Neuromuscular control during roundhouse kick in elite and amateur karateka.

Neuromuscular control during roundhouse kick in elite and amateur karateka Quinzi F1, V Camomilla1, F Felici1, P Sbriccoli1 1DiSMUS, Rome University Foro Italico, Faculty of Movement and Sport Sciences (Roma, Italy) Introduction. Karate practice requires a fine control of movement associated to a great ability to perform the main technical actions as fast as possible (Zehr et al., 1997; Sørensen et al., 1996). To this respect, a major role of antagonist activation has been demonstrated recently in karateka while performing the Front Kick, consisting of increased antagonist activation with respect to amateurs during the knee extension phase (Sbriccoli et al., 2010). Because of its high speed and excellent accuracy, the roundhouse kick (RK) seems to be a good model to quantify the ability of a karateka to perform complex actions combining high movement velocities with high precision. This work was thus designed to characterize the neuromuscular control adopted by a top level karateka while performing the roundhouse kick (RK) using two different techniques: Low Roundhouse Kick (LRK) and High Roundhouse Kick (HRK). Methods. Surface electromyographic (sEMG) signals have been recorded through a wi-fi transmission EMG amplifier (BTS Pocket EMG, Italy) from the Vastus Lateralis (VL), Rectus Femoris (RF), Biceps Femoris (BF), Gluteus Maximum (GM) and Gastrocnemious (GA) muscles of the kicking leg during the execution of LRK and HRK. Six top level Karateka (K) and six graduated students practicing karate as amateurs (Controls, C) have been tested (25±1yrs; 1.78±0.03m; 73.8±4kg). Co-activation ratios of antagonist vs. overall activity were computed for knee and hip flexion and extension. Considering the bi-articular role of RF, for the knee joint three co-activation indexes were computed: extension with mono and bi-articular muscles (KCIextM and KCIextB, respectively), and flexion (KCIflex). For the hip joint, the Hip flexion (HCIflex) and Hip extension (HCIext) co-activation indexes were calculated. Muscle Fiber Conduction Velocity (CV) obtained from VL and BF muscles was assessed as well. The effect of Group (Karateka and Controls) and Kick (LRK and HRK) on all co-activation indexes and on VLCV and BFCV was tested through a two-way ANOVA (p<0.05). Results. The ANOVA demonstrated an effect of Group on all co-activation indexes computed (p<0.001). Namely, Elite Karateka showed lower HCIflex, KCIextM and KCIextB and higher KCIflex and HCIext. An effect of group was also found as regards the BFCV, that was higher in Karateka compared to Controls for both LRK (5.1±2.0 vs. 2.5±1.3 m*s-1) and HRK (5.7±2.6 vs. 3.5±1.9m*s-1, p<0.05). Discussion. The results obtained suggest the presence of a peculiar muscle activation strategy adopted by the Karateka with respect to Controls during the execution of the RK. CV results suggest the presence of an improved ability of elite karateka to recruit fast MUs as a part of training induced neuromuscular adaptation that can be interpreted supposing a re-organization of spinal and/or supraspinal circuits. References. Sbriccoli P et al., Eur J Appl Physiol, 108:1269–80, 2010 Sørensen H, et al., J Sports Sci, 14: 483-95, 1996 Zehr EP, et al., Med Sci Sports Exerc, 29(10): 1366-73, 1997