Sex difference in muscular strength in equally-trained men and women

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Abstract
Although the magnitude of the sex difference in muscular strength is well documented, the extent to which it reflects long-term behavioural differences in physical activity compared to innate biological differences in muscle mass or neuromuscular function is unclear. The purposes of this study were to determine: (1) the magnitude of the sex difference in upper- and lower-body strength in groups of men and women with similar backgrounds of physical activity and (2) the extent to which the difference in strength could be explained by indices of muscle size. Maximum curl, bench press, handgrip, leg press and leg extension strengths; fat-free weight (FFW); and upper-arm, forearm and thigh fat-free cross-sectional areas (FFCSA) were measured on 24 male and 25 female swimmers and 23 male and 25 female non-athletes, 15-28 years of age. Sex differences in absolute strength for both groups were typically smaller than those previously reported. Sex differences in absolute strength were generally smaller for the swimmers than for the non-athletes. The sex difference in upper-body strength was larger than that in lower-body strength. Adjusting strength measures for FFW and/or FFCSA eliminated the sex difference for all measures except curl and bench press strengths. When strength was predicted from FFW and the appropriate limb FFCSA, the combination of these two variables accounted for an average of 97% of the sex-related variance (sex difference) in strength for both swimmers and non-athletes. The sex-related variance in strength associated with differences between men and women in FFW and limb FFCSA was similar for both upper- and lower-body strengths. The findings suggest that the sex difference in muscular strength in equally trained men and women is almost entirely accounted for by the difference in muscle size. For occupations and sports activities in which strength is important, FFW and limb FFCSA may be more valid qualification criteria than sex.