Stretching improves your muscles' range of motion and helps keep them long. That's important because they tend to shorten as you get older, making you creaky and a figure of fun for badly dressed skateboarding teenagers. It's also important because an injury to a tendon or ligament could leave it permanently stretched, which raises the likelihood of a recurrent injury.

Ideally, you should do so for at least five minutes. Get some help to develop a routine involving stretching, a nifty yoga move called the Sun Salutation, followed by a few minutes on a bike or treadmill.