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©Journal of Sports Science and Medicine (2006)
CSSI,
122-131
http://www.jssm.org
Combat Sports Special Issue
Research article
A THREE-DIMENSIONAL ANALYSIS OF THE CENTER OF
MASS FOR THREE DIFFERENT JUDO THROWING
TECHNIQUES
Rodney T. Imamura
, Alan Hreljac, Rafael F. Escamilla and W. Brent Edwards
California State University Sacramento, USA.
Published (online): 01 July 2006
ABSTRACT
Four black belt throwers (
tori
) and one black belt faller (
uke
) were filmed and analyzed in three-
dimensions using two video cameras (JVC 60 Hz) and motion analysis software. Average linear
momentum in the anteroposterior (x), vertical (y), and mediolateral (z) directions and average resultant
impulse of
uke’s
center of mass (COM) were investigated for three different throwing techniques;
harai-goshi
(hip throw),
seoi-nage
(hand throw), and
osoto-gari
(leg throw). Each throw was broken
down into three main phases;
kuzushi
(balance breaking),
tsukuri
(fit-in), and
kake
(throw). For the
harai-goshi
and
osoto-gari
throws, impulse measurements were the largest within
kuzushi
and
tsukuri
phases (where collision between
tori
and
uke
predominantly occurs). Both throws indicated an
importance for
tori
to create large momentum prior to contact with
uke
. The
seoi-nage
throw
demonstrated the lowest impulse and maintained forward momentum on the body of
uke
throughout
the entire throw. The
harai-goshi
and
osoto-gari
are considered power throws well-suited for large and
strong judo players. The
seoi-nage
throw is considered more technical and is considered well-suited for
shorter players with good agility. A form of resistance by
uke
was found during the
kuzushi
phase for
all throws. The resistance which can be initiated by
tori’s
push or pull allows for the
tsukuri
phase to
occur properly by freezing
uke
for a good fit-in. Strategies for initiating an effective resistance include
initiating movement of
uke
so that their COM is shifted to their left (for right handed throw) by
incorporating an instantaneous “snap pull” with the pulling hand during
kuzushi
to create an opposite
movement from
uke
.
KEY WORDS
: Biomechanics, impulse, kinematics, martial art, momentum, collision.
INTRODUCTION
Modern judo is an Olympic sport with roots dating
back to the ancient martial arts of the samurai
warriors. It incorporates a variety of throwing,
pinning, choking, and arm lock techniques to subdue
an opponent. Judo means the “gentle way” which
reflects the philosophy of defeating an opponent
with the least amount of effort or strength.
Therefore, judo as a sport inherently emphasizes the
use of proper technique and mechanics. To date,
only a handful of studies have investigated judo
from a biomechanical perspective (Harter and Bates,
1985; Imamura and Johnson, 2003; Minamitani et
al., 1988; Pucsok et al., 2001; Serra, 1997;
Sacripanti, 1989; Sannohe, 1986; Tezuka et al.,
1983).
The founder of modern judo, Jigoro Kano
Imamura et al.
123
Table 1
. Participant information.
Participant Weight (kg) Height (m) Age Rank (Degree Black)
1
84
1.78
22
Shodan
(1
st
)
2
118
1.68
42
Yondan
(4
th
)
3
89
1.78
32
Sandan
(3
rd
)
4
75
1.68
39
Sandan
(3
rd
)
Uke
89
1.75
38
Yondan (4
th
)
(1860-1838), formulated judo as a collection of ju-
jitsu techniques that he felt were scientifically
effective. Kano classified techniques into phases
with the intent of developing judo through analytical
thinking. Judo throwing techniques are comprised of
three main phases:
kuzushi
the preparatory phase
defined as breaking an opponent’s balance or simply
to prepare them for a throw,
tsukuri
the process of
fitting into the throw, and
kake
the acceleration
phase describing the execution of the throw itself
(Kano, 1986). Although the judo literature has
addressed phases and defined them in theory, it has
yet to analyze them using biomechanical terms.
