Effect of ambient temperature on cardiovascular drift and maximal oxygen uptake.
OBJECTIVE
This study tested the hypothesis that the magnitude of cardiovascular (CV) drift and decrease in maximal oxygen uptake (V[spacing dot above]O2max) would be greater at 35 degrees C than at 22 degrees C.


METHODS
The increase in HR and decrease in stroke volume (SV) between 15 and 45 min of cycling at 59.2 +/- 1.9% V[spacing dot above]O2max (CV drift) was measured in hot (HEAT, 35 degrees C) and cool (COOL, 22 degrees C) ambient temperatures in 10 endurance-trained men (age = 23 +/- 3 yr, V[spacing dot above]O2max = 64.7 +/- 8.7 mL.kg.min). V[spacing dot above]O2max was measured immediately after the 45 min of cycling and again under both ambient temperature conditions on separate days after 15 min of cycling. This design permitted assessment of V[spacing dot above]O2max between the same time points that CV drift occurred. Fluid to replace sweat losses was provided during all trials.


RESULTS
CV drift and the associated decrease in V[spacing dot above]O2max was greater (P < 0.05) in HEAT versus COOL. HR increased 11% (P < 0.05), SV decreased 11% (P < 0.05), and V[spacing dot above]O2max fell 15% (P < 0.05) between 15 and 45 min in HEAT, whereas HR and SV changed less (+2% and -2% for HR and SV, respectively, P < 0.05), and there was no significant decrease in V[spacing dot above]O2max (5%, P > 0.05) between 15 and 45 min in COOL.


CONCLUSIONS
These data demonstrate the magnitude of CV drift during prolonged submaximal exercise, and the accompanying decrease in V[spacing dot above]O2max measured immediately thereafter is greater in a hot than in a cool environment.
Lafrenz
Andrew J
AJ
Department of Biology, University of Portland, Portland, OR, USA.
Wingo
Jonathan E
JE
Ganio
Matthew S
MS
Cureton
Kirk J
KJ
D000328:Adult; D054874:Athletic Performance / Q000502:physiology*; D005080:Exercise Test; D006339:Heart Rate / Q000502:physiology; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006801:Humans; D008297:Male; D010101:Oxygen Consumption / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology