Mechanomyography and tissue oxygen saturation during electrically‐evoked wrist extensor fatigue in people with tetraplegia

Abstract

Background Repetitive electrically‐evoked muscle contractions lead to the early onset of muscle fatigue. This study assessed the relationship between muscle mechanomyography (%RMS‐MMG) and tissue oxygen saturation (%TSI) in extensor carpi radialis (ECR) during electrically‐evoked fatiguing exercise in individuals with tetraplegia. Methods Skin‐surface mechanomyography (MMG) and near‐infrared spectroscopy (NIRS) sensors were placed on the ECR of seven individuals with tetraplegia. All participants performed repetitive electrically‐evoked wrist extension to fatigue while their muscle MMG and NIRS responses were monitored against their power output (PO). Findings: One out of seven participants showed no changes in %TSI throughout the repeated wrist FES‐evoked contraction. The other six participants' %TSI was positively correlated with %PO before fatigue onset. At 50%POpeak, %TSI was negatively correlated (0.489) significantly with declining %PO as the ability of the muscle to take up oxygen became limited. The %RMS‐MMG behaved analogously during pre and post‐fatigue against declining %PO, whereby both displayed positive correlations of 0.443 and 0.214, respectively, (%RMS‐MMG decreased) throughout the exercise session. Regression analysis revealed that %TSI was proportional to pre‐fatigue and inversely proportional to %RMS‐MMG during post‐fatigue. Conclusion The significant changes in muscle mechanomyography and tissue oxygenation correlations after 50%POpeak implied that the muscle contraction mechanical‐and‐physiological behavior association had been altered following FES‐evoked fatigue.