Dr.Hab., PhD, Professor L.S. Dvorkin¹
Dr.Hab., Professor N.I. Dvorkina¹
S.I. Popova^2
1Kuban State University of Physical Education, Sport and Tourism, Krasnodar
²V.N. Machuga Children and Youth Sports School, Pereyaslovskaya vil., Bryukhovetsy district, Krasnodar region

Keywords: total bioelectrical muscular activity, static tension of wrist and forearm muscles, dominant arm, non-dominant arm, junior (13-14 year-old) weightlifters.

Introduction. The mechanisms of influence of physical exercises on the functional state of the human neuro-muscular system have been studied for many years now [2]. Thus, according to M.R. Mogendovich [4], regulation of the physiological functions during physical exercises is as follows: the flow of the nerve impulses from the proprioceptors of the musculoskeletal system changes the functional state of the central nervous system and provides urgent regulation of the functions of the internal organs through the autonomous centers. At the same time, the humoral regulation of these functions is also carried out, as the metabolic products in muscles during physical exercises affect the nervous and endocrine systems, causing the release of hormones. Metabolites, formed in muscles, also have a local effect, namely, they dilate the blood vessels and increase the blood supply to the muscles [5]. Therefore, muscle work along the nervous and humoral channels is carried out in the central nervous system and the center of the endocrine system (hypothalamus), which become integrated, and then these systems regulate the functionality of the internal organs and their trophic functions [1, 3]. Possible direct influence of muscle work on the higher parts of the central nervous system is emphasized by many authors [6, 7], who managed to register conditioned reflexes based on the proprioceptive stimulation during electromyography. Some authors observed falling bioelectrical muscular activity in children during fatigue, just like in adults [2]. Such studies in children and adolescents are conducted as part of the study of age-specific features of motor functions in terms of vocational training and sports specialization [2, 9]. At the same time, we have no precise information on the results of electrochemical studies of the neuro-muscular system performance of junior weightlifters aged 13-14.

Objective of the study was to profile the junior weightlifters’ age-specific neuro-muscular system performance rates.

Methods and structure of the study. Subject to the study were junior (13-14 year-old) weightlifters (n=14) from Pereyaslovskaya village, Bryukhovetsy district, Krasnodar region, forming Experimental Group (n=23). The Reference Group was made of 23 non-sporting schoolchildren of the same age studying at comprehensive school No 15 in the same village. Prior to the experiment, all participants underwent a medical examination. The training sessions for junior weightlifters were carried out three times a week and lasted 2 hours. Comprehensive physical training took at least 50% of the training time, 50% of the time was given to the special weightlifting program, which aimed to improve junior weightlifters’ technical skills and competitive and special auxiliary exercise performance skills, both dynamic and static ones. The Reference Group subjects were engaged in physical education three times a week under the body conditioning program.

During the training session, the bioelectrical activity of the following muscles (BMA) was registered using a portable myomonitor (surface electromyographic monitoring system): musculus flexor carpi radialis, musculus flexor carpi ulnaris, musculus brachialis and musculus palmaris longus. During the study a dynamometer was used – accessible for determining not only strength, but also static endurance of the hand and forearm muscles. The dynamometer scale was calibrated in cmHg. The subject was to draw two handles together with his middle phalanges, while squeezing a rubber bulb, placed in a small chamber partially open on one side, with the proximal parts of the metacarpal bones. The volume of the chamber and the bulb was approximately the same, so the handles were dragged close even with a low effort. One of the handles was removable, so it could be adjusted depending on the size of the subject’s hand. The subject was to press the dynamometer, applying 1/3 of the maximal strength i.e. till the last moment when the static tension could still be kept at the required level.

Strength abilities and BMA rates were registered taking into account the dominant (DA) and non-dominant (NA) arms. At the first stage of the study, the maximum and minimum BMA rates ​​were recorded for 5 seconds, and their mean values ​​were calculated. At the second stage of the experiment, all electromyographic calculations were carried out for five phases of static load: 1) warming-up period; 2) "stable" state; 3) appearance of initial signs of fatigue; 4) period of fatigue withstanding; and 5) period of increasing fatigue. For this purpose, the electromyographic data on the work of four muscles were summed up - the total bioelectrical muscular activity (TBMA). The electromyography results were processed using a software application in an automatic mode according to the following algorithm: input of the parameters to be registered, preliminary signal processing, calibration of the input parameters, output of the graphical representation of the input parameters, mathematical processing of the motor action parameters.

