Is stretching before exercise necessary to prevent injury?
No. Although sports injuries can happen for a variety of reasons, it is not true that pre-exercise stretching prevents injury. In fact exercise physiologists and other fitness experts do not agree at all upon the necessity for stretching before exercising. However, most do advocate proper warmup of the muscles involved in whatever kind of exercise you do plan to do. Put another way, warming up for exercise does not necessarily include stretching; in fact the stretching isn't necessary. What is decidedly necessary is pre-exercise warmup of the muscles that will be pressed into service during the exercise itself.

Does stretching improve flexibility?
Indeed it does and there is ample proof of that. If one stretches regularly over a long period of time, say, months, there will almost always be an increase in the range of motion around any given joint including the spine. Muscles will become longer, more pliable and less easily stressed and tear-prone. Proper stretching for flexibility can be found in all yoga class, some Tai chi classes, other martial arts classes, ballet classes, dance classes and fitness classes that pay more than lip-service to stretching.

When is the best time to stretch?
 A good fitness class will spend a good deal of time AFTER the activity is finished in stretching. The purpose is to take the already warmed muscles while they are still pliable and do static stretching to prevent muscles from shortening up post-exercise. This technique maintains suppleness, range of motion, strength and pliability of the muscles and will more than likely prevent injuries when the next exercise session rolls around.
If you don't exercise (and you should, you already know that), there is no bad time to stretch except if the muscles are cold, meaning most of the time. To "warm" the muscles, that does not mean you can lie in the sunlight, it means you need to activate the muscle fibers and the blood circulation to the muscles before stretching.

What are the most common causes of stretching injuries?
One of the most common causes of injury to muscles is stretching cold muscles. Another cause is overstretching - pushing a stretch a little too hard. Yet another is "bouncing" or "pulsing" cold muscles. And last, skipping the stretching segment of your exercise program will leave you prone to injury the next time you go to exercise because the muscles tend to shorten and stiffen if you skip the stretches.

What are the most important things to remember about stretching?
• There is no direct evidence that pre-exercise stretching prevents injury.
• Over time, stretching improves mobility and flexibility.
• Stretching incorrectly or stretching cold muscles can cause injury.
• Stretching should be done only after muscles are warmed up from exercising.
• Stretching should be firm, not painful, and they should be static, not "bouncy".