Effect of Hypohydration on Peripheral and Corticospinal Excitability and Voluntary Activation

Journal article


Bowtell, JL, Avenell, G, Hunter, SP and Mileva, KN (2013). Effect of Hypohydration on Peripheral and Corticospinal Excitability and Voluntary Activation. PLoS ONE. 8 (10), p. e77004. https://doi.org/10.1371/journal.pone.0077004
AuthorsBowtell, JL, Avenell, G, Hunter, SP and Mileva, KN
Abstract

We investigated whether altered peripheral and/or corticospinal excitatory output and voluntary activation are implicated in hypohydration-induced reductions in muscle isometric and isokinetic (90°.s-1) strength. Nine male athletes completed two trials (hypohydrated, euhydrated) comprising 90 min cycling at 40°C, with body weight losses replaced in euhydrated trial. Peripheral nerve and transcranial magnetic stimulations were applied during voluntary contractions pre- and 40 min post-exercise to quantify voluntary activation and peripheral (M-wave) and corticospinal (motor evoked potential) evoked responses in m. vastus medialis. Both maximum isometric (-15.3±3.1 vs -5.4±3.5%) and isokinetic eccentric (-24.8±4.6 vs -7.3±7.2%) torque decreased to a greater extent in hypohydrated than euhydrated trials (p<0.05). Half relaxation time of the twitch evoked by peripheral nerve stimulation during maximal contractions increased after exercise in the hypohydrated (21.8±9.3%) but stayed constant in the euhydrated (1.6±10.7%; p = 0.017) condition. M-wave amplitude during maximum voluntary contraction increased after exercise in the heat in hypohydrated (10.7±18.0%) but decreased in euhydrated condition (-17.4±16.9%; p = 0.067). Neither peripheral nor cortical voluntary activation were significantly different between conditions. Motor evoked potential amplitude increased similarly in both conditions (hypohydrated: 25.7±28.5%; euhydrated: 52.9±33.5%) and was accompanied by lengthening of the cortical silent period in euhydrated but not hypohydrated condition (p = 0.019). Different neural strategies seem to be adopted to regulate neural drive in the two conditions, with increases in inhibitory input of either intracortical or corticospinal origin during the euhydrated trial. Such changes were absent in the hypohydrated condition, yet voluntary activation was similar to the euhydrated condition, perhaps due to smaller increases in excitatory drive rather than increased inhibition. Despite this maximal isometric and eccentric strength were impaired in the hypohydrated condition. The increase in peripheral muscle excitability evident in the hypohydrated condition was not sufficient to preserve performance in the face of reduced muscle contractility or impaired excitation-contraction coupling. © 2013 Bowtell et al.

KeywordsMuscle, Skeletal; Motor Cortex; Spinal Cord; Motor Neurons; Humans; Dehydration; Electromyography; Fluid Therapy; Exercise; Electric Stimulation; Evoked Potentials, Motor; Muscle Fatigue; Isometric Contraction; Torque; Adult; Male; Transcranial Magnetic Stimulation; Athletes
Year2013
JournalPLoS ONE
Journal citation8 (10), p. e77004
ISSN1932-6203
Digital Object Identifier (DOI)https://doi.org/10.1371/journal.pone.0077004
Publication dates
Print02 Oct 2013
Publication process dates
Deposited29 Jan 2019
Accepted02 Sep 2013
Publisher's version
License
EditorsPhillips, William
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https://openresearch.lsbu.ac.uk/item/878w8

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