Maximal eccentric-concentric strength determines stretch-shortening cycle leg power across biological sexes

The ratio of eccentric-to-concentric force output (E/C ratio) is higher in female compared to male individuals, however, the functional implications for stretch-shortening cycle (SSC) leg power output remains unknown. Thus, in the present study, male and female competitive athletes (n = 178; females: 53%, n = 95) performed maximal leg extensor strength testing to determine the E/C ratio along with an assessment of leg power during SSC countermovement jump (CMJ) testing. A whole-body force-velocity relationship was assessed to determine the maximum leg extensor shortening velocity (V_max). The E/C ratio was 7% higher in the female group compared to the male group independent of muscular strength (p < 0.001), and a higher E/C ratio was weakly associated with a reduced V_max in the female group (R² = 0.05) but not the male group (R² = 0.004). However, greater eccentric force production was associated with a higher E/C ratio independent of sex (R² = 0.33). Finally, CMJ propulsive work (R² = 0.64) and mechanical power (R² = 0.62) were associated with increased leg extensor concentric strength, while CMJ braking power was modestly associated with increased leg extensor eccentric strength (R² = 0.05). The present study demonstrates the diversity that may exist in the expression of whole-body muscle mechanics between the sexes, whereas absolute leg extensor strength was the primary determinant of SSC leg power independent of sex.