BIOMECHANICAL MONITORING OF TECHNICAL AND SPEED AND POWER FITNESS OF WEIGHTLIFTERS

Фотографии: 

A.A. Shalmanov, professor, Dr.Hab.
V.F. Skotnikov, professor, Ph.D.
Russian state university of physical culture, sport, youth and tourism, Moscow

Key words: control of sports training, biomechanical monitoring, hardware and software complex, sports technical skills.

Training process can be controlled effectively, especially of elite athletes, in case of constantly available actual information on their fitness, comparing it with training loads and, if necessary, correcting of the training plan.

Three types of control are distinguished in sport: on-line, current and phased. These types of control have their specifics in sports biomechanics, mainly studying technique of sports exercises and athlete's motor abilities.

On-line control is aimed at estimation of the quality of execution of sports exercise after finishing a motor task.

Current control provides information on the athlete's fitness in weekly training cycles, preferably daily. In this type of control estimation of the dynamics of the most informative motor indices in test tasks is important along with its comparison with dynamic changes of training loads.

Phased control is meant to estimate athlete's fitness level after long-term training (pre-season, off-season, regular season).

The first two types of control are the hardest to realize, since they need the receipt of immediate information on athlete’s fitness. We believe, on-line and current monitoring can be applied in weight lifting in case of fulfilling the following requirements:

1. The testing procedure should not bother an athlete and interfere anyhow with the natural course of the training process or competition.

2. Test tasks are to be presented by traditional and some special and auxiliary weight lifting exercises.

3. One should have all the necessary equipment and software to fix kinematic and dynamic motor indices.

4. Data collection and processing during competitions are to be carried out within 2 minutes after exercise execution. At trainings it can take a little bit more time.

5. Test result of every athlete is saved in the database and can be analyzed immediately after exercise or after training or competition.

6. Dynamic changes of informative indices of athletes' technique and speed and power fitness should lay the basis of correction of the training process and “conditioning” of weightlifters' technical and physical fitness.

The purpose of the study was to design the method of on-line and current biomechanical monitoring of technical and speed and power fitness of weightlifters satisfying the requirements stipulated above.

The suggested method is made of two hardware and software complexes (Fig. 1).

Fig.1. Method of biomechanical monitoring. 1 – camera and rangefinder. 2 – light emitter fixed on a barbell. 3 – timing source. 4 – force platform built in the stand.

The “AMTI” force platform promoting registration of the vertical and horizontal components of support reaction force, three-axis force moments and longitudinal and lateral coordinates of center of pressure (CP). The platform is built in the weight lifting stand. Signals from the platform come to the analog-to-digital converter produced by L-card and then to the computer.

Photo and video camera “Canon” was supposed to record the barbell trajectory using an attached light emitter fixed on the end of the barbell. The distance from the camera lens to emission source was estimated by the rangefinder.

The joint operation of these hardware and software complexes is promoted by a timing source. There is a special software program for data collection and processing and demonstration on the laptop screen.

In this variant of the method the vertical and longitudinal horizontal components of support reaction force and axial coordinate of center of pressure were registered using a force platform. The acquisition frequency - 1000 Hz.

Photo and video camera was placed beside the stand at the distance of 4,5 m from the emission source at the height of 1,5 m from the stand with the lens optical axis perpendicular to the shooting plane. Shooting speed – 50 frames per second.

Three software programs were designed to test athletes: “snatch”, “jerk” and “jump”.

The “snatch” software program is for testing athlete in the following exercises: classic snatch, snatch from plinths, snatch and clean pulls.

The “jerk” software program is meant for tests only in this exercise.

In the “jump” software program one can test athlete in various standing vertical jumps: squat jump without arm swing, jump without arm swing and jump with arm swing. Jumps are executed with the setup from the stationary starting position as good as possible.

The relevant software is to be chosen before the test with athlete’s information to be entered there (full name, age, body weight and length, barbell weight). Then the data acquisition program is launched, during its work one can check operability of all setups, register the stipulated above kinematic and dynamic motor characteristics and save the data in the computer’s memory. The data collection process takes less than one minute.

Data can be processed immediately after its collection via the second software program or after training or competition. The processing lasts less than a minute followed by saving of the processed data in the computer’s memory. So results can be looked through any time.

Let us consider the work of the “snatch” software program. After processing the software program displays the diagrams of power, speed and intensity changes for common center of mass (CCM) of the “weightlifter-barbell” system and of the barbell, as well as the apparatus motion trajectory (Fig. 2). The Figure shows only vertical components of the stipulated characteristics. Besides, the software finds time points automatically (markers T1, T2 etc.), splitting movement into phases (vertical lines on diagrams), and calculates the system and barbell kinematic and dynamic motor indices, that can be printed in the form of a closing statement (Tab. 1). If an error occurs within data processing, it can be corrected by changing the position of the first and the last markers.

