Sex Differences in Lower Limb Muscle Activation Patterns in Participants with Knee Osteoarthritis and Healthy Controls

Muscular stabilisation strategies during activities of daily living alter in the presence of knee osteoarthritis (OA). By examining neuromuscular adaptations using our weight-bearing target match protocol, the main objective of this research is to establish sex differences in adaptations of neuromuscular control that are associated with older males and females with and without OA. 66 participants completed the protocol while EMG, ground reaction forces (GRF), and kinematics were recorded. Muscle activation patterns were presented in polar plots with an EMG vector representing normalised muscle activation in twelve directions, each representing a GRF vector scaled to 30% maximal effort. Asymmetry about the polar plot (activation occurring in one direction more than another) was determined and specificity index (SI) and mean direction of activation were calculated when appropriate. Healthy females demonstrated greater rectus femoris (RF) mean muscle magnitude (XEMG) (p=0.067) and less biceps femoris (BF) XEMG than healthy males (p=0.084) and females with OA (p=0.041), and males and females with OA demonstrated greater RF XEMG than healthy controls of the same sex (p=0.016, 0.072, respectively). Females with OA had significantly greater medial gastrocnemius XEMG than healthy females (p=0.031) and males with OA (p=0.020). Females with OA have less specificity in all muscles compared to males with OA and OA participants generally had less specificity compared to healthy controls of the same sex. Healthy males had the largest SI for lateral gastrocnemius with an asymmetrical activation pattern contrasting the more symmetrical activation pattern of all other groups. In conclusion, we suggest OA-affected adults and healthy females use a quadriceps dominant strategy to stabilise the joint, and that this strategy may be a compensatory mechanism for reduced quadriceps function. We suggest RF, BF, MG, and LG should be targeted for prophylactic intervention as they displayed altered activation strategies in participants with OA and healthy females