The purpose of this study was to
analyze the vertical ground reaction forces (VGRFz) generated on a hip
throwing technique [Uchi Mata-Inner Thigh Throw (UM)] in novice and
high level Greek judo athletes. A heterogeneous group of 20 male and
female judo competitors participated in this study. Each subject was
required to perform three successful trials in this technique. Kinetic
data were collected by a ground mounted 40 x 60 cm force plate. Data
were collected in order to quantitatively and qualitatively analyze the
vertical forces of the support leg during execution of the throwing
technique when the Tori (the person who throws) was positioned under
the Uke (the person who was thrown). The study revealed significant
differences in vertical force application. High level judokas presented
higher relative (VGRFz) compared to novice ones. As well as that, high
level judokas applied these peak values earlier compared to their
counterparts. Magnitude and timing of VGRFs of lower extremities are
important components in combat sports and their optimum development
characterizes high level athletes.
Key-Words: - biomechanics, ground reaction forces, throwing techniques,
The purpose of the current study was to analyse and compare the
vertical ground reaction forces (VGRFz) generated in a judo hip
throwing technique in novice and advanced Greek judokas. Technique was
selected according to the biomechanical classification of Sacripanti
(1997), in that the couple of forces are coupled by trunk and leg. Uchi
Mata is considered a power throw well-suited for upper categories and
strong judo players (Sterkowicz & Maslej, 1998). Throw techniques
are dominant factor in the complex fighting movements of judo
(Nowoiski, 2005). The way that forces acting upon body influence
athletic movement and emphasizes the use of proper and ideal technique.
To date, only few studies have investigated judo from a biomechanical
perspective (Harter et al. 1986). Differences are depicted among
different level of judo players as a result of VGRFz application. This
will provide a biomechanical basis of what the thrower and person being
thrown are executing during the support phase of a specific throwing
technique and ultimately provide a better understanding of the factors
that constitute a mechanically efficient throw. Forces are effective in
a judo battle when they are applied at the right timing and ideal
quantitative, in order not to have waste of energy as Kano Jigoro
(judo’s founder) first stated. The basic mechanical concepts for judo
according to Kano (1986) are that “Minimum forces to be applied for
maximum results” and “intelligent use of energy". Thus, this study
examined the way that the two groups of judokas applied these forces
and how fast these forces were generated (timing and quantity of VGRFs).
Methods and Materials
The two groups of competition participants were designed according to
their category and due to their level (novice/advanced) and of course
according to their sex (male/female). All participants used in this
study had at least 5 years of national competition experience and in
addition to this advanced group had international one [participation to
Greek National Team]. Information including age, weight, and height
were collected for all participants (Table 1).
Table 1: Participants’ physical characteristics
(Values express mean ± standard deviation)
Body fat %
The measurements were recorded in a well-simulated and controlled
environment of the laboratory where mats were placed for the drops of
athletes and to remind of a real event picture (1). The subject was
instructed to perform the throwing conventional hip technique
(uchi-mata) with an adequate combination of maximal effort and proper
technique. The conventional hip technique in Judo is that Uke is in the
basic natural standing position with his feet spaced wide apart and his
body bent slightly forward. Thus, the subject performed the throw with
maximal effort while maintaining their balance (keeping the support
foot on the force plate). This procedure was designed to simulate the
throw under ideal conditions (picture 1), with the three general phases
of judo throwing technique, Unbalance: Kuzushi; Fit-in: Tsukuri; Throw:
Kake. (Sogabe et al, 2008). For the purposes of the current study, only
the two first phases of throwing technique were analyzed. Each
participant served both for the Tori (thrower) and the one Uke
(receiver) and only with the participant who was competed. For
kinetics, only the vertical ground reaction forces (Fz) and
the timing of their application (ms) were calculated.
Picture 1. Judokas
execution of uchi-mata throwing technique
Ground reaction forces were recorded with a ground mounted 40 x 60 cm
force plate (Bertec Type 4060, Bertec Corporation, Columbus, OH, USA).
The sampling frequency for ground reaction force signals was set at 100
Data were further processed online using scripts of Matlab 6.1 (The
MathWorks Inc.). All trials were averaged. The peak vGRF was normalized
to the body weight of each subject. As well as that, the timing of peak
value in VGRFs in milliseconds (ms.) was calculated from the force-time
curve (Lazaridis et al. 2010). The time of contact with the ground was
derived from the force plate after the vGRF exceeded 20 N.
Statistics were performed with the SPSS/PC 16.0 (SPSS Inc.) statistical
package. Mean, standard deviation of the mean was assessed for all
dependent variables. One way ANOVA with repeated measures has been used
to identify significant differences between the groups and throwing
technique. The significance level was set to 0.05 with Bonferroni
The absolute values of VGRFz were higher in the examined technique in
advanced judokas compared to novice ones. The same was true when these
values were normalized to each participant’s body weight (BW). Advanced
judokas generated higher relative VGRFs compared to novice ones
(P=0.05). Regarding the timing of appearance of this peak VGRFs,
judokas presented earlier generation of this magnitude (P=0.005). In
fact, advanced participants applied these VGRFs almost 140 ms following
the onset of each throwing technique. The same was not occurred in the
case of novice judokas who in fact presented their peak values of VGRFs
almost 200ms after the same onset.
Graph 1. Relative VGRFz applied in uchi-mata (UM) in novice and expert
Graph 2. Timing of Peak VGRFz
onset applied in uchi-mata (UM) in
novice and expert judokas players.
The purpose of this study was to examine the VGRFz generated in novice
and advanced Greek judokas in a specific hip throwing technique.
Significant differences were revealed between these two groups
peak VGRFz applied during the support phase of throwing. Expert judokas
presented higher absolute values of VGRFz compared to novice ones. This
occurred even when these values were normalized to BW. The results of
the current study are in agreement with those of Yabune, 1994 who also
concluded that rear GRF forces during a similar technique (Uchi Mata,
HG) were found to be greater with advanced judo players. This is also
consistent with the findings of Pucsok, Nelson, & Ng (2001) who
found that leg sweep velocity is a major factor of GRF application. In
a similar manner, rapid application of GRF in hip throwing techniques
may be the major factor which represents an expert judoka player.
Relationships and correlations between high level judokas players and
high application of VGRF has been shown by Serra (1993), who concluded
that experts, in a specific throwing technique,
generated higher values of vertical impulse compared to novice judokas.
Within the limitations of this study and based on the obtained data of
the study, it can be concluded that the level of VGRFs application is
consistent with the level of training background. In addition to this,
the timing differentiation that these vertical forces are applied in
the two groups, gives evidence that rapid application of these in
combination with higher peak values (magnitude) characterizes an expert
athlete of judo.
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