Results and discussion. The study found that 13-14 year-old weightlifters were hardier and stronger than their peers not doing sports (Table 1). Thus, if in 13-14 year-old weightlifters the strength of the dominant arm was equal to 91±3.2, in their peers it was 49.3±3.2 cmHg, that of the non-dominant arm - 87.3±2.9 and 47.5±2 cmHg, respectively; the static endurance of the dominant arm equaled 216±9.2 s and 154.3±5.4 s and that of the non-dominant arm - 212.5±9.2 s and 149.6±4.3 s, respectively; the time of emergence of fatigue in the dominant arm was 148±8.3 s, and in their non-sporting peers - 123±4.2 s, and respectively, that in the non-dominant arm - 138.1±7.6 s and 118.5±3.9 s.

Further studies using the electromyographic tests made it possible to evaluate the above results from the point of view of their physiological significance. The study findings are presented in Tables 2 and 3.

Table 1. Strength indicators in 13-14 year-old adolescents during wrist dynamometry tests with 1/3 of submaximal strength

Table 2. Maximum bioelectrical muscular activity rates during wrist dynamometry test,  mV/5s

Table 2 shows that the maximum BMA of the musculus flexor carpi radialis of the dominant arm in junior weightlifters was higher by 0.02 mV/5s than that of the non-dominant arm, and in their non-sporting peers - by 0.04 mV/5s, and respectively, that of the musculus flexor carpi ulnaris - by 0.03 and 0.03 mV/5s, musculus brachialis - by 0.19 and 0.08 mV/5s, musculus palmaris longus- by 012 and 0.11 mV/5s. The minimum BMA of the dominant arm in all cases was higher than that of the non-dominant arm (Table 3). Thus, the minimum BMA of the musculus flexor carpi radialis of the dominant arm in junior weightlifters was higher than that of the non-dominant arm by 0.004 mV/5s, and in their non-sporting peers - by 0.002 mV/5s, and respectively, that of the musculus flexor carpi ulnaris - by 0.007 and 0.005 mV/5s, musculus brachialis - higher by 0.040 and lower by 0.010 mV/5s, the TBMA of the musculus palmaris longus in weightlifters was higher by 0.020, and in their non-sorting peers - lower by 0.010 mV/5s.

Table 3. Minimum bioelectrical muscular activity rates, mV/5s

The mean values of the bioelectrical muscular activity of the dominant arm of junior weightlifters throughout all 5 phases of static tension of 1/3 of the maximal strength ranged from 0.27 to 0.32 mV/5s (D=0.05 mV/5s), and in the non-dominant arm - from 0.24 to 0.33 mV/5s (D=0.09 mV/5s), while in non-sporting peers, respectively: that in the dominant arm - from 0.40 to 0.48 mV/5s (D=0.08 mV/5s) and in the non-dominant arm - from 0.43 to 0.57 mV/5s (D=0.14 mV/5s).

So, junior weightlifters were found to have a more positive dynamics of BMA under static loads, which is obviously due to the improved mechanisms of adaptation of the motor cortex to static tension and changes in the motor neuron impulsation during exercises with heavy weights. Thus, it is known that fatigue is accompanied by irradiation of excitation of the central nervous system, which, in turn, reaches a considerably larger number of nerve centers than is necessary to perform the given muscular load [1, 5].

Conclusions. Weightlifting sports improve those functional systems that participate in the voluntary muscle contraction when lifting dynamic and static loads. Thus, as opposed to non-sporting adolescents, junior athletes demonstrate a more prolonged excitation of the nerve centers, as evidenced by a relatively more regular bioelectrical activity of the muscles in terms of static tension. According to the studies, the changes in the neuro-muscular system performance are influenced by the motor-visceral reflexes intended to develop the adaptive mechanisms (as a result of sports training) that would increase the coordination role of the nerve centers of the motor analyzer.

References

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Abstract

Presently the research literature on the subject provides little if any trustworthy data on the electrokymographic tests of the junior weightlifters’ age-specific neuro-muscular system performance rates. Objective of the study was to profile the junior weightlifters’ age-specific neuro-muscular system performance rates. Subject to the study were junior (13-14 year-old) weightlifters (n=14) forming Experimental Group (EG) versus Reference Group (n=23, RG) of their non-sporting peers. Tests under the study were designed to obtain wrist dynamometric data for the dominant/ non-dominant arms versus the bioelectrical activity of the following muscles: musculus flexor carpi radialis, musculus flexor carpi ulnaris, musculus brachialis and musculus palmaris longus. The groups were requested to apply 1/3 of the maximal strength till the last moment when the static tension could still be kept at the required level. The junior athletes were tested with gradual growth of the total bioelectrical muscle activity rates in the wrist strength tests versus the their non-sporting peers tested with falling bioelectric muscuar activity rates – that may be indicative of the athletes’ nervous mechanism control system operating more efficiently i.e. the muscular performance control by the CNS being better developed versus their non-sporting peers.