Assessment of the reliability of central and peripheral fatigue after sustained maximal voluntary contraction of the quadriceps muscle.

The aim of the present study was to further confirm the validity of measurements for characterizing neuromuscular alterations by establishing their reliability both before and after fatigue. Thirteen men (28 +/- 5 years) volunteered to participate in two separate identical sessions requiring the performance of a sustained maximal voluntary contraction (MVC) with the quadriceps muscle for 2 min. MVC and transcutaneous electrical stimulations were used before and immediately after the fatiguing contraction to investigate the reliability of MVC torque, central activation, and peripheral variables (M-wave properties, peak twitch, peak doublet) within and between sessions. Based on previous and present results, we advise the use of (1) voluntary activation level with potentiated doublet as a reference to describe central fatigue, (2) electromyographic activity of vastus lateralis muscle as a surrogate for quadriceps for both voluntary and evoked contraction, and (3) potentiated peak doublet amplitude to investigate contractile fatigue. These findings can be useful in the choice of the parameters describing central and peripheral fatigue of the quadriceps muscle in future studies.