Dr. Hab., Professor V.I. Zagrevskiy^{1, 2}
Dr.Hab., Professor O.I. Zagrevskiy^2
1Mogilev State A. Kuleshov University, Mogilev, Belarus
²National Research Tomsk State University, Tomsk

Keywords: competitive routine, technique, motor skill, biomechanical system, kinetic moment.

Background. Lately the sport community tends to consider physical and sport skills mastering processes in many aspects [3-8, 11] with a special emphasis on the objective movement logics applied for the competitive routine design process with account on the individual execution specifics [1, 2,9, 10]. The modern physical movement biomechanics consider a sport movement sequence as the combination of movements of a few material bodies with the body elements moving in some coordinate system within the certain timeframe.

Positioning of these bodies in the coordinate system makes it possible to track their movements and, hence, analyze the system configuration. However, analyses using only the system coordinates fail to provide a full description of the system at moment t. To obtain the means for a comprehensive description of the system and predict its evolution in space beyond the specific time point, the analyst needs to apply both the coordinates and the system elements/ bodies movement speeds.

It is commonly assumed that the correlations of the acceleration rates with coordinates and movement speeds are describable by movement equations [2], with the classical mechanics commonly applying three approaches to the movement equations based on the formal logics by Newton, Lagrange and Hamilton [2].

One of the still underexplored areas of the modern sport movement biomechanics is the transition from the supported phase to areal phase of the movement.

Objective of the study was to rate competitive routines by quantitative biomechanical indices characteristic of the aerial-phase body element rotation rates and vectors.

Study results and discussion. The study was intended to obtain and analyze video captures of the Tkachev reverse hecht on a horizontal bar executed by A. Golotsutskov, Honorary Master of Sport. The video data arrays were analyzed to obtain the quantitative biomechanical rates including the following:

1. Kinematic diagrams (kinematograms) of the competitive routines: Figure 1.
2. Support-phase kinetic moments of every bodily element and biomechanical system (BS) on the whole: see Figure 2A.
3. Kinetic moments of the every bodily element and biomechanical system (BS) on the whole versus the body mass center (BMC): see Figure 2B.

Figure 1. Tkachev reverse hecht on a horizontal bar: kinematic diagrams of the support phase (A) and aerial phase (B)

Support phase Aerial phase

Technically the movement sequence is geared to create such aerial-phase rotation impulse at the starting/ launching point that secures the countermove of the bodily elements in the aerial phase of the routine: see Figure 1B. This critical kinematical mechanism of the hecht is referred to as the countermove [1], and its goal, among other things, is to secure the right landing of the gymnast’s hands on the bar in a hang/ rest position.

The countermoves of the bodily elements in the aerial phase shall be considered and rated versus the support-phase rotation vector rather than versus the elementary rotations of some bodily elements versus the others: see Figure 1A, points 28-34. It should be underlined that it is the support phase with the thrust sub-phase that provides a starting point for the countermove formation rather than the aerial phase: see Figure 1A, points 28-34. There is no way for the athlete to change the body rotation vector in the aerial phase unless he manages to change its angular rotation rates.

Physical mechanism of the countermove is formed based on the kinematic moment retention law that implies that the kinematic moment of a rotating body keeps constant unless the body is affected by external forces/ force moments, with the following considerations:

1. Kinematic moment of a combination of bodies amounts to the summated kinematic moments of the individual bodies.
2. Kinematic moment will be computed versus both the rotation axis (i.e. the bar in the case: see Figure 2A) and the athlete’s BMC.

The above item 1 is clear and causes no problems in practical calculations. Having modeled the subject competitive routine by a triple-element model, we may compute separately the kinematic moments of the hands, trunk and legs; with the sum of the elementary kinematic moments giving us the total kinematic moment of the biomechanical system: see Figure 2.

Kinematic moment versus the support

Figure 2. Kinematic moments of the bodily elements and the biomechanical system on the whole versus the support (A) and body mass center (B)

Kinematic moment versus the BMC

Hands Legs Trunk System

Let us now spell out the above item 2:

1. For the support stage, we will compute the kinetic moment versus the bar (rotation axis) by summarizing the elementary kinematic inputs of every elements of the biomechanical system in the rotation sequence.
2. In the aerial phase, when the support has no more physical effect on the body rotation in the hecht sequence, the support-phase kinematic moment is assumed irrelevant and needs not be factored in and analyzed.
3. The kinematic moment versus the BMC in the support phase (see Figure 3) determines the rotation effect when the contact of the hands with the bar is lost. The lost-contact moment (referred to as the ‘starting point’) was found associated with the following elementary kinematic moments versus the BMC: hands +14 kgm²/s; trunk +7 kgm²/s); legs +125 kgm²/s; and the total system -104 kgm²/s.

The support-phase kinematic moment versus the BMC was tested to peak at +91 kgm²/s; with the positive sign indicative of the counterclockwise rotation. The starting-point kinematic moment versus the BMC is negative (-104 kgm²/s) and stays the same in the aerial phase. The negative starting-point kinematic moment propels the clockwise rotation of the body versus the BMC in the aerial phase. This effect is secured by the countermove i.e. the action to rotate the body versus the BMC opposite to the BMC radius-vector rotation in the support phase, for success of this challenging element of the routine.

Conclusion

• The biomechanical pattern of the Tkachev reverse hecht on a horizontal bar was found to secure the aerial-phase body rotation with the right vector and pace. This vector determined by the countermove is opposite to the support-phase BMC rotation vector at the starting point.
• Since the aerial-phase body rotation axis goes via the BMC and the kinematic moment of the biomechanical system versus the BMC (-104 kgm2/s) stays constant, the extension-flexion joint movements in the aerial phase help only vary the angular speeds of the body elements causing no effect on the kinematic moment of the biomechanical system versus the body mass center.

References

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Corresponding author: a.zagrevskaya@yandex.ru

Abstract

Individual technical mastery is fundamental for competitive success in the sport disciplines that imply specific routines being executed and scored. The study analyzes the ways to apply a set of biomechanical indices for the technical mastery rating purposes, with the Tkachev reverse hecht video captures taken for the case study and analyses. The biomechanical indices were quantified by the video material analyses with a special priority to the rotation elements of the vaulting movement sequence.

The study data demonstrate that the countermove element in the Tkachev reverse hecht is pivotal for the required rotation impulse in the controlled over-bar aerial phase of the movement sequence. The countermove direction is opposite to the body mass center (BMC) radius-vector rotation in the contact phase, particularly in the starting-point (throw) phase. Since the aerial-phase body rotation axis goes via the BMC and the kinematic moment of the biomechanical system versus the BMC (-104 kgm2/s) stays constant, the extension-flexion joint movements in the aerial phase help only vary the angular speeds of the body elements causing no effect on the kinematic moment of the biomechanical system versus the body mass center.