Reliability of SEMG spike parameters during concentric contractions.

This study examined the reliability of four surface electromyographic (SEMG) spike parameters during concentric (isotonic) contractions: mean spike amplitude, mean spike frequency, mean spike slope, and the mean number of peaks per spike. Eighteen subjects performed rapid elbow flexion on a horizontal angular displacement device that was used to measure joint torque. The SEMG activity of the biceps brachii was monitored with Beckman Ag/AgCl electrodes. The testing schedule consisted of four hundred trials distributed equally over four sessions. The stability of the means across sessions and the consistency of scores within subjects was determined for the first five (1-5) and last five (96-100) trials of each session to examine the possible influence of a "warm up" effect. All measures exhibited a significant (p < 0.01) increase across test days. However, the intraclass correlation coefficients for the first five (1-5) trials ranged from 0.76 to 0.83, which was quite good. The stability and consistency for most of the criterion measures increased for the last five (96-100) trials of each session. This resulted in a higher range of coefficients from 0.85 to 0.93. Subjects became more homogeneous with respect to the mean number of peaks per spike and the R decreased to 0.65. It was concluded that the four SEMG spike parameters could be reliably measured to assess changes in muscle activity patterns. The adaptations in SEMG spike activity suggest that repetitive dynamic contractions enhanced the ability to recruit more fast-twitch motor units across test days.