Differences in myoelectric manifestations of fatigue during isometric muscle actions

Muscle fatigue has been studied for a long time with the use of a wide variety of exercise models, protocols and assessment methods, among which surface electromyography (sEMG) is most commonly used. The main sEMG parameters (amplitude and frequency) are prevalently used to evaluate the level of muscle fatigue in static and dynamic contractions.

The purpose of this study is to determine and compare 2 separate indices: IF₁ basis of the sEMG signal amplitude analysis and IF₂ basis of the sEMG median frequency analysis, related to muscles fatigue during an isometric contraction.

The study was performed on 60 professional runners divided into 2 equal groups. The first group comprised sprinters, competing in short distance track and field events (100 and 200 meters). The second group consisted of middle-distance runners, competing in middle-distance track and field events (800 and 1,500 meters). The electrical activity of the VMO muscles of the right and left lower limbs was recorded simultaneously during isometric activity in a squatting position. The sEMG data was used to determine and compare IF₁ and IF₂ indices.

During isometric measurement, sprinters presented a much more significant increase in the mean amplitude of sEMG signal in comparison to middle-distance runners (mean IF₁ difference: 0.228; p=0.007). Analysis of the median frequency did not show significant differences between the 2 groups (mean IF₂ difference: 0.037; p=0.12).

Change in sEMG amplitude during isometric exercise may be related to muscles fatigue. The use of fatigue indices, based on sEMG amplitude, as an objective indicator of the efficacy of an endurance training programme for sportsmen requires further research.