Cortical voluntary activation testing methodology impacts central fatigue

• Published in: European journal of applied physiology Vol. 117; no. 9; pp. 1845 - 1857
• Main Authors: Mira, José, Lapole, Thomas, Souron, Robin, Messonnier, Laurent, Millet, Guillaume Y., Rupp, Thomas
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.09.2017; Springer Nature B.V; Springer Verlag
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Central Nervous System - physiology; Chronic fatigue syndrome; Cortex; Electromyography - methods; Electromyography - standards; Evoked Potentials, Motor; Fatigue; Human Physiology; Humans; Isometric Contraction; Knee; Knee - physiology; Life Sciences; Magnetic fields; Male; Motor evoked potentials; Motor task performance; Muscle Fatigue; Occupational Medicine/Industrial Medicine; Original Article; Random Allocation; Recovery (Medical); Sports Medicine; Transcranial magnetic stimulation; Maximal muscle contraction; Central fatigue; Corticospinal excitability; Transcranial magnetic stimulation; Intracortical inhibition; Recovery
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-017-3678-x

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  < 0.001). Differences were also observed between TRADI and CONTI for MEP and CSP immediately after the fatiguing exercise. All differences between the two methods disappeared after 2 min of recovery. Conclusion After a 2-min sustained MVC, a few seconds of recovery change the amount of measured VA TMS and associated parameters of central fatigue. The continuous method should be preferred to determine deficits in voluntary activation.