ORCID Profile
0000-0002-8441-9292
Current Organisation
University of Southampton
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Publisher: Elsevier BV
Date: 08-2021
Publisher: Wiley
Date: 20-02-2023
DOI: 10.1113/EP090644
Abstract: What is the central question of this study? Hyperthermia reduces the human capacity to produce muscular force, which is associated with decreased neural drive: does mitigating a reduction in neural drive by altering localised thermal sensation help to preserve voluntary force output? What is the main finding and its importance? Altering thermal sensation by cooling and heating the head independent of core temperature did not change neural drive or benefit voluntary force production. Head cooling did slow the rate of rise in core temperature during heating, which may have practical applications in passive settings. This study investigated altered local head and neck thermal sensation on maximal and rapid torque production during voluntary contractions. Nine participants completed four visits in two environmental conditions: at rectal temperatures ∼39.5°C in hot (HOT ∼50°C, ∼39% relative humidity) and ∼37°C in thermoneutral (NEU ∼22°C, ∼46% relative humidity) conditions. Local thermal sensation was manipulated by heating in thermoneutral conditions and cooling in hot conditions. Evoked twitches and octets were delivered at rest. Maximum voluntary torque (MVT), normalised surface electromyography (EMG) and voluntary activation (VA) were assessed during brief maximal isometric voluntary contractions of the knee extensors. Rate of torque development (RTD) and EMG were measured during rapid voluntary contractions. MVT ( P = 0.463) and RTD ( P = 0.061) were similar between environmental conditions despite reduced VA (−6% P = 0.047) and EMG at MVT (−31% P = 0.019). EMG in the rapid voluntary contractions was also lower in HOT versus NEU during the initial 100 ms (−24% P = 0.035) and 150 ms (−26% P = 0.035). Evoked twitch (+70% P 0.001) and octet (+27% P 0.001) RTD during the initial 50 ms were greater in the HOT compared to NEU conditions, in addition to a faster relaxation rate of the muscle (−33% P 0.001). In conclusion, hyperthermia reduced neural drive without affecting voluntary torque, likely due to the compensatory effects of improved intrinsic contractile function and faster contraction and relaxation rates of the knee extensors. Changes in local thermal perception of the head and neck whilst hyperthermic or normothermic did not affect voluntary torque.
Publisher: Canadian Science Publishing
Date: 11-2020
Abstract: The effect of localised head and neck per-cooling on central and peripheral fatigue during high thermal strain was investigated. Fourteen participants cycled for 60 min at 50% peak oxygen uptake on 3 occasions: thermoneutral control (CON 18 °C), hot (HOT 35 °C), and HOT with head and neck cooling (HOT cooling ). Maximal voluntary force (MVF) and central activation ratio (CAR) of the knee extensors were measured every 30 s during a sustained maximal voluntary contraction (MVC). Triplet peak force was measured following cycling, before and after the MVC. Rectal temperatures were higher in HOT cooling (39.2 ± 0.6 °C) and HOT (39.3 ± 0.5 °C) than CON (38.1 ± 0.3 °C P 0.05). Head and neck thermal sensation was similar in HOT cooling (4.2 ± 1.4) and CON (4.4 ± 0.9 P 0.05) but lower than HOT (5.9 ± 1.5 P 0.05). MVF and CAR were lower in HOT than CON throughout the MVC (P 0.05). MVF and CAR were also lower in HOT cooling than CON at 5, 60, and 120 s, but similar at 30 and 90 s into the MVC (P 0.05). Furthermore, they were greater in HOT cooling than HOT at 30 s, whilst triplet peak force was preserved in HOT after MVC. These results provide evidence that central fatigue following exercise in the heat is partially attenuated with head and neck cooling, which may be at the expense of greater peripheral fatigue. Novelty Central fatigue was greatest during hyperthermia. Head and neck cooling partially attenuated the greater central fatigue in the heat. Per-cooling led to more voluntary force production and more peripheral fatigue.
Publisher: Springer Science and Business Media LLC
Date: 13-01-2023
DOI: 10.1007/S00421-022-05127-7
Abstract: This study investigated the effects of acute hyperthermia and heat acclimation (HA) on maximal and rapid voluntary torque production, and their neuromuscular determinants. 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. 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. 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.
Publisher: Springer Science and Business Media LLC
Date: 14-09-2015
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Ralph Gordon.