Predicting Bone Mass in College Aged Female Gymnasts

Abstract

Achieving peak bone mass in a female's life is imperative to avoid osteoporotic fractures. According to the National Osteoporosis Foundation, about 85-90% of a females bone mass will be developed by the age of 18. There are several lifestyle and behavioral characteristics that are well documented to be detrimental to peak bone mass development including excessive alcohol consumption and smoking. Less documented are the activities, such as motor activity, that have positive effects on bone mineral density. PURPOSE: The purpose of this study is to see if body weight and muscular strength are valid predictors of bone mineral density in college aged female gymnasts. METHODS: Ten female athletes participated in the study with mean (± SD) age and body weight at 20.15 ± 1.49 yr. and 131.39 ± 14 pounds. All athletes were tested on two days. Day one consisted of bone density scans with height and weight measures taken prior to the scan. Day two consisted of a vertical power test, isokinetic leg strength, and horizontal power test. RESULTS: A multiple regression analysis was used with isokinetic strength of the dominant leg at 60°/second and body weight as the predictor variables regressing on the criterion variable, bone mineral density. Statistical significance was set at a =.05. The output was analyzed for influential data points using leverage (hi >.60) and Cook's D to determine if there were any misleading data. Leverage and Cook's D both indicated that there were not influential outliers in the data. Results indicated that significant differences existed; F (2, 9) = 5.45, p <.05 and that the predictors accounted for over half of the variance in bone mineral density (R2 =.61). Follow up analysis indicated that neither muscle strength, F (1, 9) = 4.86, p =.06, or body weight, F (1, 9) =.50, p =.50 were individually significant. The semi-partial squared correlations revealed that isokinetic strength accounted for 27% of the variance, (b =.64, p =.06), whereas body weight accounted for 3%, (b =.21, p =.50). CONCLUSION: Muscle strength and body weight are predictors of bone mineral density in college aged female gymnasts, with muscular strength accounting for more of the variance.