126 ISBS'98 ­Proceedings II
BIOMECHANICAL ANALYSIS OF STRAIGHT AND FLEXURAL LEG SWINGS
OF THE CHINESE MARTIAL ARTS JUMPING FRONT KICK
Chung-Yu Chen, Chenfu Huang,
National Taiwan Normal University, Taipei, Taiwan,
Chih-Ming Lee, Yu-Ping Lin, Chinese Culture University, Taipei, Taiwan
INTRODUCTION: Fighting skills have a certain relationship with distance. In
Chinese martial arts, there is a proverb for leg technique: 'Kick when far; using
knee when near.' This traditional fighting theory also applied in Chinese martial arts
routines to express the different levels of players' fighting thought. The Front Slap
Kick belongs to the kick of slapping which asks the kicker to slap the back of his
foot with his palm. It is separated into kicking with a straight leg swing (SLS), which
merely focuses on the kick, and kicking with a flexural leg swing (FLS), which has
both functions of kicking and using the knee.
The Jumping Front Kick (Figure 1) is a required movement in the routines of the
Wushu event in the Asian Games which contains four phases: run-up, takeoff,
flight, and landing. In the flight, a front slap kick should be completed in the air.
According to the Rules of Wushu, the front slap kick in the jumping front kick is a
way of kicking with a straight leg swing, but it is illustrated as kicking with a flexural
leg swing in the textbook of Wushu. Kan (1991) has the same contradictory
description in his book, too.
Figure 1 The Movement of the Jumping Front Kick. (Kan, 1991)
Cheng & Hong (1994) found that there were two different kicking technical features
in the jumping front kick, kicking with a straight leg swing and kicking with a flexural
leg swing, when players kicked. But they did not discuss the biomechanical
differences between the two kicking skills. Nor did the other research about the
jumping front kick analyze the fact that there were two different kicks (Chen, Tang,
Lee, Huang, & T. Chen, 1997). So, the biomechanical analysis on the two kicking
styles not only explained the different fighting thought levels of kicking in Chinese
martial arts, but also offered a reference for similar movements in the martial arts.
Park (1990) expressed that kicking with a flexural leg swing could cause a fast
lower extremity velocity. Cheng (1995) showed that the horizontal velocity of the
kicking toe with a straight leg swing was faster than the flexural leg swing, but
kicking with straight leg swing was better than a flexural leg swing on the fighting
effect and expression of consciousness. The kicking movements in the above two
studies conducted on the standing leg on the ground, so the effect of kicking might
be influenced by the standing leg (Liu, Chuang, & Lang, 1996; Cheng, 1995).
The research on the comparison of the differences in biomechanical character
showed that kicking with a straight leg swing was faster than a flexural leg swing.
On the other hand, Hwang (1987) indicated that the velocities of the toes of elite
athletes were faster than those of beginners when kicking a target. In this research
we would like to compare the difference between elite Chinese martial arts players
ISBS'98 ­ Proceedings II 127
and beginners when kicking without a target. The study would focus on analyzing
the biomechanical characteristics of the kick after jumping in the air for two
different Jumping Front Kicks and discuss their differences.
METHODS: Ten elite male Chinese martial arts players with six flexural leg swing
and four straight leg swing techniques, and ten male PE major students (beginner)
with four flexural leg swing and six straight leg swing techniques were selected as
subjects for this study. The subjects' information is listed in Table 1.
Table 1 Mean and Standard Deviations of Subjects' Information and the Basic Kinematical
Parameters of Movement Performance of Subjects.
Group Style
H
(cm)
W
(kg)
Age
(years)
Age of
learning
(years)
Normalized
flight height
Vertical velocity
at takeoff (m/s)
Horizontal
velocity at
takeoff(m/s)
Elite
Player
FLS
n=6
167.3
(3.7)
62.0
(4.9)
19.9
(2.7)
3.1
(2.2)
1.77
(0.04)
2.12
(0.42)
3.02
(0.07)
SLS
n=4
168.0
(7.0)
62.5
(3.3)
20.3
(3.4)
3.2
(2.4)
1.80
(0.05)
2.17
(0.52)
2.95
(0.52)
Begin-
ner
FLS
n=4
176.8
(3.6)
74.0
(6.8)
26.6
(7.1)
0.4
(0.2)
1.63
(0.16)
2.56
(0.26)
2.41
(0.57)
SLS
n=6
174.0
(6.0)
73.0
(9.3)
20.9
(0.7)
0.5
(0)
1.64
(0.13)
2.50
(0.39)
2.80
(0.27)
Note. H = height; W = weight; Normalized flight height = the highest flight height of
the body center of gravity above the standing height of the body center of gravity;
velocities means the velocity of the body center of gravity.
One Peak high speed camera was set up at the National Taiwan Normal University
outdoor track perpendicular to the plane of the action to record the movements of
the Jumping Front Kick performed by subjects. The camera was operated at a
speed of 120 fields per second and a shutter speed of 1/2000 s. The distance
between the camera and the plane of action was 20 m. The vertical distance from
the ground to the center of the camera lens was 1.2 m. Each subject had 10-15
minutes of warm up exercise and was introduced to the experimental task during a
practice session. The purpose of the practice session was to allow each subject to
become comfortable with the experimental task and data collection conditions.
Each subject wore his own Chinese martial arts shoes and performed three
Jumping Front Kicks. Each subject was asked to select a trial which he felt the
most successful to him. The trial representing the best by each subject was
selected for analysis. Seventeen body landmarks served as the source for the
digitized points. A 1.4 meter stick positioned in the plane of the action was
videotaped to determine the conversion factor from digitizing to metric units. The
17 body landmarks were digitized field by field with the Peak Performance system.
