Running in Summer: How to Train in the Heat Safely and Without Unnecessary Fatigue

Why Running in the Heat is More Challenging: Physiology and Cardiovascular Drift

Why does a light summer training session feel like a gruelling interval battle, even though your fitness level hasn't changed? The answer lies in the human body's thermoregulation.

When you run, your muscles produce a massive amount of heat. To prevent overheating, the body triggers two main cooling mechanisms:

1. Skin Vasodilation: Blood vessels in the skin dilate, diverting some oxygenated blood from working muscles toward the body's surface, where heat can be released into the environment.
2. Sweating: The evaporation of sweat from the skin effectively cools the body's core.

However, this process puts pressure on the cardiovascular system. The heart must perform a dual role—oxygenating muscles while simultaneously pumping blood to the skin for cooling. The result is known as cardiovascular drift. According to physiological studies (Périard et al., 2015), this is a phenomenon where heart rate gradually increases (often by 10 to 20 beats per minute) at the same or even lower intensity. This is not a sign of poor fitness, but rather the body's natural and logical response to heat stress.

The Best Time to Run During Summer

If you want to train effectively and avoid unnecessary thermal shock, the key is to avoid the window of peak solar activity (roughly between 10:00 AM and 5:00 PM).

• Early Morning Hours: The ideal time for summer training. Air temperatures are at their lowest, the asphalt hasn't had time to accumulate heat energy, and humidity levels are generally more stable.
• Evening After Sunset: A suitable alternative, though you must account for the fact that cities and paths can radiate accumulated heat long after dark.

Focus on Heart Rate and Perceived Exertion, Not Pace

One of the most common mistakes made by both beginners and advanced runners is trying to maintain the same pace as they would during spring or autumn months. In summer, it works differently.

• Monitor your heart rate, or ideally, your perceived exertion: Stop looking only at your pace per kilometre. Use heart rate monitoring via a chest strap, but also learn to gauge your perceived exertion (the RPE scale from 1 to 10). In heat, your watch might show a higher heart rate due to thermoregulation, even if the muscular effort is light. Heart rate is not a direct indicator of performance, but rather a mediated physiological response to the body's current needs.
• How should a runner feel? During standard aerobic runs, you should be able to speak in full sentences (the so-called conversational pace). If you are gasping for air and feel overwhelmed by the heat, your effort is too high—regardless of how slow your pace is.

Table: Rate of Perceived Exertion (RPE) Scale for Running

What to Wear for a Summer Run (Including Advanced Cooling Tips)

Choosing the wrong clothing can turn a run into an unpleasant experience. Forget traditional cotton—it absorbs sweat, retains moisture against the body, becomes heavy, and causes painful chafing.

• Technical Fabrics: Opt for ultra-lightweight synthetic materials (polyester/elastane) or fine merino wool, which wick sweat away from the skin instantly.
• Light Colours: White and light shades reflect sunlight, whereas dark colours absorb heat.
• Headwear and Sunglasses: A light, breathable white cap protects your head from direct radiation, and sunglasses with UV protection safeguard your eyes.

Advanced Tips Against Overheating:

• Cool Water-Soaked Arm Sleeves: White compression or running arm sleeves protect against UV rays. When you soak them in cold water before a run, you create an evaporative cooling effect that helps lower skin temperature. The forearms have a high density of blood vessels, so cooling this area helps improve overall thermal comfort.
• Ice Bandana: A bandana or neck gaiter filled with ice cubes tied around the neck. The ice cools the blood flowing to the brain via the carotid arteries, and the melting water provides a refreshing sensation on the chest.
• Ice Directly in Water Bottles: Add not just cold water, but also ice cubes to your sports bottle. A cold drink helps lower your internal core temperature more effectively.

