Leg cramps are a common problem, especially when people get older. The term cramp is used to describe various pains, but mostly refers to a painful spasm of the muscles.

If your leg cramps occur during or immediately after exercise, this may be a sign your muscles aren't getting an adequate supply of oxygen, or that toxic chemicals produced by the activity of busy muscles aren't being cleared fast enough from the area.

For most people who are otherwise healthy, this is a common problem while the muscles get used to an increased amount of exercise, and it should settle as the body adapts to this new healthy habit.

But leg cramps may be a sign of arteriosclerosis (or 'hardening of the arteries'), where the arteries are clogged by fatty deposits, limiting the supply of blood to the muscles.

When you exercise, your leg muscles need more oxygen, and this is supplied by the blood flowing to the muscles. But in atherosclerosis the arteries are narrowed, so the blood supply to the muscles is limited, meaning the muscles can't get enough oxygen.

The muscles switch to anaerobic metabolism, which doesn’t need oxygen but results in the build-up of chemicals that can trigger pain and spasm, usually in the calves. When you rest, the pain lessens. This is called intermittent claudication.

In mild cases, you may notice your legs are cold, with dry skin and few hairs. As it gets worse, the limbs may become blue, ulcerated and even gangrenous. Smokers, people with high cholesterol levels or diabetes and those with a family history of heart disease are all at particular risk. Intermittent claudication needs thorough investigation, so go to your GP for a check up.

Cramps may also occur when a muscle is injured. Although the cramps or spasms may be felt in the legs, the underlying cause may actually be somewhere else, for example, in the back or knee. In very rare cases, leg cramps are caused by medical conditions such as an underactive thyroid gland (hypothyroidism), Addison's disease and kidney problems.

When cramps persist, it's important you see a doctor, who'll be able to check for these underlying causes.

Many people find leg cramps cause particular trouble at night, when the pain hinders sleep or wakes them up. These are known as night cramps and are rarely serious, but can cause a lot of discomfort.

Simple ways to avoid cramps

When you start to exercise, warm up gently, gradually building up the intensity of what you're doing so that the muscle isn't suddenly overworked or torn. After a short warm-up, stretch the muscles out gently. You should make sure you stretch after exercise, too, as it helps during the cramp to relieve the spasm and so the pain.

Don't let yourself get dehydrated during exercise as this can upset calcium and phosphorous levels in the body, which may trigger cramps. Drink plenty of fluid before and during activity, and consider non-phosphate calcium supplements, which may also help.

Very heavy or tight bed covers can force the toes downwards, straining the leg muscles, so try to sleep under a light, loose duvet.

Sometimes quinine is used to prevent leg cramps, particularly at night, but its use is controversial and potential side-effects are dizziness, blurred vision or blood problems.

Tonic water contains very small amounts of quinine, which may be enough to relieve night cramps. Some people recommend vitamin E creams, but there's little evidence they have any effect that betters a good massage.

If cramps persist, seek advice from your pharmacist because there are simple drug treatments that can be bought over the counter. These are certainly worth trying, especially for cramps at night but, if they don’t help, it’s time to talk to your GP.

This article was last medically reviewed by Dr Trisha Macnair in April 2008