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103POWER SNATCH AND JERK SEQUENCES IN CLASSICAL WEIGHTLIFTING MOVEMENTS: PHASING AND TIMING TEST METHOD
UDC 796.012
Dr. Hab.,Professor A.A. Shalmanov1 PhD,Associate Professor E.A. Lukunina1
1Russian State University of Physical Education, Sport, Youth and Tourism (SCOLIPE), Moscow
Corresponding author:
shalmanov bio@bk.ru
Annotation
Objective of the study was to develop a phase structure of weightlifting exercises based on the kinematic characteristics of barbell movement and dynamic characteristics of the athlete's interaction with the support.
Methods and structure of the study. The ways to distinguish periods and phases of classical weightlifting exercises were developed using two video cameras for bilateral video captures that helped profile the weight movement trajectory at the ends of the grip, and a dynamometric platform for recording support reaction force vector and computing pressure center coordinates. In determining the boundary moments of phases of movement, the authors proceeded from the logical and content analysis of the exercise, knowledge of the physical mechanism underlying its performance, and requirements for a rational snatch and clean and jerk technique.
Results of the study. According to the developed phase structure of the snatch exercise, based on registration of the kinematic characteristics of the barbell movement and dynamic characteristics of the athlete's interaction with the support, the authors distinguish: pre-acceleration phase, transition phase, final acceleration phase, unsupported squat phase, supported squat phase. When jerking the bar, the following phases are distinguished: half-squat, slowdown, pushing out, unsupported squat. Conclusion. The proposed phase structure of classical weightlifting exercises to a greater extent reflects the essence of the exercises performed, which consists in the implementation of physical mechanisms of lifting the bar and is more unambiguous in determining the boundary moments of the phases.
Keywords: technical excellence trainings, weightlifting technique biomechanics, jerk, power snatch, physical movement mechanism, joint mass center, bar mass center, pressure center, tracking analysis.
Background. Modern movement biomechanics research methods applied by the sport science basically analyze the movement sequences with the phasing and timing analyses. This analytical procedure may be described as the first stage of biomechanical analysis [1] with the routine design being substantiated by the movement biomechanics [2, 9] widely used in biomechanical studies. The sport routine categorization into periods and phases may be highly beneficial, particularly for the elementary skill mastering trainings, technical and physical excellence trainings and physical fitness control purposes. Generally a sport routine phasing study will be driven by a movement break -down logics analysis. Special attention will be given to movement phases in the special preparatory/ conditioning trainings geared to excel specific elements in the competitive routine. Such preparatory trainings will facilitate and perfect the key physical movement mechanisms of the competitive routine.
It is traditional for the modern national weightlifting sport to categorize the classical power snatch and jerk (in the clean-and-jerk) into periods and phases as provided by A.A. Lukashevin 1972 [3],i.e. into three periods and six phases, with the bar positions versus the support and leg joint angles (particularly knee joint ones) used as the key reference points in the movement kinematics analyses. Thus the A.S. Medvedev's study [4] of the classical weightlifting routine biomechanics gives a detailed analysis of every phase in the power snatch and clean-and-jerk sequence and sets the key goals for every phase.
Power jerk,a final element of the classical clean-and-jerk, is generally categorized into three periods including five phases [4]. Despite the fact that the basic semantics of these periods and phases are no more disputed,we believe that the reference/ phase limiting points need to be revised for the purposes of the execution biomechanics tests in the training and competitive processes. One of the key re-
quirements to such tests is that they should not interfere into the training process with their sensors (like goniometers attached to the knee joints) and other tools of distracting/ hampering effect on the execution. Video captures (particularly the frontal ones) are non-acceptable for the reason that they largely fail to accurately profile the leg joint angle variations in the movement sequence — particularly when the disks block visibility of the knee and hip joints in some moments and the reference points and the move — ment sequence may not be accurately tracked on the video captures. These limitations urge the research community to look for other ways to precisely phase the routine,fix the reference points and analyze benefits of the new routine breakdown/ phasing models. It is rather important for these reference/ phase delimitating points to be easily detectable to help fairly profile the movement sequence regardless of the individual anthropometric characteristics.
Objective of the study was to categorize the classi — cal weightlifting techniques into phases based on the bar movement kinematics and the athlete's ground contacting dynamics.
Methods and structure of the study. Our extensive studies [5,7,8] of the power snatch and clean — and—jerk weightlifting techniques using the special movement bio — mechanics tests (including the competitive performance biomechanics tests) showed the need for a new weight — lifting routine phasing scheme with the revised periods and phases. For the scheme design purposes,we used two video cams for bilateral tracking of the bar end movement and a dynamometric platform to record the force vector components (i.e. the support response profile) and their variations by the pressure center coordinates [3].
The movementphasing (phase delimitation) analysis was driven by the technique structuring logics, knowledge of the physical movement mechanism pattern and the classical power snatch and clean — and—jerk execution standards [7]. Let us remind that a physical movement mech — anism is interpreted herein as the movement sequencing
Figure 1. Bar mass center travel trajectories in the power snatch (A) and clean-and-jerk routines
by the applied forces, including the muscle forces, in the context of basic laws of mechanics. The core idea is to profile the movement sequence and understand the reasons for every change knowing the acting forces and their key application points.
