A fitness blog once boiled summer running down to three hazards: dehydration, heat exhaustion and blisters. Those three still cover most of what goes wrong on a hot run, and health bodies and running organisations have since added detail to each. This is general information, not individual medical advice.
How much should you drink before and during a hot run?
The blog’s advice was to drink throughout the day, not just after exercising, and to carry a bottle or plan a route past water fountains, taking sips every five or ten minutes. Sanford Health suggests 16 ounces of fluid two hours before a run, with more during and after. The Road Runners Club of America notes that runners can lose between 6 and 12 ounces of fluid for every 20 minutes of running, especially when it is hot.
Thirst is a late signal. One running guide points out that the body loses a considerable amount of fluid before you feel thirsty. For runs of more than an hour, Sanford Health recommends a sports drink to replace electrolytes lost through sweat.
A simple check is your own weight. One coaching guide suggests weighing yourself before and after a run, since the bulk of the loss is sweat and needs to be recovered. Another suggests aiming for pale yellow or clear urine as a sign of good hydration.
What are the warning signs of heat exhaustion?
The blog’s list included heavy sweating, moist skin with goosebumps, faintness, dizziness, fatigue, a weak or rapid pulse, cramps, nausea and a headache. Cleveland Clinic’s description is similar: heavy sweating, headache, dizziness, nausea and a fast heart rate, plus cold, clammy skin and muscle cramps.
The advice is to stop at once. Cleveland Clinic says to move to a cooler area, cool your body and seek medical care, because untreated heat exhaustion can progress to life-threatening heat stroke. One guide adds that signs of heatstroke include decreased sweating and hot, dry skin. That calls for urgent medical help.
One running coach notes that dizziness and a sudden feeling of cold are often the first signs, and that you should slow down, take a walk break, and seek shade and fluids.
When and how can you still run in the heat?
The blog’s first choice was to skip the run and head for the gym or the pool on the hottest days. If you are determined to run, it suggested light, breathable layers, a shorter workout, and the coolest hours, usually early morning or late at night. Sanford Health agrees that midday is the hottest time of day, so early morning is worth considering.
It also suggested a cold shower beforehand and a bandana dipped in ice water on a wet head. Coaches echo the idea of external cooling: cold water on hot skin takes heat away, and ice in a bandana works especially well in humid conditions, where evaporative cooling is compromised.
Pace matters as well. Sanford Health advises you to ditch your predetermined pace and choose a speed based on how you feel. If the heat is new to you, build up intensity and duration gradually over a week or two. A running club guide also suggests avoiding long distances alone.
Clothing should be light-coloured, loose-fitting and breathable.
How do you avoid blisters on sweaty runs?
The blog’s third point was that hot, sweaty runs make blisters more likely. Its remedy was clean, dry-wicking socks, and shoes that are fully air-dried before the next workout. Moisture is the common thread. One running guide recommends removing wet clothing that hampers evaporation, which is a good reason to change out of damp socks as soon as you finish.
When is it better not to run at all?
Humidity changes the picture. Because increased humidity blocks body cooling via evaporation of sweat, one guide suggests avoiding running when relative humidity exceeds 90%. When conditions are bad, the same guide recommends considering another form of exercise, which matches the blog’s suggestion of a gym session or a swim.