Effect of sex and fatigue on muscle stiffness and musculoarticular stiffness of the knee joint in a young active population

The purpose of this study was to investigate the influence of sex and fatigue on knee extensor peak torque (PT), muscle stiffness (MS) of the vastus lateralis (VL) and knee joint musculoarticular stiffness (MAS) in young adults. Twenty-two male and 22 female recreational athletes participated. Males were characterised by higher relaxed [pre-: males 364.43 (52.00) N m(-1), females 270.27 (37.25) N m(-1); post-: males 446.75 (83.27) N m(-1), females 307.39 (38.58) N m(-1)] and contracted [pre-: males 495.07 (71.04) N m(-1), females 332.34 (85.42) N m(-1); post-: males 546.37 (90.74) N m(-1), females 349.21 (85.55) N m(-1)] MS of the VL, and knee joint MAS [pre-: males 1450.11 (507.98) N m(-1), females 1027.99 (227.33) N m(-1); post-: males 1345.81 (404.90) N m(-1), females 952.78 (192.38) N m(-1)] than females pre- and post-fatigue. A similar finding was observed in pre-fatigue normalised knee extensor PT [pre-: males 2.77 (0.42) N m kg(-1), females 2.41 (0.40) N m kg(-1), post-: males 2.53 (0.54) N m kg(-1), females 2.26 (0.44) N m kg(-1)]. After the fatigue protocol, normalised knee extensor PT and knee joint MAS decreased, whilst relaxed and contracted MS of the VL increased in both sexes. These observed differences may contribute to the higher risk of knee injury in females and following the onset of fatigue.