COMPARISON OF REGIONAL DEXA AND MRI IN ASSESSMENT OF MASS AND STRENGTH GAINS

Abstract

1209 Prior studies have been unable to demonstrate significant relationships between change in muscle mass and change in strength as a result of progressive resistance training (PRT). Methods that measure change in muscle cross-sectional area (CSA) may not be sensitive enough to detect the qualitative changes in muscle mass that may be partly responsible for change in muscle strength. However, methods that measure density such as dual energy x-ray absorptiometry (DEXA) may provide a better assessment of the relationship between change in muscle mass and change in muscle strength. Therefore, we conducted a study to determine whether change in lean mass determined by regional DEXA or change in muscle CSA determined by magnetic resonance imaging (MRI) are better related to change in muscle strength from PRT. As part of a longitudinal AIDS clinical trial, 25 HIV positive men were randomly assigned to receive weekly injections of an anabolic agent (AA, 600mg) alone or in combination with PRT at 80% of the one repetition maximum (1RM) three times weekly for 12 weeks. Muscle strength for leg press was determined by the 1RM method. Lean slice mass (LSM) of the right thigh was measured by DEXA and muscle CSA of the right thigh was measured by MRI at baseline and 12 weeks. Change in muscle CSA by MRI and change in leg press strength were significantly correlated with change in LSM by DEXA (r=0.779, p<0.05 and r=0.720, p<0.05, respectively) in the AA+PRT group, however, these relationships were not significant in the AA alone group. Additionally, change in leg press strength and change in muscle CSA by MRI were not significantly correlated in either group. This data suggests that DEXA and MRI both provide measurement techniques to determine quantitative changes in muscle mass from the combined anabolic and PRT regimen. However, regional DEXA analysis may provide a better assessment of qualitative change in muscle mass as it relates to strength gains from PRT.