The simple answer: Strenuous activities increase pressure on the brain’s blood vessels, which could result in headaches

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It’s common to experience headaches during (or even after) exercise. They generally occur when you engage in strenuous activities like weightlifting, biking, and running since they increase pressure in the blood vessels of the brain, triggering headaches and migraines. 

There are several factors that increase the risk of headaches during exercise, and most of them involve your nutrition, hydration, and fitness habits. Here are four of the most common reasons why heads roll while sweating it out: 

1. You could be dehydrated 

Dehydration is the most common reason why headaches occur during exercise. It happens when you lose fluids more than you take in. When your body is dehydrated while working out, your brain temporarily shrinks, causing tension between your brain and skull, which then leads to a headache.

The body requires a balance of fluids and electrolytes to properly function, which is why the National Academy of Medicine recommends adults to drink at 9 1/2 to 12 cups of fluids a day.

2. Your posture might be wrong 

Another cause of headache during exercise is when your form or posture is incorrect. The International Headache Society reports that muscle tension causes 30 to 78 percent of our headaches. When working out, poor posture, especially while weightlifting, doing push-ups or crunches, and running, leads to headaches because it causes muscle tension (when the muscles in the body semi-contract) and stress that significantly affects brain function. 

There are several factors that increase the risk of headaches during exercise, and most of them involve your nutrition, hydration and fitness habits

3. You’re overexposed to the sun 

While the sun is the best source of vitamin D, too much can also trigger headaches. Exercising in the heat causes excessive sweating, which then leads to dehydration. If you know you’re going to work out under the sun (or if your sport requires it), wear sunglasses or a wide-brimmed hat to protect your face and eyes and make sure to drink the recommended number of glasses of water a day to stay hydrated. 

4. You’re experiencing low blood sugar

Low blood sugar or hypoglycemia is another reason why you experience headaches. Low blood sugar happens when you don’t eat enough carbohydrates or calories before you work out. It’s important to remember that you must consume carbohydrates like rice, potatoes, bread, fruits, and vegetables before engaging in physical activity. 

You must take at least 30 to 45 grams of both carbohydrates and protein 60 to 90 minutes before exercise. After working out, eat good carbs like sweet potatoes and fruits to promote faster nutrient absorption.