Journal of Neurophysiology, Vol 70, Issue 3 997-1008, Copyright © 1993 by APS

ARTICLES

Mechanical properties of cat soleus muscle elicited by sequential ramp stretches: implications for control of muscle

D. C. Lin and W. Z. Rymer
Department of Biomedical Engineering, Northwestern University Medical School, Chicago, Illinois.

1. Force changes in areflexive cat soleus muscle in decerebrate cats were recorded in response to two sequential constant velocity (ramp) stretches, separated by a variable time interval during which the length was held constant. Initial (i.e., prestretch) background force was generated by activating the crossed-extension reflex, and stretch reflexes were eliminated by section of ipsilateral dorsal roots. 2. For the initial 400-900 microns of the first stretch, the muscle exhibited high stiffness, classically termed "short-range stiffness." This high stiffness region was followed by an abrupt reduction in stiffness, called muscle "yield," after which force remained at a relatively constant level, achieving a plateau in force. This plateau force level depended largely on stretch velocity, but this dependence was much less than proportional to the increase in stretch velocity, in that a 10-fold increase in velocity produced < 2-fold increase in plateau force. 3. In experiments where the velocities of the two sequential ramp stretches were identical, the force plateau level was the same for each stretch, regardless of the time elapsed before the second stretch (varied from 0 to 500 ms). In contrast, measures of stiffness during the initial portion of the second stretch showed time-dependent magnitude reductions. However, stiffness recovered quickly after the first stretch was completed, returning to control values within 30-40 ms. 4. In one preparation, in which the velocities of the two sequential ramp stretches were different, the force plateau elicited during the second stretch exhibited velocity dependence comparable with that recorded in the earlier single velocity studies. Furthermore, muscle yield was still evident in the case where the force change was due solely to the change in velocity and where short-range stiffness had not yet recovered fully from the initial stretch. On the basis of these findings, we argue that the classical descriptions of short-range stiffness and yield are inadequate and that the change in force that has typically been called the muscle yield reflects a transition between short-range, transient elastic behavior to steady-state, essentially viscous behavior. 5. To examine changes in the muscle's mechanical stiffness during single ramp stretches, a single pulse perturbation was superimposed at various times before, during, and subsequent to the constant velocity stretch. The force increment elicited in response to each pulse decreased relative to the initial isometric value, remained essentially constant until the end of the ramp, and then returned to its prestretch magnitude shortly (30-40 ms) after stretch termination.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				L. Cui, E. J. Perreault, and T. G. Sandercock Motor unit composition has little effect on the short-range stiffness of feline medial gastrocnemius muscle J Appl Physiol, September 1, 2007; 103(3): 796 - 802. [Abstract] [Full Text] [PDF]

				V. K. Haftel, E. K. Bichler, T. R. Nichols, M. J. Pinter, and T. C. Cope Movement Reduces the Dynamic Response of Muscle Spindle Afferents and Motoneuron Synaptic Potentials in Rat J Neurophysiol, May 1, 2004; 91(5): 2164 - 2171. [Abstract] [Full Text] [PDF]

				C. M.J.I. Huyghues-Despointes, T. C. Cope, and T. R. Nichols Intrinsic Properties and Reflex Compensation in Reinnervated Triceps Surae Muscles of the Cat: Effect of Movement History J Neurophysiol, September 1, 2003; 90(3): 1547 - 1555. [Abstract] [Full Text] [PDF]

				W. J. Kargo and S. F. Giszter Afferent Roles in Hindlimb Wipe-Reflex Trajectories: Free-Limb Kinematics and Motor Patterns J Neurophysiol, March 1, 2000; 83(3): 1480 - 1501. [Abstract] [Full Text] [PDF]

				D. C. Lin and W. Z. Rymer Damping Actions of the Neuromuscular System With Inertial Loads: Soleus Muscle of the Decerebrate Cat J Neurophysiol, February 1, 2000; 83(2): 652 - 658. [Abstract] [Full Text] [PDF]

				D. C. Lin and W. Z. Rymer Damping in Reflexively Active and Areflexive Lengthening Muscle Evaluated With Inertial Loads J Neurophysiol, December 1, 1998; 80(6): 3369 - 3372. [Abstract] [Full Text] [PDF]

				T. G. Sandercock and C. J. Heckman Force From Cat Soleus Muscle During Imposed Locomotor-Like Movements: Experimental Data Versus Hill-Type Model Predictions J Neurophysiol, March 1, 1997; 77(3): 1538 - 1552. [Abstract] [Full Text] [PDF]