Data recording and collecting were processed via SIMI Motion 3D system, version 8.5 German company SIMI Reality Motion Systems GmbH [3, 4] by 8 synchronized high-speed infrared cameras. 20 anthropometric points were assigned and marked by passive retrospective stickers (Fig. 3). Temporal and spatial variable were observed: duration of selected phases of the elements,  acceleration (a) and velocity (v) of the leading leg, height of the centre of the mass (M). For easier analysis of the elements we select 2 phases for each: 1^st phase represents “illusion”, 2^nd phase depict “vertical split”.

Figure 3. Anthropometric points & marker placements

Results and discussion

Temporal variables. We assumed that duration of the 1^st phase of FIFVS will be affected by more difficult position in the   unsupported vertical split, and thus it will be longer than the 1^st phase of FIVS. However, in both elements, the performance time of the 1^st phase was exactly equal (1.30 s). Comparison of the 2^nd phase shows only 0.02 s difference in favour of a faster executed vertical split in FIVS. Flexibility and balance are dominant qualities of the illusion elements. However, they do not guarantee the correct execution with the necessary range and intensity as the importance of velocity and acceleration has been approved in several gymnastic studies [6, 8, 9, 10]. In our investigation maximum acceleration (a) and maximum velocity (v) of the leading leg was measured on the malleolus point. More detail values of both elements are described in table1. 

Table 1. Maximal acceleration (a_max) & maximal velocity (v_max) of the leading leg, measured on the malleolus point.

Angular variables. The most important parameter - the maximum angle between legs in vertical split, where the angle of 170° was expected as minimum requirement given by the rules. In FIVS a sufficient range of 177.77° was reached, however, only 161.31° in FIFVS.

Height & trajectory of CM. In the starting position of FIVS the CM was at 0.94 m. The highest point of the CM was detected at the end of the first phase at 0.98 m, unsurprisingly higher than the starting position as the gymnast performed on tiptoe. The lowest point of the CM was determined while entering the second phase (0.61 m). As expected, in the FIVSF there were no significant differences between height of CM during the performance of the element, all values were almost similar (table 2).  

The biggest advantage of biomechanical analysis is the improvement of gymnast´s performance. One of the important factor evaluated by judges is the fluency of the illusions. Figure 4 represents comparison of both illusions. While entering the illusion there are no mistake in fluency either FIVS or FIFVS. However, at end of the 1^st phase (finishing the “illusion part”) mistakes in balance could be seen and continuously detected in the 2^nd phase as well.

Table 2. The height of the CM of the gymnast in different parts and phases of the exercise

Based on the results of our investigation we were able to analyse errors in technique that occurred while performing both elements. All minimum requirements were met in FIVS, however the element was not performed without a mistake. Figure 5 shows the error in the body posture. Another major mistake can be seen while transferring from the 1^st to the 2^nd phase: gymnast’s trunk is moving faster than the leg causing closed angle between the leading leg and torso (Fig. 6). Figure 4. The vertical movement of the CM of the gymnast (m, m) over time (t, s)

Serious errors in technique could be detect also in FIFVS. Figure 7 demonstrates incorrect body posture (similar to FIVS) of the 1^st phase, as rigid body is required. Due to insufficient range between the legs - 161.31° in the free vertical split (Fig. 8), minimum requirement for the difficulty value (of at least 170°) has not been accomplished as well. Additionally, a small mistake in the position of standing leg, which must be perpendicular to the floor in the vertical split, was detected in both elements (FIVS = 83.04°; FIFVS = 77.58°).

Figure 5. Error in the first part of FIVS

Figure 6. Errors in transfer from 1st to 2nd phase in FIVS

Figure 7. Incorrect body posture in FIFVS

Figure 8. Insufficient amplitude between the legs in vertical split

Conclusions. The present study evaluates the kinematic characteristics of two types of difficulty elements in AG with the aspect of correct technique. The kinematic analyse demonstrates that the illusions posses all the characteristics of body rotation dynamics and flexibility as fundamentals.  On the base of the results we conclude:

• The performance time of the 1^st phase was exactly equal in both elements (1.30 s). Comparison of the 2^nd phase shows only 0.02 s difference in favour of a faster executed vertical split in FIVS.
• Minimal differences were found also in the maximum acceleration of the leading leg  between FIVS a FIVSF in the  1^st phase (64,14 m.s^-2 and 65,13 m.s^-2) as well as in the 2^nd phase (42,39 m.s^-2  and 45,07 m.s^-2).
• The maximum amplitude between legs in vertical split, where the angle of 170° was expected as minimum requirement, was reached only in FIVS (177,77°). Due to insufficient angle of the legs - 161.31 ° in free vertical split, the minimum requirement has not been met.
• Between the height of the CM during the execution of the element, all values were almost the same for both elements: the highest point of the CM was found at the end of the 1^st phase (FIVS - 0.98 m; FIVSF - 0.97 m); the lowest point CM was shown while entering the second phase (FIVS and FIVSF - 0.61 m).
• While transferring from the 1^st to the 2^nd phase serious errors in the position of the body are shown in both elements: gymnast’s trunk is moving faster than the leg causing closed angle between the leading leg and trunk.

Despite the limitation of this case study the investigation helped to ease the identification of the key phases, movement of the limbs and the CM, resulting in elimination of the errors and further improvement of gymnast´s technical preparation.

Aknowledgment

Special thanks are given to the gymnast and members of the technical staff. The study was supported by the project of Ministry of Education, Science, Research and Sport of the Slovak Republic - VEGA 1/0754/20 & VEGA 1/0089/20.

References

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Corresponding author: svetlanaueg@rambler.ru

Abstract

Biomechanical considerations as reflected in the exercise performed without or with errors, particularly in aerobic gymnastics, is still associated with insufficient scientifically approved knowledge. The purpose of the study was to identify, using 3D analysis, the kinematic characteristics in the key phases of two different difficulty elements in aerobic gymnastics, “Free illusion to vertical split” (FIVS) and “Free illusion to free vertical split” (FIFVS), and compare the differences with emphasis of execution. The elements have been performed by the female athlete and Slovakian national team member (age = 21 years, sport age = 16 years, height = 159 cm, body weight = 52 kg). The indicators that appeared to be the key in terms of correct technique were detected: duration of the phases, angular variables, the height of the centre of the mass and the acceleration and velocity of the leading leg. The results showed the major error in the second phase of FIFVS where the minimum requirement (at least 170° between the legs in the split position) has not been reached and gymnast showed only 161.31° range. Additionally, a mistake in the position of standing leg, which must be perpendicular to the floor in the vertical split, was detected in both elements (FIVS = 83.04°; FIFVS = 77.58°).