Biological determinants of the sex difference in 12-min run performance.

The extent to which differences between men and women in cardiorespiratory capacity (VO2max in ml X min-1 X kg FFW-1), percent fat, and running economy (VO2 in ml X min-1 X kg BW-1 at 188 m X min-1) account for the sex difference in 12-min run performance was investigated in 34 male and 34 female recreational runners, 19-35 yr of age. Men differed significantly (P less than 0.05) from women in VO2max (68.6 vs 65.1 ml X min-1 X kg FFW-1), percent fat, (10.8 vs 19.8%), and 12-min run performance (3294 vs 2747 m), but not in running economy (39.0 vs 39.1 ml X min-1 X kg BW-1). Simple and multiple regression and correlation analyses indicated that relations of the biological variables to 12-min run performance were similar within groups of men and women. Multiple regression analysis revealed that percent fat, VO2max (ml X min-1 X kg FFW-1), and running economy accounted for 74, 20, and 2% of the average sex difference in 12-min run performance, respectively. It was concluded that for men and women similarly trained, the average sex difference in 12-min run performance is primarily due to differences in percent fat and cardiorespiratory capacity. If the observed differences between men and women on these variables are truly a function of sex, results of this study provide a biological basis for different distance running performance expectations for men and women.