Our lab quantifies motor discoordination following brain injury isometrically in the upper extremity, lower exremity, and trunk, and dynamically in the upper extremity (including wrist/hand). We also study muscle property changes as a result of spasticity.

Previous studies have demonstrated abnormal joint torque coupling and associated muscle coactivations of the upper extremity in individuals with unilateral stroke. We investigated the effect of upper limb configuration on the expression of the well-documented patterns of shoulder abduction/elbow flexion and shoulder adduction/elbow extension. Maximal isometric shoulder and elbow torques were measured in stroke subjects in four different arm configurations.  Additionally, an isometric combined torque task was completed where subjects were required to maintain various levels of shoulder abduction/adduction torque while attempting to maximize elbow flexion or extension torque.  The dominant abduction/elbow flexion pattern was insensitive to changes in limb configuration while the elbow extension component of the adduction/extension pattern changed to elbow flexion at smaller shoulder abduction angles. This effect was not present in control subjects without stroke.  The reversal of the torque coupling pattern could not be explained by mechanical factors such as muscle length changes or muscle strength imbalances across the elbow joint. Potential neural mechanisms underlying the sensitivity of the adduction/elbow extension pattern to different somatosensory input resultant from changes in limb configuration are discussed along with the implications for future research.

Mean with standard error bars of normalized elbow flexion torque (a) and extension torque (b) during various percentages of maximum shoulder adduction in positions 2 and 4. Subjects were able to generate more elbow flexion and less elbow extension during adduction in position 4.

Our group has developed an isometric device that allows studying lower limb synergies in stroke subjects using two six degree of freedom load cells in order to measure hip, knee and ankle joint forces and torques. This totally adjustable device allows controlling amount of weight bearing, flexion, extension, abduction and adduction angle of each joint and incline. We aim to characterize the synergistic patterns elicited during the stance phase on the paretic extremity.  

Using a custom-built device with a 6-DOF load cell, multi-directional isometric trunk control of stroke and control subjects in a seated posture are currently being evaluated.

Previous studies have demonstrated abnormal joint torque coupling and associated muscle coactivations of the upper extremity in individuals with unilateral stroke.

In the muscle performance laboratory, we are investigating potential changes in muscle properties in the upper extremity after a unilateral brain lesion as seen in hemiparetic stroke. Muscle is an extremely hierarchical structure that consists of muscle fibers, which contain bundles of myofibrils, which are then made up of a series of units called sarcomeres – the basic unit of muscle function. Muscle is extremely adaptable to the stresses imposed on it, which can include altered neural input, changes in length, altered use, and alterations in the stress imposed on the muscle. After an UMN lesion such as a stroke, one or all of these changes can occur, leading to possible alterations in the properties of the muscle tissue. This project will use a Biodex machine and electrical stimulation of UE elbow musculature to look at changes in muscle properties in the paretic and non-paretic arm. The proposed study will seek to demonstrate that optimal fiber lengths, and therefore optimal joint positions, are altered following stroke. The knowledge generated by this study will form the cornerstone for future clinical research and provide a rational basis for the design of interventions that seek to overcome muscle alterations following stroke.

Lab members involved:
Jules Dewald
Ana Maria Acosta
Michael Ellis
Carolina Carmona
Justin Drogos
Theresa Moulton
Jacob McPherson
Laura Miller
Christa Nelson
Sam Perlmutter
Natalia Sanchez