Quantification through the surface EMG of muscle fatigue and recovery during successive isometric contractions.

The surface electromyogram (EMG) was analyzed from above the handgrip muscles of the forearm in six male volunteer graduate and medical students during brief and fatiguing isometric contractions in order to assess the influence of successive isometric contractions on the amplitude and frequency components of the surface EMG. Isometric contractions were sustained at three tensions; 25, 40 and 70% of each individual's maximum voluntary strength (MVC). Two successive isometric contractions were conducted in each series of experiments. The interval between these contractions was set at 2, 4, 6, 8, 10, or 12 min. In the first series of experiments, the second contraction in the series consisted of a fatiguing isometric contraction conducted at the same tension as the first contraction. In the second series of experiments, the second contraction was an MVC. From the data, a computer program was written to predict the degree of fatigue and recovery following fatiguing isometric contractions. The program was based on an analysis of the frequency components of the EMG and proved to be quite useful for showing fatigue and recovery in this muscle group.