Myoelectric alterations after voluntary induced high- and low-frequency fatigue

The aim of the study was to find whether voluntary induced high- and low-frequency peripheral fatigue exhibit specific alteration in surface EMG signal (SEMG) during evoked and maximum voluntary contractions. Ten male students of physical education performed 60 s long stretch-shortening cycle (SSC) exercise with maximal intensity and 30 s long concentric (CON) exercise with maximal intensity. To verify voluntary induced peripheral fatigue, knee torques during low- (T-20) and high-frequency electrical stimulation (T-100) of relaxed vastus lateralis muscle (VL) were obtained. Contractile properties of the VL were measured with passive twitch and maximal voluntary knee extension test (MVC). Changes in M-waves and SEMG during MVC test were used to evaluate the differences in myoelectrical signals. T100/T20 ratio decreased by 10.9 +/- 8.4 % (p < 0.01) after the SSC exercise and increased by 35.9 +/- 17.5 % (p < 0.001) after the CON exercise. Significant SEMG changes were observed only after the CON exercise where peak to peak time of the M-waves increased by 9.2 +/- 13.3 % (p < 0.06), SEMG amplitude during MVC increased by 32.9 +/- 21.6 % (p < 0.001) and SEMG power spectrum median frequency decreased by 11.0 +/- 10.5 % (p < 0.05). It is concluded that high frequency fatigue wasn't reflected in SEMG, however the SEMG changes after the CON seemed to reflect metabolic changes due to acidosis.