Impact of Sex and Stretch-Shortening Cycle Induced-Fatigue on Limb Stiffness and Limb Stiffness Asymmetry During the Stop-Jump

Abstract

Sports-related injuries have a 67% incidence of occurring during competitive play, particularly in sports where fatigue is thought to negatively affect the way that the lower extremities attenuate forces being placed on the body.72 With the overall incidence of anterior cruciate ligament (ACL) injuries increasing, there is a growing incidence of these injuries occurring in the female population.117,12 Landing mechanics that are more erect, and those that are more asymmetrical, are known to increase the risk of injury, and may be heightened by the onset of fatigue.32 This study aimed to assess the effect of sex and fatigue induced by the stretch-shortening cycle on lower limb mechanics and asymmetry values in the stop-jump task. The first purpose of the study was to assess the effect of sex and stretch-shortening cycle fatigue on limb stiffness and limb stiffness asymmetry. The second purpose was to assess landing mechanics that are known to be indicators of how forces are being attenuated by the limbs. The components of limb stiffness were also assessed, including the resultant ground reaction force (rGRF) and change in limb length. A significant interaction was found for nondominant limb change in limb length (p=0.005), where males showed an increase in the change in limb length, while females showed a decrease following the fatigue protocol. The rGRF of both limbs was also different between pre- and post-fatigue conditions, decreasing in both sexes with the onset of fatigue. Asymmetry values for peak knee flexion angle, absolute value of knee flexion angle at initial contact (IC), and loading rate were also assessed before and after fatigue. Significant interactions for asymmetry values of peak knee flexion angle and absolute value of knee flexion angle at IC indicated that only female participants had an increase in asymmetry of knee flexion at IC and peak knee flexion values after the fatigue protocol. These results suggest that females adopt a more asymmetrical landing strategy than males after fatigue. A significant increase in peak knee flexion was also found for both sexes after fatigue. Thus, the decrease in rGRF may be due to the increase in peak knee flexion, which aids in the attenuation of the forces placed on the body. The results of this study indicate that, with fatigue, female participants may adopt landing strategies that put them at greater risk of sustaining lower extremity knee injuries during sport.