LAUSR

BACKGROUND Repetitive electrically-evoked muscle contractions lead to 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 6 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 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 behaviour association had been altered following FES-evoked fatigue.