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Bone mass in pre- and peri-pubertal Canadian children : subtitle effects of a high impact exercise intervention, maturity, and ethnicity MacKelvie, Kerry Jane


INTRODUCTION: Osteoporosis has, in part, been attributed to physical inactivity. The direct health care costs of osteoporosis in Canada exceed 650 million dollars annually. Targeted physical activity may be an effective and feasible primary prevention strategy to lessen the burden of this debilitating disease. AIM: The primary aim was to determine the effects of a randomized, controlled, school-based, bone-loading exercise intervention on bone mineral accrual. METHODS AND RESULTS: Subjects: Children were a mixed ethnic group of 383 initially 9-11 year old boys and girls. Ethnic comparisons at baseline: For prepubertal girls (n=56), general physical activity, calcium intake, and total body (TB) and femoral neck (FN) bone mineral content (BMC) (adjusted for body size) were significantly (p<0.05) lower in Asians than Caucasians. For early pubertal girls (n=75), loaded physical activity and sport nights, calcium intake, TB, proximal femur (PF) and FN BMC and areal bone mineral density (aBMD) (adjusted for body size) were significantly lower (-10%) in Asians than Caucasians. 7-month change (girls): Fourteen schools were randomized to intervention (n=7) or control (n=7). I evaluated the effect of a 10-minute, 3x/week, exercise program on bone accrual at the TB, LS, PF, FN and trochanter (TR) in girls. Early pubertal (n=43), but not prepubertal (n=44) intervention girls gained significantly more (+~2%) adjusted BMC, aBMD, and vBMD (FN only) at the FN and LS than same-maturity controls (pre: n=26, early: n=63). 7-month change (boys): Prepubertal Asian and Caucasian boys in the exercise schools (n=61) gained significantly more adjusted TB BMC and PF aBMD (+1-2%) than prepubertal controls (n=60) over 7 months. Accrual was similar between ethnicities. 20-month change (girls): I investigated the continued bone health benefits from exercise over 20 months in girls. Intervention girls (N=32) gained significantly more adjusted FN and LS BMC (+4-5%) than controls (N = 43). CONCLUSIONS: Risk factors for osteoporosis were more prevalent in early pubertal Asian girls compared with Caucasians. A targeted, inexpensive and feasible school-based exercise program, implemented over 7 or 20 months, offered an effective strategy to enhance bone mineral accrual during growth. The skeletal response to loaded physical activity was sex-, site- and maturity-specific.

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