Repetitive electrically-evoked muscle contraction leads to accelerated muscle fatigue. This study assessed electrically-evoked fatiguing muscle with changes to mechanomyography root mean square percentage (%RMS-MMG) and tissue saturation index (%TSI) in extensor carpi radialis. Forty healthy volunteers (n=40) performed repetitive electrical-evoked wrist extension to fatigue and results were analyzed pre- and post-fatigue, i.e. 50% power output (%PO) drop. Responses of %PO, %TSI and %RMS-MMG were correlated while the relationships between %RMS-MMG and %TSI were investigated using linear regression. The %TSI for both groups were negatively correlated with declining %PO as the ability of the muscle to take up oxygen became limited due to fatigued muscle. The %RMS-MMG behaved in two different patterns post-fatigue against declining %PO whereby; (i) group A showed positive correlation (%RMS-MMG decreased) throughout the session and (ii) group B demonstrated negative correlation (%RMS-MMG increased) with declining %PO until the end of the session. Regression analysis showed %TSI was inversely proportional to %RMS-MMG during post-fatigue in group A. Small gradients in both groups suggested that %TSI was not sensitive to the changes in %RMS-MMG and they were mutually exclusive. Most correlation and regression changed significantly post-fatigue indicating that after fatigue, the condition of muscle had changed mechanically and physiologically.
This study compared muscle oxygenation (StO2) during arm cranking (ACE), functional electrical stimulation–evoked leg cycling (FES-LCE), and hybrid (ACE+FES-LCE) exercise in spinal cord injury individuals. Eight subjects with C7-T12 lesions performed exercises at 3 submaximal intensities. StO2 was measured during rest and exercise at 40%, 60%, and 80% of subjects’ oxygen uptake (VO2) peak using near-infrared spectroscopy. StO2 of ACE showed a decrease whereas in ACE+FES-LCE, the arm muscles demonstrated increasing StO2 from rest in all of VO2) peak respectively. StO2 of FES-LCE displayed a decrease at 40% VO2 peak and steady increase for 60% and 80%, whereas ACE+FES-LCE revealed a steady increase from rest at all VO2 peak. ACE+FES-LCE elicited greater StO2 in both limbs which suggested that during this exercise, upper- and lower-limb muscles have higher blood flow and improved oxygenation compared to ACE or FES-LCE performed alone.
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.
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