title: Prefrontal cortex oxygenation is preserved and does not contribute to impaired neuromuscular activation during passive hyperthermia.
abstract: We investigated the role of passive hyperthermia upon motor unit activation and prefrontal cortex oxygenation. Six healthy males were passively heated, using a liquid conditioning garment in a hot environment (35 degrees C, 50% relative humidity). Maximal force output and voluntary activation were examined during a 10 s maximal isometric knee extension. Of the initial 6 subjects, 1 experienced syncope at a rectal temperature (Tre) of 38.0 degrees C and was removed from the study. The remaining 5 subjects completed heating and testing to a Tre of 38.5 degrees C (n = 1), 39.0 degrees C (n = 3), or 39.5 degrees C (n = 1), and then were cooled back to baseline. Force production decreased from 553 +/- 133 to 430 +/- 176 N (p < 0.01) with passive heating, as did voluntary activation (from 90 +/- 5% to 84 +/- 7%). Percent heart rate reserve increased from 8 +/- 5% to 59 +/- 3% before returning to 4 +/- 8% (p < 0.001). Although mean arterial pressure remained unchanged, there were significant decreases in diastolic blood pressure with heating (80 +/- 3 to 63 +/- 8 mm Hg). Passive heating did not alter prefrontal cortex oxygenation, but cooling back to baseline core temperature attenuated cerebral oxygenated and total hemoglobin levels (p < 0.05). Passive heating to the point of voluntary exhaustion elevated cardiovascular and thermal strain and subjective perceptions of thermal discomfort. However, while this resulted in a marked decrement in maximal isometric force production and central voluntary activation, no concomitant changes in cerebral oxygenation were observed, suggesting that overall cerebrovascular regulation was maintained.
authors.affiliation: Human Performance Laboratory, Faculty of Kinesiology, University of New Brunswick, P.O. Box 4400, Fredericton, NBE3B5A3, Canada.
authors.forename: Shawnda A
authors.initials: SA
authors.lastname: Morrison
authors.forename: Gordon G
authors.initials: GG
authors.lastname: Sleivert
authors.forename: J Patrick
authors.initials: JP
authors.lastname: Neary
authors.forename: Stephen S
authors.initials: SS
authors.lastname: Cheung
mesh_terms: D000328:Adult; D001794:Blood Pressure; D001831:Body Temperature; D002560:Cerebrovascular Circulation; D005334:Fever / Q000378:metabolism* / Q000503:physiopathology / Q000523:psychology; D006339:Heart Rate; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D053580:Muscle Strength; D018482:Muscle, Skeletal / Q000294:innervation*; D009469:Neuromuscular Junction / Q000503:physiopathology*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000378:metabolism; D017397:Prefrontal Cortex / Q000098:blood supply / Q000378:metabolism*; D013315:Stress, Psychological / Q000378:metabolism / Q000503:physiopathology; D055815:Young Adult
chemical_list: D010108:Oxyhemoglobins; D010100:Oxygen