Dr.Hab., Professor A.G. Levitskiy¹
D.A. Matveyev²
PhD, Associate Professor A.A. Potsipun¹
A.V. Shabaev^2
1National State University of Physical Culture, Sport and Health named after P.F. Lesgaft, St. Petersburg
²Saint Petersburg State University, St. Petersburg

Keywords: sambo, judo, wrestling, throwing technique, advanced foot sweep

Background. In modern judo, two standard advanced foot sweep (De Ashi Harai) throwing techniques are used. In one of them, the role of the body mass centre is virtually negligible at the onset of the throw sequence and, hence, the body pitch angle in this version is lower or close to zero. In the second version of the technique, the opponent is off-balanced at the onset of the sequence by the attacker’s body mass centre being actively engaged in the move. It is unlikely possible to say which of the two versions is more energy-efficient. In one version, the movement sequence is highly energy-efficient at the onset of the throw sequence due to gravity being actively used, and the other is more efficient in the later phases of the throw sequence.

Objective of the study was to profile the optimal body pitch angles at the onset of the advanced foot sweep (De Ashi Harai) throwing technique.

Methods and structure of the study. Subject to the analysis were the video captures of the advanced foot sweep throwing technique [1, 3 et al.]. The records were dominated by the online judo and sambo demos/ tutorials. The material was analyzed using the DVD player programming tools in slow replays averaging 0.25 of the normal replay speed. We interpreted an onset of the throw sequence as the moment when the attacker (Tori) starts sweeping the advanced foot of the attacked (Uke) fighter, with the moment being referred herein as throw starting point. The key frames capturing the throw starting points were then copied by Print Screen command and input to Paintbrush software in a *.bmp format. The body pitch angle of Tori was modelled by a visually drafted straight AC line (see Figure 1). A key section of the line was highlighted and a triangle was drawn by straight lines going down to the coordinate axis.

The triangle leg lengths were identified on the coordinate axes (see Figure 1) and thereby the body pitch ratio (tangent) was calculated. Precise values of the angles were rounded to integer quantities since such accuracy was deemed to be reasonable for the visual constructions. The output data inaccuracy was rated at 5^о [2].

Subject to the analysis and body pitch angle calculations were the front and side snapshots of the attacking movement sequence plus the ones taken at the angle of 45^о. 

Figure 1. Snapshot for the body pitch angle calculation procedure

Study results and discussion. Given on Figure 2 hereunder are the front-plane body pitch angles fixed at the advanced foot sweeping throw starting moments on the men’s judo technique demo/ tutorial videos.  

Figure 2. The front-plane body pitch angles fixed at the advanced foot sweeping throw starting moments on the judo technique demo/ tutorial videos

The output study data indicative of the body pitch angles may be grouped as follows (see Figure 2):

Group 1: body pitch angles close to 0^о (no pitch); and

Group 2: body pitch angles variable within 16-18^о.

Figure 3. The side-plane body pitch angles fixed at the advanced foot sweeping throw starting moments on the judo technique demo/ tutorial videos

Given on Figure 3 are the side-plane body pitch angles fixed at the advanced foot sweeping throw starting moments on the judo technique demo/ tutorial videos. The obtained body pitch angles may be grouped as follows: 15^о minus group; and 20^о plus group. The difference may be due to the individual variations of the attacker’s body mass centre input to the throwing sequence. The higher is the body pitch angle the higher is the body mass centre input to the throwing action. In case of the lower body pitch angles, the attacker’s body mass centre appears to be less mobilized, the deficit being offset by the couple of forces applied by Tori in the throw sequence.

Given of Figure 4 are the body pitch angles for the 45^о snapshots of the advanced foot sweeping throw starting moments on the men’s judo technique demo/ tutorial videos. The obtained body pitch angles in this case may be also broken down into two groups as follows: 10^о minus group and 10^о plus group. And again the body mass centre is a higher contributor in one Tori group and lower in the other group. The couple of the direct off-balancing forces applied to Uke will play a larger role in one group and smaller role in the other group, respectively.

Figure 4. The body pitch angles for the 45^о snapshots of the advanced foot sweeping throw starting moments on the men’s judo technique demo/ tutorial videos

We have found no strict separation lines between these two groups of the throw techniques. Therefore, there are good reasons to expect the two basic techniques being highly variable in different spatial projections. Theoretically, we could further break down the body pitch angles into 3, 4 and more groups, albeit, in our opinion, it would be counterproductive in terms of too high complexity of the analyses that would unlikely yield totally different results. 

Conclusion. In the advanced foot sweeping throw mastering process, we recommend the guiding body pitch angles of the trainees being kept under 30-40^о. In the beginner phase of the training process, it may be beneficial to focus attention on the body-pitch-free version of the advanced foot sweeping throw (De Ashi Harai) technique for the reason that the body-mass-centre-driven version of the technique requires higher motor coordination skills and may be challenging for beginner athletes, particularly junior ones.

References

1. http://yandex.ru/video/search?filmId=eWroqD5XUXI&text=de%20ashi%20harai&...
2. Levitskiy A.G. Osobennosti polozheniya korpusa pri broske obkhvatom (Specifics of body posture at throw with arms put around) / A.G. Levitskiy, D.A. Matveev, O.V. Kholodkova, M.S. Danilova // Uchenyie zapiski universiteta im. P.F. Lesgafta - 2016. - № 4.
3. http://yandex.ru/video/search?filmId=pzX8diOuUXI&text=de%20ashi%20harai&...

Corresponding author: khubbiev@gmail.com

Abstract
The study offers a body position profiling analysis of the advanced foot sweep (De Ashi Harai) throwing technique applied in judo. Subject to the analysis were the demo/ tutorial video captures of sambo and judo foot throwing techniques downloaded from the internet sources. The records were analyzed using the DVD player programming tools in slow replays averaging 0.25 of the normal replay speed. The key frames capturing the throw starting sequence were copied by Print Screen command and input to Paintbrush software in a *.bmp format. The Paintbrush toolkit was used to model the body pitch angle by straight lines. Then a right-angled triangle was drafted and the body pitch angle to the vertical axis was calculated as a ratio of triangle sides and angles. Subject to the analysis were the front and side snapshots of the movement sequence plus the ones taken at the angle of 45о. The study resulted in two versions of the advanced foot sweep throw technique being identified. In one of them, the role of the body mass centre was found to be minimal at the onset of the throw sequence and, hence, the body pitch angle in this version is low or close to zero. In the second version of the technique, the opponent is off-balanced by the attacker at the onset of the sequence by the attacker’s body mass centre being actively engaged in the move. This finding may be beneficial for the judo education and training systems applied in national Children’s and Youth Sport Schools (CYSS), youth sport clubs, university sport groups etc.