The role of proprioceptive reflexes during active movement is still a matter of controversy despite decades of study. Arguments have focused on what mechanical variable (e.g., muscle length, force) the central drive tries to control during movement. The proposed research addresses the question of what does the central drive in fact accomplish, i.e., what combination of mechanical variables is found to be regulated in postural states and controlled during active movement. It has been claimed, and there is support for this view, that the variable regulated by proprioceptive reflexes is a simple combination of muscle length and force. This hypothesis is often referred to as """"""""stiffness regulation"""""""". For measurements on a joint the regulated variable translates into a combination of joint angle and joint torque provided there is no cocontraction of antagonists. However, it is not clear whether the dynamic changes in torque and angle that ensue when a perturbation is imposed on the joint are a reflection of the inertia and damping associated with the joint or reflect, in part, the speed of response of the regulatory system.
The first aim i s to identify the regulated variable while the joint angle and torque change dynamically in response to perturbation.
The second aim i s to determine whether or not the combination of mechanical variables that was found to be regulated in postural states is what is controlled during active movement. The third and fourth aims address questions related to the commonly observed contraction of antagonist muscles when the need for such contraction is not apparent. Specifically, what external conditions are sufficient to elicit contraction of antagonist and whether the electromyographic stretch reflex of the agonists is affected. The answers to the questions raised above would provide an understanding of the role of proprioceptive reflexes in the control of movement by healthy subjects. Such an understanding is a necessary prerequisite for delineation of the role these reflexes play in pathological conditions characterized by movement disorders.

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National Institute of Neurological Disorders and Stroke (NINDS)
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Orthopedics and Musculoskeletal Study Section (ORTH)
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University of Arizona
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Pfann, Kerstin D; Corcos, Daniel M; Moore, Charity G et al. (2002) Circle-drawing movements at different speeds: role of inertial anisotropy. J Neurophysiol 88:2399-407
Koshland, G F; Hasan, Z (2000) Electromyographic responses to a mechanical perturbation applied during impending arm movements in different directions: one-joint and two-joint conditions. Exp Brain Res 132:485-99
Gram, M C; Hasan, Z (1999) The spinal curve in standing and sitting postures in children with idiopathic scoliosis. Spine (Phila Pa 1976) 24:169-77
Tyler, A E; Hasan, Z (1995) Qualitative discrepancies between trunk muscle activity and dynamic postural requirements at the initiation of reaching movements performed while sitting. Exp Brain Res 107:87-95
Koshland, G F; Hasan, Z (1994) Selection of muscles for initiation of planar, three-joint arm movements with different final orientations of the hand. Exp Brain Res 98:157-62
Karst, G M; Hasan, Z (1991) Timing and magnitude of electromyographic activity for two-joint arm movements in different directions. J Neurophysiol 66:1594-604
Karst, G M; Hasan, Z (1991) Initiation rules for planar, two-joint arm movements: agonist selection for movements throughout the work space. J Neurophysiol 66:1579-93
Hasan, Z; Karst, G M (1989) Muscle activity for initiation of planar, two-joint arm movements in different directions. Exp Brain Res 76:651-5
Hasan, Z; Stuart, D G (1988) Animal solutions to problems of movement control: the role of proprioceptors. Annu Rev Neurosci 11:199-223
Karst, G M; Hasan, Z (1987) Antagonist muscle activity during human forearm movements under varying kinematic and loading conditions. Exp Brain Res 67:391-401

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