Reliability of M-wave amplitude measurement from paired stimulations across different muscle groups before and after submaximal contraction to failure

PURPOSE: In exercising humans, contractility is usually investigated using paired/tetanic transcutaneous electrically-evoked contraction, while single stimulations are used to quantify sarcolemmal excitability through M-wave amplitude. Here, we aim at investigating the reliability and validity of M-wave peak-to-peak amplitude and first phase amplitude obtained from paired stimulation compared to those obtained from single stimulation (gold standard) before and after a sustained submaximal isometric contraction of the knee extensor, plantar flexor, elbow flexor and thumb adductor muscles. METHODS: M waves, in response to single and paired (10 Hz and 100 Hz) stimuli, were collected in thirteen young, healthy men (25 ± 2 year) before and immediately after an isometric contraction sustained at 50% maximal voluntary force until failure. Lin's concordance correlation coefficient was used to measure the reliability of M-wave parameters obtained from single and paired stimuli. RESULTS: Variability in the changes in M-wave amplitude was observed following exercise depending on the muscle considered and underscores the need to analyze both phases of the M wave. This study also demonstrates that the M-wave elicited by the first stimulation in a 10-Hz (as opposed to 100-Hz) paired pulse provides an accurate and reliable estimate of sarcolemmal excitability under both resting and fatigued conditions across all investigated muscles. CONCLUSION: When using 10-Hz paired stimuli to assess peripheral adjustments, single stimulations may be unnecessary for evaluating sarcolemmal excitability.