STRETCHING THE FACTS

Dr Jonathan King

It has become widespread thinking that one has to stretch before exercising to prevent injury. An extension of this concept is whether stretching prior to competition or whether regular stretching improves performance. We may go through the motions of stretching, because we’ve been conditioned to do so, or is it from personal experience? Is it possible to say that one’s 10km time trial will improve by 30secs (or anything) after regular stretching?

From a biomechanical point of view, it makes sense to stretch one’s hamstrings prior to running activities, because flexible hamstrings mean increased stride length, and decreased quadriceps force to extend the knee. Furthermore stretching the hip flexors and quadriceps should ensure balanced forces around the pelvis, and this relates to posture, and running biomechanics. Explosive contraction in a tight muscle group may well lead to tearing of the structure. Fear of a major hamstring tear is enough to encourage stretching (and strengthening) of this muscle group.

A stretched muscle group has less stiffness, and theoretically requires less force to move the limb. However, decreased stiffness of leg muscles may result in increased energy absorption during foot stance, and less energy is available for recoil and toe-off.

Dr Ian Shrier published a review of scientific literature looking at whether stretching improved performance. He examined 23 articles, and in 22 he found no evidence that supported improved isometric force, isokinetic torque, or jumping height after stretching. This data refers to strength sports and not distance running. Seven studies suggested that regular stretching improved performance- measures such as maximum voluntary contraction, contraction velocity, eccentric and concentric contraction force, and 50-yard dash were improved after regular stretching.

No studies found that stretching worsened performance.

He reviewed 5 studies that related to running and one study found improved running economy after stretching. Four studies looked at running speed after stretching, and 2 studies had equivocal results, while the other 2 studies had contradicting results. Relating this to running, an acute bout of stretching decreases the stiffness of a muscle and tendon; this requires less force to contract the muscle, and less energy to move the joint. This translates to increased running economy where one uses less energy to complete a submaximal task such as a 10km run or marathon.

Regular stretching is thought to increase one’s tolerance of a stretched muscle, rather than actual muscle length in the short-term. Also, stretched muscle gets bigger (hypertrophy), and this is a proposed mechanism of how regular stretching may improve performance.

To apply such knowledge to running is not straightforward. It is probably safe to advise the following:

Ø Pre-run warm up of a brisk walk or slow jog for a few minutes.

Ø Stretch after exercise, or between exercise bouts.

Ø Moderate stretching is fine, as over-stretching can result in injury.

Happy stretching!