Influence of body mass normalization on the correlations between muscle cross-sectional area and physical performance outcomes in older women.

Aims: Normalization is a method used to account for body mass in clinical practice and research. It is unclear if this method will improve the correlation between muscle cross-sectional area (CSA) and physical performance. We examined the correlations between quadriceps muscle morphology parameters and physical performance outcomes in older women. Material and methods: Twenty older women participated in this study. Ultrasound imaging was used to measure quadriceps muscle CSA and echo intensity. Muscle CSA was expressed as an absolute value (cm2) and as a relative value normalized to body mass (cm2/kg). Physical performance was assessed from timed up-and-go and 6-min walk tests.

Results: Relative CSA was significantly related to timed up-and-go scores (r=-0.489, p=0.029) and 6-min walking speed (r=0.606, p=0.005), whereas absolute CSA was not significantly associated with these performances (r=-0.231, p=0.327 and r=0.373, p=0.105). There was a significant correlation between absolute CSA and body mass (r=0.456, p=0.043). There were also significant correlations between echo intensity and timed up-and-go scores (r=0.556, p=0.011) and 6-min walking speed (r=-0.484, p=0.031).

Conclusions:  Our study showed that relative CSA correlated better than absolute CSA with physical performance. These findings support the need to normalize measurements of muscle CSA to body mass in older adults.