Steven L. Lehman

Research Interests

Neuromuscular control, muscle mechanics, biomechanics, mathematical models.

Research Summary

In the Motor Control Laboratory, we study of the control of voluntary human movement. Our center is the basic science of control of movements of one degree of freedom. Our approach is from the outside in, inferring aspects of control from the kinematics and dynamics of the object moved (eye, head, hand). In particular, we have always taken a strong interest in the relationship between muscle mechanics and control.

The human hand is an excellent system for study of motor control: it is controlled voluntarily; it has large representation in motor and sensory cortex and corticospinal tracts; it is easily perturbed mechanically. By restricting movements to one degree of freedom (e.g. flexion and extension of the wrist), it is possible to simplify the mechanics so that only a few muscles are active. We use this simple motor system to investigate control of voluntary movement in humans. We have characterized the mechanics of the hand and the muscles that drive wrist flexion and extension. Our model of the hand and muscle mechanics is adequate to predict movement of the hand about the wrist in many movements, and has been applied to robotic control. We have also investigated coordination of the two hands, in movements in which the two hands move and object, and in movements requiring bimanual grasp. We have elucidated both feedback and feedforward control mechanisms, and have discovered some bimanual
reflexes.

Over the past few years, we have attempted to apply our knowledge of motor control and muscle mechanics to rehabilitation. Our idea is that the devices we use to test bimanual coordination may be used to train bimanual coordination in patients who lose motor ability on one side due to stroke. Another aspect of rehabilitation that has captured our imaginations is urinary bladder control and its artificial stimulation in patients.

Our studies have shown that the mechanics of lengthening muscle play an important but poorly understood role in control of movement. We therefore investigate the mechanics of single muscle fibers in vitro, with the aim of developing a simple model of lengthening muscle. Thus we integrate, in one lab, mechanics experiments from the single fiber level to the whole human
level.

Selected Publications

Burmeister Getz, E., Cooke, R. and Lehman, S.L., Phase transition in force during ramp stretches of skeletal muscle, Biophysical Journal, in press, 1998.

Burmeister Getz, E.E. and Lehman, S.L., Calcium removal kinetics of the sarcoplasmic reticulum ATPase in skeletal muscle, American Journal of Physiology 272(Cell Physiol. 41):C1087-C1098, 1997

Lum, P.S., Lehman, S.L., Reinkensmeyer, D.J., The bimanual lifting rehabilitator: an adaptive machine for therapy of stroke patients, IEEE Transactions on Rehabilitation Engineering, 3(2):166-174, 1995

Damaser, M.S. and Lehman, S.L., The effect of urinary bladder shape on its mechanical properties during filling, Journal of Biomechanics 28(6):725-732, 1995

Reinkensmeyer, D.J., Lum, P.S. and Lehman, S.L., Human control of a simple two-hand grasp, Biol. Cybern. 67:553-564, 1992