Neuromotor control associates with muscle weakness observed with McArdle sign of multiple sclerosis

Abstract

Objective Multiple Sclerosis (MS) is often accompanied by myelopathy, which may be associated with progressive worsening. A specific finding of MS‐associated myelopathy is McArdle sign, wherein neck flexion is associated with prominent increased limb weakness relative to that detected with neck extension. In this study, we characterized neuromotor control properties of finger extensors in association with the McArdle sign. Methods A custom‐built device was utilized to monitor torque production of the wrist extensors with simultaneous recording of surface electromyography of the extensor digitorum. The electromyography was decomposed and analyzed via both linear and nominal regressions. Results Linear regressions demonstrated a strong difference between groups for MS from healthy controls and other myelopathies for motor unit action potential amplitude and average firing rate (p < 0.001). Further, linear regression demonstrated good correlations of neuromotor variables to mechanical torque output (0.24 ≤ R2 ≤ 0.76). Nominal regression distinguished MS from healthy controls with an AUC of 0.87, specificity of 0.97, and sensitivity of 0.64. Nominal regression of MS from other myelopathies demonstrated an AUC of 0.88, specificity of 0.85, and sensitivity of 0.79. Interpretation These data demonstrate the neuromotor control factors that largely determine muscle force production change with the observation of McArdle sign; these neuromotor control factors can differentiate MS from both healthy controls and other myelopathy conditions.

Differences in psychological readiness for return to sport after anterior cruciate ligament injury is evident in thigh musculature motor unit characteristics

“…AvgFR appears to follow what has been demonstrated about AMI—inhibited quadriceps and facilitated hamstrings 6 60. Changes in MU recruitment threshold have previously been demonstrated with pathology 37. Similarly, a previous study has shown that intervention in strength training could change the MU recruitment threshold 61.…”

“… 6 60 Changes in MU recruitment threshold have previously been demonstrated with pathology. 37 Similarly, a previous study has shown that intervention in strength training could change the MU recruitment threshold. 61 However, it is imperative to consider the entire range of recruitment (regression with least squares mean; figures 1–3 ).…”

“…This study aimed to determine the relationship of a subjective psychological readiness metric to RTS to objective measures of bilateral motor CTRL. Specifically, we measured MU common drive, MU recruitment, MU rate coding, MU action potential (MUAP) peak-to-peak amplitude and delta frequency (ΔF) 37 38. The last two metrics are surrogate measures of MU size39 40 and synaptic activity,41–43 respectively.…”

“…Specifically, we measured MU common drive, MU recruitment, MU rate coding, MU action potential (MUAP) peak-to-peak amplitude and delta frequency (ΔF). 37 38 The last two metrics are surrogate measures of MU size 39 40 and synaptic activity, 41–43 respectively. We hypothesised that ACL-injured athletes with lower ACL-RSI scores would recruit smaller MUs and have increased synaptic neuromodulation (ΔF) values across the recruitment of MUs compared with athletes with higher ACL-RSI scores and CTRLs.…”

Arthrogenic muscle inhibition after anterior cruciate ligament injury: Injured and uninjured limb recovery over time

“…In addition to internal validation by the development group, the decomposition algorithm has been externally validated against spike triggered averaging technique and further details of the methodology can be found elsewhere ( 33 , 34 ). This technique has been able to determine differences between both healthy and pathological conditions ( 26 , 35 ).…”