Weight Bearing Exercise Predicts Total Body Bone Mineral Content in Female Midshipmen.

Abstract

LEARNING OUTCOME: To state two effects of weight bearing exercise on the bone mineral content of college aged females. Prevention of osteoporosis and the subsequent reduction in fracture risk depends on the identification of those lifestyle factors that increase peak bone mass. We investigated the relationship between weight bearing exercise (WBE) and total body bone mineral content (TBMC) and hip bone mineral density (BMD) in 22 United States Naval Academy female midshipmen (MIDN). Each received four Norland XR-26 dual energy X-ray absorptiometry scans to measure TBMC and hip BMD over the 2.8 year study period. Frequency of WBE was determined at each visit using a questionnaire. Calcium intake was determined at baseline and the 2.8 year follow-up point using a food frequency questionnaire. Body weight, calcium intake and WBE were predictive of TBMC (p<.01), but the effect of WBE was only positive in subjects weighing greater than 60 kg.Eleven subjects weighing less than 60 kg exercised 2 hrs ∗week-1 compared to the 11 heavier subjects who exercised 2.8 hrs ∗week-1. The heavier subjects exercised 30% longer (p<.05) and had 5.2% greater hip BMD. Calcium intakes were not significantly different between the two groups. These findings suggest that there is a threshold level of weight bearing (from exercise and body weight) necessary to stimulate osteogenesis. Subjects weighing less than 60 kg may have felt less pressure to exercise since they were well within USNA standards for body weight. These individuals may gain an osteogenic benefit from more frequent WBE. In future public health messages, WBE should be promoted to college aged females as a means for attaining peak bone mass in addition to its role in weight control and cardiovascular fitness.