More is known about the time course for the acquisition of human heat acclimation
during exercise than its decay or loss. Pioneering research in the 1940s led to our
early understanding of the heat acclimation process and its subsequent decay with
further knowledge concerning the associated physiological mechanisms in later years.
For both hot-dry and hot-humid environments, nearly complete exercise-heat acclimation
occurs after 7 to 10 days of exposure. However, about two-thirds to 75 % of the physiological
adjustments and improvements in performance are seen in 4 to 6 days. Individuals with
high levels of aerobic fitness are partially but not fully acclimated to the heat.
Most of the early studies on decay or loss of heat acclimation are flawed by very
small samples, incomplete heat acclimation or inappropriate measurements. Nevertheless,
these studies are pioneering in a sense because they indicate that the retention of
heat acclimation is quite variable between individuals and environments. Retention
of the benefits of heat acclimation appears to remain longer for dry compared to humid
heat. High levels of aerobic fitness seem associated with greater retention of heat
acclimation. Further well-designed and definitive studies on decay or loss of heat
acclimation appear necessary.
Key words
Aerobic fitness - athletic competition - core temperature - exercise-heat acclimation
- heart rate - retention of acclimation - sweating
