The interrelationship among muscle mass, strength, and the ability to perform physical tasks of daily living

The purpose of this study was to objectively compare the difficulty and determine the contribu-tion of strength and muscle mass to the performance of physical tasks of daily living in a group of younger and older women. A cross-sectional design was used. Volunteer participants were from the community of Birmingham, AL; there were 21 older (aged 60–75 years) and 20 younger (23–34 years) healthy women in the study. Subjects were matched for height and weight. Their testing included total and regional body composition evaluation by use of dual-energy x-ray absorptiometry, isometric strength tests of elbow flexors and knee extensors, and in-tegrated electromyography (IEMG) evaluation while the subjects were standing from and sitting into a chair, and while they were carrying a small load (weight relative to strength). A two-way analysis of variance and a two-way analysis of covariance with repeated measures, Pearson product correlation, and first-order partial correlations were used to analyze the data. A signifi-cant inverse correlation was observed between age and isometric strength of both the knee ex-tensors and elbow flexors. Adjusting for upper leg lean tissue did not change the significant inverse correlation between age and knee extensor strength. However, after an adjustment for arm lean tissue, there was no significant correlation between elbow flexor strength and age