gms | German Medical Science

Objective: In the general population, men, on average, are stronger than women. However, it remains unclear whether the sex-related differences in muscle strength observed are due to greater skeletal muscle mass in men or also to qualitative differences in skeletal muscle between men and women. The aim of this study was to investigate whether differences between men and women in muscle strength, as measured by isometric knee extension force and torque, persist after normalization by skeletal mass using an age-stratified, random sample of community men and women.

Material/Methods: In 311 men (mean age, 56 yrs; range, 23–91 yrs) and 356 women (mean age, 57 yrs; range, 21–97 yrs) representing an age-stratified, random sample of community adults, we assessed both isometric knee extension force (in Newtons [N]) and torque (in N-meters [N-m]) using a custom-built chair dynamometer. Total lean muscle mass was measured from whole body DXA scans. Skeletal muscle mass was estimated using the appendicular lean muscle mass from the arms and legs regions from these scans multiplied by 1.33. Using ratio standards, we normalized knee extension force for each subject by total skeletal mass. Knee extension torque was normalized using skeletal mass as well as by height (in m). Then, for each decade in age strata (20–29 yrs, 30–39 yrs, etc), we compared isometric knee extension force and torque between men and women, before and after normalization.

Results: Non-normalized knee extension force and torque were both significantly higher in men than in women across all age strata. However, when we normalized by skeletal mass (for force) or by skeletal mass and height (for torque), there was no significant difference between men and women in either strength measure and results were consistent across all age groups.

Conclusion: Although we found that knee extension strength was greater in men than women across all age groups, these differences were no longer apparent after normalization for skeletal mass. These results suggest that sex-related differences in strength are attributable to differences in muscle mass, rather than muscle quality between sexes, even with aging.