Analyzing the movement of an individual’s
center of mass (COM) is a general descriptor of
whole body mass movement and has been used to
study sport technique. Hay and Nohara (1990) used
COM measurements to evaluate elite long jumpers
in preparation for take-off. Other studies have
investigated vertical oscillation of COM to
differentiate running techniques (Williams, 1985). In
addition, kinetic measures at the COM such as
changes in momentum and impulse can be
particularly useful for analyzing sports like judo
since manipulation of an opponent’s body motion
through an applied force is the basis for all judo
techniques. Impulse (
I
) is defined as the change in
momentum (
mv
) and related to force (
F
) through the
following equations:
I = F
∆
t
thrower (
tori)
and person being thrown (
uke)
are
doing during the phases of various throwing
techniques and ultimately provide a better
understanding of the factors that constitute a
mechanically efficient throw.
METHODS
Four highly advanced (black belt) participants
served as the
tori
for this study. A single highly
advanced participant (black belt) was used as the
uke
and accepted the throws for all participants. All
participants used in this study had at least 5 years of
national competition experience. Information
including age, weight, and height were collected for
all participants (Table 1). All participants signed
informed consent, consistent with University
guidelines concerning the testing of human
participants. Each participant performed three
different types of throwing techniques:
seoi-nage
(hand throw),
harai-goshi
(hip throw), and
osoto-
gari
(leg throw). To ensure an adequate combination
of maximal effort and proper technique, the
participants were required to perform the throws
with maximal effort while maintaining their balance
(staying on at least one foot and no more than one
hand touching the ground) after the throw was
executed. This procedure was designed to simulate
throwing under ideal conditions, where
uke
began
each throw in a stationary position and elicited no
conscious resistance to
tori’s
efforts. The procedure
is similar to typical throwing practice, referred to as
nage-komi
.
Two video cameras (JVC 60 Hz) synchronized
by LED were used to collect the data. The cameras
were positioned approximately 90 degrees apart
facing one side of
uke
and
tori
so that a sagittal view
of the action was seen. Directions for the
harai-
goshi
and
seoi-nage
throws were set such that
uke
always began each trial facing the positive x
(anteroposterior) direction and his right shoulder
facing the positive z (mediolateral) direction. For the
osoto-gari
throw the z orientation was changed such
that
uke’s
right shoulder was facing the positive z
direction and the front of the body facing the
negative x direction at the start of the throw. This
process was to insure that
uke
was always thrown
predominantly towards the positive x direction with
where
F
∆
t = mv
2
– mv
1
or
F
∆
t =
∆
mv
Judo enthusiasts have long been intrigued by
the concept of a perfect throw (Kano, 1986). Those
who have experienced it in training or competition
often describe it as effortless and requiring very little
energy. This experience is generalized under judo’s
philosophy of maximum efficiency with minimal
effort. To begin studying this phenomenon,
analyzing the COM movement of
uke
during a
simulated perfect throw may be an ideal approach,
much like studying the mechanics of a ball player by
analyzing the movement of the ball.
Currently there are very little quantifiable data
on the biomechanics of judo. Therefore, the purpose
of this study was to analyze COM information from
judo players engaged in different types of throwing.
This will provide a biomechanical basis of what the
124
Center of mass analysis of Judo throws
his right shoulder initially facing the positive z
direction. The upward direction was designated as
positive y (vertical) for all throws. Power spectrum
analysis consistent with the Nyquist Theorem
indicated that 60 Hz was an adequate collection
frequency for judo movements.
A three dimensional motion analysis system
(Peak Performance Technologies, Inc., Englewood,
CO) and the DLT (Direct Linear Transformation)
procedure were used to analyze three-dimensional
kinematic data. As judo requires that all participants
wear a judo uniform (judo
gi
), joint markers could
not be used. Therefore, manual digitization of 18
body points for both
tori
and
uke
were performed for
all trials by a single digitizer who was experienced
with the sport of judo. The digitized data were
smoothed using a 4
th
order zero lag Butterworth
filter with a cut-off frequency of 5 Hz based on
power spectrum analysis.
COM calculations were based on anatomical
parameters from Clauser et al. (1969) and computed
by the motion analysis software into a virtual point.
