The role of muscle is to generate the forces required for movements. Thus, the long term objective of this laboratory is to understand how different muscle properties actually work together to produce the forces required for normal movements. This is an area where little is known because most studies of muscle either characterize its diverse mechanical properties or investigate their molecular mechanisms. The main thesis of this proposal is that a lack of understanding of how muscle properties behave during normal activation is the primary limit to understanding their roles in normal movements. The experiments focus on two of the most fundamental properties of muscle, the length-tension (L-T) and force-velocity (F-V) functions. Norman activation consists of recruitment and rate modulation of motor units, whereas the L-T and F-V functions are typically measured during maximal tetanic stimulation of either whole muscle or single muscle fibers.
In Aim 1, the goal is to obtain the first measurements of the L-T and F-V functions during normal recruitment and rate modulation of motor units. An areflexive animal preparation has been developed for this purpose. Preliminary data show that both functions are much steeper at low recruitment and rate levels than would be expected from their tetanic behaviors.
Aim 2 seeks to understand how this occurs by measuring the L-T and F-V functions of single motor units at rates that correspond to the physiological range.
In Aim 3, the role of the L-T and F-V functions during a variety of dynamic changes in muscle length are investigated. Activation is again supplied by a normal pattern of recruitment and rate modulation in the areflexive preparation. In these conditions, several muscle properties can contribute to force generation, but it is expected that most of the force modulations can be accounted for by the L-T and F-V functions seen during the appropriate level of natural activation. The results of these studies are expected to show that natural activation patterns play a key role in shaping the mechanical output of muscle. This information is important for understanding how muscle is used in motor control in both normal and pathological states.

Agency
National Institute of Health (NIH)
Institute
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Type
Research Project (R01)
Project #
5R01AR041531-08
Application #
6374943
Study Section
Special Emphasis Panel (ZRG4-GRM (01))
Program Officer
Lymn, Richard W
Project Start
1993-01-01
Project End
2002-09-26
Budget Start
2001-05-01
Budget End
2002-09-26
Support Year
8
Fiscal Year
2001
Total Cost
$153,981
Indirect Cost
Name
Northwestern University at Chicago
Department
Physiology
Type
Schools of Dentistry
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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