Why exercise headaches happen and whether hydration helps

Getting a headache while you’re exercising, or soon afterwards, can be incredibly irritating - particularly when you’ve made a point of staying well hydrated in the hope of preventing it.

So what’s behind these headaches? And does hydration actually change anything?

What are exercise headaches?

Exercise headaches - sometimes called "exertional headaches" - are just that: headaches that develop during exercise or in the period after you’ve finished.

They were first described in medical writing by the French physician Jules Tinel in 1932, and they have been debated regularly ever since.

Typically, exercise headaches feel like a throbbing ache on both sides of the head. They are most likely to appear following strenuous activity - though what counts as "strenuous" varies from person to person, depending on fitness. Symptoms may last from a few minutes up to a couple of days.

Estimates suggest around 12% of adults experience exercise headaches, although reported rates range widely - from 1% to as high as 26% - across different studies.

In most cases, they are not dangerous and tend to settle on their own with time. Some studies indicate they may disappear after a few months of taking up a new style of workout.

Even so, while they’re usually harmless, they can occasionally point to an underlying problem that needs medical assessment.

What causes exercise headaches?

Although exertional headaches have been studied quite extensively, the precise cause is still unclear - but there is a strong idea about why they happen.

The main theory is that they stem from changes in blood flow within the brain. With high-intensity exercise, blood vessels in the brain widen, which boosts blood flow and pressure and may trigger pain.

This explanation also fits with the observation that exercise headaches often ease over time: regular training improves cardiovascular health, including how well blood vessels widen and narrow. That may also help explain why evidence suggests people with higher fitness levels are less prone to exercise headaches.

Those who experience migraines also seem to be at greater risk of exercise headaches, which are thought to arise through the same process.

Does heat and dehydration cause exercise headaches?

Evidence indicates exercise headaches are more likely in hot conditions.

Unlike the rest of the body, the brain cannot cool itself through sweating. When it’s warm, the body may increase blood flow to the brain to help lower its temperature - which can raise pressure.

In a similar way, exercise headaches also appear to occur more frequently, and feel worse, when someone is dehydrated.

However, the reason for this is not fully understood. Some research shows dehydration increases the overall strain of exercise.

So dehydration may not directly cause the headache, but it could make one more likely to happen.

Red flags: when to see a doctor

Most exercise headaches go away within a few hours and do not cause lasting harm.

On rare occasions, they may be a sign of a more serious issue in the brain - for example, a subarachnoid haemorrhage (bleeding between the brain and the tissues covering it), reversible cerebral vasoconstriction syndrome (spasms in blood vessels), cervical artery dissection (a tear), intracranial hypertension (raised pressure in the brain), or an infection.

See a doctor to rule out anything serious if:

• it’s your first exercise headache
• the headache is severe and sudden (also known as a thunderclap headache)
• it comes with other symptoms, such as changes to vision, confusion, or feelings of weakness
• you develop a stiff neck, nausea, or vomiting alongside the headache
• it continues for more than 24 hours and does not seem to be improving.

Can you prevent exercise headaches?

There is no guaranteed way to stop exercise headaches from occurring.

That said, a recent review suggests staying adequately hydrated and doing a gradual warm-up to reach your target intensity may reduce the chances of them happening.

Beyond that, it may help to keep your training intensity in a light-to-moderate range for a couple of months.

This gives your cardiovascular system time to adjust before you move on to more strenuous sessions, which may lower the likelihood of exercise headaches altogether.

Exercise headaches are unpleasant, but they are generally harmless and should fade over time.

Hunter Bennett, Lecturer in Exercise Science, University of South Australia

This article is republished from The Conversation under a Creative Commons licence. Read the original article.