Dr.Biol., Professor R.M. Gorodnichev
A.G. Belyaev
Associate professor, Ph.D. V.N. Shlyakhtov
Velikie Luki State Academy of Physical Culture and Sport, Velikie Luki

Keywords: magnetic stimulation, muscles, strength abilities, sports activity

Introduction. It is a matter of general knowledge today that strength ability is paramount for any sports activity since individual accomplishments in many sport disciplines heavily depend on how physically strong the athlete is [3, 6]. We have once studied the practical effects of the magnetic stimulation (MS) courses on relaxed skeletal muscles of healthy young individuals and the relevant induced strength-ability improvements [1] and proved that the magnetic stimulation training (MST) may be viewed as a quite efficient tool to enhance the skeletal muscular strength. The positive training effect was achieved when the relatively strong stimulating pulses were applied that totaled 60% of the maximum output of the magnetic stimulator unit operating at the pulse frequency of 17 Hz.

The purpose of the study was to examine the potential for the muscular strength ability improvements when the relatively weaker magnetic impacts are applied to the antagonistic muscles involved in some movement when this movement is performed.

Materials and methods. The sample for the experimental study was represented by 18 healthy male volunteers 19 to 28 years of age who gave their informed consent in writing for participation in the studies, with the test procedure and conditions being duly approved by the Committee for Bioethics of Velikie Luki State Academy of Physical Culture and Sport (VLGAFK).

The subjects were broken down into two groups of 9 people each, one being nominated the control group (CR) and the other experimental group (EG). Every tested individual was asked to perform plantar flexions (concentric muscle contractions) for fifteen days of training with the applied force of 80% of the Maximum Angular Momentum (MAM) value as recorded by the Biodex Multi-Joint Therapeutic and Diagnostic System. Ten (10) muscle contractions were performed in every training session, with the 50-second rest breaks between the movements. Every plantar flexion foot movement lasted for 5 seconds and the movement amplitude was around 40°. Furthermore, the tested subjects performed concentric flexion of the ankle joint in a sitting position. The individual provisional MAM values were computed based on three maximum contraction tests divided by the 30-second rest breaks.

The experimental group members were stimulated in the plantar flexion process by magnetic pulses generated by Magstrim 200 Magnetic Stimulator equipped with 50 mm flat coil. The MS pulses with 5 Hz frequency rate were applied to the m. gastrocnemius muscle. The stimulating pulse intensity was rated at 50% of the maximum output capacity of the MS system, and the test time was fixed at 5 seconds. The control group subjects performed the same movements at the same time, but their muscles were free of any electromagnetic effects.

The tests were designed to record MAM data, H-reflex data and m. gastrocnemius (GM) and m. soleus (SOL) muscle (M) response data for every subject from both the experimental and control groups prior to the training (reference data) and after 5, 10 and 15 days of the training sessions; plus the same data were obtained on days 3, 6, 13, 24 and 35 following final date of the training course.

During the voluntary MAM test performance time, the electromyographic (EMG) activity data for the GM/ SOL/ and TA (tibialis anterior) muscles was recorded. The shin-muscle EMG signals were generated by skin-fixed electrodes connected to the electroneuromyograph Neuro-MEP-8 using the regular test procedure.

Results and discussion. The test data indicative of the strength abilities of the volunteers, as far as the reference MAM (Maximum Angular Momentum) values are concerned, were found to be virtually and reliably the same for both the control group and the experimental group, namely 119.3 ± 5.3 Nm and 124 ± 8.8 Nm, respectively (Table 1). These data confirm that both of the groups showed virtually the same starting strength abilities prior to the studies.

As seen from Table 1, the 15-day training sessions resulted in reliable growths of the Maximum Angular Momentum values in the both groups. In more specific terms, the control group’s MAM values increased on average by 9.5% after 5 days; by 28.2% after 10 days; and by 32.5% after 15 days of training as compared to the reference values; whilst in the experimental group these values amounted to 24.9%, 52.2% and 51.9%, respectively (with Р < 0.05 for all the tests). Therefore, we have good grounds to state that the average strength abilities of the experimental group were 15.4%, 24.1% and 19.4% higher than those of the control group (Р < 0.05).

Table 1. Maximum Angular Momentum values for both groups (M ± m, n=18), Nm

*Difference reliability rate is p < 0.05, for the difference between the process data and the reference value, in %

It was after 10 days of the controlled training process that the experimental group members achieved the highest Maximum Angular Momentum values for the whole period of training.

Table 2 hereunder gives the EMG parameters for different shin muscles in the MAM test process for the both groups as of the days 5, 10 and 15 of the training process. Our analysis of these data gives reasons to maintain that the EMG amplitude and frequency values for the antagonistic muscles showed reliable growths after days 5, 10 and 15 of the training exercises. Both the control group and the experimental group showed notable growths of the EMG parameters in the process. It should be emphasized, however, that it was the experimental group in which the GM/ SOL muscle EMG amplitude and frequency values were growing more intensively compared with the values of the control group.

