Taekwondo (TKD) is a Korean martial art form that was originally taught for warfare, self-defense and physical fitness. In competition Taekwondo, points are scored when contact to the torso or head produces a 'trembling shock' (WTF rule book). With the opponent required to produce a 'trembling shock' for the acknowledgement of points, there have been many injuries caused (Zemper and Pieter, 1989). As a direct result of these high number of injuries chest protection and head protection are now required for participation in Kyorugi. With this in mind the evaluation of chest gear and head protection must be considered.

Yongmudo (YMD) is a martial art that has been developed by Yong-In University professors and it was created by combining and modifying the techniques of Taekwondo, Hapkido, Judo, Fencing and Ssireum (Lee et al., 2002). It is considered a third generation martial art; first generation being one of action, second generation of mental endurance and the third generation a combination of the two generations. With the purpose of YMD as being an overall self defense system the turning kick was slightly modified so that as to be able to use proceeding techniques.

According to Sidthilaw, 1996, the impact forces recorded for a beginner Muai Thai Kickboxer's roundhouse kick are estimated to be 6702 ± 3514 N, 7240 ± 3477 N and 5618 ± 3253 N for low, medium and head target height respectively. In terms of body weight this is approximately 10BW, 12 BW and 8BW for low, medium and head target heights. For the estimation of force, 3 one dimensional 50g accelerometers were fixed perpendicularly inside a bowling ball, which was then placed in a sand bag. In another related research (Chiu et al., 2007), the kicking force of the roundhouse and back kick and the speed of the kicking foot were measured. Chiu et al., 2007) used a different method to measure the kicking force, an air bag was fixed to a wall and the difference in air pressure caused by the force of the kick was measured. The roundhouse kick and back kick force measured at 8252 ± 720 N and 8023 ± 836N. The kicking forces of various kicks were measured by a force transducer and they ranged from 2759 to 9711.9 N (Gray, 1979). Even with these other studies (Chiu et al., 2007; Gray, 1979; Sidthilaw, 1996) related to the forces created by martial artists it is believed that the results in these studies could be improved by reviewing other researchers' designs and modify them.

With the purpose of the Yongmudo and Taekwondo turning kick being slightly different, the YMD technique has been modified for this. Taekwondo players tend to use a more snapping motion so as to be able to prepare them for another attack using their legs whereas the Yongmudo players follow many of the turning kicks with other attacks using various methods i.e. punch, grappling etc. It was therefore deemed that a comparison between the impact forces of these two styles could be used as a comparison between the technique of kicking with a snap (TKD) and a swing (YMD).

Participants
Five Yongmudo and Taekwondo players were recruited through Yongin University. Each of these participants has over 10 years experience in various martial arts and were asked to complete a medical history form and a consent form (TKD: mass 66.9 ± 6.1 kg, height 1.74 ± 0.03 m, leg length 0.92 ± 0.03 m YMD: mass 71.5 ± 6.5 kg, height 1.75 ± 0.02 m, leg length 0.91 ± 0.02 m). Participants suffering from serious musculoskeletal injury within the last two years were excluded.

Data collection
The experimental equipment used were 7 vicon cameras, two 3D accelerometers and two AMTI force platforms. The 7 Vicon cameras (MX 13) were used to record the kinematical data at a 150Hz and all data was processed and filtered by the Woltring filter (Woltring, 1986) at 15 Hz. Two PCB 356A15 tri-axial 50g limit accelerometers measured the acceleration of the PVC pipe located in the sandbag. These accelerometers were fixed onto a PVC pipe by the wedging and gluing the accelerometers to a wooden panel which was screwed into position at both ends of the PVC (Figure 1).

To calibrate the accelerometers, punching bag was dropped from several varying heights onto the AMTI force platform. The acceleration outputs from the accelerometer and the force platform was recorded at 1500 Hz and compared. There were many trials performed however due to the sensitivity of the accelerometers only the reliable data was used to calibrate the system for estimation of the kicking force (Figure 2).

A value of Pearson's correlation coefficient r= 0.914 was recorded and it was deemed to be adequate. In relevant research r = 0.978 was obtained (Sidthilaw, 1996). The kicking force was estimated by entering the accelerometers acceleration value into the Equation 1 below.

Experimental procedure
The participants were encouraged to warm up after signature of the consent forms. The warm up consisted of 10 jumping jacks and light stretching of the following muscles, quadriceps, biceps femoris, soleus, gastrocnemius, external abdominal obliques, lumbar, erector spinae and the muscles surrounding these. Each of the stretches were held statically for 10 seconds. In total the warm up took approximately 10 minutes. After this warm up, each of the participants was instructed to perform the roundhouse kick twenty times in total. Ten kicks were done at trunk height and ten kicks were done at approximately head height. This process was randomly rearranged. Each kick had to be done efficiently according to the following conditions; correct height, appropriate direction and balance, etc.

Both the kinetic and kinematic data were exported from Workstation©, Polygon© and imported into Microsoft Excel to generate the necessary graphs and results. The ground reaction forces (GRFs), acceleration of the pipe in the punching bag, the motion of the center of mass (COM) of the participants, the range of motion (ROM) and angular velocity for each of the involved joints, hip and knee, kicking foot speed and phase times were all analyzed.

Statistical analysis
To perform the statistical analysis all the most accurate data (data with the most central impact) were exported into SPSS 12.0. For each of the groups the kick height, the mean and standard deviations were calculated. Two way ANOVA with repeated measures were used to investigate statistical difference with significance set at p < 0.05.

Terminology
1) Estimated Kicking Force was calculated from the calibration equation.
2) Normalized GRFs of the kicking foot at push off were calculated by dividing the maximum force of the kicking foot pushing off to initiate the kick by subject's body weight.
3) Knee chamber defines the body's position where the knee extension angle is minimum.
4) Swing phase is defined as the period from the foot off to the impact.
5) Recovery phase is defined as the period from the impact to the foot down.

• This impact force measuring device had a significantly smaller standard deviation then that of impact force measuring devices.
• There was a significant difference between the impact forces according to the height approximately 6400 ± 898N, 6393 ± 1382N for the mid section and 5419 ± 659N, 5475 ± 1293N for the high section of TKD and YMD groups.
• The turning kick was performed quicker by the TKD players with a similar impact force and more forward motion.