline. No group differences were detected for 8-month change in anthropometric, maturity, strength, or flexibility variables for boys or girls. At eight months, boys in the intervention group had experienced significant improvements in calcaneal BUA (+5.0%, p = 0.012), and fat mass (-10.5%, p = 0.023), while controls did not (+1.4% and -0.8% respectively). Girls in the intervention group, however, experienced significant improvements in FN BMC (+13.9%, p = 0.05) and LS BMAD (+5.2%, p = 0.04), which were not observed in controls (+4.9% and +1.5% respectively). Other bone strength parameters improved significantly for both groups, such that between group comparisons of percent change revealed significant intervention effects only for WB BMC (+10.6% vs +6.3%, p = 0.029) for boys. Short duration, regular jumping activity during adolescence appears to improve bone accrual in a sex-specific manner. Boys improved whole body bone mass and BUA, and reduced fat mass, while girls improved bone mass at the hip and spine.