COM momentum values were calculated using
three-dimensional COM linear velocity
measurements and participant mass. These values
were averaged for each phase. Impulse values were
calculated as the difference between average
momenta of
tsukuri
and
kake
phases or the phases in
which collision between the two bodies occur. Both
descriptive and inferential statistics were used to
interpret the data. Differences in momenta between
phases, directions, and throws were statistically
analyzed with a three-way repeated measures
analysis of variance (p < 0.05). Differences in
impulse between different throws were analyzed
with a one-way repeated analysis of variance (p <
0.05). Tukey post hoc tests were used to analyze
significant interactions. Only measurements based
on the average COM momentum values of
uke
were
reported in this study, since
uke’s
motion is
considered the product of
tori’s
throw.
Since throwing phases have yet to be defined
in biomechanical terms, they were set according to
popular opinion in instructional literature (Kano,
1986; Kim and Shin, 1983; Koizumi, 1960;
Harrison, 1952). The
harai-goshi
and
seoi-nage
phases were broken down in similar fashion. The
kuzushi
phase begins with the first movement
towards the entrance of the throw by
tori
and ends
with the placement of
tori’s
supporting (left) foot to
the ground so that both feet are planted on the
ground.
Tsukuri
immediately follows
kuzushi
and
begins with
tori’s
feet pushing off the ground and
ends with
uke’s
heels beginning to rise from the
ground.
Kake
immediately follows
tsukuri
and
begins with
uke’s
toes and feet rising from the
ground, the body being thrown into the air, and
ending when
uke’s
body and any part of both legs
hitting the ground (Figure 1). For the
osoto-gari
throw,
kuzushi
begins with the onset of
tori’s
leg
drive from the sweeping (right) leg allowing the
supporting (left) leg to move towards
uke
and ends
with
tori’s
sweeping leg moving up to
uke’s
body.
Tsukuri
immediately follows
kuzushi
and begins
with
tori’s
sweeping leg passing
uke’s
body and
ends with
tori’s
sweeping leg making sweep contact.
Kake
immediately follows and begins with sweep
contact to
uke’s
body and any part of both legs
striking the ground (Figure 1).
(a)
Harai-goshi
(b)
Seoi-nage
(c)
Osoto-gari
Figure 1
. Illustration of (a)
harai-goshi
, (b)
seoi-nage
, and (c)
osoto-gari
throws.
Imamura et al.
125
Table 2
. Participant resultant impulse mean (N•s) and standard deviation values with force (N) and time (s)
components for the
harai-goshi
,
seoi-nage
, and
osoto-gari
throws.
Harai-goshi
Seoi-nage
Osoto-gari
Participant 1
(129.2)x(.68) = 87.8
(88.5)x(.86) = 76.1
(175.8)x(.70) = 123.0
Participant 2
(175.9)x(.61) = 107.3
(175.6)x(.67) = 117.7
(181.5)x(.72) = 130.6
Participant 3
(193.6)x(.55) = 106.5
(130.0)x(.67) = 86.1
(122.7)x(.73) = 89.5
Participant 4
(136.6)x.68) = 92.8
(87.5)x(.76) = 66.5
(145.4)x(.75) = 109.0
Mean
SD
(158.9)x(.63) = 100.1
9.9
(120.4)x(.74) = 89.0
18.8
(156.3)x(.73) = 113.0
17.7
RESULTS
Statistical
analysis revealed significant differences
in average COM momentum for each phase and
each direction (p < 0.001). Thus, each throw
demonstrated different momenta in the x, y, and
directions during kuzushi, tsukuri, and kake phases.
The seoi-nage depicted significantly different
momenta from the harai-goshi and osoto-gari throws
(p = 0.008), while the latter two were not
significantly different from one another (p = 0.069).
Resultant impulse values were not significantly
different between throws (p = 0.096). Nonetheless,
impulse as well as force and time components for
each throw are reported to describe collision
characteristics between tori and uke (Table 2).
Comparing the three different types of throws, harai-
goshi created the greatest force onto uke with a force
value of 158.9N averaged over a period of 0.63s
(time period of tsukuri and kake), followed by osoto-
gari (156.3N; 0.73s), and seoi-nage (120.4N; 0.74s),
respectively. The seoi-nage demonstrated the
smallest impulse and force values indicating a
relative weak collision between tori and uke.
