Sex differences of lower limb stiffness and muscle activation during hopping and jumping tasks

Some degree of lower extremity stiffness is necessary for joint stability during dynamic activities with higher levels generally shown to benefit athletic performance. Quantifying levels of muscle activation during dynamic tasks (i.e., hopping, jumping) helps to establish the potential relationship between hopping frequency and stiffness. Previous research predominantly focused on whole-body stiffness with limited focus on individual lower extremity muscles and joints. To address these gaps, stiffness and muscle activation were assessed, both unilaterally and bilaterally during hopping and jumping in 20 recreationally active adults (10 male, 10 female). Results showed significant effects in ankle and lower limb stiffness (p = 0.031; d = 1.55) during CMJ, influenced by sex and overall lower limb stiffness measures. Moreover, distinct differences between dominant and non-dominant limbs during countermovement jumps, particularly in the gluteus medius (p < 0.001; d = 3.89) and vastus medialis (p < 0.001; d = 5.61) muscles were identified. Additionally, hopping frequency significantly impacted activation levels in the gastrocnemius (p = 0.004; d = 0.09), rectus femoris ( p = 0.015; d = 0.04), and vastus medialis (p < 0.001; d = 0.06). Notably, sex differences in muscle activation patterns were revealed in the gastrocnemius (p = 0.035; d = 0.22) and gluteus medius (p = 0.034; d = 0.23) during single-leg hopping. These insights contribute valuable information to injury prevention strategies, emphasizing the importance of considering both sex- and limb-specific factors in lower limb stiffness and muscle activation dynamics. Overall, this study highlights aspects of lower limb function, informing targeted interventions for injury prevention and performance optimization.