Effects of very short pauses on electromyographic variables measured during fatiguing isometric contractions

15 healthy men (26.6 ± 4.6 years old, weight of 70.7 ± 8.6 kg, and height of 1.750 ± 0.072 m) performed three 30-seconds isometric contractions at 60% MVC, with two 10-seconds resting intervals between them. The goal was to study the effect of the resting intervals on the variables that are most commonly used to analyze surface electromyographic (S-EMG) signals (conduction velocity [CV], root mean square [RMS], average rectified value [ARV], mean power frequency [MNF], and median power frequency [MDF]). For the first 30-second contraction, the S-EMG variables behaved exactly like described in the literature. However, after the first and second pauses, the CV variable ceased to behave like in the literature. In the first contraction, the conduction velocity had a statistically significant decreasing trend, in the second contraction, it had a statistically non-significant positive trend, and, in the third contraction, a statistically significant positive trend. These results suggest that short pauses between isometric constant-force contractions lead to changes in the recruiting strategies of the muscles involved in the contraction. The causes of these changes are not yet clear, and further work is needed in order to understand this effect.