Heat and humidity: reduce heat risk before chasing pace

Heat illness is not something to endure

Heat and humidity make it harder for the body to lose heat. The National Weather Service warns that heat exhaustion can cause heavy sweating, weakness, dizziness, nausea, headache or fainting. Heat stroke is an emergency and can involve confusion, slurred speech, a very high body temperature, a rapid pulse or loss of consciousness. Neither is solved by willpower or “one more kilometre”.

Check temperature, humidity, sun and wind before training or racing. When humidity is high, sweat evaporates less effectively, so the felt load can be greater than the temperature number suggests. If you are dizzy, chilled, nauseated, confused or unsteady, stop and treat it as a potential emergency.

Change the time and the intensity

The most direct risk management is to avoid the hottest, sunniest part of the day and choose early morning, evening, shade or indoors. When first entering a hot environment, use a lower intensity and shorter duration and allow gradual adaptation; do not test your limit on the first hot run.

In heat, pace targets should give way to breathing and perceived effort. Easy running should still allow sentences; if holding the old pace leaves you gasping, headachy or chilled, the effort is beyond the conditions. In a race, especially do not use “normal pace” in the opening kilometres to compensate for nerves.

Fluid and electrolytes

There is no single fluid volume that suits everyone. The NHS suggests using urine colour as a everyday hydration guide, and needs may rise with long exercise or heat. During training and racing, combine thirst, sweat rate, aid stations and personal tolerance; drinking a large amount at once is not automatically safer than drinking smaller amounts more often.

Electrolyte drinks can replace some salt lost in sweat, but more is not always better. Do not try a concentrated drink, salt tablets or a new supplement for the first time on race day; if you feel bloated, nauseated or uncomfortable, reduce concentration and speed first.

Racing and long runs

Check aid stations, shade, showers and medical points in advance, and plan where to drink and where you can withdraw. In heat, change the goal from “hit a time” to “finish steadily and cool down early”; ice, a wet towel or a cap soaked in water may help more than chasing pace.

If a race is delayed, cancelled or moved, follow the organiser and medical team. Do not add a solo hot run to replace it.

Stop signals

Stop and call emergency services for confusion, slurred speech, fainting, seizures, unusually hot or cold skin, persistent vomiting, chest pain or severe breathlessness. Do not leave the person alone in the heat, and do not substitute “walking it off” for medical assessment.

The NWS safety sequence is to call emergency services first and cool the person while waiting; specific first aid should be delivered by trained responders and the medical system.

Scope and limits

This page does not provide field treatment for heat stroke, individual fluid prescriptions or medical clearance for a race. Heat illness is a medical emergency; people with a medical condition, medication, pregnancy or a previous heat illness should discuss exercise plans with a clinician.

Sources and scope

Recognition of heat exhaustion and heat stroke follows the NWS heat-safety page; hydration and urine-colour guidance follows the NHS; intensity judgement follows the CDC talk test. This is general risk education, not field medical care.