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Physiological tremor is suppressed and force steadiness is enhanced with increased availability of serotonin regardless of muscle fatigue
Journal article   Peer reviewed

Physiological tremor is suppressed and force steadiness is enhanced with increased availability of serotonin regardless of muscle fatigue

T. T. Henderson, J. R. Thorstensen, S. Morrison, M. G. Tucker and J. J. Kavanagh
Journal of neurophysiology, Vol.127(1), pp.27-37
01/2022
DOI: https://doi.org/10.1152/jn.00403.2021
PMID: 34851768

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Abstract

Central fatigue Muscle activation Neuromodulation Paroxetine Tremor
Although there is evidence that 5-HT acts as an excitatory neuromodulator to enhance maximal force generation, it is largelyunknown how 5-HT activity influences the ability to sustain a constant force during steady-state contractions. A total of 22healthy individuals participated in the study, where elbow flexion force was assessed during brief isometric contractions at 10%maximal voluntary contraction (MVC), 60% MVC, MVC, and during a sustained MVC. The selective serotonin reuptake inhibitor,paroxetine, suppressed physiological tremor and increased force steadiness when performing the isometric contractions. In par-ticular, a main effect of drug was detected for peak power of force within the 8–12 Hz range (P = 0.004) and the coefficient ofvariation (CV) of force (P < 0.001). A second experiment was performed where intermittent isometric elbow flexions (20% MVCsustained for 2 min) were repeatedly performed so that serotonergic effects on physiological tremor and force steadiness couldbe assessed during the development of fatigue. Main effects of drug were once again detected for peak power of force in the8–12 Hz range (P = 0.002) and CV of force (P = 0.003), where paroxetine suppressed physiological tremor and increased forcesteadiness when the elbow flexors were fatigued. The findings of this study suggest that enhanced availability of 5-HT inhumans has a profound influence of maintaining constant force during steady-state contractions. The action of 5-HT appears tosuppress fluctuations in force regardless of the fatigue state of the muscle. New & Noteworthy: Converging lines of research indicate that enhanced serotonin availability increases maximal force gen-eration. However, it is largely unknown how serotonin influences the ability to sustain a constant force. We performed twoexperiments to assess physiological tremor and force steadiness in unfatigued and fatigued muscle when serotonin availabilitywas enhanced in the central nervous system. Enhanced availability of serotonin reduced physiological tremor amplitude andimproved steadiness regardless of muscle fatigue

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