Sex differences in limb and joint stiffnessin recreational runners

Purpose. Female runners are known to be at greater risk from chronic running injuries than age-matched males, although the exactmechanisms are often poorly understood. The aim of the current investigation was to determine if female recreational runnersexhibit distinct limb and joint stiffness characteristics in relation to their male counterparts. Methods. Fourteen male and fourteenfemale runners ran over a force platform at 4.0 m · s–1. Lower limb kinematics were collected using an eight-camera optoelectricmotion capture system operating at 250 Hz. Measures of limb and joint stiffness were calculated as a function of limb length andjoint moments divided by the extent of limb and joint excursion. All stiffness and joint moment parameters were normalizedto body mass. Sex differences in normalized limb and knee and ankle joint stiffness were examined statistically using independentsamples t tests. Results. The results indicate that normalized limb (male = 0.18 ± 0.07, female = 0.37 ± 0.10 kN · kg · m–1) and kneestiffness (male = 5.59 ± 2.02, female = 7.34 ± 1.78 Nm · kg · rad–1) were significantly greater in female runners. Conclusions. Onthe basis that normalized knee and limb stiffness were shown to be significantly greater in female runners, the findings from thecurrent investigation may provide further insight into the aetiology of the distinct injury patterns observed between sexes.Key words: running, sex, limb stiffness, biomechanic