KEY WORDS: Electromyography, wavelet transform, impact, martial arts, biomechanics.

Chinese Martial Arts has a history of thousands of years. During the past 1500 years, many different styles of Kung Fu (KF) have been developed in China and several of them are still being practiced. The Yau-Man style of KF was developed during the Ch'ing Dynasty (1644-1911) with the purpose to help Chinese revolutionaries in the war against the Manchu invaders (Neto et. al, 2007). The Yau-Man KF was developed from the collective knowledge of several other ancient styles. The strikes of Yau-Man KF differ from most other combat sports' strikes because they usually begin closer to the target or opponent. Other distinguished characteristic of the Yau-Man strikes is that the movements are terminated before full extension of the arms (Neto et al., 2007).

In most martial arts and contact sports strikes are often trained in two different ways: with and without impacts. In the last couple of years, there have been studies that focused on strikes with impacts (Neto et al., 2007; Walilko et. al., 2005) and without impacts (Neto and Magini, 2007; Ribeiro et al., 2006). However, the authors are not aware of any article that compared either physiological or biomechanical variables in both scenarios. This study aims to compare the EMG of the triceps brachii (TB), biceps brachii (BB) and brachioradialis (BR) muscles during strikes with and without impacts.

Both rms (see Table 1) and SSP (see Table 2) results indicate a significant higher TB and BR muscle activity for the strikes with impacts considering the repeated measures for all eight participants (p < 0.01 for both rms and SSP). No significant difference was found in the EMG of the BB for the two different scenarios (p = 0.26 for rms and p = 0.12 for SSP). The average of all 48 values of SSP IACV (0.074 ± 0.043) was smaller than the corresponding average rms IACV (0.095 SD 0.088) (p = 0.03 for paired t-test). The average of all 6 values of SSP IECV (0.153 ± 0.041) was also smaller than the corresponding average rms IECV (0.275 ± 0.139), however because of the sample sizes the statistic reliability is lower (p = 0.05 for paired t-test).

Although it was collected three seconds of EMG signals from the muscles, in average, only a period of one second presented significant contours on the power spectra. The results show that the wavelet power spectra pattern for the three analysed muscles obtained from the strikes with and without impacts were similar (see Figure 1 and Figure 2). For all strikes, it was observed that the TB was the first muscle to present a significant contour on their spectra. The TB spectra present three main regions of significant contour(s). The third region in general presents more than one contour and it extends more in time. The BB and BR presented very similar spectra. They also presented three distinct main regions containing significant contour(s); the regions were shifted by approximately 100-200 ms in relation to the regions in the TB spectra.

The coefficients of variation found for the rms values are in agreement with values reported by other researchers (Bolgla and Uhl, 2007). According to many researchers, the normalization method used in this experiment to calculate the values of rms provides lower IACV and IECV (Burden et al., 2003; Knutson et al., 1994). A comparison of the rms and the original SSP methods used in this study revealed that the SSP method resulted in lower IACV and IECV (see Tables 1 and 2). Lower IACV indicates greater reliability of the measurements, while the advantages of using methods that result in lower IECV are well documented in the literature (Yang and Winter, 1984). These results confirm the validity of the SSP method used. Since there were only six data points for the comparison of the IECV of the rms and SSP, further studies should be done to confirm the hypothesis that the SSP method may be a more stable and precise method for measuring significant muscle activity than the rms method.

The reason for the higher TB (an agonist muscle for the strike) activity in the strikes with impact might be more psychological than biomechanical, possibly due to greater participant's motivation when performing the strikes with impact. The reason for the higher BR activity, on the other hand, is probably due to the importance of this muscle in stabilizing the wrist and elbow joints when receiving the reaction force from the impact.

The result that an approximate time of only one second presented significant contours on the power spectra suggests that the participants took approximately one second to perform the sequences of five palm strikes. This result is in agreement with previous high-speed camera study that found the duration of one palm strike to be in the order of 200 ms (Neto et al., 2007).

The wavelet power spectra from the three analysed muscles (Figure 1 and 2) illustrate the muscle roles during the five strikes performed in each sequence. The first significant contour on the TB powers spectra demonstrates a muscle activity responsible for pushing the right hand during the first palm strike. This region is followed in time by a significant contour both in the BB and BR spectra, which correspond to muscle activity responsible to brake the right hand's movement and pull it back while the left hand is being pushed during the first left hand palm strike. After that, the same pattern in wavelet power spectra repeats for the second right hand palm strike followed by the second left hand palm strike. For the third right hand palm, more extended significant regions in the spectra can be seen, which implies longer muscles' activity. It can be speculated that, for both strikes with and without impact, the participants keep tightening their muscles once the arm stops. These isometric muscles' contractions, once the movement stops, are often performed in martial arts.

• EMG analysis of a sequence of Kung Fu strikes demonstrates higher Triceps Brachii and Brachioradialis muscle activity for strikes with impact than strikes without impact.
• An original reliable method for quantifying EMG wavelet transform results is presented.
• EMG wavelet power spectra describe muscle roles during a Kung Fu sequence of strikes.