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O2 kinetics during intense exercise
1 Department of Human Physiology, Institute of Exercise and Sport Sciences, University of Copenhagen, and 2 The Copenhagen Muscle Research Centre, Rigshospitalet, DK-2100 Copenhagen, Denmark
This study determined whether marked hyperthermia alone or in
combination with dehydration reduces the initial rate of rise in
O2 consumption (
O2
on-kinetics) and the maximal rate of O2 uptake
(O2 max) during intense cycling
exercise. Six endurance-trained male cyclists completed four
maximal cycle ergometer exercise tests (402 ± 4 W) when
euhydrated or dehydrated (4% body wt) with normal (starting esophageal
temperature, 37.5 ± 0.2°C; mean skin temperature, ~31°C) or
elevated (+1 and +6°C, respectively) thermal strain. In the
euhydrated and normal condition, subjects reached
O2 max (4.7 ± 0.2 l/min) in
228 ± 34 s, with a mean response time of 42 ± 2 s, and fatigued after 353 ± 39 s. Hyperthermia alone or in
combination with dehydration reduced mean response time (17-23%),
O2 max (16%), and performance time
(51-53%) (all P < 0.01) but did not alter the
absolute response time (i.e., the time to reach 63% response in the
control trial, 3.2 ± 0.1 l/min, 42 s). Reduction in
O2 max was accompanied by proportional
decline in O2 pulse and significantly elevated maximal
heart rate (195 vs. 190 beats/min for hyperthermia vs. normal).
Preventing hyperthermia in dehydrated subjects restored O2 max and performance time by 65 and
50%, respectively. These results demonstrate that impaired
high-intensity exercise performance with marked skin and internal body
hyperthermia alone or in combination with dehydration is not associated
with a diminished rate of rise in O2 but
decreased O2 max.
maximal heart rate; hydration; core temperature; skin temperature, oxygen uptake
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