Current Projects

Intraoperative Sarcomere Length Measurements

Muscle spasticity may cause severe joint deformity and dramatically affect quality of life. Evidence suggests that spastic muscles are themselves different from normal muscles, likely an effect of their abnormal neural input. For example, it has been shown that muscle fiber size variability and fiber type distribution different from that of normal muscle. Additionally, experiments have demonstrated that while some spastic muscles have a normal stretch reflex, intrinsic muscle stiffness is significantly higher compared to control muscle. These studies suggest that the properties of spastic muscle are not normal and yet, in spite of the prevalence of this entity, the muscle changes due to spasticity are poorly understood.

We have developed an intraoperative method to measure sarcomere length in human muscles during reconstructive surgery using laser diffraction, and have used this method to evaluate surgical reconstructive procedures that restore function in patients who have lost function after peripheral nerve injury or spinal cord injury. As the sarcomere length at the time of tendon transfer is probably important to optimize muscle function (previously demonstrated by our lab using mathematical modeling), studies of in vivo sarcomere length are being done in Sweden in close collaboration with Dr. Jan Fridén of the Göteborg University. Recent findings suggest that spasticity causes a major reorganization of the normal muscle–joint relationships.

Mechanical properties of Human Muscle Cells

To further understand the properties of spastic muscle, it becomes necessary to test the mechanical properties of the cells, and also assess any protein differences that exist between them and normal muscle. Because with living human muscle, one does not have the luxury of being to dissect out full length muscle fibers (the patients wouldn't appreciate it), these tests need to be conducted on muscle biopsies. These muscle biopsies can then be dissected down to a single muscle fiber segment, which can then be tested for mechanics in a chamber such as the one below. Recent findings suggest that Spastic muscle cells are shorter and stiffer than normal cells.

Muscle Response to Eccentric Contraction

Eccentric contraction (lengthening of an active muscle) can be extremely destructive. This damage results in reduced strength and "delayed onset muscle soreness." It has been shown to cause morphological changes in muscle, such as streaming of z-disks, loss of muscle proteins, and subsequent "remodeling" of the muscle. Currently, we are working to determine the time course of this protein loss and for the upregulation of mRNA expression for these muscle proteins in response to the injury. Recent results can be found in Biological and biomechanical response of rat dorsiflexors to eccentric exercise, and Increased desmin in rat dorsiflexors after a single bout of eccentric exercise.

Relationship Between Intramuscular Pressure and Muscle Force

Muscle force in living human beings is difficult to determine, because most methods are highly invasive. Electromyography (EMG) and joint kinematics are the most widely-used methods to assess muscle function, but are limited in their usefulness in dynamic motion. Intramuscular pressure, measured by placing a fiber optic pressure sensor into the muscle may be a new tool to bridge this gap. Recent results in the lab have shown that Intramuscular pressure is a good predictor of isometric stress at long lengths in rabbit tibialis anterior muscle.

Direct Determination of Lower Extremity Muscle Design

Models of the human lower extremity have been used to advance the fields of orthopaedic surgery, neurology, and rehabilitation. These models are valuable because they allow individual components or the entire musculoskeletal system rapidly and non-invasively tested. For example, the design and placement of new prosthetic components are often tested with models before experiments involving living patients. However, one limitation of current modeling approaches is the primary data used to represent skeletal muscles. This study aims to; 1) define the architectural features of twenty-six key muscles in the human lower extremity, 2) define the operating ranges of the microscopic subunits of these muscles (sarcomere-length operating ranges, and 3) develop an international accessible database for the bony and muscular features of the lower extremity. Recent studies on the lab have demonstrated key differences in the architectural features of the muscle surrounding the knee.

Real-Time Imaging of Muscle Cell Cytoskeletal Proteins During Passive Loading

Understanding functional relationships among cellular structures is a fundamental problem facing biologists today. Elucidation of the mechanisms by which a protein or protein complex elicits a physiological response depends in part upon our ability to accurately define a protein’s physical connections to surrounding structures. While current approaches, such as solution biochemistry, theoretical analysis of protein structure and electron microscopy, yield critical information regarding the identity of proteins within a complex, they do not assess mechanical connections between proteins, or their relationship to cellular function. Conversely, within striated muscle, several systems have been developed to quantify mechanical properties of intact single cells and single myofibrils, however, the extension of these results to the mechanical performance of a single cell with an intact cytoskeletal lattice necessitates further study of connections between sub-cellular structures.

We have developed a system that allows simultaneous confocal imaging of protein interactions and measurement of mechanical properties during passive loading of muscle cells. Additionally, we developed image processing algorithms to quantify connectivity between subcellular structures. We have recently used this method to demonstrate the Structural and functional roles of desmin in skeletal muscle during passive loading.