The Gale Encyclopedia of Alternative Medicine defines headaches as a 'pain in the head'. They're such a common malady there's even an international headache society to provide the latest research information, diagnosis, and a classification system of the various types. Few adults in the modern world will get through their lifetime without experiencing at least one, and the causes or triggers are often as unique as the person experiencing it. Most people understand that certain things or events can trigger a headache, such as eating the wrong foods (especially those with monosodium glutamate), having an allergy, stress, head and neck muscular tension. If you don't exercise on a regular basis, you might think exercise was a likely cure rather than a cause. But running, tennis, lifting weights, scuba diving and more contact sports such as boxing, rugby, football have all been cited for causing that 'pain in the head'. These exercise-induced headaches are so common that, if you work out, the chances are good that you've experienced one. In a New Zealand study done in 1994, more than 60 per cent of the 129 university athletes questioned said that they'd experienced a so-called effort or exertion headache at some time. Yet the most frustrating aspect isn't how painful an exercise-induced headache can be, but how unpredictable they are. Even though they're usually a benign problem, they can hit you out of the blue, knocking your game or training sideways. Most headaches unique to athletes and sport tend to be labelled as effort, exertion or trauma-related. According to an article in The Physician and Sportsmedicine Journal by Dr Paul McCrory, effort headaches are the most common. They're usually felt on both sides of the head and come on after you've finished a workout. Even though they're slow to hit, they can cause your head to throb. They can as easily occur in those new to physical exercise as well-trained athletes. The type of workout isn't necessarily the cause. You can do the same workout on different days and only experience a headache on one of them. Exertional headaches are similar. Recent studies have found that there's a clear pattern to these sudden and intense throbbing pains. Straining or holding your breath - such as when you're lifting a heavy weight or sprinting - can bring on an exertion headache. The pain may last only a few seconds or up to a few hours, usually becoming a dull ache afterwards. Such headaches can also be unpredictable. Some weeks you may get one and on other weeks you're fine. A third cause of exercise -induced headaches is the classic blow to the head, known as post-traumatic headaches. Many footballers, rugby players or boxers are familiar with this type of pain. The headache can start suddenly and be excruciating, or begin small and grow. Often it's more intense than the initial blow to the head. The reason effort or exertional headaches hit some people and not others doing the same workout is a mystery. Some experts say a change in blood pressure and accompanying changes in blood vessels may bring about a headache in some people. Others say the position of the head may be a cause. Since the average head weighs about 3kgs, holding it in a position that causes excess muscular tension or stain in the neck can restrict blood flow and cause muscle spasms. Hydrating, warming up, cooling down and breathing properly during a workout offer relief. Some sufferers go for over-the-counter medications such as anti-inflammatory agents, but if you're experiencing them on a regular basis, see a doctor.