Cortical voluntary activation testing methodology impacts central fatigue

Purpose Currently, cortical voluntary activation (VA TMS ) is assessed by superimposing transcranial magnetic stimulation (TMS) on a maximal voluntary contraction (MVC), 75% MVC and 50% MVC, each contraction being interspersed with 5–10 s of relaxation. Here, we assessed whether this traditional approach (TRADI) underestimates central fatigue due to this short recovery compared to a continuous method (CONTI). Methods VA TMS , motor-evoked potential (MEP), and cortical silent period (CSP) of the vastus lateralis were determined in 12 young healthy adults before and after a 2-min sustained MVC of knee extensors in two randomly assigned sessions. In TRADI, evaluations comprised a 7-s rest between the three contractions (100, 75, and 50% MVC) and evaluation following the 2-min sustained MVC started after a minimal rest (3–4 s). In CONTI, evaluations were performed with no rest allowed between the three levels of contraction, and evaluation after the 2-min sustained MVC commenced without any rest. Results MVC was equally depressed at the end of the 2 min in both conditions. Post 2-min sustained MVC, VA TMS change was greater in CONTI than in TRADI (−29 (15)% [−42, −17] vs. −9 (4)% [−13, −5], respectively, P