Background: Strength training is a sound method to improve body composition. However, the effect of age, diet, menopause, and physical activity on the relationship between strength training and body composition in women remains unknown. The purpose of this study was to examine the intricacies of the relationship between strength training and body composition in 257 middle-age women and to quantify the effect of these factors on the association.
Methods: The study was cross-sectional. Five variables were used to index strength training participation. Body composition was assessed by dual-energy X-ray absorptiometry. Diet was assessed by 7-day weighed food records, and physical activity was measured objectively using accelerometers.
Results: There were 109 strength trainers in the sample. For each day per week of strength training, body fat was 1.3 percentage points lower (F=14.8, P<0.001) and fat-free mass was 656 g higher (F=18.9, P<0.001). Likewise, the more time women spent lifting and the more intensely they trained, the better their body composition tended to be. Differences in age, energy and protein consumption had little effect on the associations. However, adjusting for differences in physical activity, and to a lesser extent, menopause status, weakened the relationships significantly.
Conclusions: The more days, time, and effort women devote to strength training, the lower their body fat and the higher their fat-free mass tend to be. A significant portion of the differences in body composition seems to result from lifters participating in more physical activity than non-lifters. Menopause status also contributes significantly to the relationship.