Table 2. Electromyographic (EMG) values for skeletal shin muscles (M ± m, n=18)

*Difference reliability rate is p < 0.05, for the difference between the process data and the reference values, in %

It is important to note that the GM EMG amplitude values of the experimental group after the 5^th, 10^th and 15^th training days were 24.1 %, 37% and 65.8% higher than that of the control group, respectively. The GM EMG frequency rates grew 14.3%, 45.4% and 74.2% faster than that of the control group, respectively. The TA EMG amplitude and frequency values showed no reliable variations in both of the groups for the whole period of fifteen training days (Table 2). It may be also of special interest that the absolute values of the EMG amplitudes and frequencies were higher for the control group. However, the achieved strength values of the control group were lower than that of the experimental group.

In addition, the study detected reliable changes in the H-reflexes of m. gastrocnemius for the experimental group. The amplitudes of the Н-reflexes for the experimental group grew up by as much as 39% after 5 days and by 30.1% after ten days of training. The maximum M response rates showed no statistically valuable changes for both of the groups.

It was on the days three and six after the strength training sessions were stopped that the Maximum Angular Momentum values showed some increase as compared to the day fifteen of the training course. The control group showed the 7.5% growth on the third rest day and the 9% growth on the sixth rest day as compared to the same data as of day fifteen of the training course; whilst the experimental group showed the growths of 1.4% and 8%, respectively.

The increased muscular strength levels were maintained for thirteen days after the training process was stopped. The MAM values turned back to the reference levels by day thirty five following the date the training was stopped both for the control group and the experimental group.

It is widely known today that the voluntary contraction strengths of skeletal muscles may be increased through the actions to recruit high-threshold motor units and increase their pulsing frequencies [2, 4]. Motor units of this type make much larger contributions to the general muscle tension than the low-threshold units. The high-threshold motor units are involved only when great muscle efforts are taken. It is further known that electric stimulation can mobilize the high-threshold motor units even when the impulses are low enough that means that these units act like the low-threshold ones in this case [5]. Therefore, there are good grounds to expect that magnetic stimulation of a muscle when it contracts will help activate its high-threshold motor units that normally stay non-involved in the active contraction process. Their activity will contribute to the muscle strength and the acquired increased strength will be retained by the muscle for some period of time.

Conclusion. Magnetic stimulation of antagonistic muscles in the deliberate contraction process is offered as a new method to help enhance the muscular strength. Operational specifications of the magnetic stimulator may be varied so as to painlessly stimulate the affected skeletal muscles and thereby activate their high-threshold motor units that normally stay non-involved in the process. The proposed new method may be applied to contribute to the training processes in those sports that require high strength abilities being mobilized for success; it may be also applied to support rehabilitation processes when motor functions need to be restored after spinal cord and/or skeletal muscles are affected by some injuries or diseases.

References

1. Gorodnichev, R.M. Primenenie magnitnoy stimulyatsii v sport: ucheb. posobie (Magnetic stimulation in sport: study guide) / R.M. Gorodnichev, D.A. Petrov, R.N. Fomin, D.K. Fomina. Velikie Luki. – 2007. – 95 P.
2. Gurfinkel', V.S. Skeletnaya myshtsa: struktura i funktsiya (Skeletal muscle: structure and function) / V.S. Gurfinkel', Yu.S. Levik. – Moscow: Nauka, 1985. – 143 P.
3. Zatsiorskiy, V.M. Fizicheskie kachestva sportsmena: osnovy teorii i metodiki vospitaniya (Athlete's physical qualities: theoretical and methodological foundations of training) / V.M. Zatsiorskiy. – 3rd ed. – Moscow: Sovetskiy sport, 2009. – 200 P.
4. Komantsev, V.N. Metodicheskie osnovy klinicheskoy elektroneyromiografii (Methodological foundations of clinical electromyography) / V.N. Komantsev, V.A. Zabolotnykh. – St. Petersburg, 2001. – 350 P.
5. Kotz, Ya.M. Trenirovka myshechnoy sily metodom elektrostimulyatsii. Soobshchenie I (Muscle strength training using electrical stimulation. Message 1) / Ya.M. Kotz // Teoriya i praktika fizicheskoy kul'tury. – 1971. – № 3. – P. 64–67.
6. Netreba, A.I. Otsenka effektivnosti trenirovki, napravlennoy na uvelichenie maksimal'noy proizvol'noy sily bez razvitiya gipertrofii myshts (Evaluation of effectiveness of training, aimed at increasing maximum voluntary strength without developing muscle hypertrophy) / A.I. Netreba, Ya.R. Bravy, V.A. Makarov, D.V. Ustyuzhanin, O.L. Vinogradova // Fiziologiya cheloveka. – 2011. – V. 37. – № 6. – P. 89–97.

Corresponding author: gorodnichev@vlgafc.ru