Utilising Natural Resources and Cooling the Head

The head and neck act as the body's primary "radiator." If your route passes natural water sources, don't be afraid to make full use of them:

• Cap as a Cold Compress: If you are wearing a running cap, don't hesitate to soak it under a public drinking fountain, spring, or dip it in a stream. A wet cap and cold water act as an effective cooling compress—thanks to the physical principle of conduction, heat is transferred directly from the warmer surface of the head to the cooler water. This contact helps quickly cool the head area and provides immediate relief to an overheated body. During hot days, you can also put a handful of ice directly into your cap if available.
• Refreshing in Streams and Fountains: During longer summer trails or runs in hot cities, a great tactic is to use a natural stream, mountain river, or city fountains for a quick refresh. Dipping your wrists, splashing your face, letting a few drops fall down your neck, or running through cool water for a few seconds brings immediate psychological relief and helps effectively lower heart rate strain and reset your overall thermal comfort.

Hydration, Gut Training, and Cramp Myths

Fluid loss through sweat during long runs can reach 1 to 2 litres per hour. Dehydration directly impairs thermoregulation and increases the load on the heart.

• Conscious Intake and Longer Runs (Over 90 minutes): For longer runs exceeding an hour and a half, don't rely solely on thirst—many people aren't aware of how much they actually sweat. Conscious and regular fluid intake is key. You should also train your stomach (gut training) to handle larger volumes of fluid—start with smaller doses and gradually increase them during training.
• Connection with Pace: It is perfectly normal and beneficial to briefly slow down your pace when drinking during a run to allow the fluid in your stomach to be absorbed safely. Over time, you will learn to drink adequately while maintaining your best possible performance. For runs over 60 minutes, don't forget electrolytes.
• The Myth of Cramps: For many years, it was believed that cramps during running were caused solely by dehydration or magnesium deficiency. However, modern sports medicine has shifted this view—the primary cause of acute muscle cramps is neuromuscular fatigue (Nelson & Churilla, 2016). They occur when a muscle is chronically overloaded, leading to a failure in neuromuscular control. While hydration and electrolytes are important for overall health, they won't magically eliminate cramps if the muscle is simply exhausted.

Prep your summer running kit: electrolytes, a gel for longer runs, and a light bottle.

Signs You Should Stop Training

The body is a perfect machine and sends early warning signals if the load exceeds a sustainable level. No need to panic, but treat these bodily warnings rationally. It is sensible to interrupt, walk, or end your training if you feel:

1. Light-headedness, sudden fatigue, or unusual heaviness in your legs.
2. Nausea or general weakness.
3. A significant drop in performance accompanied by the feeling that you cannot "catch your breath."
4. Any signs of disorientation—in such a case, it is essential to immediately seek shade, stop the activity, and cool down.

Example of a Summer Running Week for a Beginner

This model shows how to reasonably dose exertion during the hot summer months, with an emphasis on early morning or evening hours:

• Monday: 35 minutes light aerobic jog (maintain a comfortable pace, monitor heart rate, and keep RPE 3-4). At the very end, add 5x 20-second "strides" (accelerations) with 20 seconds of jogging/walking for recovery (helps maintain form and dynamics without overloading).
• Tuesday: Rest / home stretching or core strengthening in the shade.
• Wednesday: 30 minutes – light interval training in the shade (e.g., alternating 1 minute of brisk running and 2 minutes of walking/jogging).
• Thursday: Rest or 30 minutes light active recovery (swimming, cycling in mild heat).
• Friday: 45 minutes longer, slow endurance run (bring a bottle with an isotonic drink). Alternative: If you don't want to run, swap this for hiking in the forest under the shade of trees.
• Saturday: 20-minute recovery walk in the fresh air.
• Sunday: Complete rest for well-deserved recovery.

Table: How to Adjust Training to Temperature

Article Sources

• Nelson, N. L., & Churilla, J. R. (2016). A narrative review of exercise-associated muscle cramps: Factors that contribute to neuromuscular fatigue and management implications. Muscle & Nerve, 54(2), 177–185.
• Périard, J. D., et al. (2015). Cardiovascular Drift and Maximal Oxygen Uptake during Running and Cycling in the Heat. Frontiers in Physiology.