Naeryo chagi, also known as axe or downward kick, is a vertical taekwondo kick, which usually strikes the opponent’s scull, face or clavicle, in imitation of an axe’s movement. From the initial position, the knee is raised in an arc up and forward in front of the body, the leg then extended and pulled down with the heel pointed downward. The arc can be performed in either a clockwise or a counter- clockwise direction. Surface electromyography is a valid method for the assessment of neuromuscular function (Winter, 1990). However, prior to an electromyographic study of the naeryo chagi, it is important to establish the reliability of the measurement procedure, because the myoelectrical activity that is recorded by surface electrodes depends on a great number of factors. These factors include mainly the length, the size, the number and the contraction velocity of the muscle fibers within the detection area of the electrodes (Basmajian and de Luca, 1985). In most cases, it is very difficult to control all these factors during several trials of the same athlete, either within the same measurement period for the determination of the athlete’s muscle activity pattern or in different periods (pre- and post-measurements) to determine the effects of an intervention (i.e. a training program) in the athlete’s muscular activity. For this reason the electromyographic (EMG) activity that is recorded in a naeryo chagi trial cannot recur, in exactly the same way, in any other trial. Consequently, intra- measurement or inter-measurement differences of an athlete’s EMG activity during a naeryo chagi depend on the repeatability of the EMG waveforms during the kick. Despite of its importance, the repeatability of EMG waveforms in naeryo chagi kicks has not been studied yet. However, the repeatability of myoelectrical parameters has been studied in other movements. Finucane et al., 1998 studied the repeatability of a single EMG parameter, the rmsEMG, in maximal isometric and sub-maximal concentric and eccentric contractions in an isokinetic dynamometer. Their results showed that the rmsEMG was repeatable in all contractions and that the EMG normalization has not any significant effect on the parameter’s repeatability. Golhofer et al., 1990 studied the repeatability of the EMG area of the gastrocnemius, soleus and tibialis anterior muscles during stretch-shortening cycles in various activities: running at a constant speed of 12 km/h, one-leg and two-leg hopping at preferred frequency and drop jumps from 40cm. The results showed different correlation coefficients for different muscles and activities. However, most coefficients had values greater than 0.85. Goodwin et al., 1999 studied the repeatability of the EMG area of several muscles in countermovement vertical jumps. The results showed that the intraclass correlation coefficients (ICC) were 0.88 for rectus femoris, 0. 70 for vasturs mediallis, 0.24 for biceps femoris and only 0.01 for the gastrocnemius. Consequently, it was concluded that the repeatability of EMG parameters is lower than other biomechanical parameters and depends on the recorded muscle. Karamanidis et al., 2004 studied the repeatability of several myoelcetrical parameters during different running techniques, combining three different running speeds (2.5, 3.0 and 3.5m·s-1) and three different stride frequencies (preferred and ± 10%). EMG signals were recorded in three trials for each running condition. The results showed that the ICC of the EMG parameters of gastrocnemius were greater than 0.69 in 73% of the data, while those for vastus lateralis, hamstrings and tibialis anterior were much lower. They also found that the repeatability of EMG parameters depended on the muscle and the parameter studied. The above researchers studied the repeatability of discrete EMG parameters and not that of EMG waveforms, in activities other than the naeryo chagi. Moreover, their findings were inconsistent and cannot be generalized because EMG repeatability depends on the muscle and the activity studied (Karamanidis et al., 2004). So, the purpose of this research was to determine the repeatability of the EMG waveforms of major muscles of the lower limb in naeryo-chagi (axe or downward kick) in taekwondo. |