Exploring the Role of Muscle Mass, Obesity, and Age in the Relationship Between Muscle Quality and Physical Function

Background: Divergent conclusions emerge from the literature regarding the relationship between muscle quality (defined as muscle strength per unit of muscle mass) and physical function. These contrasted results may be due to the influence of factors such as age, obesity, and muscle mass itself. Consequently, the aim of the present study was to explore the role of these factors in the relationship between muscle quality (MQ) and physical function. Methods: Data are from 312 individuals (97 men and 215 women) aged 50 years and older. Body composition (dual energy X-ray absorptiometry) and knee extension strength of the right leg (1 repetition maximum) were assessed. Appendicular lean body mass index (AppLBMI) and MQ (knee extension strength/right leg lean mass) were calculated. A composite score of physical function was created based on the timed up-and-go, alternate step, sit-to-stand, and balance tests. Results: MQ was significantly associated with physical function when AppLBMI (beta = 0.179; P = .004) and body mass index (BMI) (beta = 0.178; P = .003), but not age (beta = 0.065; P = .26), were included in regression analysis. AppLBMI (beta = 0.221; P < .001), BMI (beta = 0.234; P < .001), and age (beta = 0.134; P = .018) significantly interacted with MQ to determine physical function. Conclusions: Our results show that muscle mass, obesity, and age influence the relationship between MQ and physical function, suggesting that these factors should be taken into account when interpreting MQ. Even so, higher levels of MQ were associated with higher physical function scores. Nutritional and physical activity interventions may be designed in this regard. (C) 2014 - American Medical Directors Association, Inc. All rights reserved.