Relationship between muscle mass and physical performance: is it the same in older adults with weak muscle strength?

Background: the relationship between muscle mass and physical performance has not been consistent among studies. Objective: to clarify the relationship between muscle mass and physical performance in older adults with weak muscle strength. Design: cross-sectional analysis using the baseline data of 542 older men and women from the Korean Longitudinal Study on Health and Aging. Methods: dual X-ray absorptiometry, isokinetic dynamometer and the Short Physical Performance Battery (SPPB) were performed. Two muscle mass parameters, appendicular skeletal mass divided by weight (ASM/Wt) and by height squared (ASM/Ht(2)), were measured. We divided the participants into a lower-quartile (L25) group and an upper-three-quartiles (H75) group based on the knee-extensor peak torque. Correlation analysis and logistic regression models were used to assess the association between muscle mass and low physical performance, defined as SPPB scores < 9, after controlling for confounders. Results: in the L25 group, no correlation between mass and SPPB was detected, whereas the correlation between peak torque and SPPB was significant and higher than that in the H75 group. Results from the logistic models also showed no association between muscle mass and SPPB in the L25 group, whereas muscle mass was associated with SPPB in the H75 group. Conclusion: muscle mass was not associated with physical performance in weak older adults. Measures of muscle strength may be of greater clinical importance in weak older adults than is muscle mass per se.