Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups

Abstract

Neyroud D, Rüttimann J, Mannion AF, Millet GY, Maffiuletti NA, Kayser B, Place N. Comparison of neuromuscular adjustments associated with sustained isometric contractions of four different muscle groups. J Appl Physiol 114: 1426 -1434, 2013. First published March 7, 2013 doi:10.1152/japplphysiol.01539.2012.-The extent and characteristics of muscle fatigue of different muscle groups when subjected to a similar fatiguing task may differ. Thirteen healthy young men performed sustained contractions at 50% maximal voluntary contraction (MVC) force until task failure, with four different muscle groups, over two sessions. Per session, one upper limb and one lower limb muscle group were tested (knee extensors and thumb adductor, or plantar and elbow flexors). Changes in voluntary activation level and contractile properties were derived from doublet responses evoked during and after MVCs before and after exercise. Time to task failure differed (P Ͻ 0.05) between muscle groups (220 Ϯ 64 s for plantar flexors, 114 Ϯ 27 s for thumb adductor, 77 Ϯ 25 s for knee extensors, and 72 Ϯ 14 s for elbow flexors). MVC force loss immediately after voluntary task failure was similar (Ϫ30 Ϯ 11% for plantar flexors, Ϫ37 Ϯ 13% for thumb adductor, Ϫ34 Ϯ 15% for knee extensors, and Ϫ40 Ϯ 12% for elbow flexors, P Ͼ 0.05). Voluntary activation was decreased for plantar flexors only (from 95 Ϯ 5% to 82 Ϯ 9%, P Ͻ 0.05). Potentiated evoked doublet amplitude was more depressed for upper limb muscles (Ϫ59.3 Ϯ 14.7% for elbow flexors and Ϫ60.1 Ϯ 24.1% for thumb adductor, P Ͻ 0.05) than for knee extensors (Ϫ28 Ϯ 15%, P Ͻ 0.05); no reduction was found in plantar flexors (Ϫ7 Ϯ 12%, P Ͼ 0.05). In conclusion, despite different times to task failure when sustaining an isometric contraction at 50% MVC force for as long as possible, diverse muscle groups present similar loss of MVC force after task failure. Thus the extent of muscle fatigue is not affected by time to task failure, whereas this latter determines the etiology of fatigue. endurance time; fatigue; maximal voluntary contraction; contractile properties; surface electromyography TIME TO TASK FAILURE of a sustained submaximal isometric contraction (i.e., endurance time, ET) depends on physiological factors such as relative force level (30, 35), muscle fiber type composition (16,51,77), muscular activation strategy (6,19,38), muscle size (36), and length (54, 58) but also depends on psychological factors such as motivation, mood, and expectation (24). Whereas the task dependency of ET is well documented (23,25,26), little is known about muscle fatigue characteristics induced by a given task sustained until failure in different muscle groups, in the same individuals. Frey-Law and Avin (28) suggested that no single fatigue model applies to all muscles. Their meta-analysis showed large differences in ET depending on the muscle group considered, especially at low contraction intensities. However, it is unknown whether the extent of maximal voluntary contraction (MVC) force loss immediately after task ...

Assessment of Neuromuscular Function Using Percutaneous Electrical Nerve Stimulation

“…tibialis anterior 43,44 , quadriceps muscles 45,46 ) and upper limb muscles (e.g. biceps brachii 32 , flexor carpi radialis 47 , finger muscles 48 ). However, nerve stimulation presents potential methodological limitations for some muscles.…”

“…For instance, obtaining a H-reflex from biceps brachii muscle can be difficult to obtain at rest 49 . Furthermore, stimulating the musculocutaneous nerve over the brachial plexus leads to contraction of both agonist and antagonist muscles 32 , inducing the erroneous evaluation of the voluntary activation level. Recording nearby muscle activity allows the experimenter to ensure that only the target muscle is activated, or at least to limit activation of these nearby muscles.…”

“…Recording nearby muscle activity allows the experimenter to ensure that only the target muscle is activated, or at least to limit activation of these nearby muscles. To overcome these limitations, some authors have suggested that stimulation over the muscle belly with larger electrodes can be a reliable method to evoke M-wave and twitches 32,50 . However, the spatial organization of axonal terminal branches within the muscle can differ between muscles.…”

“…Thus, sampling frequency must be high enough to preserve signal shape during EMG recording. Amplify and filter EMG signals (gain = 500-100) using a bandwidth frequency between 10 Hz and 1 kHz 8,21,32 . 8.…”

Electromyographic, cerebral, and muscle hemodynamic responses during intermittent, isometric contractions of the biceps brachii at three submaximal intensities

“…The extent of central and peripheral fatigue and their interplay depend on the type of muscular activity and the particular circumstances. Surface electromyography (EMG), combined with transcutaneous electrical stimulation, has been extensively used to evaluate the relative contributions of central and peripheral factors limiting muscle force development (Burnley et al, 1985; Gauche et al, 2009; Millet et al, 2011; Neyroud et al, 2013). But despite decades of research, the understanding of the underlying mechanisms remains incomplete.…”