-15
-10
-5
0
5
10
15
0.00 0.20 0.40 0.60 0.80 1.00
Time (s)
Angularvelocity(rad/s)
Knee velocity
Hip velocity
BIOMECHANICS OF THE KARATE FRONT-KICK
D. Gordon E. Robertson, Carlos Fernando, Michael Hart and François Beaulieu
Biomechanics Laboratory, School of Human Kinetics, University of Ottawa, Ottawa, Ontario, Canada
INTRODUCTION
The front-kick (mae geri) in karate is one of the strongest
and most easily mastered kicks. This project examined the
powers produced by the lower extremity joints of the
kicking leg of two elite (fourth dan) martial artists
performing both closed and open stance front-kicks. The
purpose was to determine the contributions and sequencing
of the ankle, knee and hip moments.
METHODS
The subjects (one a specialist in Tae-kwon-do, the other in
Karate) kicked against a padded board held by an assistant
while filmed by a VHS camera. The subjects performed
several trials each using both an open stance (kicking leg
back) and closed stance (legs beside each other). The video
was digitized with the Ariel Performance Analysis System
and analyzed with the Biomech Motion Analysis System
(Robertson, 2002). Inverse dynamics were used to compute
the net moments and their associated powers for the ankle,
knee and hip joints.
RESULTS AND DISCUSSION
The powers produced by the ankle moment of force were
too small to warrant analysis. Figure 1 shows the angular
velocities, moments of force and their powers for the knee
and ankle of a typical trial. Notice that the moments of force
of the hip and knee reverse direction at precisely the same
instant just prior to contact with the board (right arrow). This
was common to all trials and both subjects.
The powers produced by the closed stance kicks, as
expected, always produced larger moments and powers than
the closed stance kicks. Obviously, the added range of
motion enabled the subjects to generate greater impulses and
foot velocities.
The sequencing of the moments were consistent across all
trials and both subjects. The motion began with almost
simultaneous flexing of the hip and knee joints. The hip
flexors were responsible for flexing both joints as shown by
the burst of positive work done by the hip flexors while the
knee moment of force was relatively inactive.
After the hip reached its maximum velocity, the hip moment
of force became extensor (presumably due to eccentric
contraction of the gluteals) causing the hip to slow its
flexion and begin knee extension. Not surprisingly, based on
similar research on the mechanics of soccer kicking
(Robertson & Mosher, 1985) and sprinting (Lemaire &
Robertson, 1989) the knee extensor moments did not
contribute to increasing knee extension. Instead, the knee
moment was flexor producing negative (eccentric) work to
presumably protect the knee from hyperextension at the end
of the kick.
SUMMARY
Peak powers were greater for the open stance than the closed
stance. The hip extensors and flexors were the prime movers
of both the hip and knee actions. The knee moments were
primarily used to reduce knee flexion and extension.
REFERENCES
Lemaire, E.D., Robertson, D.G.E. (1989) Track & Field J,
35, 13-17.
Robertson, D.G.E., Mosher, R.E. (1985) Biomechanics IX-B,
533-538
Robertson, D.G.E. (2002) http://www.health.uottawa.ca/-
biomech/csb/software
Figure 1: Typical angular velocities (top), moments of force
(middle) and moment powers (bottom) of the knee and hip
moments during an open stance karate front-kick. Left arrow
indicates lifting of kicking leg; right arrow is contact.
-300
-200
-100
0
100
200
0.00 0.20 0.40 0.60 0.80 1.00
Time (s)
Moment(N.m)
Knee moment
Hip moment
-2000
-1500
-1000
-500
0
500
1000
1500
2000
0.00 0.20 0.40 0.60 0.80 1.00
Time (s)
Power(W)
Knee power
Hip power