Muscle mass and muscle function over the adult life span: A cross-sectional study in Flemish adults

Background: Aging is accompanied with a progressive deterioration of skeletal muscle mass (SMM) and muscle function, also termed sarcopenia. Methods: The aim was to describe SMM (based on bioelectrical impedance) and muscle function of the leg extensors over the adult age span in 819 men and 578 women, aged 18-78 years. The distribution of skeletal muscle index (SMI; SMM/height(2)) groups was described and muscle force-velocity characteristics were examined between SMI-groups over the adult life span. Subjects were divided into age categories and SMI groups to compare their muscle strength characteristics. Isometric and isokinetic strength, ballistic movement speed and muscular endurance of the knee extensors were evaluated on a Biodex dynamometer. Results: Age by gender interaction effects were found significant (P < 0.01) for all strength tests. In general, the overall drop in slow and faster knee extension strength was larger than the isometric component, with women showing larger losses by the age of 60-70 years compared to men. Regression analysis revealed significant (P < 0.01) age-related reductions, with the largest explained variance for the muscular endurance parameter (24%). No age by SMI-group interaction effect was observed for muscle function, but main effects of age and SMI were significant (P < 0.01). Conclusion: The age-related decline in muscle function was stronger in women. Furthermore, a low SMI results in a weaker muscle function compared to a normal SMI in each age-category, pointing out that its relationship with physical disability should therefore be further examined over the adult life-span. (C) 2015 Elsevier Ireland Ltd. All rights reserved.