Neuromuscular control during isokinetic knee extension in top level karateka

Aim: The present study was designed to assess the neuromuscular response of knee flexor and extensor muscles during isokinetic contractions in 12 top level male karateka. Methods: The surface Electromyographic signal (sEMG) was recorded with a 4-array electrode from the right vastus lateralis (VL) and biceps femoris (BF) during maximal isometric knee flexions and extensions (MVC) and during isokinetic contractions at different angular velocities (30°, 90°, 180°, 270°, 340°, and 400°/s). Torque/Velocity (TV) curves was computed for VL and BF muscles. The level of activation of VL and BF muscles while acting as antagonist was quantified through normalized sEMG Root Mean Square value (RMSAnt (%)). The average muscle fibre conduction velocity (MFCV) was also computed for VL and BF. Results: For VL muscle, torque ranged from 314.1±56.8Nm (MVC) to 101±13.5Nm (400°/s,); BF torque values ranged from 168.3±22Nm to 79.4±12.9Nm (MVC and 400°/s, respectively). Normalized T/V curves showed higher values of torque for BF muscle compared to VL at any angular velocity except for 30°/s. MFCV reached its peak at 30°/s in both VL and BF muscles (6.48±0.7m/sec and 3.83±0.52 m/sec, respectively). The level of activation of VL and BF while acting as antagonists was low. Namely, VL-RMSAnt(%) ranged from 2.54% during the MVC to 24.15% at 400°/s; BF-RMSAnt ranged from 1.5% to 12.5% (MVC and 400°/s, respectively). Conclusion: The results obtained support the hypothesis of a peculiar neuromuscular control strategy adopted by these athletes, consisting of selectively activating agonist muscles with a minimal intervention of antagonist muscle groups (low values for BF-RMSAnt and VL-RMSAnt).