Evaluation of Vertical Ground Reaction Forces During a Hip Technique in Novice and Advanced Greek Judo Athletes

 Introduction


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


Participants

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)
	Novice (n=10)	Advanced (n=10)
Sex (male/female)	8/2	8/2
Age (y)	21,5±4,6	20,2±4,3
Height (cm)	175,6±5,9	176,5± 5,4
Body mass (kg)	87,7±21	86,8± 16,1
Body fat %	20,2±2,7	15,6± 3,5

Exercise Protocol

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.

Equipment

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 Hz.


Data analysis

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.


Statistical analysis

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 correction.


Results

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.

 
 Conclusion

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 regarding the 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.


References

Harter, R.A. & Bates, B.T. (1985). Kinematic and temporal characteristics of selected judo hip throws. In: Teraud, J. and Barham, J.N. (Eds), Biomechanics in Sport II. Proceedings of ISBS, (pp. 141-150). California, CA: Del Mar Research Center for Sports.

Imamura, R.T., Hreljac, A., Escamilla, R.F., & Edwards, W.B. (2006). Three dimensional analysis of center of mass for three different judo throwing techniques. Journal of Sports Science and Medicine 5, (CSSI), 122-131.

Kano, J. (1986). Kodokan judo. Tokyo: Kodansha International.

Lazaridis, S., Bassa, E., Patikas, D., Giakas, G., Gollhofer, A., Kotzamanidis, C. 2010. Neuromuscular differences between prepubescents boys and adult men during drop jump. Eur J Appl Physiol 110(1): 67-74.

Nowoisky, H. (2005). The biomechanics of loss of balance in Olympic sport judo, possibilities of measurement of biomechanical parameters. In: Quing Wang (Eds), ISBS-Conference Proceedings Archive of 23rd International Symposium on Biomechanics in Sports (pp. 600-605), Beijing – China: International Society of Biomechanics in Sports.

Pucsok, J.M., Nelson, K., & Ng, E.D. (2001). A kinetic and kinematic analysis of the harai-goshi judo technique. Acta Physiologica Hungarica 88 (3-4), 271-280.

Sacripanti, A. (1997). Biomechanical Classification of Judo Throwing Techniques (Nage Waza). ENEA technical report, 181-194.

Serra C. (1993). A kinetic analysis of the one-arm shoulder throw by judo players of varying skill levels. Unpublished master’s thesis, University of Pennsylvania, Slippery Rock, USA.

Sogabe, A., Sasaki, T., Sakamoto, M., Ishikawa, Y., Hirokawa, M., Kubota, H., et al (2008). Analysis of patterns of response to kuzushi in eight directions based on plantar pressure and reaction movement Archives of Budo, 4, 70-77

Sterkowicz, S & Maslej, P (1998). An Evaluation of the Technical and Tactical Aspects of Judo Matches at the Seniors Level. Retrieved February 22, 2002, from http://judoinfo.com/research.htm

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