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[RC] CV Drift - Ridecamp Guest

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Authors JE Wingo, AJ Lafrenz, MS Ganio, GL Edwards, KJ Cureton
Title   Cardiovascular drift is related to reduced maximal oxygen uptake during 
heat stress
Full source     Medicine and Science in Sports and Exercise, 2005, Vol 37, Iss 
2, pp 248-255

WINGO, J. E., A. J. LAFRENZ, M. S. GANIO, G. L. EDWARDS, and K. J. CURETON. 
Cardiovascular Drift Is Related to Reduced Maximal Oxygen Uptake during Heat 
Stress. Med. Sci. Sports Exerc., Vol. 37, No. 2, pp. 248-255, 2005. 
Introduction/Purpose: This study investigated whether the progressive rise in 
heart rate (HR) and fall in stroke volume (SV) during prolonged, constant-rate, 
moderate-intensity exercise (cardiovascular drift, CVdrift) in a hot 
environment is associated with a reduction in VO2max. Methods: CVdrift was 
measured in nine male cyclists between 15 and 45 min of cycling at 60% VO2max 
in 35degreesC that was immediately followed by measurement of VO2max. VO2max 
also was measured after 15 min of cycling on a separate day, so that any change 
in VO2max between 15 and 45 min could be associated with the CVdrift that 
occurred during that time interval. This protocol was performed under one 
condition in which fluid was ingested and there was no significant body weight 
change (0.3 +/- 0.4%), and under another in which no fluid was ingested and 
dehydration occurred (2.5 +/- 1%, P < 0.05). Results: Fluid ingestion did not 
affect CVdrift or change in VO2max. A 12% increase in HR (151 +/- 9 vs 169 +/- 
10 bpm, P < 0.05) and 16% decrease in SV (120 +/- 12 vs 101 +/- 10 
mL(.)beat(-1), P < 0.05) between 15 and 45 min was accompanied by a 19% 
decrease in VO2max (4.4 +/- 0.6 vs 3.6 +/- 0.4 L(.)min(-1), P < 0.05) despite 
attainment of a higher maximal HR (P < 0.05) at 45 min (194 +/- 5 bpm) vs 15 
min (191 +/- 5 bpm). Submaximal VO2 increased only slightly over time, but 
%VO2max increased from 63 +/- 5% at 15 min to 78 +/- 8% at 45 min (P < 0.05). 
Conclusion: We conclude CVdrift during 45 min of exercise in the heat is 
associated with decreased VO2max and increased relative metabolic intensity. 
The results support the validity of using changes in HR to reflect changes in 
relative metabolic intensity during prolonged exercise in a hot environment in 
which CVdrift occurs.


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