Stretching prepares the body for exercise, increases your range of motion and prevents muscle imbalances that can lead to serious injury. The American Council on Exercise advises performing a light five minute cardiovascular warm-up before stretching. This increases blood flow to the muscles, thus increasing muscular elasticity and preventing injury from stretching the muscles too far. If you are coming off an injury and experience decreased range of motion, talk to a doctor to ensure the injury is fully healed before starting a stretching routine.
There are two major categories of stretching, passive stretching and active stretching. Passive stretching involves some other force acting on your muscles to produce the stretch. In this type of stretch, the person being stretched does not do any work. Having a partner pull the targeted muscles to aid in the stretch, or lifting a leg up on a platform to do a hamstring stretch is considered passive. Active stretching is when you contract the opposing muscles to stretch the targeted muscle with no outside force. An example would be to sit with your legs extended and flex your toes. This stretches the calves by tightening the muscles on the top of the shins, the anterior tibialis muscle. All stretches are either passive or active. Both passive and active stretches can either be dynamic or static.
Dynamic stretching comprises controlled movements, such as leg and arm swings, that slowly bring the muscles close to their range of motion limit without exceeding it. This type of stretching is ideal before sporting events, weight-bearing exercise sessions that involve the whole body, or training involving quick changes of direction. Dynamic stretching is meant to prepare the muscles for the activity at hand. Examples include torso twists, arm circles, knee-high jogs, stretching lunge walks and standing leg lifts or circles.
Static stretching is when you stretch and hold the muscle just beyond its normal range of motion. Each stretch is ideally held for 15 to 30 seconds at a time and is repeated until you've held the stretch for a total of one minute. Its primary purpose is to increase flexibility of the muscles and ligaments. Following a workout, static stretching helps re-lengthen the muscles that have been tightened during the workout, preventing muscle imbalances and future injury. It is currently not recommended to do static stretching before intense total body activity, such as sporting events or competitions, because the pre-lengthening of muscles can decrease your muscles' power output, thus decreasing performance.
Ballistic stretching used to be incorporated as a method of increasing flexibility, however it is no longer recommended because it has a high injury rate. It involves uncontrolled bouncing motion that stretches the muscles far beyond their normal range of motion. An example of ballistic stretching would be sitting with your feet extended and reaching for your toes repeatedly, trying to extend farther with each bounce. It is not to be confused with dynamic stretching, which involves controlled movements.