Regular hamstring stretching increased range of motion

updated Oct 4, 2019

Tags: treatment, stretch, self-treatment, biomechanics, etiology, back pain, exercise, muscle, pro, pain problems, spine

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A nicely done experiment showing that regular hamstring stretching substantially increased range of motion in normal university kids. Specifically, after “a 4-week stretching program consisting of 4 hamstring and hip stretches performed 5 times per week,” their range increased about 16˚ or 20%. That is, when stretched with the same force (torque) applied, to the same level of discomfort, they could go 20% farther. The take-home message is that stretching can definitely increase range of motion — for whatever that’s worth.

The authors followed this data into an overinterpretation about how range increased, perhaps trying to score points for Team Plasticity — that is, for the idea that the body adapts physically to stretch, rather than neurologically. Because range increased, but pain at the end of the range did not, they unwisely concluded that, although they “cannot completely rule out volitional stretch tolerance as a possible explanation for changes in extensibility, it does seem that hamstring pain elicited during a passive stretch has little involvement in explaining training related improvements.” But an increase in range with no change in pain does constitute an increase in tolerance! Although it wasn’t measured, it’s safe to assume the subjects’ pain would have been less if stretched only to the end of their original range.

But the study is actually agnostic about mechanism. The authors place their bet on tissue plasticity, while I put mine on tolerance, but this experiment cannot actually settle the bet — it demonstrated only greater range and reduced stiff, and not whether it was due to neural or structural adaptations.

~ Paul Ingraham

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.

To measure hamstring extensibility, stiffness, stretch tolerance, and strength following a 4-week passive stretching program. Randomized controlled trial. Twenty-two healthy participants were randomly assigned to either a 4-week stretching program consisting of 4 hamstring and hip stretches performed 5 times per week, or a non-stretching control group. Hamstring extensibility and stiffness were measured before and after training using the instrumented straight leg raise test (iSLR). Stretch tolerance was measured as the pain intensity (visual analog scale; VAS) elicited during the maximal stretch. Hamstring strength was measured using isokinetic dynamometry at 30 and 120° s(-1). Hamstring extensibility increased by 20.9% in the intervention group following 4 weeks of training (p<0.001; d=0.86). Passive stiffness was reduced by 31% in the intervention group (p<0.05; d=-0.89). Stretch tolerance VAS scores were not different between groups at either time point, and no changes were observed following training. There were no changes in hamstring concentric strength measured at 30 and 120° s(-1). Passive stretching increases hamstring extensibility and decreases passive stiffness, with no change in stretch tolerance defined by pain intensity during the stretch. Compared to previous research, the volume of stretching was higher in this study. The volume of prescribed stretching is important for eliciting the strong clinical effect observed in this study.

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.

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