2007, Piran, Slovenia

Environmental Ergonomics XII
Igor B. Mekjavic, Stelios N. Kounalakis & Nigel A.S. Taylor (Eds.), © BIOMED, Ljubljana 2007
EXERCISE HYPERVENTILATION FOLLOWING ACCLIMATION TO
A HOT ENVIRONMENT.
Andrew E. Beaudin, Matthew D. White
Laboratory for Exercise and Environmental Physiology, School of Kinesiology, Simon Fraser
University, British Columbia, CANADA
Contact person: abeaudin@sfu.ca
INTRODUCTION
Human ventilation (V . E) increases linearly as a function of oxygen consumption (V . O2) until
~70-85 % of maximal attainable work rate during incremental exercise to exhaustion. Above
these intensities, V . E increases faster than V . O2 and the mechanisms underlying this
disproportionate change are still under debate. During passive body warming, subsequent to a
core temperature (TC) threshold at ~1°C above normothermic levels, there are proportional
increases in TC and V . E. A similar TC threshold and relationship between TC and V . E has also
been demonstrated during incremental exercise tests from rest to exhaustion. These examples
of hyperventilation are thought to be thermoregulatory heat loss responses. In this study, we
hypothesized that, similar to that seen for eccrine sweating and cutaneous blood flow, the TC
thresholds for exercise ventilation and its components would decrease following acclimation
to a hot environment.
METHODS
Six male participants performed two maximal exercise tests to exhaustion on a cycle
ergometer separated by a 10-day passive heat acclimation. Each exercise test consisted of a 5
min warm-up after which work rate was increased 40 W every two minutes until exhaustion.
Acclimation was performed in a climatic chamber controlled at 50°C and 20 % relative
humidity where participants remained seated at rest for 2 hr·day -1 for 10 consecutive days,
with their rectal temperature maintained between 38.5-39.0°C.
RESULTS
Acclimation was confirmed by a significant decrease in resting esophageal temperature (TES)
from 37.70 ±0.19 (mean ± SD) to 37.31 ±0.11°C (p=0.001), as well as by significant
decreases in the TES thresholds for temple cutaneous blood velocity from 37.71 ±0.23 to 37.43
±0.15°C (p=0.039), and for forehead eccrine sweating from 37.68 ±0.20 to 37.30 ±0.12°C
(p=0.005) during exercise tests. Acclimation decreased TES thresholds for the ventilatory
equivalent for oxygen (i.e. V . E/ V . O2) from 38.25 ±0.16 to 37.85 ±0.14°C (p=0.001) and
likewise for carbon dioxide (i.e. V . E/ V . CO2) from 38.28 ±0.19 to 37.94 ±0.14°C (p=0.004).
Additionally, during the incremental exercise tests, the TES thresholds for the plateau in tidal
volume decreased from 38.14 ±0.23 to 37.68 ±0.29°C (p