Your body functions properly within only a very narrow range of internal core temperatures. Change in core temperature of even a few degrees in either direction, hot or cold, can be life threatening. Led by the hypothalamus in your brain, a combination of systems work together to regulate your body temperature, keeping it as close to normal (37C / 98.6F) as possible.
During intense physical activity, your own body can rival a 1000W electric space heater in terms of the amount of heat generated. This is because heat is a normal byproduct the metabolic process that transforms stored energy into performance. The harder your effort, the more heat is produced.
To maintain a healthy core temperature, all this extra heat needs to go somewhere, somehow. This is achieved primarily through a combination of sweating, evaporating sweat has a cooling effect, and increasing the amount of blood flow to the skin.
The ability of your body to cool itself in this way is heavily dependent on your environment. Cool external temperatures make it easier to dissipate excess body heat. As external temperatures increase, it becomes harder and harder for your body to cool itself and as a result these processes must become more efficient.
Exposure to hot, humid environments trigger physiological adaptations that enable you to perform better in those specific conditions. These changes include an increase in your ability to sweat and changes to your cardiovascular system that facilitate more blood flow closer to the surface of the skin. This allows more heat to escape the body.
How long does it take to adapt to a hotter climate?
It can take several weeks to fully acclimate to a hotter climate, but much of the adaptation process takes place shortly after your initial exposure. Average acclimatization rates are roughly 50% after the first week of exposure, and roughly 80 % after the second week of activity in the new environment.
Of course, everyone is different and the details about your situation and what you are doing matters. Simply going for a walk outdoors on a hot day doesn’t signal the same degree of urgency for adaptation as going for a 5k training run. At the same time, you shouldn’t expect that going for a 10k run will help you acclimate any faster. Your physiology simply can’t change significantly overnight.
The ability to track your own personal acclimatization progress provides invaluable insight. This insight empowers you to set the right expectations and guide a safe transition to more challenging conditions.
Variation in the acclimatization process
At an individual level, your acclimatization rate is influenced by the amount of your daily exposure to the conditions combined with the intensity and duration of your activities. Resting in the heat will only produce partial acclimatization.
As a rule, you can accelerate your own acclimatization by focusing on improving your cardiorespiratory fitness (VO2max) prior to transitioning to a hotter environment. If your new environment is an extreme one, like traveling to a desert region, much hotter than your previous one, it might be wise to focus on low-intensity recreational efforts for the first couple of days. These efforts would be in line with those typical of active rest or efforts used to promote recovery. Light runs of 20-40 minutes are typically introduced on the third day of your exposure.
Special considerations for specific athletes
It’s true that all athletes should be generally aware of the impact heat has on their performance. However, two types of athletes, in particular, need to pay attention to their own situation with regards to heat adaptation.
The first type are athletes with lower cardiorespiratory fitness levels, whose acclimatization process will be longer and more difficult. These individuals, who may otherwise be in good health and physical condition, are likely to experience greater heat related strain over the course of their adaptation period.
Highly motivated athletes comprise the second group of individuals at greater risk during the acclimatization process. This is due to the simple fact that they are more likely to simultaneously overexert themselves while ignoring the warning signs that accompany potentially life-threatening heat related situations.