-Sharone Aharone, USAT Elite Level 3 Coach


Heat acclimation is a topic that comes up every Summer. Most athletes are concerned with acclimation for a race and how the heat will affect their pace and finish time. Acclimation training will produce better results on a hot race day, make your summer running more pleasant, and help you improve performance on a cool day.

Most of us prefer to train in cooler conditions, with 45 to 55 degrees Fahrenheit being optimal. Experts suggest performance impairments of between 1.6 to 3% in marathon time for every 10 degrees above 55.

Pace and Heat relationship
Figure 1 – pace reduction due to increasing temperatures (Ben Shatto July 31, 2018, marathon training academy)

The effect of running in hot conditions includes many things. The most common are increased heart rate, increased blood pressure, and excessive fluid loss.

Heat training adaptation will reduce the effect of heat on the body and help maintain your performance in hot conditions. Furthermore, heat training will improve your performance by 5-6% in cooler conditions.

It takes 7 to 14 days to become fully heat acclimated. However, within five days, 70% acclimation can be achieved. Once thoroughly adapted, you will see the following

  • you will sweat more
  • your cardiovascular function will improve
  • your exercise performance will increase

Adaptation time is different for each athlete, but here are some general guidelines for heat acclimation.

Training Guidelines

During the acclimation period, train outdoors daily at the hot times of the day. Reduce volume in the first few days and use perceived exertion and not pace to monitor your work. Start with 30 to 45 minutes at an easy aerobic pace, and gradually increase your activity time to about an hour. Choose your easy aerobic run for your heat acclimation and save the high-intensity intervals for indoor/treadmill runs. Adaptation happens quickly, and you should not hesitate to increase volume and some intensity.

In addition, using a sauna and doing hot yoga can accelerate heat adaptation and is used by many athletes. Add these two modalities to your heat training routine for quicker results.

Hydration Guidelines

Make sure you drink properly to replenish your fluid loss as fluid consumption does not affect acclimation. However, failure to do so will intensify the heat stress on the body and negatively impact adaptation to heat. This additional heat stress will cause a decrease in blood flow to the skin, a decrease in sweat rate, and ultimately limited heat dissipation, leading to an increase in core temperature.

To assess how much fluids you need to drink during your hot run, you need to determine your sweat rate. The process is simple, and you need to do a few basic calculations at the end.

  1. Record the temperature where you are going to run (indoors or outdoors)
  2. Weigh yourself naked and dry before your run
  3. Run for a 45–60-minute run
  4. Weigh yourself naked and dry at the end of the run
  5. Record how much fluid you consumed during the run (weigh the full bottle before and after the run)
  6. Weight loss = (pre-Body W- post Body W)
  7. Fluid consumption = (pre-Bottle W – post Bottle W)
  8. (Sweat rate = bodyweight loss + fluid consumption) / time

It is impossible (or very hard) to drink to replace 100% of your fluid loss. Your goal is to replenish as much as possible to prevent a weight loss greater than 2% body weight.

In conclusion, the body is brilliant and will adapt to most conditions, including managing your body temperature in heat conditions. Build your tolerance to heat early in the summer, enjoy your hot runs, perform better in heat, and ultimately run faster.