Stretching

Some coaches, trainers and textbooks recommend stretching before and after your workout because it can help your performance and reduce the risk of injuries. However, numerous research has shown that some types of stretching can enhance your workout while others do not improve or reduce your athletic capabilities. Exercise physiologist Len Kravitz recommends that you perform dynamic stretching before your workout and static stretching afterward.

Dynamic flexibility is often used as a warmup to stimulate your nervous system and muscles to be better prepared for the upcoming activity. It involves moving your muscles and joints repetitively within your range of motion. The movement is usually specific to the exercise or sport that you're going to play. For example, soccer players warm up by doing leg and hip swings in different directions, and boxers do a couple of standing torso and shoulder twists while working on their footwork and punches. Static stretching, which involves stretching a muscle for 20 to 30 seconds, decreases neural stimulation to the muscles and enhances relaxation. This type of stretching is usually non-sports specific, working on fixed muscle groups instead of movement like dynamic stretching. Therefore, static stretching should be performed after a workout

--Livestrong.com