Category: Running

Running in the heat can improve endurance, increase heat tolerance, and prepare you for summer races—but it also increases the risk of dehydration and heat illness if done incorrectly. Learn what the research says and how runners—especially those over 50—can train safely.

Running in hot weather has both significant benefits and significant risks. Done correctly, heat training can improve endurance, increase heat tolerance, prepare you for summer races, and even enhance performance in cooler conditions. Done poorly, it can lead to dehydration, heat exhaustion, or worse.

When I began triathlon at age 58, I avoided running in hot, humid weather whenever possible. I scheduled runs before sunrise or moved them indoors. After learning more about heat acclimation—and experiencing it myself—I came to appreciate that carefully managed heat training can provide meaningful performance benefits. Like many aspects of training after 50, the key isn’t avoiding the challenge but approaching it wisely.

Benefits of Running in the Heat (When Done Safely)

Research shows that running in the heat can improve endurance, increase heat tolerance, and prepare you for races in warm conditions. Surprisingly, many of these adaptations also improve performance when racing in cooler weather.

These benefits don’t come simply from enduring uncomfortable runs. They come from allowing your body to gradually adapt to higher temperatures while training safely.

“Aerobically fit persons who are heat acclimatized and fully hydrated have less body heat storage and perform optimally during exercise-heat stress.”

Michael N. Sawka, C. Bruce Wenger, Andrew J. Young, and Kent B. Pandolf, (1993), ‘Physiological Responses to Exercise in the Heat’ in Marriott BM, editor, Nutritional Needs in Hot Environments: Applications for Military Personnel in Field Operations. Washington (DC): Available from National Academies Press (US).

In practical terms, runners who gradually acclimate to heat generally feel more comfortable, maintain a lower heart rate at a given pace, and tolerate hot-weather training better than those who avoid it entirely.

Improve Endurance and Performance

Beyond improving heat tolerance, heat training can also accelerate endurance adaptations—sometimes producing greater physiological benefits than training at higher altitude.

An article in the Journal of Applied Physiology titled Heat acclimation improves exercise performance (Lorenzo et al., 2010) reports the major benefits of endurance training in high temperatures as:

• Higher blood plasma volume and increased cardiac output, which together can improve VO₂max—the maximum amount of oxygen your body can use during exercise. A higher VO₂max generally supports better endurance performance.
• Higher lactate threshold, allowing you to sustain a faster pace before fatigue forces you to slow down. Many experienced triathletes consider this one of the most important adaptations for improving race performance.

Together, these adaptations help explain why runners who train safely in the heat often perform better not only in warm-weather races but also when they return to cooler conditions. The improvements are temporary, however, with most of the benefits beginning to diminish after one to two weeks unless heat training continues.

Read the complete Journal of Applied Physiology study on heat acclimation for additional technical detail.

Cons of Running in the Heat

The benefits of heat training are real, but so are the risks. High temperatures place additional stress on the cardiovascular system and increase the likelihood of dehydration, heat exhaustion, and declining performance if training is not managed carefully. For runners over 50, these risks deserve even greater attention.

Running Will Feel Harder

Running in the heat almost always feels harder than running in cooler weather. As more blood is diverted toward cooling the body, less is available to working muscles. Heart rate rises, breathing becomes more labored, and maintaining your usual pace requires noticeably more effort.

Understanding that these responses are a normal part of heat adaptation has helped me accept slowing down rather than fighting the conditions. Instead of chasing my usual pace, I focus on effort and let my body gradually adapt.

Risk of Heat Exhaustion

Without properly hydrating or adjusting your training plan, high temperature can lead to heat exhaustion or muscle cramping.

Warning signs include dizziness, chills, confusion, nausea, excessive fatigue, and stopping sweating despite the heat. If any of these occur, stop exercising immediately, move to a cool location, and begin rehydrating.

In “Physiological Responses to Exercise in the Heat“, authors Michael N. Sawka et al. (1993) included among their conclusions:

“Dehydration from sweat loss increases plasma tonicity and decreases blood volume, both of which reduce heat loss and result in elevated core temperature levels during exercise-heat stress.”

Sweat Creates New Challenges

Sweat is our body’s way of controlling its core temperature. And, my sweat mechanism works very well.