DISCUSSION
In this study, it was assumed that
uke’s
movement
was the product of
tori’s
effort to throw
uke
. Since
all throws were considered “perfect throws” (no
conscious resistance by
uke
), analyzing
uke’s
100
50
0
1
2
3
-50
-100
-150
x AP y VT z ML
y
x
Figure 2.
Harai-goshi
throw momentum mean ((kg•m)/s) and standard deviation values in the
anteroposterior (x AP), vertical (y VT), and mediolateral (z ML) directions (left to right
columns respectively) for each phase (1 =
kuzushi
, 2 =
tsukuri
, 3 =
kake
).
z
126
Center of mass analysis of Judo throws
100
80
60
1
2
3
40
20
0
0
0.2
0.4
0
.6
0.8
1
1.2
1.4
-20
-40
Time (seconds)
Figure 3.
Illustration of momentum in the mediolateral (z) direction within the
kuzushi
(1),
tsukuri
(2), and
kake
(3) phases for the
harai-goshi
throw. A theoretical resistance by
uke
is
present within phases 1 and 2.
movement would conceivably offer explanations as
to what factors determine a perfect throw, a throw
which competitors refer to as an
ippon
(full point)
throw. Statistical analysis revealed that COM
momenta in each direction for each phase of the
throw were different. The following discusses COM
momentum and impulse characteristics for each
throw separately.
segments, where momentum is progressively
increased from the feet,
legs, trunk, to the arms (Morehouse and Cooper,
1950). Further analysis did indicate that peak
momentum in the forward direction typically
occurred just after right foot touch. Therefore, judo
players should strive to create the greatest forward
momentum on the body of
uke
just after right foot
touch.
From
tsukuri
to
kake
phases, momentum in the
forward direction sharply decreased from 52.6 to 4.6
(kg•m)/s respectively. This was representative of
uke
and
tori
colliding and likely explaining the sudden
drop in
uke’s
momentum. This observation is very
consistent with the definition of
tsukuri,
in that,
there is an attempt to fit into
uke
with close body
contact through collision. From this perspective the
harai-goshi
throw requires the ability for the thrower
to create large momentum either through high
velocity, large mass, or both. Two of the heaviest
players in this study created the greatest resultant
impulse and force onto
uke
. Therefore, from a
practical standpoint this throw may be better suited
for heavy players with enough mobility skills to turn
their body 180 degrees fairly quickly and create a
plastic collision such that
uke
and
tori’s
bodies
become one.
Momentum of
uke
in the vertical direction for
the
kuzushi
and
tsukuri
phases displayed a trend in
the upward direction but was considered weak due
to high standard deviation values. It is possible that
the relative height of
tori
compared to
uke
affected
these measurements. It is also possible that
momentum generated in this particular direction,
while important to the success of throw, is quite
small. A study by Sannohe (1986) indicated that
pulling upwards and forward with
tori’s
pulling
Harai-goshi
(hip throw)
During the
kuzushi
phase
uke’s
COM depicted
momentum forward along the anteroposterior (x)
direction, upward along the vertical direction (y),
and moving away from
tori’s
pulling hand (left hand
for a right handed throw) along the mediolateral (z)
direction. The
tsukuri
phase indicated a continuation
of forward momentum, a change from an upward to
a downward momentum, and a change in
mediolateral momentum towards
tori’s
pulling hand.
The
kake
phase indicated a continuation of
momentum forward, downward, and towards
tori’s
pulling hand (Figure 2).
The
harai-goshi
throw in general terms is a
hip toss with
uke
being thrown in the forward
direction. The study indicated as such with
uke’s
momentum increasing from
kuzushi
to
tsukuri
phases at 20.6 to 52.6 (kg•m)/s respectively. This
can be considered a skilled trait by
tori
considering
that they must continually pull
uke
forward while
simultaneously shifting their feet and turning their
body 180 degrees. The momentum is generated by
the force created by
tori’s
arms, most notably from
the pulling arm (left arm), but ultimately originating
from the pushing force of the feet or ground reaction
force (Tezuka et al., 1983; Harter and Bates, 1985;
Serra, 1997). Thus, the
harai-goshi
and judo throws
in general incorporate a kinetic link between
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