Postgraduate S.A. Fedorov
Dr.Biol., Professor R.M. Gorodnichev
Velikie Luki State Academy of Physical Culture and Sport, Velikie Luki

Keywords: electrical stimulation, maximum torque, electromyography, M-response, muscle response induced by transcutaneous electrical stimulation of spinal cord.

Introduction. The method of electrical stimulation of human spinal cord is currently used to determine the physiological mechanisms of adaptation (plasticity) to muscle work of various kinds (O.V. Lanskaya et al., 2015), to initiate activity of the step pattern generator (Y. Gerasimenko et al., 2015) as well as for a purposeful change of speed-strength capacities of athletes (E.A. Mikhaylova et al, 2015). Two-phase stimuli of rectangular shape with a carrier frequency of 10 kHz were used when studying the impact of electrical stimulation of the spinal cord on the motor abilities. Such stimulation parameters do not cause much pain. In this connection it was interesting to study the characteristics of human motor system changes under spinal cord stimulation by unipolar stimuli of rectangular shape that are widely used in electrophysiological research. 

Methods and structure of research. Six male subjects aged 19 to 23 took part in the experiment. Electrical stimulation by monopolar rectangular stimuli was applied to all the subjects while lying on a coach during 20 minutes. The stimulating active electrode was placed on the middle line of the spine at the level of thoracic vertebrae T11-T12 between acanthae, the indifferent electrodes – bilateraly over the iliac crests. The intensity of the stimulus gradually increased from 30 to 40 mA, its duration was 0.5 ms, the frequency of the stimuli sequence – 10 Hz. The parameters recorded before and after the application of electrical stimulation were as follows: maximum torque (MT) with simultaneous recording of the electrical activity of the muscles (EMG), muscle response induced by transcutaneous electrical stimulation of spinal cord (IMR) and M-response of m. gastrocnemius and m. tibialis anterrior. MT (with plantar foot flexion) was recorded on Biodex Multi-Joint System. The result in each MT measuring test was assessed by the best of three trials. Resting time between the trials was 30 seconds. When recording muscle response induced by electrical stimulation of spinal cord, localization of the electrodes, shape and duration of the stimuli were similar to those used during the 20-minute electrical stimulation of the spinal cord. Total EMG, IMR and M-response were registered by lead electrodes from m. gastrocnemius and m. tibialis anterior by the standard technique using the 8-channel device Neuro-MEP-8 (Neurosoft) [1, 2]. A sample record of muscle response induced by the electrical stimulation of the spinal cord is shown in Figure 1.   

Figure 1. Muscle response of m. tibialis anterior and m. gastrocnemius induced by spinal cord stimulation.

Statistical processing of the findings was done using Microsoft Office Excel 2010 and Statistica 6.0 softwares.

Research results and discussion. Results of the analysis of the recorded MT values showed that a significant increase of this parameter took place immediately after the 20-minute transcutaneous electrical stimulation of the spinal cord (Table 1).

Table 1. MT and EMG changes of m. gastrocnemius under electrical stimulation of spinal cord.

Note: *- p < 0.05 – significance of differences between the respective indicators and their baseline values. 

So, during the first minute after the stimulation termination the MT value reached its maximum and amounted to 132.3 Nwm, which exceeded the baseline value by 6.3%. During the last minutes of recording a decrease of MT almost to the baseline level could be observed, indicating a gradual recovery of the studied parameter.

The EMG amplitude of m. gastrocnemius, recorded during MT performance, exceeded the background value through all 30 minutes after the electrical stimulation session (Table 1). The maximum increase of the mean group amplitude of EMG was observed during the fifth minute, the amplitude exceeded the baseline value by 25.4%. A gradual decrease of the amplitude of integrative EMG was observed 10 minutes after the termination of the stimulation session. It should be noted that total EMG recorded during the MT performance reflected a supraspinal motor command.    

The amplitude of M-response of m. gastrocnemius reached its maximum during the fifth minute of the recovery, the baseline value increased by 14.4% (Table 1).

The amplitude of the muscle response induced by the session of electrical stimulation of the spinal cord increased significantly during the fifth and tenth minutes of the termination of the stimulation session, the background level was exceeded by 13% (Table 1).

The studied indicators did not undergo any statistically significant changes and remained almost at the background level in m. tibialis anterior. Comparative analysis of the quantitative changes of total EMG, IMR and M-response under the stimulation of the spinal cord gives reason to believe that the increase of MT immediately after the end of the stimulation is caused mainly by modification of the motor command on its way from the cerebral cortex to m. gastrocnemius, the activity of which ensures the performance of the studied motor action – plantar foot flexion.  

Сonclusion. Long-term transcutaneous electrical spinal cord stimulation allows to purposefully change the state of motor system and strength capacity in man.  

References

1. Gorodnichev R.M. Magnitnaya stimulyatsiya myshts kak novy metod povysheniya ikh silovykh vozmozhnostey (Magnetic stimulation of muscles as new method to increase their strength abilities) / R.M. Gorodnichev et al. // Teoriya i praktika fiz. kultury. – 2015. -№6. – P. 8-10.
2. Lanskaya O.V. Plastichnost' sheynykh i poyasnichno-kresttsovykh spinal'nykh neyronal'nykh setey dvigatel'nogo kontrolya pri zanyatiyakh sportom (Plasticity of cervical and lumbosacral spinal neural networks of motor control in sport) / O.V. Lanskaya et al. // Teoriya i praktika fiz. kultury. – 2015. - № 6. – P. 14-16.
3. Mikhaylova E.A. Povyshenie effektivnosti makhovykh dvizheniy pri bege posredstvom chrezkozhnoy elektricheskoy stimulyatsii spinnogo mozga (Effectivization of swing movements when running through transcutaneous electrical stimulation of spinal cord) / E.A. Mikhaylova et al. // Teoriya i praktika fiz. kultury. – 2015. - № 6. – P. 29-31.
4. Gerasimenko Y.P. Initiation and modulation of locomotor circuitry output with multisite transcutaneous electrical stimulation of the spinal cord in noninjured humans / Y.P. Gerasimenko et al// J Neurophysiol. – 2015. – Р. 834-842.