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The effects of an 18-month weight-training and calcium-supplementation program on bone mineral of adolescent girls Stewart, Sally Rutherford (Willis)

Abstract

Physical activity and adequate calcium intake have the potential to increase peak bone mass and reduce the incidence of osteoporosis later in life. This study investigated the effects of 18-months of weight training and calcium supplementation on adolescent bone mineral and bone size and the bone remodeling transient. After screening, 108 female volunteers, mean age 14.1 y, from 4 high schools were assigned to a non-exercise or exercise group, based on the school they attended. Exercise subjects were matched for weight, months past menarche and height to non-exercise subjects. Pairs were randomly given 1000 mg/d calcium supplement or placebo. Calcium and placebo pairs were matched to form blocks of 4 subjects forming 4 treatment groups: exercise/calcium (EC), exercise/placebo (EP), no exercise/calcium (NC), no exercise/placebo (NP). The PRECEDE PROCEED model of health promotion program planning and evaluation was used to plan the intervention program. Exercise subjects strength trained, 3x/wk in 5 week cycles of 1 easy, 1 moderate, and 3 high intensity weeks. High intensity was 3 sets of 5-7 repetitions to fatigue. The nonexercising group was instructed to continue with their current activity level. Subjects recorded calcium/placebo intake, physical activity, weight training and menstrual cycles. Bone mineral content (BMC) and density (BMD) of whole body, hip and spine were measured using a Norland XR 26 dual-energy X-ray absorbtiometer initially, and at 6 and 18 months. Strength tests, anthropometry, dietary, lifestyle and program compliance questionnaires were also completed. Eighty-seven girls completed the study with a mean exercise and supplementation compliance of 48.3% and 75.8% respectively. Program dropouts and poor compliance necessitated revision of subject sets to examine the effects in participants who had at least 50% program compliance. Repeated measures ANCOVA tested for changes across time and between groups, and ANCOVA tested for effects and interactions of calcium and exercise. Correlations with bone mineral changes and calculations of calcium retention efficiency were completed. Femoral neck and lumbar spine BMD were converted to bone mineral apparent density (BMAD) to account for bone size. Factors affecting program compliance were identified through rating scales. Significant results between 0-6 mo., the bone remodeling transient period, were: i) interaction of calcium supplementation and weight training at the femoral neck indicating benefits of calcium in the no-exercise group ii) positive effect of calcium for lumbar spine BMD, iii) negative effect of exercise for total body and trochanter skeletal area, iv) total calcium intake was related to increases in femoral neck and lumbar spine BMD. From 6-18 mo., the true intervention period, significant results included: i) interaction of calcium supplementation and weight-training for femoral neck BMD indicating that calcium was beneficial in the exercise group ii) negative effect of calcium for lumbar spine BMD and area. Other significant results included greater increases in lower body strength and bicristal bone breadth in the exercise group, associations of maturation, weight change, and lean body mass change with changes in bone mineral measures, higher P values for BMAD results than for areal density results, negative association between calcium retention efficiency and maturation, and high calcium intake (>1200 mg/ vs.

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