Are There Sex Differences in Lower-Limb Biomechanics and Muscle Activation During Rope Jumping in Muay Thai Athletes?

Sex-related differences in lower-limb biomechanics and neuromuscular strategies during rope jumping remain underexplored, particularly in combat-sport athletes. This study investigated leg stiffness and muscle activation in ten female (22.8 ± 0.8 years) and ten male (22.9 ± 1.4 years) Muay Thai athletes. Participants performed rope skipping under three conditions: dominant leg, non-dominant leg, and double leg at 2.2 Hz. Ground reaction forces were recorded at 1000 Hz, center of mass displacement at 200 Hz, and electromyographic activity of the vastus lateralis, biceps femoris, tibialis anterior, and medial gastrocnemius at 3000 Hz. Vertical stiffness (K_vert) was calculated as the ratio of peak vertical force to displacement. Results showed no significant sex differences in peak ground reaction force (e.g., dominant leg: females 2.83 ± 0.42 vs. males 3.22 ± 0.57 kN; double leg: females 4.04 ± 0.83 vs. males 4.35 ± 0.73 kN; p > 0.05), vertical stiffness (females 17.02 ± 3.66 vs. males 16.21 ± 4.09 kN/m; p > 0.05), contact time (females 0.280 ± 0.03 vs. males 0.275 ± 0.05 s; p > 0.05), or flight time (females 0.205 ± 0.03 vs. males 0.245 ± 0.05 s; p > 0.05). In contrast, females exhibited significantly higher co-activation ratios during unilateral skipping, including BF/VL (0.76 ± 0.18 vs. 0.63 ± 0.10; p < 0.05) and TA/MG (0.38 ± 0.11 vs. 0.29 ± 0.07; p < 0.05), suggesting a neuromuscular strategy to enhance joint stability. These findings highlight rope jumping as a practical drill that can promote neuromuscular control and stability in Muay Thai training.