Reliability of corticospinal excitability estimates for the vastus lateralis: Practical considerations for lower limb TMS task selection

• Published in: Brain research Vol. 1761; p. 147395
• Main Authors: Proessl, F., Beckner, M.E., Sinnott, A.M., Eagle, S.R., LaGoy, A.D., Conkright, W.R., Canino, M.C., Sterczala, A.J., Midhe Ramkumar, P.P., Sciavolino, B.M., Connaboy, C., Ferrarelli, F., Germain, A., Nindl, B.C., Flanagan, S.D.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-06-2021
• Subjects: Cortical excitability; Lower extremities; Motor cortex; Motor evoked potentials; Cortical excitability; Lower extremities; Motor evoked potentials; Motor cortex
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/j.brainres.2021.147395

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•Corticospinal excitability estimates were more reliable during knee extensions compared to squats.•Force and muscle activity were similarly reliable between tasks.•Lower stimulation intensities may improve test–retest reliability during squats.
Transcranial magnetic stimulation (TMS) is increasingly used to examine lower extremity corticospinal excitability (CSE) in clinical and sports research. Because CSE is task-specific, there is growing emphasis on the use of ecological tasks. Nevertheless, the comparative reliability of CSE measurements during established (e.g. knee extensions; KE) and more recent ecological (e.g. squats; SQT) lower extremity tasks has received less attention. The aim of this study was to compare the test–retest reliability of CSE, force, and muscle activity (EMG) during isometric SQT and KE. 19 right-footed men (age: 25 ± 5 yrs) with similar fitness and body composition performed SQT (N = 7) or KE (N = 12) on two consecutive days. Force and EMG were recorded during maximum voluntary isometric contractions (MVC). Corticospinal excitability was determined in the dominant leg during light (15% MVC) contractions based on motor evoked potential (MEP) stimulus–response-curves (SRC). Test-retest reliability, absolute agreement, and consistency were determined for force, EMG, and SRC MEP maximum (MEPMAX) and rising phase midpoint (V50). As a secondary analysis, all outcomes were compared between groups with mixed-methods ANCOVAs (Task × Time, covariate: body-fat-percentage). Compared with SQT, KE displayed better test–retest reliability and agreement for MEPMAX whereas V50, force, and EMG were similarly reliable. Force (p = 0.01) and MEPMAX (p = 0.02) were also greater during KE despite a similar V50 (p = 0.11). Differences in test–retest reliability, absolute agreement, and between-group comparisons highlight the need to carefully select lower limb TMS assessment tasks and encourage future efforts to balance ecological validity with statistical sensitivity.