Is muscle-tendon unit length a valid indicator for muscle spindle output ?

Maas, H. and Lichtwark, G.A. (2009) Is muscle-tendon unit length a valid indicator for muscle spindle output ?. The Journal of Physiology, 587 1: 13-14. doi:10.1113/jphysiol.2008.165555

Author Maas, H.
Lichtwark, G.A.
Title Is muscle-tendon unit length a valid indicator for muscle spindle output ?
Journal name The Journal of Physiology   Check publisher's open access policy
ISSN 0022-3751
Publication date 2009-01
Sub-type Discussion - responses, round table/panel discussions, Q&A, reply
DOI 10.1113/jphysiol.2008.165555
Volume 587
Issue 1
Start page 13
End page 14
Total pages 2
Editor William A. Large
Place of publication Oxford , United Kingdom
Publisher Blackwell for the Physiological Society
Language eng
Subject 1106 Human Movement and Sports Science
Abstract An important role of feedback from muscle and cutaneous receptors is to regulate the magnitude and timing of muscle activity to satisfy the mechanical demands during locomotion (Rossignol et al. 2006). Such sensory information can be used to modulate the walking system of the central nervous system, but it is also suitable to compensate for acute mechanical perturbations via rapid spinal pathways. The latter is likely to be important during walking on uneven surfaces, preventing the body from getting off balance and in the worst case falling. This hypothesis was tested in a well-designed study by af Klint et al. (2008), who assessed changes in within-step activity of the triceps surae muscles during over-ground walking. In this study, natural variations in ground surface were mimicked with small (i.e. ± 3 deg) slope changes of a robotic platform that was embedded in the walkway. Modulation of proprioceptive feedback as a result of an altered ground was assessed by changes in muscle–tendon unit (MTU) length, Achilles tendon force (ATF) and electromyography. MTU length was calculated using kinematic data of the ankle and knee joints as well as regression equations from the literature. ATF was assessed using a E-shaped buckle transducer externally clamped to the tendon. It was found that stepping on an inclined surface increased triceps surae activity as well as MTU length and ATF. The opposite occurred during steps on a negative slope. These results clearly show acute modulation of neural drive to the muscle. As the slopes were imposed in a random order, these compensatory responses most likely rely on within-step reflex pathways (through proprioceptive and/or cutaneous afferents) in contrast to feed-forward control. This significant finding opens the door for our understanding of which of the reflex pathways might be critical for maintaining stability during walking on uneven terrain.
Keyword Human walking
Q-Index Code CX

Document type: Journal Article
Sub-type: Discussion - responses, round table/panel discussions, Q&A, reply
Collection: School of Human Movement and Nutrition Sciences Publications
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Created: Tue, 15 Jun 2010, 12:01:47 EST