I suffer from migraines and have noticed that they can get worse with some workouts, while at other times I'm fine. Any advice?

Certain types of exercise can trigger headaches in migraine-prone individuals. Recent research has shown that dilation of the blood vessels in the brain relates to nitric oxide. Bouts of acute, high-intensity exercise tend to have a greater impact on nitric oxide levels than lower, more sustained aerobic activity. Even 30-second bouts of intense cycling have been shown to induce migraines four or five hours later. If you are experiencing pain every time you exercise, you may be prone to what are known as exertional vascular headaches - if they persist, ask your GP about anti-inflammatory medication.

Strength training, for all its benefits, can aggravate tension-type headaches. Minimise this by completing a thorough warm-up and cool-down, mixing strength training with lighter toning and flexibility exercises. And don't be tempted to hang up your kit altogether: exercise with lifestyle management and appropriate medication has been shown to decrease the number and severity of migraines by up to 50%; what's more, 30-40 minutes of moderate to vigorous exercise three or four times a week increases endorphins and serotonin, which may have a beneficial effect on the brain.

Remember, also, that nutritional status and hydration levels have a direct bearing on susceptibility. Always start exercise well hydrated and sip water throughout. When progressing your workouts, build intensity gradually, adding a few minutes to each workout each week.

· Joanna Hall is a fitness expert (joannahall.com). Send your exercise questions to Weekend, 119 Farringdon Road, London EC1R 3ER (weekend@theguardian.com).