These raw data points were scaled to metric units through the use of the video
camera aspect ratio and the digitized coordinates of the 1.4 meter stick within the
plane of interest. Each horizontal and vertical spatial coordinate of the digitized
body landmarks was filtered with a fourth-order Butterworth Digital Filter with an
optimum cutoff frequency selected by the Peak System.
Because of the different flight times from subject to subject, we described the
important event in the normalized timing (NT) that was calculated by way of the
time of descriptive event to takeoff over the time of the highest body center of
128 ISBS'98 ­Proceedings II
gravity to takeoff. The selected variables for kick leg were tested by completely
randomized design two-way ANOVA at =0.05 significant level.
RESULTS: Figure 2 were the stick figures that depicted the different kick styles of
movement behavior. They clearly showed significant conspicuous to tell the
difference between them. The style of kicking with a flexural leg swing was shown
to flex the knee after takeoff, therefore the knee joint went ahead to perform the
attack intention during the midstream of the kick (Figure 2(1)). After the knee attack
phase, they started to extend the knee joint to do a kick. But the stick figure of
kicking with a straight leg swing showed the behavior had no complexity of
performance, it was just a simple kick (Figure 2(2)).
Figure 2 The stick figures of two styles of kick performed by two elite Chinese martial arts
players. (1) showed one subject kicking with a flexural leg swing, and (2)
showed another subject kicking with a straight leg swing.
We made the comparison between two styles of kick on maximum angular velocity
of extending knee joint and normalized timing which are listed in Table 2. It showed
that there were significantly larger angular velocities and longer normalized timing
in kicking with a flexion swing.
Table 2 Mean Values and Significant Level for Angular Velocity of knee and the
Normalized Timing.
Group
Style
Max. angular velocity
of flexion
knee?ldeg/s?s
NT of Max. angular
velocity of flexion
knee
Max. angular velocity
of extension
knee?ldeg/s?s
+
NT of Max. angular
velocity of extension
knee
Elite
Player
FLS 757(185) 0.20(0.06) 1040(384) 0.79(0.09)^
SLS 187(98)^ 0.15(0.05) 150(95) 0.44(0.10)^
#
Begin-
ner
FLS 825(46)
#
0.12(0.12) 966(265) 0.99(0.21)
SLS 451(202)^
#
0.30(0.33) 300(164) 0.93(0.33)
#
( ): Standard deviation +
Style, p<.05 ^#
Simple main effects, p<.05
The flexural leg swing was significantly faster than the straight leg swing in
maximum vertical velocity of the knee joint. There was no significant difference
between flexural leg swing and straight leg swing in maximal toe velocity and
maximal ankle velocity. However, there was a significant difference in time to the
maximal toe velocity and time to the maximal ankle velocity between the flexural
leg swing and the straight leg swing (Table 3). In addition, the beginners had
significantly greater maximal ankle velocity (9.580.62m/s) than the elite Chinese
martial arts players. Figure 3 also indicates that the flexural leg swing had two
maximal values of ankle and toe vertical velocities, and the maximal velocity of the
knee appeared between the two peaks of toe and ankle. But the peak velocities of
toe and ankle in the straight leg swing were always concurrent with the maximal
velocity of the knee.
ISBS'98 ­ Proceedings II 129
Table 3 Mean Values and Significant Level for Velocities of Toe and Knee.
Group
Style
Max. Vertical
Velocity of
Toe?am/s?s
Max. Horizontal
Velocity of
Toe?xm/s?s*
Max. Vertical
Velocity of
Knee?xm/s?s
+
NT of Max. Vertical
Velocity of Knee
Elite
Player
FLS 9.64(0.60) 8.68(1.31) 5.37(0.61) 0.49(0.06)
SLS 8.76(1.13) 7.96(0.59) 4.24(0.45) 0.53(0.10)
Begin
-ner
FLS 8.53(0.98) 10.04(0.72) 5.12(0.40) 0.57(0.17)
SLS 8.95(0.94) 9.20(1.28) 4.55(0.38) 0.50(0.11)
( ): Standard deviation +
Style, p<.05 *Group, p<.05
Figure 3 The lower extremity's vertical velocities of two styles of kick performed by two elite
Chinese martial arts players. (1) showed one subject kicking with a flexural leg
swing, and (2) showed another subject kicking with a straight leg swing.
CONCLUSIONS: The results indicated that the flexural leg swing technique might
have advantages during actual combat situations which matched the fighting
theory of Chinese martial arts. So the research suggested that the rules of Wushu
on the Jumping Front Kick should be changed to match the textbook of Wushu and
fit for the theory of Chinese martial arts. The data indicated that there was no
difference in the lower extremity's velocity when performed the flexural leg swing
and straight leg swing. This might be because the Jumping Front Kick did not have
the standing leg. The data also indicated that the beginners' lower extremity
velocity is faster than that of the elite players. This might be the reason the elite
Wushu players did not emphasize power, but rather coordination.
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Chen, C. Y., Huang, C., Tang, J. P., Chen, T. Y. (1997). Biomechanical Analysis of the
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Cheng, S. Y., Hong, D. M. (1994). A Qualitative Analysis of "Flying Kicks" in Chinese Martial
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Cheng, S. Y. (1995). A Biomechanical Analysis of Straight Leg Swing Kick & Flexor Kick
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