Reliability of neurophysiological measures in the upper- and lower-limb skeletal muscles of people experiencing high and low levels of multiple sclerosis fatigue.

This study investigated the test-retest reliability of a broad range of knee extensor (KE) and wrist flexor (WF) neurophysiological measures in people with multiple sclerosis (PwMS) and matched healthy controls, before and after a submaximal intermittent exercise bout to task failure. PwMS were dichotomised according to whether they were experiencing high (MS-HF) or low (MS-LF) levels of perceived MS fatigue at baseline using the Fatigue Severity Scale (FSS) cut-points (MS-HF ≥5; MS-LF <4). Average (SD) FSS scores were 6.0 (0.6) vs 3.5 (1.1), respectively (p<0.001). With the caveat of wide 95% confidence intervals for some measures, intraclass correlation coefficients (ICC) for KE and WF in MS-HF and MS-LF (pre- and post-fatigue task) were good to excellent (ICC 0.76-0.98) for maximum voluntary force production and peak M-wave amplitude (Mmax); moderate to excellent for voluntary activation (ICC 0.57-0.96) and peak motor evoked potential (MEP)/Mmax (ICC 0.72-0.94) and poor to good for short‑interval intracortical inhibition (SICI; ICC 0.48-0.87) and cortical silent period (SP; ICC 0.23-0.89). Coefficient of variation scores for several measures pre- and post-fatigue task in MS-HF and MS-LF were <20%. This study provides a comprehensive dataset of reliability estimates for KE and WF neurophysiological measures in PwMS and many measures were shown to have good to excellent test-retest reliability, although some had moderate to poor reliability. There was no evidence that high levels of perceived MS fatigue adversely impact reliability estimates for these neurophysiological measures at baseline or after fatiguing muscular work.