For the power snatch or clean—and—jerk movements being successful, the athlete must secure the individual — anthropometrics — specific optimal vertical speed and height of the bar by a facilitating squatting move — with a special attention to the body balancing/ postural and bar controls in the bar movement phases. This goal is achieved by the bar being moved by an S — shaped trajectory (Figure 1) — for the reason that this trajectory, in contrast to the rectilinear one,secures the vertical speed in the final ac — celeration phase being contributed by the horizontal force element of the curvilinear bar move — with the centripetal force generated by a power backward thrust of the body in the final phase [7]. This power backward thrust is typical for every elite athlete.
Results and discussion. Our power snatch phasing scheme is basically different from the A. A. Lukashev's for we prioritize the bar movement kinematics and the athlete's ground contacting dynamics to fix the reference/ phase delimitation points for every phase (see Figure 2) as follows.
Pre-acceleration phase starts from the moment when the vertical vector of the support response force crosses with the athlete — and—weight joint mass center and ends up when the pressure center moves to the extreme point towards the heels. The bar moves in this phase towards and along the athlete's body by the legs being extended and pressure center shifted towards the heels. Note that the body move is mainly translational with a slight rotation counterclockwise (Figure 2, snapshots 1 and 2). The bar move towards the body is required to facilitate the horizontal acceleration vector and enter the transitional phase.
Transitional phase follows the above phase and ends up at the moment when the bar mass center starts speeding up horizontally from the body (Figure 2, snapshots 2 and 3). The athlete in this phase will as soon as possible take due posture for the final acceleration so as to prevent the verti — cal bar move being slowed down and maintain the optimal horizontal speed. The pressure center in this phase moves forward from the heels to the toes. It should be mentioned that some beginner athletes use to sub—squat under the bar at this point,but this error results in the vertical speed of the pressure center movement being slowed down.
Final acceleration phase follows the above phase and ends up at the moment when the vertical vector of the bar mass center is maximal (Figure 2,snapshots 3 and 4). Note that the phase starts from a sort of a forward—up push to force the bar speed up horizontally off the body [12]. Then the athlete reverses the bar movement down—upward along a curved line as dictated by the centripetal force with the arms being straight.
Aerial squat phase follows the prior phase and ends up when the ground contact is restored (Figure 2, snapshots 4 and 5). At the beginning of this phase,the athlete moves to the aerial position with the bar still controlled by the centripetal force. Many skillful athletes make a small jump
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Figure 2. Power snatch phases. Note that the body positions, numbers and points on the chart refer to the limiting points of the phases
Figure 3. Jerk sequence phases. Note that the body positions, numbers and points on the chart refer to the limiting points of the phases
back in this phase to speed up the bar in the back — up — ward direction [7].
And the supported semi-squat phase follows the prior phase and ends up when the bar is fixed in the full squat position (Figure 2 , snapshots 5 and 6).
Jerk movement sequence in the classical clean — and — jerk technique shall secure the optimal lift speed and top point of the weigh. The physical movement mechanism of this element is geared to create an optimal vertical force impulse and facilitate the movement by the bar elasticity being controlled in the movement inhibition and acceleration phases. We phased the jerk movement sequence as follows (Figure 3).
Semi-squat phase starts begins from the athlete — and—weight joint mass center moved downward,and ends up when the joint mass center speed comes to maximum (Figure 3,snapshots 1 and 2).
Inhibition phase follows the prior phase and ends up at the lowest point of the semi—squat when the vertical speed of the mass center falls to zero (Figure 3,snapshots 2 and 3),with a special role played by the bar elasticity and weight control skills of the athlete.
Push-up phase follows the prior phase and ends up when the joint mass center speed is maximal (see Figure 3 , snapshots 3 and 4). A special priority in this phase is given to the push—up and backward move with power extension in the knee joints and coming to the toes in the final point of the phase.
Aerial semi-squat phase follows the prior phase and ends up when the ground contact is restored (Figure 3,snapshots 4 and 5). Note that the athlete pushes up the bar to come to the aerial position.
Further phasing of the movement sequence was con— sidered impractical since the dynamometer platform size (90H90cm) was too small for accurate rating of the re — sponse force.
Note that Figure 3 gives the jerk phasing pattern based on the athlete—and—weight joint mass center tracking analysis. Similar phasing may be made based on the bar mass center tracking analysis, although the phase limiting points in the both cases are mostly different in timing. It can
be assumed that the closer are the limiting points in the both analyses , the "tougher" is the athlete's control of the weight in the semi — squat and push — up phases.
Conclusion. We believe that the classical weightlift — ing moves phasing scheme outlined herein gives a closer approximation to the essence of the standard weightlifting motor skills, more accurate in delimitation of the movement phases and,therefore , may be efficient for the execution biomechanics and physical fitness tests and analyses in trainings and competitions — with application of the bilateral video captures and a dynamometric platform.
References
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