Author(s): KIPPELEN, P., RACINAIS, S., PÉRIARD, J.D., Institution: LIVERPOOL JOHN MOORES UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 2031

INTRODUCTION:
During constant-load, light-to-moderate intensity exercise, ventilation increases with elevations in core temperature (hyperthermia-induced hyperventilation). The aim of this study was to examine the influence of hot environmental conditions and associated hyperthermia on ventilation during high-intensity, self-paced exercise.
METHODS:
A retrospective analysis was conducted on data obtained in eleven cyclists (1 female, age = 33 ± 6 yr; VO2max = 4.3 ± 0.4 L/min) during a 750 kJ self-paced time trial performed in HOT (35°C and 60% relative humidity) and COOL (20°C and 40% relative humidity) conditions (average ± SD completion time 55.8 ± 14.4 and 48.8 ± 12.7 min, mean power output 231 ± 52 and 261 ± 53 W in HOT and COOL, respectively) [1]. Intermittent measurements of rectal temperature (Tre) and ventilatory parameters [i.e. minute ventilation (VE), tidal volume (VT), breathing frequency (f), respiratory equivalents VE/VO2 and VE/VCO2, and end tidal CO2 (PETCO2)] were made throughout. Linear mixed models were used with ‘subjects’ as a random effect and ‘environment’ and ‘time’ as fixed factors. The analysis was conducted twice for each independent variable, once with and once without ‘Tre’ as a covariate. P values <0.05 were considered significant.
RESULTS:
As expected, Tre increased significantly more in HOT (from 37.2 ± 0.31 to 39.6 ± 0.65°C) vs COOL (from 37.3 ± 0.27 to 38.8 ± 0.53°C; ‘interaction’ effect P<0.001), with differences becoming significant from halfway through the trials. A significant ‘time’ effect (P<0.001) was noticed for all ventilatory variables in both environments, whereby VE increased by 41 ± 37 and 56 ± 26 L/min, f by 22 ± 12 and 27 ± 10 breaths/min, VE/VO2 by 10 ± 9 and 11 ± 4 and VE/VCO2 by 9 ± 7 and 12 ± 4 in HOT and COOL, respectively. VT and PETCO2 decreased by 490 ± 511 and 384 ± 576 ml and 4 ± 5 and 8 ± 4 mmHg in HOT and COOL, respectively. Only for PETCO2 did the outcome change (i.e., non-significant ‘time’ effect, P=0.054) when Tre was added as co-variate. No ‘interaction’ effects were observed (neither with, nor without Tre as co-variate), indicating that the change in ventilatory parameters over time did not significantly differ between HOT and COOL (despite higher Tre in HOT). A significant main effect for ‘environment’ (P<0.001) was noticed for VE/VO2 only, with mean value higher in HOT (35 ± 6) vs COOL (33 ± 5).
CONCLUSION:
In contrast to findings obtained during constant-load, light-to-moderate exercise, hyperthermia per se does not appear to be a primary driver of hyperventilation during high-intensity, self-paced exercise. Rather, ventilation is as elevated in COOL as in HOT due to a similar relative intensity induced by a higher power output in cool conditions.
REFERENCE:
1. Périard, J.D. & Racinais, S. Scand J Med Sci Sports 2015: 25 (Suppl. 1): 135–144