Scuba diving is, like golf, one of those wonderful activities you can enjoy in your teenage years as well as your grandparenting days. Part of the appeal lies in the feeling of going into an unknown environment, yet at the same time having the equipment and training to make you feel safe. But it's not entirely risk free. One problem associated with scuba diving is decompression sickness, also known as the bends. Decompression sickness occurs when the diver inhales compressed air from the scuba tank while underwater (that is, elevated pressure) and returns to the surface too quickly. Symptoms include fatigue, joint pain, dizziness, nausea, loss of hearing and sight. Death may occur. Even before Jacques Cousteau and Emile Gagnan developed the first scuba-diving regulator in 1943, scientists were trying to find out more about the physiological processes of the bends. When a diver breathes air underwater, there's an increase in the concentration of nitrogen dissolved in the blood and tissues. The longer the diver stays below the sea surface, the higher the level of this concentration. Even though the nitrogen dissolves in the blood during dives, it comes out of the solution if the diver returns to sea-level pressure too quickly. It's when these nitrogen bubbles are under the skin or around the spinal cord and brain that skin rashes, seizures, coma and death occur. It's well known that decompression sickness can be reduced or eliminated by slowing down the rate of ascent to the surface after being exposed to elevated pressure. Now, scientists from the Norwegian University of Science and Technology have found that physical exercise before diving can reduce the risk. According to physiologist Alf Brubakk, a workout can turn an 'unsafe dive into a safe dive' - at least in rats. The researchers placed rats into four groups: sedentary, unfit rats, and three other groups that worked out on a treadmill for six weeks, two weeks or one day, respectively. The next day these rats were sent on a dive equivalent of 60 metres in a pressure chamber. The scientists found nitrogen bubbles formed only in the unfit rats. And the one-day group reaped the same benefits as the rats that trained for two or six weeks. If the fit rats stopped exercising for two days before a dive, they developed just as many nitrogen bubbles. The researchers think nitric oxide is the key to unravelling decompression sickness. During exercise, the body produces this chemical, which is critical to regulating breathing and blood flow. They also found nitric oxide makes the inside surface of blood vessels more slippery, making it harder for bubbles to form. This new information runs counter to existing beliefs about the sickness. Even though some research shows fit divers as being less likely to get the bends, vigorous exercise is discouraged before and after dives. Moreover, scientists say that the amount of exercise and the duration of the benefit will be different between rats and humans, and warn against applying the findings to humans. The scientists are now working with pigs to further investigate how nitric oxide affects decompression sickness.