Sport Expertise and Twitch-Derived Agonist–Antagonist Contractile Ratio in Karate Athletes

Objectives: Agonist–antagonist coordination is traditionally defined as simultaneous neural activation assessed by electromyography (EMG). The present study adopts a mechanical perspective, examining twitch-derived contractile ratio indexes between antagonistic muscle groups using tensiomyography (TMG). The aim was to determine whether sport expertise differentiates mechanical agonist–antagonist coordination in karate athletes. Methods: Fifty male participants were divided into four groups: elite karate athletes (EK; n = 7), national team members (NK; n = 14), basically trained karate practitioners (BK; n = 16), and physically active non-athlete controls (CG; n = 13). Bilateral TMG assessment of rectus femoris, vastus lateralis, vastus medialis, biceps femoris, and semitendinosus was performed. Contraction time (Tc), total contraction time (TcT), and rate of muscle tension development (RMTD) were extracted. Twelve twitch-derived contractile ratio indexes (CRI) were calculated separately for dominant (D) and non-dominant (ND) limbs. Results: Significant between-group differences were observed in the temporal coordination of the non-dominant leg. EK demonstrated the lowest index for average contraction time (CRITcAVGND = 17. 13%; ANOVA p = 0. 005; EK vs. NK p = 0. 003) and total contraction time (CRITcTAVGND = 9. 72%; ANOVA p = 0. 003; EK vs. NK p = 0. 002). In contrast, velocity-related coordination in the dominant leg was highest in EK (CRIRMTDcVD = 63. 66%; ANOVA p = 0. 002), differing from NK (p = 0. 003), BK (p = 0. 002), and CG (p = 0. 009). Conclusions: Elite karate athletes exhibit distinct twitch-derived mechanical coordination profiles characterized by highly efficient temporal interplay in the non-dominant (supportive) limb and elevated velocity-related contractile ratio in the dominant (executive) limb. These findings suggest that sport expertise is associated with task-specific mechanical modulation between antagonistic muscle groups detectable through involuntary contractile responses.