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This Article Free via Open Access: OA OA Full Text Full Text (PDF) OA All Versions of this Article: 586/19/4751    most recent jphysiol.2008.157420v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Racinais, S. Articles by Grantham, J. PubMed PubMed Citation Articles by Racinais, S. Articles by Grantham, J. Related Collections Skeletal Muscle and Exercise

¹ ASPETAR, Qatar Orthopaedic and Sports Medicine Hospital, Exercise and Sports Science Department, Doha, Qatar

The aims of this study were to determine (i) the effect of passive hyperthermia on motor drive and cognitive function, and (ii) whether head cooling can limit the hyperthermia-induced alterations. Sixteen subjects were randomly exposed for 2 h to three different conditions: control (Con, 20°C), hot (Hot, 50°C) and hot head cool (HHC – where cold packs were applied to the head under Hot conditions). Three cognitive tests measuring attention and two measuring memory were performed. Neuromuscular testing included electrically evoked muscle action potentials (M-waves) and reflex waves (H-reflex) at rest and during brief (4–5 s) and sustained (120 s) maximal voluntary contractions (MVC) of the plantar flexors. All the tests were performed in the environmental room. During brief MVC, torque was significantly lower in both Hot and HHC as compared to Con (P < 0.05). The decrease in muscle activation was significant in Hot (P < 0.05) but not in HBC (P = 0.07). This was accompanied by peripheral failures in the transmission of the neural drive at both spinal (significant decrements in H-reflexes and V-waves, P < 0.05) and neuromuscular junction (significant decrements in M-waves, P < 0.05) levels. During sustained MVC, muscle activation was further depressed (P < 0.05) without any concomitant failures in M-waves, suggesting neural activation adjustments occurring probably at the supraspinal level. Cerebral perturbations were confirmed by significant decrements in both memory tests in Hot as compared with Con (P < 0.05) but not in simple tests (attention tests) that were not affected by hyperthermia. The decrement in memory capacity suggested the existence of frontal lobe activity impairments. Thus, HHC preserved memory capacity but not the visual memory.

(Received 27 May 2008; accepted after revision 8 August 2008; first published online 14 August 2008)
Corresponding author S. Racinais: ASPETAR – Qatar Orthopaedic and Sports Medicine Hospital, Exercise and Sports Science Department, PO Box 29222, Doha, Qatar.  Email: contact{at}sebastienracinais.com