Induction and decay of short-term heat acclimation.
The purpose of this work was to investigate adaptation and decay from short-term (5-day) heat acclimation (STHA). Ten moderately trained males (mean +/- SD age 28 +/- 7 years; body mass 74.6 +/- 4.4 kg; VO2peak 4.26 +/- 0.37 l min(-1)) underwent heat acclimation (Acc) for 90-min on 5-days consecutively (T (a) = 39.5 degrees C, 60% RH), under controlled hyperthermia (rectal temperature 38.5 degrees C). Participants completed a heat stress test (HST) 1 week before acclimation (Acc), then on the 2nd and 8th day (1 week) following Acc (T (a) = 35 degrees C, 60% RH). Seven participants completed HSTs 2 and 3 weeks after Acc. HST consisted of 90-min cycling at 40% peak power output before an incremental performance test. Rectal temperature at rest (37.1 +/- 0.4 degrees C) was not lowered by Acc (95% CI -0.3 to 0.2 degrees C), after 90-min exercise (38.6 +/- 0.5 degrees C) it reduced 0.3 degrees C (-0.5 to -0.1 degrees C) and remained at this level 1 week later (-0.5 to -0.1 degrees C), but not two (0.1 degrees C -0.4 to 0.5 degrees C; n = 7) or 3 weeks. Similarly, heart rate after 90-min exercise (146 +/- 21 b min(-1)) was reduced (-13: -6 to -20 b min(-1)) and remained at this level after 1 week (-13: -6 to -20 b min(-1)) but not two (-9: 6 to -23 b min(-1); n = 7) or 3 weeks. Performance (746 s) increased 106 s: 59 to 152 s after Acc and remained higher after one (76 s: 31 to 122) but not two (15 s: -88 to 142 s; n = 7) or 3 weeks. Therefore, STHA (5-day) induced adaptations permitting increased heat loss and this persisted 1 week but not 2 weeks following Acc.
Garrett
Andrew T
AT
School of Physical Education, University of Otago, Dunedin, New Zealand. a.t.garrett@herts.ac.uk
Goosens
Niels G
NG
Rehrer
Nancy J
NJ
Rehrer
Nancy G
NG
Patterson
Mark J
MJ
Cotter
James D
JD
D000064:Acclimatization / Q000502:physiology*; D000328:Adult; D000450:Aldosterone / Q000097:blood; D001642:Bicycling; D001810:Blood Volume / Q000502:physiology; D002248:Carbon Monoxide / Q000097:blood; D006339:Heart Rate / Q000502:physiology; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology; D055815:Young Adult
D000450:Aldosterone; D002248:Carbon Monoxide; D006854:Hydrocortisone