Running in heat is not always dangerous. The body has highly effective mechanisms to keep core temperature stable even during intense exertion. The problem arises when those ‘tricks’ stop working because ambient temperature, humidity, exercise intensity, or dehydration surpass the body’s ability to cool itself. At that moment exertional heat stroke can develop, a potentially life-threatening medical emergency that requires immediate action. Knowing how to identify warning signs can prevent very serious consequences.
Heat stroke does not appear suddenly
One of the biggest mistakes is thinking that heat stroke arrives without warning. In reality, most runners experience a progression of symptoms that indicate the body is losing the battle against the heat. During exercise, the body loses heat mainly through the evaporation of sweat. When ambient temperature is high, humidity prevents sweat from evaporating or the workout intensity is too high, the body temperature begins to rise progressively. When it exceeds approximately 40 °C and central nervous system disturbances appear, we are talking about exertional heat stroke, a situation that requires immediate medical attention.
The first sign is usually in the head
Long before losing consciousness, the brain starts to warn. It is common to notice a feeling of confusion, difficulty concentrating, or an inability to think clearly. There are runners who describe that they stop calculating pace, forget the usual route, or begin making illogical decisions.
They may also appear:
If any of these symptoms appear while you’re running in the heat, the correct action is to stop the workout immediately.
When the legs stop responding
Another very characteristic symptom is that the legs suddenly seem to lose strength. This is not normal fatigue from a hard workout. It is a feeling of extreme exhaustion that appears even if the pace is not particularly high. Many runners try to continue, thinking it is just a slump or poor hydration. That mistake can accelerate the condition’s progression.
Chills in the middle of summer: a warning sign
It may seem contradictory, but having chills while running under intense heat is a very troubling sign. It indicates that the body’s temperature regulation system is starting to fail. If, in addition, very hot skin, intense weakness, or a feeling of being “very odd” appear, you must stop the exercise immediately.
Nausea and vomiting can also indicate danger
The digestive system receives less blood flow when the body is trying to cool itself.
As a consequence, these symptoms may appear:
Although these symptoms can also be due to digestive problems, when they appear alongside intense heat they should raise suspicion of a possible heat stroke.
Sweating can be confusing
There is a belief that in a heat stroke the person stops sweating. This occurs frequently in classic heat stroke, but not necessarily during exertional heat stroke. In fact, many runners continue sweating heavily even when they already have a dangerously elevated body temperature. Therefore, sweating continued does not rule out a heat stroke.
What you should do immediately
If you suspect you are developing heat stroke:
The speed at which you lower your body temperature is the main factor that improves the prognosis.
Who is at higher risk?
Although it can affect any runner, the risk increases when several factors coincide:
How to avoid reaching that situation
The best strategy remains prevention. Slowing down when it’s hot, training in the early hours of the day, staying properly hydrated, acclimating for one or two weeks, and listening to the body’s signals greatly reduce the risk. Abandoning a workout will never be a failure if doing so prevents a medical emergency.
What science says
Diversas publicaciones del American College of Sports Medicine y de la National Athletic Trainers’ Association coinciden en que el diagnóstico precoz y el enfriamiento inmediato durante los primeros 30 minutos son los factores que más reducen la mortalidad y las posibles secuelas del golpe de calor por esfuerzo. Asimismo, investigaciones publicadas en el British Journal of Sports Medicine destacan que la alteración del estado mental es el signo clínico más importante para diferenciar esta situación de un simple agotamiento por calor.