Electrically evoked wrist extensor muscle fatigue throughout repetitive motion as measured by mechanomyography and near-infrared spectroscopy

Abstract

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.

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

“…Regression analyses between %TSI and %RMS‐MMG over repetitive ECR contractions revealed a minor positive regression coefficient before fatigue’s “cut‐point” definition at 50%PO peak (Table 5). In this study, the small positive relationship showed that the more negative NIRS %TSI was, the more negative was %RMS‐MMG over a declining %PO, emulating the behavior of a group of healthy, non‐disabled participants (Group A) undergoing a similar protocol as reported by Muhammad Saadon and colleagues 24 . The healthy participants categorized under Group A had a fatigue point, i.e., 50%PO peak that occurred beyond 60% total contractions, while the Group B healthy participants in that study reached a much earlier fatigue point before reaching 40% total contraction.…”

“…The participants' relationship between %TSI and %RMS‐MMG was calculated from linear regression analysis fitted to each dependent measure for decreasing %PO. They were represented by Equations (3–5) 24 …”

“…This inverse association suggested that as the ECR became more fatigued, its ability to “unbind” O 2 Hb was more constrained during FES‐evoked muscle contractions even in the presence of adequate blood‐borne oxygen supply 40 since %RMS‐MMG decreased toward fatigue‐failure 23 . Notably, this inverse relationship between muscle oxygenation and muscle myography in SCI performing repeated wrist extensions also suggests the association driven by the method of muscle recruitment (i.e., FES) and not the differences between the ECR muscle qualities of non‐disabled persons versus individuals with tetraplegia 24,25 …”

“…Before starting the experiment, one separate session measured the maximum wrist extension power output by determining the maximum load (force) the participant's muscle could lift using FES. Each participant's muscle was electrically stimulated to lift a maximum load that they could over 1 s until full wrist extension was reached with FES, and the amount of load for successive trials was established by a binary selection method 24 . The binary selection method was where the load was doubled from the initial load of 100 g each time the subject was able to lift with full wrist extension and reduced to half when the subject was unable to lift with full wrist extension.…”

“…This issue has motivated authors to investigate the relationship between muscle performance during FES‐evoked exercise and fatigue using physiological muscle oxygenation markers from near‐infrared spectroscopy (NIRS) and muscle force outputs from mechanomyography (MMG). However, while MMG and NIRS responses during wrist extension to volitional fatigue have been recently reported, 24,25 it has not been established if these are similar in paretic or paralyzed hand muscles in people with tetraplegia.…”