Examining the Associations Between Lean Mass, Muscular Strength, Muscle Quality and Physical Function

Abstract

Objective: The determinants of physical function are not well characterized among middleaged women. The primary aim of this cross-sectional study was to determine the strength of the associations between lean mass, muscular strength, muscle quality, and physical functional ability in a cohort of middle-aged women. The secondary aim was to determine the measure of muscle quality most highly associated with measures of physical function. Methods: Middle-aged women (N=111, age, 53.14 ±6.15 years) had body composition (via dual energy x-ray absorptiometry), physical activity (via accelerometer), and physical function (via Transfer Task (TRANSFER), 30-Second Chair Stand (30-CS), 6-Minute Walk Test (6MWT), 8-Foot-Up-And-Go (UP-GO)) assessed objectively. A lower body physical function composite score was also calculated. Lower body strength was measured using isokinetic dynamometry for isometric knee flexion and extension at 60 degrees, isokinetic flexion and extension at 60 degrees per second, and isokinetic flexion and extension at 180 degrees per second. Muscle quality was defined as muscular strength normalized for upper leg lean mass and calculated using: 1) isometric knee flexion and extension at 60 degrees (MQ-ISO), 2) isokinetic knee flexion and extension at 60 degrees per second (MQ-KN60), 3) isokinetic knee flexion and extension at 180 degrees per second(MQ-KN180). Results: The lower body physical function composite score was significantly associated with percent lean mass, MQ-ISO, MQ-KN60, and MQ-KN180. Partial correlations, controlled for age and average steps per day, found that MQ-KN60 was the variable most highly associated with the physical function composite score. Results from a hierarchical linear regression showed that 1) age, average steps per day, and MQ-KN60 are independently associated with physical function composite score, explaining 3%, 18.1% and 14.3% respectively, and 2) age, average steps per day, MQ-KN60 were significantly associated with , TRANSFER, 30-CS, and 6MWT. Conclusion: In middle-aged women, percent lean mass, muscular strength, and muscle quality were all significantly associated with physical functional ability. The association between MQ-KN60 and the physical function composite score was stronger than all other measured variables. This data provides insight into the most relevant measures to consider when examining the independent contributors to physical functional ability in middle-aged women. iv ACKNOWLEDGMENTS I would like to acknowledge Dr. Ward-Ritacco, who was my major professor. All the comments and guidance through this process really helped and helped me become a better researcher and student. I would also like to acknowledge Dr. Sabik and Dr. Riebe. Your comments and feedback were very helpful in helping me truly understand this process and aided me in becoming a better researcher. I would like to thank my co-investigators Sydney Sweck and Olivia Finnegan, who helped with data collection, and cleaning of the data. Your help with all parts was greatly appreciated. I w...