Abstract
Passive properties of muscles and tendons, including their elasticity, have been suggested to influence motor control. We examine here the potential role of passive elastic muscle properties at the rat ankle joint, focusing on their potential to specify an equilibrium position of the ankle. We measured the position-dependent passive torques at the rat ankle before and after sequential cuts of flexor (a.k.a. dorsiflexor) and extensor (a.k.a. plantarflexor) ankle muscles. We found that there was a passive equilibrium position of the ankle that shifted systematically with the cuts, demonstrating that the passive torques produced by ankle flexor and extensor muscles work in opposition in order to maintain a stable equilibrium. The mean equilibrium position of the intact rat ankle ranged from 9.3° to 15.7° in extension relative to the orthogonal position, depending on the torque metric. The mean shift in equilibrium position due to severing extensors ranged from 4.4° to 7.7°, and the mean shift due to severing flexors was smaller, ranging from 0.9° to 2.5°. The restoring torques generated by passive elasticity are large enough (approximately 1.5-5. mNm for displacements of 18° from equilibrium) to affect ankle movement during the swing phase of locomotion, and the asymmetry of larger extension vs. flexion torques is consistent with weight support, demonstrating the importance of accounting for passive muscle properties when considering the neural control of movement.
Original language | English (US) |
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Pages (from-to) | 1728-1732 |
Number of pages | 5 |
Journal | Journal of Biomechanics |
Volume | 45 |
Issue number | 9 |
DOIs | |
State | Published - Jun 1 2012 |
Funding
This research was supported by NIH NIAMS R01AR053608 and NIH NINDS R21NS061208 to Matthew C. Tresch, National Defense Science and Engineering Graduate Fellowship to Mengnan (Mary) Wu, and by the Canada Research Chairs Program, NSERC, and Peter Wall Institute for Advanced Studies to Dinesh K. Pai. Special thanks to Prof. H. David Smith of Northwestern University for advice on statistical analysis.
Keywords
- Ankle joint
- Elastic properties
- Equilibrium position
- Muscle
- Passive properties
- Rat
- Stiffness
ASJC Scopus subject areas
- Biophysics
- Biomedical Engineering
- Orthopedics and Sports Medicine
- Rehabilitation