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Flexibility gains due to changes in sensation, not muscle length

PainSci » bibliography » Ch et al 2010
Tags: stretch, biology, exercise, self-treatment, treatment, muscle

Five articles on PainSci cite Ch 2010: 1. The Complete Guide to Trigger Points & Myofascial Pain2. Quite a Stretch3. The Complete Guide to Low Back Pain4. The Complete Guide to Neck Pain & Cricks5. Vibration Therapies, from Massage Guns to Jacuzzis

PainSci notes on Ch 2010:

People seem to be more flexible when they stretch regularly for a while, but why? A number of explanations have been proposed, and none have panned out. This article reviews them all in great detail, and the full text is free. It’s not light reading, but there are some fascinating highlights.

For instance, the popular theory that muscles actually change length (“plastic deformation”) is dismissed: “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.” After reviewing several more disproven popular theories, the authors conclude:

Increases in muscle extensibility observed immediately after stretching and after short-term (3 to 8-week) stretching programs are due to an alteration of sensation only and not to an increase in muscle length. This theory is referred to as the sensory theory throughout this article because the change in subjects’ perception of sensation is the only current explanation for these results.

In short, elongation is normally limited by strict neurological edict, in much the way that we have much greater muscle power available than we can normally, safely use. But to some extent we get used to stretching — we can learn to tolerate greater elongation.

original abstract Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.

Various theories have been proposed to explain increases in muscle extensibility observed after intermittent stretching. Most of these theories advocate a mechanical increase in length of the stretched muscle. More recently, a sensory theory has been proposed suggesting instead that increases in muscle extensibility are due to a modification of sensation only. Studies that evaluated the biomechanical effect of stretching showed that muscle length does increase during stretch application due to the viscoelastic properties of muscle. However, this length increase is transient, its magnitude and duration being dependent upon the duration and type of stretching applied. Most of these studies suggest that increases in muscle extensibility observed after a single stretching session and after short-term (3- to 8-week) stretching programs are due to modified sensation. The biomechanical effects of long-term >8 weeks) and chronic stretching programs have not yet been evaluated. The purposes of this article are to review each of these proposed theories and to discuss the implications for research and clinical practice.

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