Improving your flexibility is often recommended as a way to increase your speed of movement. It's a reasonable idea, since too-tight muscles, tendons and ligaments can restrict motion at a joint and thus decrease stride length, in addition to creating a need to burn excess energy to overcome this motion-resisting stiffness.

Increased flexibility is also supposed to thwart injuries, but does it really work that way? To find out, researchers at the New Jersey Medical School recently tested the flexibility of connective tissues and muscles in the legs and hips of 200 college athletes before their competitive seasons began. Then, the researchers monitored the athletes for injury for several months (Archives of Physical Medicine and Rehabilitation, vol 77, pp 1139-1143, 1996).

As it turned out, in male athletes the risk of injury decreased as flexibility increased. In fact, for each additional point on the ligament-flexibility scale (the researchers graded flexibility on a 10-point scale), the chances of injury declined by about 15 per cent. In addition, for each one-point increase in muscle tightness, the risk of injury climbed by over 20 per cent.

In female athletes, the situation was quite different. There was no relationship between flexibility and injury risk. However, the females were more flexible than the men and had considerably fewer injuries. The most flexible women had an injury rate which was 60 per cent lower than that of the men.

What does this study mean to you? If you're a female athlete, you're probably fairly flexible already, and there's no evidence to support the idea that increased flexibility will keep you out of the injury clinic. If you're a male, on the other hand, there seems to be strong evidence that being more flexible will help you avoid injuries. So, in spite of the fact that this is a special issue for female athletes, here's some advice for any men who happen to be kibitzing.

Regular stretching of your muscles, tendons and ligaments, either after a thorough warm-up or after your workout is over (you should never stretch 'cold' muscles) can be a great way to keep your body intact, Research carried out recently with Honolulu Marathon participants revealed that individuals who stretched thoroughly after workouts had a considerably lower risk of injury compared to those who didn't stretch.

In addition to improving flexibility, stretching may provide another key benefit, and this applies to women as well as men: it may actually boost the rate at which muscles recover after workouts and races. Research has shown that stretching stimulates the transport of amino acids (the building blocks of protein) into muscle cells, accelerates protein synthesis inside cells and inhibits protein degradation ('Stretch and skeletal myotube growth: what is the physical to biochemical linkage?', Frontiers in Exercise Biology, Human Kinetics Publishers, pp 71-84, 1983). Other studies have shown that stretching increases muscle growth and inhibits atrophy. Overall, stretching after exercise appears to be a key element in the muscle-restoration process.

Of course, there has been considerable debate about which type of stretching is best for improving flexibility, but recent evidence suggests that PNF, or 'contract-relax' stretching, may be the most effective technique (Research Quarterly for Exercise and Sport, vol 63(3), pp 311-314, 1992). Fortunately, PNF is easy to do. For example, if you want to use PNF on your calf muscles, simply stretch your calves passively for a while, contract your ankle flexors (the 'shin' muscles in the front part of your lower leg) and then elongate your calf muscles again. Or you can stretch your calves, CONTRACT your calf muscles vigorously (doing so initiates a reflex which helps the calves loosen), relax your calves and tighten your shins, and then stretch our your calf muscles again. Regular stretching can improve your flexibility by 10-15 per cent in just four to six weeks.