Stretching Flexibility Exercises

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Don't overdo it!
As a general guide, when it comes to preventing injury, one should make sure that athletes have a normal ROM is all the major muscle groups and correct postural alignment in the back. For instance, hamstring mobility should allow for 90° of straight-leg hip flexion. Any further ROM should be developed only if analysis of the sport's movements suggests that extra mobility is required. The obvious example is gymnastics, where contestants must perform movements with extreme ROMs. A footballer who developed the kinds of flexibility a gymnast needs would be at greater risk of injury since hypermobile joints become unstable. This relationship has been shown in American football players, with those who have over-developed hamstring flexibility suffering more from ACL strain. A likely reason is that the flexible hamstrings allow the knee to hyperextend more readily.
So the general rule regarding the relationship between flexibility and injury is that a normal ROM in each muscle group will protect against injury. However, specific movements in each sport that require extra ROM will need extra flexibility development to guard against injury. This may mean that an endurance runner's hamstring ROM may be less than a sprinter's, while a sprinter may not need such a large ROM in the groin as a tennis player, whose sport demands large lateral lunging movements. Extreme ROMs should only be developed out of necessity, since they lead to higher joint-injury risks, just as small ROMs lead to higher muscle-strain risks


What type of stretches?
The job of the coach and therapist is to know the normal ROM for each muscle group and to ensure the athlete achieves and maintains these standards. Christopher Norris's book (see references) describes in detail how to assess posture and flexibility in all major muscles and should be used as a guide. If any extra flexibility in specific muscles for specific movements is required, then this should also be developed. To develop flexibility, research suggests (see Alter, 1996) that static stretches should be held for at least 20 seconds, possibly up to 60 seconds, to gain a benefit. The stretches should also be performed regularly, ideally twice a day, every day. Stretches should not be painful, and should not cause the muscle to shake. Instead, one should feel a mild-intensity stretch and maintain that position. If the tension eases, taking the stretch a little further and holding the new position will help gains in ROM.
Using partner-assisted stretches and PNF stretching will also produce the same effect. PNF stretches involve applying an isometric contraction against the stretch to invoke a greater relaxation response and thus enable further ROM to be reached. The protocol is for the partner to take the stretch to the initial end point and hold that position. After about 20 seconds, the athlete opposes the position with a strong 10-second isometric contraction pushing against the partner. The athlete then relaxes, breathes out, and the stretching muscle should relax, allowing the partner to take it further. This is repeated. Some research has shown that PNF stretches are very effective, although one very recent study by Golhofer et al (European Journal of Applied Physiology, 1998, 77: 89-97) casts doubt on this. These researchers found that while there was a relaxation response post-isometric contraction, it only lasted for a very short time, and so no real benefit was gained.

Getting the mechanics right
Regardless of whether you choose conventional or PNF stretches, by far the most important factor for stretching effectiveness is to choose an exercise with the correct mechanics. The purpose of static stretches is to improve or maintain the ROM of a particular muscle, and the mechanics of the exercise must ensure that the target muscle is being stretched effectively.
For example, a popular, if old-fashioned, way to stretch the hamstrings is to perform a touch-toes stretch. However, the touch-toes position requires lower-back flexion, which leads to a change in pelvic position, and so the effectiveness of the stretch for the hamstrings is compromised. The mechanically correct way to isolate the hamstrings is to place one foot slightly in front of the other, leaning forward from the hips and keeping the back arched. Supporting your weight with your hands on the rear leg, you should then feel the stretch in the front leg. This position ensures the back does not flex and the pelvis remains tilted forward, so the hamstrings are lengthened optimally. Try the two different positions for yourself and you should feel a significant improvement in hamstring stretch. You may even find that by keeping your back in a strict arch you may not need to lean forward very far to achieve an effective hamstring stretch

The message here is that you must ensure that any static stretching exercise you perform allows the target muscle to be lengthened effectively, without being limited by other structures. The mechanics of the stretch should also ensure that the athlete is stable and that there are no undue stresses on any of the joints. For example, the hurdles stretch places a strain on the medial ligaments of the knee and is no longer recommended. Similarly, with the hamstring stretch discussed above, it is important to support one's weight with the hands on the rear leg so that the lower back is protected - leaning forward unsupported from a standing position places a great strain on it (see both Norris, 1998, and Alter, 1996, for safe and effective stretches for all muscle groups)


The bottom line?
There is still much to be researched about stretching methods before all the definitive answers can be given. However, it is probably fair to say that some of us need to look again at certain stretching techniques and ask why we do them. In particular, static stretching as part of a warm-up is very common, and yet the research, and logic, suggest that static stretches will do little to help prevent injuries or improve muscle function before an activity. Instead, active mobility exercises, those that take the muscles dynamically through the full ROM, starting slowly and building up to sports-specific speeds, are more appropriate, both pre-exercise and generally to develop active ROM for sports performance.
The role of static stretches is separate from the active flexibility exercises. Rather than as part of a warm-up, static stretches are necessary to develop the correct maximum static ROM that is needed to avoid muscle-strain injuries. Thus static stretches should be used either after training, when the muscles are warm, or in a separate context. These stretches must be effective, safe and stable in terms of their mechanics. As mentioned, a normal ROM in all muscle groups, plus any sports-specific ROMs, should be developed or maintained with static stretches following the above guidelines. If flexibility is well below normal, then PNF stretches may be considered to improve flexibility more quickly

Some of you may not agree with my conclusions about the role of the different types of stretching. However, I ask you to consider carefully the specificity principle of training and apply that to flexibility in the same way as you would to strength. For instance, no one would consider using only isometric contractions to develop strength in athletes. Instead, coaches try to devise strength exercises that are as specific as possible, both in terms of speed and mechanics, to the sports-specific condition. That said, why do so many people use only static stretches at the maximum ROM to develop flexibility for sport which involves active motion through various ROMs depending on the movements?
For further reading, you will find most of the references discussed, and more, in the list of recommended books and articles that accompanies this one

Raphael Brandon


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Stretching Flexibility Exercises

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