期刊
APPLIED PHYSIOLOGY NUTRITION AND METABOLISM
卷 34, 期 1, 页码 66-74出版社
CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
DOI: 10.1139/H08-139
关键词
near-infrared spectroscopy; interpolated twitch; fatigue; liquid conditioning garments; critical internal temperature
资金
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- Gatorade Sport Science Institute
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 (T-re) of 38.0 degrees C and was removed from the study. The remaining 5 subjects completed heating and testing to a T-re 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.
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