Stretching for sport and exercise improves flexibility, which increases the ability of a joint to move through its full range of motion; in other words, how far it can bend, twist and reach. Some activities, such as gymnastics, require more flexibility than others, such as running.Different types of stretches
Static stretch: Stretching a muscle to the point of mild discomfort and holding that position, typically for at least 30 seconds or longer.

Proprioceptive neuromuscular facilitation (PNF): Methods vary, but typically PNF involves holding a stretch while contracting and relaxing the muscle.
Dynamic stretch: Performing gentle repetitive movements, such as arm swings, where one gradually increases the range of motion of the movement, but always remains within the normal range of motion.

Ballistic or bouncing stretches: Involves going into a stretch and performing bouncing or jerking movements to increase range of motion.
Most of the research on stretching has focused on static stretching; there is less evidence on other forms.

What happens when we stretch?
While the exact mechanics of what happens are not fully understood, regular stretching is thought to increase flexibility, both by making muscles suppler and by retraining the nervous system to tolerate stretching further. Flexibility from regular stretching gradually disappears once you stop stretching – typically after four weeks.

How much flexibility do I need?
It depends on your activity. The flexibility demands of a gymnast or a ballet dancer are clearly different to those of a runner. There is little to be gained for a jogger or runner from having the flexibility of a gymnast.
To generate power during exercise, the muscles and tendons store and release energy like a spring. Too much flexibility may reduce the muscle’s natural spring, which may be detrimental for activities involving running, jumping and sudden changes in direction, such as running, football or basketball.
Too little flexibility may increase the risk of muscle strain injury, as the muscles are unable to lengthen and absorb this energy.

Does stretching reduce soreness?
There is no evidence that stretching helps to reduce or prevent a type of pain that can show up a day or two after exercising – also called delayed onset muscle soreness (DOMS).
Researchers found that pre- or post-exercise stretching didn’t stop bothersome aches and pain. (The likely reason: Micro-tears in the muscle and surrounding connective tissue are to blame for soreness, which stretching won’t repair.)

Should I stretch before exercising?
Your decision to stretch or not to stretch should be based on what you want to achieve. If the objective is to reduce injury, stretching before exercise is not helpful. Your time would be better spent by warming up your muscles with light aerobic movements and gradually increasing their intensity.
If your objective is to increase your range of motion so that you can more easily do the splits, and this is more beneficial than the small loss in force, then you should stretch.

For most recreational exercisers, stretching before exercise is therefore a matter of personal preference. If you like stretching, do it, and if you don’t like stretching, don’t do it.

Should I stretch after exercising?
There is some evidence that regular static stretching outside periods of exercise may increase power and speed, and reduce injury. The best time to stretch is when the muscles are warm and pliable. This could be during a yoga or pilates class, or just after exercising.
However, there is very limited evidence about specifically stretching after exercise. Since people tend not to set aside one time to stretch and one time for other activities, I recommend that they stretch after exercise.

A post-exercise stretch will also slow down your breathing and heart rate, and bring the mind and body back to a resting state.