AIMTo explore the factors affect the change of sEMG signal by investigating the relationship between power spectral changes of sEMG signal and H+ in muscle during the short period of recovery after muscular fatigue.

METHODSAfter a fatiguing constriction of the muscle, its pH value would not be featured any apparent changes in a short period of time. However, we were able to observe the movement rule of the sEMG power spectrum within 30 s of its reversion duration. Surface EMGs of biceps brachii muscle were recorded from 8 healthy human volunteers during tasks. Muscle fatigue induced by isometric loading that included 60% of maximal voluntary contraction. Restitution of sEMG by recording 2 s, 4 s, 6 s, 8 s, 10 s, 20 s and 30 s by the same load after the end of the fatigue experiments of 60% MVC.

RESULTSThere was a significant monotonous decline in MPF during isometric fatigue contraction of 60% MVC. MPF was restituted rapidly in the short recovery period after muscular fatigue. It was recovered 26.5% of its whole declining scope only 2 s by the end of muscle movement, and has been reached 87.7% of its total decreasing value till 30 s after the exercise.

CONCLUSIONOur results suggested that the accumulation of H+ in muscle was not the only factor that affected "spectrum shift" during muscle fatigue. The change of CNS drive strategy might be the important mechanisms that attributed to the change of SEMG signal during isometric contractions.