Muscle has been extensively studied to identify its mechanical properties and their molecular mechanisms. The goal of our lab is to investigate how muscle properties contribute to normal motor behaviors. In posture and locomotion, the endpoint of the limb forms the primary interface with the environment. This endpoint not only needs to generate force but must also be stable to perturbations in all 3 dimensions (3D). Consider for example the case of locomotion across an uneven surface: the foot is undergoing constant 3D changes in angle and orientation and failure to deal with these changes can result in serious injury. In this proposal, we investigate the contribution of muscle properties to stability of the limb endpoint in 3D space. The key mechanical property for stability is the stiffness of the endpoint. Previous studies of endpoint stiffness have been limited by use of manipulators with only 2 degrees of freedom. Our studies utilize a 6 degree of freedom load cell coupled to a sophisticated 6 degree of freedom robotic arm to allow full exploration of endpoint stiffness in 3D space. We study the cat hind limb to allow precise measurements of individual muscle properties without intervention from reflexes.
Our aims trace the sources of endpoint stiffness from single muscles, to muscle combinations, to whole limb interactions.
In aim 1, we test the hypothesis that variations in muscle architecture are the primary source of differences in stiffness between muscles.
In aim 2, we test the hypothesis that the force and stiffness for synergist muscles acting at single joint sum linearly.
Aim 3 considers the challenge for endpoint stability generated by exertion of forces against the environment, which result in de-stabilizing reaction forces. We hypothesize that maintenance of endpoint stability during antigravity tasks actually requires co-activation of at least some flexors with the extensors that generate the primary forces. These studies will reveal how the unique design of each muscle acts to stabilize the limbs against the perturbations that actually occur during real 3D movements. These results will be important for rehabilitation engineering, providing a quantitative guide for muscle selection in tendon transfer surgeries and functional neuromuscular stimulation.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR041531-13
Application #
7121672
Study Section
Special Emphasis Panel (ZRG1-GRM (01))
Program Officer
Boyce, Amanda T
Project Start
1993-01-01
Project End
2008-08-31
Budget Start
2006-09-01
Budget End
2008-08-31
Support Year
13
Fiscal Year
2006
Total Cost
$244,383
Indirect Cost
Name
Northwestern University at Chicago
Department
Physiology
Type
Schools of Medicine
DUNS #
005436803
City
Chicago
State
IL
Country
United States
Zip Code
60611
Cui, Lei; Maas, Huub; Perreault, Eric J et al. (2009) In situ estimation of tendon material properties: differences between muscles of the feline hindlimb. J Biomech 42:679-85
Sandercock, Thomas G; Maas, Huub (2009) Force summation between muscles: are muscles independent actuators? Med Sci Sports Exerc 41:184-90
Cui, Lei; Perreault, Eric J; Maas, Huub et al. (2008) Modeling short-range stiffness of feline lower hindlimb muscles. J Biomech 41:1945-52
Maas, Huub; Sandercock, Thomas G (2008) Are skeletal muscles independent actuators? Force transmission from soleus muscle in the cat. J Appl Physiol 104:1557-67
Cui, Lei; Perreault, Eric J; Sandercock, Thomas G (2007) Motor unit composition has little effect on the short-range stiffness of feline medial gastrocnemius muscle. J Appl Physiol 103:796-802
Sandercock, Thomas G (2006) Extra force from asynchronous stimulation of cat soleus muscle results from minimizing the stretch of the common elastic elements. J Neurophysiol 96:1401-5
Perreault, Eric J; Day, Scott J; Hulliger, Manuel et al. (2003) Summation of forces from multiple motor units in the cat soleus muscle. J Neurophysiol 89:738-44
Perreault, Eric J; Heckman, Charles J; Sandercock, Thomas G (2003) Hill muscle model errors during movement are greatest within the physiologically relevant range of motor unit firing rates. J Biomech 36:211-8
Sandercock, T G; Heckman, C J (1997) Force from cat soleus muscle during imposed locomotor-like movements: experimental data versus Hill-type model predictions. J Neurophysiol 77:1538-52
Sandercock, T G; Heckman, C J (1997) Doublet potentiation during eccentric and concentric contractions of cat soleus muscle. J Appl Physiol 82:1219-28

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