Fig. 2. Kinematic and dynamic motor characteristics, barbell trajectory and calculated indices in two hand snatch

The software program has an option of viewing of athlete’s position at any time point of weight lifting and seeing the values of some indices of barbell movements in the trajectory window (lifting height, speed, vertical deviation), related to selected athlete’s position (Fig. 3). The position of x along the trajectory corresponds to the pose and the numbers on the curve comply with markers in diagrams. Besides, you can start viewing the whole trial from the moment of lifting the barbell from the stand till its peak in the end of the lift. While scrolling images in diagrams synchronously with barbell movement you can estimate the value of any of subjected characteristics of the system and barbell movements by moving the vertical line (marker). This line can be placed anywhere in the record and estimate the subjected characteristics of the system and barbell movements. X in the barbell trajectory moves synchronously with it.

Table.  Kinematic and dynamic motor indicators in two hand snatch

Name of Indicator

System

Barbell

1.

Max. speed at pre-acceleration (m/s)

1,25

1,62

2.

Min. speed in amortization phase (m/s)

1,08

1,53

3.

Loss of speed in amortization phase (m/s)

-0,18

-0,09

4.

Max. speed in final stride (m/s)

1,57

2,17

5.

Pre-acceleration time (s)

0,382

0,412

6.

Amortization time (s)

0,096

0,051

7.

Time of final stride (s)

0,103

0,114

8.

CCM level at pre-acceleration (m)

0,234

0,487

9.

CCM level in the end of final stride (m)

0,480

0,749

10.

Max. power at pre-acceleration (Н)

2520

1365

11.

Max. power in amortization phase (Н)

1211

918

12.

Max. power in final stride (Н)

3120

1266

13.

Max. abs. strength at pre-acceleration (Wt)

2703

2025

14.

Max. rel. strength at pre-acceleration (Wt(kg))

30,7

23,0

15.

Max. abs. strength in final stride (Wt)

4344

2601

16.

Max. rel. strength in final stride (Wt/kg)

49,4

29,6

Fig. 3. Athlete’s position at the end of the final stride phase

The given information in the software program can be supplemented by a phase diagram (force hodograph) showing the direction (force vector angle) and force the athlete applied to barbell when lifting (Fig. 4). This information is of special interest in jerks, since when making a jerk one can see in which direction the athlete forced on the apparatus. The software program provides these data at any time point, from the moment of lifting the barbell from the stand till its peak in the end of the lift.

Fig. 4. Maximal force applied to barbell and its direction at the final stride phase (second window to the left)

While doing classic weightlifting exercises, specifically in the two hand snatch, athletes find it difficult to maintain anterior-posterior balance when fixing a barbell in a squat. Moreover, while doing the whole exercise one should know the point of support reaction force relative to feet. For instance, how the athlete “fell”, on his toes or heels, when performing pre-acceleration of the barbell in a two hand snatch. To get information one can deduce a graph of variance of the CP axial coordinate in a supplemental window of the program, a graph of the vertical component of support reaction force and markers related to boundary moments of phases of movement (Fig. 5). For example, in the trial adduced on Fig. 5 CP shifted for almost 10 cm to the toes in the pre-acceleration phase (T0) and for 4 cm to the heels in the amortization phase (between T2 and T3) related to its position in the beginning of the exercise.

Fig. 5. Graphs of variance of the vertical component of support reaction force and axial coordinate of center of pressure (on the left)

The “jerk” program has similar options of estimation of motor kinematics and dynamics of the system and barbell CCM, center of pressure and hodograph of the force vector applied to a barbell. However, more indices are calculated automatically by the program due to added information on the athlete's and barbell’s movement at jerk. The additional indices calculated are as follows: squat time and speed, push-out time and speed, maximal absolute and relative strength of push-out. The total of the calculated indices is 23.

The third software program is designed for testing athletes in jump exercises. The tasks are performed on the force platform without video recording. Fig. 6 contains a load curve of the vertical component of the support reaction force and indices, calculated automatically immediately after a jump. The indices include maximum positive strength at toeing off, which is the most informative, but other indices are also important for estimation of athlete’s jump technique and speed and power abilities.

Fig. 6. Vertical component of support reaction force and jump test indicators (Translation: Force (H); Time (s); Full name of the athlete Egerev, Ya. jump with arm swing; Date of birth 13.07.1990; Height (cm) 182; Body weight (kg) 74,6; Date and time of test 01.10.2012 13:48:51; Jump height (m); Maximum positive strength (Wt); Relative maximum positive strength (Wt (kg); Squat time (s); Squat speed (m/s); Deceleration time (s); Take-off time (s); Take-off speed (m/s); Jump duration (s); Flight duration (s);

Athlete’s result in the jumping test depends on his motivation. So trainers should to take into account that this testing procedure is hardly useful for current monitoring if the athlete is not eager to achieve maximum results.

Thus, the designed method of instrumental biomechanical monitoring can be applied not only within a training process but also at official competitions. But nowadays it is possible only based on the weightlifting hall of Russian state university of physical culture, sport, youth and tourism, where the force platform is arranged. The advantage of this methodology compared to existing ones is in the capacity of immediate (within 2 minutes) receipt of information on the movement of the common center of mass of the "weightlifter-bar" system and motor dynamic indices.

Bibliography

  1. Shalmanov, A.A. Biomechanical Monitoring Of Technical And Speed And Power Fitness Of Weightlifters / A.A. Shalmanov, V.F. Skotnikov // Teoriya i praktika fizicheskoy kultury. – 2013. – № 2. – P. 104–106. (In Russian)

Author’s contacts: shalmanov_bio@bk.ru