How to Run in the Heat: Summer Running Tips That Actually Work

When you run, your muscles generate heat as a byproduct of the energy they burn. In cool weather, that heat dissipates easily. In hot or humid conditions, your body has to work much harder to keep core temperature in a safe range — mostly by sweating and routing extra blood to the skin for cooling.

That rerouted blood is blood that would otherwise be delivering oxygen to your muscles. The result is a higher heart rate at any given pace, faster glycogen depletion, and a lower ceiling on how hard you can sustain effort before the body overrides you. Humidity compounds this: sweat evaporation is the primary cooling mechanism, and humid air slows evaporation, so the same temperature feels harder when the humidity is high.

Research consistently finds that performance slows by about 1 to 3 percent for every 10 degrees Fahrenheit above approximately 55 degrees Fahrenheit. A runner who normally runs easy miles at 9:00 pace might find 9:30 to 9:45 is the equivalent effort on a 85-degree day. That is not a fitness regression; it is an appropriate physiological response.

The most important rule of summer running: train by effort, not by pace. Run easy days at an easy effort — conversational, relaxed breathing — regardless of what the number on your watch says. Trying to hit the same pace times you ran in spring puts excessive stress on your cardiovascular system and raises injury risk.

A rough guide: on days above 60 degrees Fahrenheit, add 30 seconds per mile to your easy pace target for every 10 degrees of temperature above that baseline. On very hot or humid days, slow even more. The anystride pace calculator gives you your training paces based on current fitness — treat those as good-weather targets and use effort on hard days.

Dehydration accelerates every problem heat causes. Even mild dehydration of 2 percent of body weight measurably reduces performance and increases perceived effort. The goal is to arrive at the run well-hydrated and replace enough fluid during the run to avoid significant deficit — not to drink a fixed volume regardless of thirst.

For runs under 45 minutes in moderate heat, drinking to thirst is usually sufficient. For longer efforts, carry fluids or plan a route with fountains, and drink before you feel thirsty. On long runs or very hot days, include electrolytes — sodium in particular — to replace what you lose in sweat. Drinking large volumes of plain water without sodium can dilute blood sodium levels and cause hyponatremia, which is rare but serious.

The single most effective change most runners can make is shifting the time of day they run. The coolest periods are before sunrise and in the evening after sundown. Running at 6 a.m. instead of noon on an 88-degree day is not just more comfortable — it is meaningfully safer and produces better training stimulus because you can actually hit your target effort.

Route choices matter too. Shaded trails are significantly cooler than exposed roads under direct sun. Running near water — rivers, lakes, parks — often means noticeably lower temperatures. When the only option is a hot road, go out and back so the wind is in your face on the return, or run in loops near your car so you can access water frequently.

Here is an underappreciated upside: your body adapts to heat with consistent exposure. Over 10 to 14 days of running in warm conditions, plasma volume increases, sweating starts earlier and at lower core temperature, and sweat rate rises — all of which improve heat dissipation and reduce cardiovascular strain at a given pace. Runners who build this acclimatization over summer often perform better in fall races than runners who moved all their training indoors.

The practical implication: do not avoid running outside in summer entirely. Run in the heat at appropriate effort, protect yourself with hydration and timing choices, and let acclimatization build naturally. By late summer, effort that felt crushing in June will feel manageable.

Heat exhaustion and heat stroke are real risks. Know the warning signs and stop running immediately if they appear.