During a run in humid heat, I quickly become a sweaty mess. On some days, this includes sloshing wet shoes. (There is hardly anything more unsettling than to see my wet shoe prints on the otherwise dry running trail.)

The problem with sweaty running gear is that it can rub against the skin, laying the groundwork for painful abrasions.

Accept a Slower Pace

One of the biggest mistakes runners make during summer training is trying to maintain the same pace they run in cool weather. Heat naturally increases heart rate and perceived effort. Learning to slow down isn’t a sign of declining fitness—it’s part of training intelligently in hot conditions.

Fortunately, most of these risks can be reduced—or avoided entirely—with sensible planning. A few adjustments to hydration, pacing, clothing, and recovery allow runners to gain the benefits of heat training while minimizing the dangers.

How to Train Safely in the Heat and Humidity

The benefits of heat training come from adapting to the heat—not from pushing yourself into heat illness. A few practical habits will help you gain the benefits while reducing the risks.

Avoid Becoming Dehydrated

For seniors, it is even more important to be conscious of our hydration. In Six Principles of Triathlon Training for Seniors, I noted that our thirst sensation becomes less sensitive with age. Waiting until we become thirsty can give a false sense of hydration.

First, it is important to begin the run properly hydrated. Urine color is a useful general indicator of hydration; a light yellow color generally indicates adequate hydration. However, remember that certain medications and vitamin supplements can affect our urine’s appearance.

Then, during the run, Motion Works Physical Therapy recommends drinking 6-8 ounces of water or sports drink every 15-20 minutes. 

Finally, be sure to rehydrate after the run. An approach to rehydrating recommended by Motion Works is to weigh yourself before (dry clothing) and after a run (sweaty clothing) without clothing to determine the water lost during the run. Knowing the amount of fluid lost during a run will help determine how much water to drink after the run.

Consider Electrolyte Supplements . . . Carefully

Electrolyte supplements may be beneficial during acclimatization. Hyponatremia, a condition resulting from electrolyte depletion caused by consuming too much water during exercise, can be avoided by consuming low doses of electrolytes (e.g. sodium, potassium, and chloride are the main ones) along with water during exercise. Our guide Electrolytes: Vital for Hydration and Performance of Senior Triathletes provides current strategies for maintaining electrolyte balance.

Many runners now use electrolyte mixes such as LMNT or similar products during longer runs in hot weather because they provide substantially more sodium than traditional sports drinks.

Use the Right Gear

Using lightweight, light colored (to reflect the sun) wicking fabrics can promote evaporative cooling and reduce irritation from sweat-soaked running gear.

Similarly, a light-colored cap or visor can also reduce direct sun exposure and improve comfort during long runs.

I have found that snug fitting shirts that cling to my body prevent the irritation when wet. Conversely, even loose fitting, wicking fabrics rub against sensitive parts of the body making for a painful post-run experience. Tape also works but can fall off when it becomes wet.

Adjust Your Expectation

On a recent run, I realized that my running form had worsened as I became tired.

Heat naturally changes running mechanics. Fatigue accumulates sooner, posture may deteriorate, and cadence often slows. Focus on maintaining relaxed, efficient form rather than chasing your normal pace.

Let Effort Guide Your Run

Trying to maintain your normal pace in hot weather often leads to excessive fatigue and unnecessary risk. Instead, slow your pace and use perceived effort or heart rate to guide your workout. The goal of heat training is adaptation—not setting personal records.

Recover Well After Heat Training

Recovery becomes increasingly important after age 50. After each run, be sure to:

• Cool down gradually.
• Hydrate.
• Replace electrolytes.
• Eat.
• Sleep.

Doing so will produce the benefits you worked so hard for.

Final Thoughts

Running in the heat isn’t about proving toughness. It’s about allowing your body to adapt safely so you can become a stronger runner in every season. After beginning triathlon at age 58, I spent years avoiding hot-weather training whenever possible. Today, I still respect the heat—but I no longer fear it. I slow down, hydrate carefully, and let the conditions become part of the training rather than something to escape.

If you have experience training in hot or humid conditions, I’d love to hear what has worked best for you. Your ideas may help another runner train more safely this summer.

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