Training and Racing in the Heat

By: Rick Prince

Whether you enjoy or loathe running in hot weather, there is no doubt that running in hot weather poses a unique challenge and moreover, can be quite dangerous.


  • Individuals will differ greatly in their ability to deal with heat and humidity.
  • The more body fat an individual has, the less efficient the person will be at dissipating body heat.
  • Generally, the larger the runner, the more energy is required to reduce body heat. This is because the smaller the individual, the larger the skin surface compared with body volume. This enables small individuals to dissipate heat better than large individuals .
  • Novice endurance athletes and deconditioned individuals are often the most negatively affected by hot weather.
  • Heat acclimatization takes approximately 2-4 weeks and must be done gradually
    • After 10 days of heat acclimatization, the capacity for sweating nearly doubles.


The body has approximately 2 million to 4 million sweat glands. Sweat secreted by the glands is cooled via evaporation. The purpose of cooling the skin is to cool the blood that has been shunted to the skin from deeper aspects of the body (organs, muscles). However, if exercising in humid conditions, the degree of evaporation is substantially lessened. Thus, exercising in hot and humid conditions can prove dangerous because of a lack of evaporative cooling. As such, wiping away sweat before it has had a chance to evaporate greatly reduces the cooling benefit of sweating.


A 2018 study looked at how competition affected one’s sense of thermoregulation and the findings were not all that surprising. If you’ve every competed in a race, you know that you can run faster at a lower rate of perceived exertion as compared to running alone. The research surrounding this seems to equate this to your attention being focused on the runners around you, versus your own sense of exertion.

In the study noted above, cyclists were put through three different types of training scenarios:

  1. Cool solo time trial
  2. Hot solo time trial
  3. Hot competition time trial

While the hot solo time trial was the slowest (36:10), the cool solo and hot competition time trial were about the same time – 35:31 and 35:17, respectively. Even though the core temperature of subjects during the hot competition time trial were higher than during the hot solo time trial, the subjects noted that their perceived exertion was about the same.

Based on this information, we can likely draw the following conclusions:

  • When racing in hot conditions, one’s perception of exertion is reduced.
    • Therefore, when racing in hot weather, perceived exertion might not be a very reliable pacing measure.
  • Runners run slower in hot weather to minimize the effects of the heat.


While this post won’t get into the nitty-gritty of the proposed benefits of running in hot weather, based on heat acclimatization studies, the following are positive adaptations:

  • Increased blood plasma
  • Reduced core temperature
  • Increased sweat rate
  • Better oxygen delivery to the muscles

As such, heat acclimatization is often termed, “Poor man’s altitude training.”

It is important to note three key points:

  1. Like all training methods, people will adapt and respond to the training in different ways.
  2. Running in the heat stresses the body. Therefore, you must balance the potential benefits with the decrease in the quality of the workout(s).
  3. At no point should training in the heat for it’s physiological benefits put a runner at risk of heat illnesses.


  • Pre-hydrating with cold fluids prior to training or racing in the heat has been shown to reduce one’s core temperature.
    • Ice vests also may help
  • Wear light clothing
  • If possible, run during the coolest part of the day
  • Pay attention to your body sensations
  • Run at a slower pace, and likely a shorter distance than you normally would.
  • If possible, pick a route with the most shade
  • On very hot days, cross train indoors or skip the training session.
  • Carry water and/or run on a route with multiple places to get water
  • Carry your phone in case of an emergency
  • Run on a short circuit near your starting point so you can stop early if need be.
  • Take breaks
  • Run with a friend that will be running your desired pace
  • If you start to feel dizzy, feel chilled, nauseous or stop sweating… STOP! Rehydrate, find shade and get help if you don’t feel better.


Heat-related issues can range from relatively minor (heat cramps) to life threatening. In respect to heat cramps (not exercise related), cessation of exercise, as well as finding a cool, shaded spot and massaging the cramped muscle can help.

Heat exhaustion occurs when the body’s thermoregulation system begins to break down. In the case of heat exhaustion, a runner must stop activity and move to a shady, cool location. They should be given an water/electrolyte drink and cooled with a fan and/or wet cloths. Additionally, they should be positioned in the supine position with legs elevated. Medical personnel should be called to check and monitor the client.

Signs of heat exhaustion include:

  • Dizziness
  • Heavy sweating
  • Confusion
  • Nausea
  • Weak, rapid pulse
  • Low blood pressure
  • Excessive thirst
  • Hyperventilation
  • Loss of appetite
  • Anxiety

Heat stroke is the most severe and life threatening heat illness. While an individual may have experienced heat cramps and exhaustion prior to heat stroke, it is not always the case. Heat stroke is caused by the body’s lack of water and electrolytes. Effectively, the body is shutting down. Symptoms include:

  • Rapid heart rate
  • No sweating
  • High body temperature (>103 F)
  • Red, dry skin
  • Confusion
  • Vomiting
  • Nausea
  • Erratic behavior
  • Difficulty breathing
  • Constricted pupils

The most important thing to do is lower the individual’s body temperature immediately and get emergency personnel on-site. Call 911.

Rick Prince is the founder of United Endurance Sports Coaching Academy (UESCA), a science/evidence-based endurance sports coaching education company that certifies running and triathlon coaches.

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About Rick Prince

Rick Prince is the founder of United Endurance Sports Coaching Academy (UESCA), a science-based endurance sports education company. UESCA educates and certifies running, ultrarunning, nutrition, cycling and triathlon coaches worldwide on a 100% online platform.


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