Postgraduate student K.V. Sergeeva¹
Dr. Biol., Professor R.V. Tambovtseva^1
1Russian State University of Physical Education, Sport, Youth and Tourism (SCOLIPE), Moscow

Objective of the study was to conduct a comparative analysis of the electrical activity of the quadriceps muscle of 9 trained males performing sitting knee extension in the eccentric and concentric contraction modes with increasing intensity in order to indirectly assess possible differences in the recruitment of motor units.
Methods and structure of the study. During the experiment, we measured the bioelectric activity of three heads of the quadriceps muscle: m. rectus femoris, m. vastus lateralis and m. vastus medialis in 9 representatives of speed-strength sports performing knee extension in the simulator.
Results of the study and conclusions. The analysis of the surface electromyogram showed that the average frequency (MPF) within the range of the studied intensities was higher in the eccentric contraction mode, which indicates a higher level of activity of rapidly contracting motor units as opposed to the concentric mode.
Based on the results obtained and theoretical substantiation, we can conclude that the higher average EMG frequency in the eccentric contraction mode is consistent with the theory that rapidly contracting motor units are recruited selectively during the eccentric contractions. Thus, the high level of reflex excitability of high-threshold afferents, improvement of their contractility, ability to achieve a higher torque (i.e., mechanical load) when performing supramaximal loads in the eccentric phase of movement can give a competitive advantage for the development of strength indicators and hypertrophy of muscle tissues which is most relevant in speed-strength sports.
The data obtained can be used when selecting the strength training methods.

Keywords: electromyography, EMG, fast muscle fibers, spectral analysis, medium frequency.

References

1. Filligoi, G.C. Detection of hidden rhythms in surface EMG signals with a nonlinear time-series tool / G.C. Filligoi, F. Felici // Medical Engineering & Physics. – 1999. – Vol.21, №6-7. – Р. 439–448.
2. Maximal eccentric and concentric strength discrepancies between young men and women for dynamic resistance exercise / D.B. Hollander [et al.] // J. Strength Cond. Res. – 2007. – Vol. 21, №1. – Р.  34–40.
3. Pasquet, B. Specific modulation of motor unit discharge for a similar change in fascicle length during shortening and lengthening contractions in humans / B. Pasquet, A. Carpentier, J. Duchateau // Journal of Physiology. – 2006. – Vol.577, №2. – Р. 753–765.
4. Relationships between surface EMG variables and motor unit firing rates / А. Christie // Eur. J. Appl. Physiol. – 2009. – Vol.107, №2. – P.  177–185.
5. Residual force enhancement following eccentric contractions: a new mechanism involving titin / W.G. Herzog [et al.] // Physiology. – 2016. – Vol.31, №4. – Р. 300–312.