Introduction In Men's Artistic Gymnastics, the gymnasts are judged during the competition through the marks given by the judges. The level expertise can be defined as the competence of the gymnast to perform the more difficult elements series with the minimum deductions. Double leg circle is the most important movement structure on pommel horse. It can be defined as "a gyrating movement in the horizontal plane with alternate support holds on pommels" (Mémento, 1997). The circle movement has four main body positions: back phase, entry phase, front phase and exit phase. Brüggemann (1994) and Karacsony & Cuk (1998) established an initial profile for pommel horse techniques: qualified gymnasts require between 0.93 sec and 1.00 sec to perform one circle with a ratio between the double arm support and the single arm support close to 1/3. In their spatial course, circle requires a maximum Body Segmental Alignment (BSA) (shoulders-pelvis-heel). The F.I.G. (2001) specifies that movement of the hips is to be penalised by a deduction of 0.10 to 0.30 points. The aim of this study was to determine the temporal and spatial variables of the circle by a comparison between a group of expert gymnasts and a non-expert group. Materials and methods Sixteen gymnasts were divided into two groups: an Expert Group (EG; n=8) and a Non-Expert Group (NEG; n=8). The subjects were asked to perform ten circles movement on a training pommel horse with the maximal segmental alignment. A three dimensional motion registration system (Vicon 512™, Oxford's metrics™, Oxford, UK) recorded the position of ten light reflecting markers (? 25.4 mm) with five cameras, at the sample rate of 50 Hz. A total of 160 circles (16 subjects * 10 circles) were analysed. Statistical analysis of the data was performed using the Student's t-test and significance was fixed at the 0.05 level of confidence. Results Temporal course - The relative duration of the two armed support phase is measured through the sum of the time spent during the double support phase (front and back phase) and transposed in percentage of the time of one circle. This variable decreased significantly with the performance level of the gymnasts (EG : 31.4 %; NEG : 17.0 %). Spatial course - The second results showed the variation of the body segmental alignment - transposed in percentage of the maximal body segmental alignment estimated in standing static position - during the circle. For a whole circle, as for each of the four phases (Table 1), the expert gymnast is characterised by a significantly higher body segmental alignment compared to the nonexpert gymnast group. Discussion Expert gymnasts demonstrated two main characteristics in the circle movement : a short time spent on two arms, a body segmental alignment close to the theoretical maximal alignment. Temporal course - The aim of the experiment reported here was to characterize the mode of coordination spontaneously adopted by the expert gymnasts during the circle compared to the nonexpert gymnasts. In agreement with Brüggemann (1994) and Karacsony and Cuk (1998), the comparative study proved that the expert group spends less time on two arm support phase than the non-expert group. For the non-expert group, the ratio between the double arm support phase and the single arm support phase was close to 1/2, compared to 1/5 for the expert gymnasts. Some studies concerning walking, showed that in mature gait. the time spent on the double support phase leads to decrease. The postural instability leads the young children to have a double support phase clearly longer than the adults (Vereijken, Bril, Ledebt, 1998). During the circle, the long double support phase of the NEG could be interpreted by two reasons: a) it shows a lack of anticipation of the support, b) the highly trained gymnasts were able to produce higher force which permits them to support body weight during a more important time than the non-expert. To conclude, the non-expert gymnast can perform circles on a pommel horse, despite the lack of the strength required to maintain balance. Nevertheless, retaking the expression used by Vereijken, Bril & Ledebt (1998) the child is "walking by falling", it seems to us that the non expert gymnast is "circling by falling". Spatial course - The results concerning the BSA during the circle performed on a pommel horse reveal a swing movement of the hip. The body is stretched during the front and back phases and slightly bent during the two laterals phases. In our study, we have shown that the mean value of the BSA of the expert (90.6%) was closer to the theoretical alignment than for the non-expert group (82.4%). The more important flexion of the hip during the circles can be explained by two main reasons. On one hand, the difference could be explained by a lack of strength of the Musculi abdominis which had a role in maintaining the firm posture of the trunk during the circle. On the other hand, the lack of alignment could be the sign of a lack of dynamic balance. The non-expert gymnast try to keep the Centre of Mass (CM) as close as possible to the hands. When the gymnast arches his body, the CM moves closer to the hands. To conclude, the non-expert gymnast performs the circle with almost the same logic as the expert gymnast: the time spent on both arm is shorter than the time spent on one arm and the trunk-legs angle decreases during the lateral phases. However, the expert gymnasts could keep his dynamic balance maintaining his body very aligned.
© Copyright 2002 Expertise in Elite sport. 2nd International Days of Sport Sciences, 12.-15. November 2002, INSEP, Paris (France). Veröffentlicht von INSEP. Alle Rechte vorbehalten.