Stretching too far or using poor form can cause injury.
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Both the American Council on Exercise and the American College of Sports Medicine state that stretching is an important component of a well-rounded exercise program. However, both organizations also urge caution about its potential negative effects. Stretching a muscle too much or before it's properly warmed up can cause injury, and performing static stretches before other forms of activity can result in worse performance.
The Benefits of Stretching
The official position statement of the ACSM is that stretching is "crucial to maintaining joint range of movement." The American Council on Exercise also lists injury prevention, decreased muscle tension and relaxation as benefits of regular flexibility training. Both organizations state, however, that these benefits can be realized with as little as 60 seconds of stretching for each muscle group twice per week. So you don't need to stretch too much to maintain flexibility and range of motion. The timing of stretching also impacts its effectiveness, with the greatest benefits of static stretching coming after a workout, rather than before.
The Potential Dangers of Stretching Too Much
Stretching a muscle that isn't warmed up, even a little bit, poses a big risk of injury. Warm-up activities should progress gradually, from light to moderate activity that will actually raise the temperature of the muscle tissue. Static stretching, or stretches where the same position is held for a length of time, does not warm the muscles and so it isn't a safe choice for a warm-up activity. Stretching too much, or past the point of discomfort is dangerous even when the muscles are warm. Listen to your body's signals and back off if you feel any pain during a stretch.
Static Stretching Decreases Performance
The Best Ways to Stretch
ACE recommends that dynamic stretching, or stretching that involves moving a joint through its range of motion, should be performed prior to other activities. Start with five minutes of light aerobic activity, like walking, to raise the body's temperature, and then perform movements that include the muscle groups and mimic the movements of the activity you'll be performing. For flexibility benefits, perform static stretches following your activity, when the body is already quite warm. Using proper form, stretch each major muscle group just to the point where movement is limited for 15 to 30 seconds, performing each stretch two to four times for best results.
A 2014 study published in The Journal of Strength and Conditioning compared the effects of dynamic stretching -- where you stretch while moving -- versus static stretching on explosive athletic performance and sprinting ability after 24 hours. Sixteen young soccer players, all male, performed 15 minutes of static stretching or dynamic stretching a full day before engaging in these types of activities. The researchers found that while the dynamic stretching enhanced participants' performance, static stretching reduced it. Static stretching can help after a workout, but is generally discouraged before intense exercise.