A review in the Clinical Journal of Sports Medicine (March 2005) shows that there is no good evidence that stretching prevents sports injuries. Muscles and tendons tear when the force applied to them is greater than their inherent strength, so anything that makes a muscle stronger helps to prevent injuries. Strengthening muscles helps prevent muscle and tendon tears, but stretching does not make muscles stronger. This review showed that stretching does not prevent shin splints, bone stress fractures, sprains, strains or other arm and leg injuries.
However, stretching can make you a better athlete. Competitive athletes need to stretch to makes muscles and tendons longer and more flexible. A longer muscle can exert a greater torque on a joint to help you run faster, lift heavier, throw further and jump higher. Stretching should always be done after your muscles are warmed up. You are likely to injure yourself if you stretch before you have warmed up or when your muscles are tired. Warming up raises muscle temperature to make them more pliable. Stretch no further than you can hold for a few seconds. Bouncing gives you a longer stretch, but can tear muscles. Only competitive athletes need to stretch further than they can hold for a few seconds. If you're over 50, be extra careful because older muscles are less springy and more likely to tear.
