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Neuromuscular factors influencing the maximum stretch limit of the human plantar flexors

PainSci » bibliography » Blazevich et al 2012
Tags: stretch, plantar fasciitis, exercise, self-treatment, treatment, muscle, foot, leg, limbs, pain problems, overuse injury, injury, tendinosis

One article on PainSci cites Blazevich 2012: Quite a Stretch

PainSci commentary on Blazevich 2012: ?This page is one of thousands in the bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.

The main contribution of this research is the finding that “more flexible subjects exhibited greater fascicle rotation during stretch and a later onset of reflex muscle activity (i.e., EMG onset) than their less flexible counterparts.”

This paper refers to the obscure concept of “fascicle rotation.” Fascicles are bundles of muscle fibres. In pennate muscles (feather-like), many fascicles merge with a tendon at an angle. Fascicle rotation is the angle at which the muscle fibres attach to the tendon. It should really just be called “fascicle angle.”

~ 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.

Maximum joint range of motion is an important parameter influencing functional performance and musculoskeletal injury risk. Nonetheless, a complete description of the muscle architectural and tendon changes that occur during stretch and the factors influencing maximum range of motion is lacking. We measured muscle-tendon elongation and fascicle lengthening and rotation sonographically during maximal plantar flexor stretches in 21 healthy men. Electromyogram (EMG) recordings were obtained synchronously with ultrasound and joint moment data, and H-reflex measurements were made with the ankle at neutral (0°) and dorsiflexed (50% maximal passive joint moment) positions; the maximum H amplitude (normalized to maximum M-wave amplitude; M(max)) and H-amplitude elicited at a stimulation intensity that evoked 10% M(max) were obtained. Maximal stretch was accomplished through significant muscle (14.9%; 30 mm) and tendon lengthening (8.4%; 22 mm). There were similar relative changes in fascicle length and angle, but planimetric modeling indicated that the contribution of fascicle rotation to muscle lengthening was small (<4 mm). Subjects with a greater range of motion showed less resistance to stretch and a greater passive joint moment at stretch termination than less flexible subjects (i.e., greater stretch tolerance). Also, greater fascicle rotation accompanied muscle elongation (9.7 vs. 5.9%) and there was a greater tendon length at stretch termination in more flexible subjects. Finally, a moderate correlation between the angle of EMG onset and maximum range of motion was obtained (r = 0.60, P < 0.05), despite there being no difference in H-reflex magnitudes between the groups. Thus clear differences in the neuromuscular responses to stretch were observed between "flexible" and "inflexible" subjects.

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