Quantification of the decay and re-induction of heat acclimation in dry-heat following 12 and 26days without exposure to heat stress

• Published in: European journal of applied physiology 2007-12, Vol.102 (1), p.57-66
• Main Authors: Weller, Andrew S, Linnane, Denise M, Jonkman, Anna G, Daanen, Hein AM
• Format: Article
• Language: English
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-007-0563-z

Compared with the induction of heat acclimation (HA), studies investigating the decay and re-induction of HA (RA) are relatively sparse and have yielded conflicting results. Therefore, 16 semi-nude men were acclimated to dry-heat by undertaking an exercise protocol in a hot chamber (dry-bulb temperature 46.1 plus or minus 0.1 degree C; relative humidity 17.9 plus or minus 0.1%) on 10 consecutive days (HA1-10) in winter UK. Thereafter, the subjects were divided into two groups and re-exposed to the work-in-heat tests after 12 and 26days until RA was attained (RA sub(12), n=8; RA sub(26), n=8). The exercise protocol consisted of 60min of treadmill walking (1.53ms super(-1)) at an incline individually set to induce a rectal temperature (T sub(re)) of 38.5 degree C during HA1 (equating to 45 plus or minus 4% peak oxygen uptake), followed by 10min of rest and 40min of further treadmill exercise, the intensity of which was increased across HA to maintain T sub(re )at 38.5 degree C. T sub(re), mean skin temperature, heart rate and rate of total water loss measured at 60min did not change after HA7, and HA was taken as the mean of the responses during HA8-10. For both groups, there was no decay in T sub(re) and for all measured variables RA was attained after 2 and 4days in RA sub(12) and RA sub(26), respectively. It is concluded that once adaptation to heat has been attained, the time that individuals may spend in cooler conditions before returning to a hot environment could be as long as one month, without the need for extensive re-adaptation to heat.