At some point- we’ve all wanted to be more flexible. Touching our toes, squatting better, kicking someone in the head(!)- these are all legitimate flexibility goals. We reason that our muscles are tight and simply need lengthening and thus need a new length to be maintained. However, is this really the case? When I think about it, I haven’t really questioned this logic. What are we actually doing when we are stretching? How is increased flexibility achieved? There has been some interesting research that has served to answer these questions…

The concept of plastic deformity is used to describe a permanent change in the length of muscles. This is the popular theory that explains increased flexibility. However, a 2010 research review of 10 studies found that,

“in 10 studies that suggested plastic, permanent, or lasting deformation of connective tissue as a factor for increased muscle extensibility, none of the cited evidence was found to support this classic model of plastic deformation.”1

More recently, a study was conducted to assess the effects of a stretching regime on Joint Range of Motion (ROM), Torque-Angle Curve, Tendon Stiffness. Before and after a 6 week stretching program, ankle dorsiflexion ROM was assessed. It was found that whilst ROM was increased, the fascicle length and pennation angle did not change. There was also no change in passive or tendon stiffness.2 In short, there was no alteration of the structures being stretched, despite an increase in Range of Motion.

This has also been supported in research into the prevention and treatment of “contractures”. Contractures occur when muscles and soft tissues seize up due to immobilization or neurological problems. A review of static stretch for the treatment and prevention of contractures, by the Cochrane Collaboration found “that stretch is not effective for the treatment and prevention of contractures.”3 Again, stretching, in this case, does not elongate muscles.

So if we can increase flexibility, but there is essentially no change in the structures being stretched. Just what is happening?

If we are not altering the structure, the mechanism by which static stretching is working may be altered stretch tolerance. Altered stretch tolerance may well be a neurological phenomenon. That said, we must explain what is going on with the proprioceptors.

Proprioceptors are sensory organs that take a physical force, which is subsequently transformed to an electrical signal. Theses signals are necessary to bring about a reaction in the muscles that will guide us away from danger or injury.4 This is useful to know when understanding the concept of stretch tolerance.

As an example, people often complain that they can’t touch their toes. This is likely to be because it is a movement they do not do so often- not because their hamstrings are tight. This being the case, it is likely that when someone does try to touch their toes (something they don’t do often), the proprioceptors that detect the lengthening and speed of muscles, the Muscle Spindles, will be more sensitive. They will then feedback to the neurological system, that it must prevent the muscles from lengthening into a range that it is not too familiar with, despite the muscle and structures around the joint having a capability to do so. So, in increasing flexibility, we are ‘tuning’ the muscle spindles. We are giving the muscle spindles new information and in so doing, saying to the muscle spindles that we are engaging in a new task (touching the toes) and we must let the muscle spindles know that this is a safe new movement. And so, overtime, the muscle spindles learn that they don’t need to be as sensitive and prevent the movement from occurring. Namely, that being able to touch the toes is fine and will not cause injury.

So given that all we are doing is influencing the neurological system, how well does this mechanism transfer to the use of techniques in the following:

• Warm Ups
• Injury Prevention
• Prevention of DOMS
• Performance Enhancement?
• Postural Correction

Is it a useful technique at all?
More to come….


1Weppler et al. Increasing muscle extensibility: a matter of increasing length or modifying sensation? Physical Therapy. 2010.

2Konrad. A, Tilp.M Increased range of motion after static stretching is not due to changes in muscle and tendon structures.
Konrad A1, Tilp M2. Clin Biomech (Bristol, Avon). 2014 May 10

3 Katalinic et al. Stretch for the treatment and prevention of contractures. Cochrane Database of Systematic Reviews. 2010.

4 Physical Therapy May 1983vol. 63 no. 5 664-673 d “Motor Control : How Posture and Movements are Governed” Vernon B Brooks


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