Heat acclimation reduces the effects of whole-body hyperthermia on knee-extensor relaxation rate, but does not affect voluntary torque production
Heat acclimation reduces the effects of whole-body hyperthermia on knee-extensor relaxation rate, but does not affect voluntary torque production
Purpose: this study investigated the effects of acute hyperthermia and heat acclimation (HA) on maximal and rapid voluntary torque production, and their neuromuscular determinants.
Methods: ten participants completed 10 days of isothermic HA (50 °C, 50% rh) and had their knee-extensor neuromuscular function assessed in normothermic and hyperthermic conditions, pre-, after 5 and after 10 days of HA. Electrically evoked twitch and octet (300 Hz) contractions were delivered at rest. Maximum voluntary torque (MVT), surface electromyography (EMG) normalised to maximal M-wave, and voluntary activation (VA) were assessed during brief maximal isometric voluntary contractions. Rate of torque development (RTD) and normalised EMG were measured during rapid voluntary contractions.
Results: acute hyperthermia reduced neural drive (EMG at MVT and during rapid voluntary contractions; P < 0.05), increased evoked torques (P < 0.05), and shortened contraction and relaxation rates (P < 0.05). HA lowered resting rectal temperature and heart rate after 10 days (P < 0.05), and increased sweating rate after 5 and 10 days (P < 0.05), no differences were observed between 5 and 10 days. The hyperthermia-induced reduction in twitch half-relaxation was attenuated after 5 and 10 days of HA, but there were no other effects on neuromuscular function either in normothermic or hyperthermic conditions.
Conclusion: HA-induced favourable adaptations to the heat after 5 and 10 days of exposure, but there was no measurable benefit on voluntary neuromuscular function in normothermic or hyperthermic conditions. HA did reduce the hyperthermic-induced reduction in twitch half-relaxation time, which may benefit twitch force summation and thus help preserve voluntary torque in hot environmental conditions.
Contractile properties, Heat adaptation, Maximum voluntary contraction, Neural drive, Rapid muscle contraction, Thermal strain
1067-1080
Gordon, Ralph Joseph Frederick Hills
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Moss, Jodie Natasha
c7b4ff42-a30b-4b95-9dec-75ec76e3c739
Castelli, Federico
e542a1a5-43c8-45fc-9727-450ad0f72b52
Reeve, Thomas
c030d60e-f932-4713-9975-3cc39108fc61
Diss, Ceri Elen
c722a9ed-ec07-45ef-8e1e-7d48f478e728
Tyler, Christopher James
9faa5e93-c463-482f-add9-92dea169d167
Tillin, Neale Anthony
da771b23-7207-400b-aa1d-4a07c82aaaab
1 May 2023
Gordon, Ralph Joseph Frederick Hills
00e4cfb1-43a6-4702-acd1-e6f2643f7531
Moss, Jodie Natasha
c7b4ff42-a30b-4b95-9dec-75ec76e3c739
Castelli, Federico
e542a1a5-43c8-45fc-9727-450ad0f72b52
Reeve, Thomas
c030d60e-f932-4713-9975-3cc39108fc61
Diss, Ceri Elen
c722a9ed-ec07-45ef-8e1e-7d48f478e728
Tyler, Christopher James
9faa5e93-c463-482f-add9-92dea169d167
Tillin, Neale Anthony
da771b23-7207-400b-aa1d-4a07c82aaaab
Gordon, Ralph Joseph Frederick Hills, Moss, Jodie Natasha, Castelli, Federico, Reeve, Thomas, Diss, Ceri Elen, Tyler, Christopher James and Tillin, Neale Anthony
(2023)
Heat acclimation reduces the effects of whole-body hyperthermia on knee-extensor relaxation rate, but does not affect voluntary torque production.
European Journal of Applied Physiology, 123 (5), .
(doi:10.1007/s00421-022-05127-7).
Abstract
Purpose: this study investigated the effects of acute hyperthermia and heat acclimation (HA) on maximal and rapid voluntary torque production, and their neuromuscular determinants.
Methods: ten participants completed 10 days of isothermic HA (50 °C, 50% rh) and had their knee-extensor neuromuscular function assessed in normothermic and hyperthermic conditions, pre-, after 5 and after 10 days of HA. Electrically evoked twitch and octet (300 Hz) contractions were delivered at rest. Maximum voluntary torque (MVT), surface electromyography (EMG) normalised to maximal M-wave, and voluntary activation (VA) were assessed during brief maximal isometric voluntary contractions. Rate of torque development (RTD) and normalised EMG were measured during rapid voluntary contractions.
Results: acute hyperthermia reduced neural drive (EMG at MVT and during rapid voluntary contractions; P < 0.05), increased evoked torques (P < 0.05), and shortened contraction and relaxation rates (P < 0.05). HA lowered resting rectal temperature and heart rate after 10 days (P < 0.05), and increased sweating rate after 5 and 10 days (P < 0.05), no differences were observed between 5 and 10 days. The hyperthermia-induced reduction in twitch half-relaxation was attenuated after 5 and 10 days of HA, but there were no other effects on neuromuscular function either in normothermic or hyperthermic conditions.
Conclusion: HA-induced favourable adaptations to the heat after 5 and 10 days of exposure, but there was no measurable benefit on voluntary neuromuscular function in normothermic or hyperthermic conditions. HA did reduce the hyperthermic-induced reduction in twitch half-relaxation time, which may benefit twitch force summation and thus help preserve voluntary torque in hot environmental conditions.
Text
s00421-022-05127-7
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More information
Accepted/In Press date: 23 December 2022
e-pub ahead of print date: 13 January 2023
Published date: 1 May 2023
Additional Information:
Funding Information:
The authors would like to thank all the participants who took part in this research for their time and effort and Professor Lewis Halsey for his assistance with data collection.
Keywords:
Contractile properties, Heat adaptation, Maximum voluntary contraction, Neural drive, Rapid muscle contraction, Thermal strain
Identifiers
Local EPrints ID: 481912
URI: http://eprints.soton.ac.uk/id/eprint/481912
ISSN: 1439-6319
PURE UUID: ff612f0e-428c-4f74-b70a-33c14fa8de2e
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Date deposited: 12 Sep 2023 17:17
Last modified: 18 Mar 2024 04:14
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Contributors
Author:
Ralph Joseph Frederick Hills Gordon
Author:
Jodie Natasha Moss
Author:
Federico Castelli
Author:
Thomas Reeve
Author:
Ceri Elen Diss
Author:
Christopher James Tyler
Author:
Neale Anthony Tillin
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