Muscle Fatigue during Dynamic Contractions Assessed by New Spectral Indices, 2006, Dimitrov et al.

PURPOSE
The aim of the present study was to test the applicability and sensitivity of new electromyography (EMG) spectral indices in assessing peripheral muscle fatigue during dynamic knee-extension exercise.

METHODS
Seven subjects completed 10 sets of 15 repetitions of right knee–extension exercise lifting 50% of their one-repetition maximum. Torque (T), knee-joint angle, and the interference EMG of rectus femoris muscle were recorded simultaneously. Maximal voluntary isometric contraction (MVC) was tested before and after exercise. Median spectral frequency (Fmed ) and new spectral indices of muscle fatigue (FInsmk ) were calculated for each repetition.

RESULTS
The rate and range of FInsmk - and Fmed -relative changes against the first repetition of the corresponding set increased gradually across successive repetitions within the set, reflecting accumulation of peripheral muscle fatigue. The maximal change of FInsmk observed in the present experiment was approximately eightfold, whereas that of F med was only 32%. Significant between-subject variability in the range of FI nsmk changes (P G 0.0001) was found, so a hierarchical cluster analysis of muscle fatigue indices was conducted. Three distinct subgroups of subjects were identified: high (N = 1, FI nsmk change 9 400%), medium (N = 4, 200% G FInsmk change G 400%), and low (N = 2, FI nsmk change G 200%) muscle fatigability. The changes in muscle performance during (last vs first repetition peak T, P = 0.03) and after (post- vs preexercise MVC, P = 0.012) exercise were significantly different between clusters (one-way ANOVA). The rate of fatigue development was also significantly different between clusters (linear regression analysis of Fmed and FI nsmk changes).

CONCLUSIONS
The new spectral indices are a valid and reliable tool for assessment of muscle fatigability irrespective of EMG signal variability caused by dynamic muscle contractions, and these indices are more sensitive than those traditionally used.

Link (Medicine & Science in Sports & Exercise)

 

@Hutan posted from it:
Further studies are needed to fully establish the validity and reliability of the new spectral indices for testing muscle performance in the clinical, rehabilitation, and sports setting.

So, a tiny study, not validated, least of all for comparing ill vs healthy.

Wallit uses this (and an overlapping set of data from 8 pwme vs 6 hv) to claim that:
"a relative decrease in the slope of the Dimitrov index17,18 (Fig. 4b) occurred in PI-ME/CFS participants but both remained constant in HVs, suggesting that the decline of force was not due to peripheral fatigue or a neuromuscular disorder."

Why is so much science half-baked?