John Hodgson

My general interest is in how mammalian movement is accomplished, from the overall limb biomechanics to the neural coordination of muscles and the structural details of muscle which transmit sarcomere activity into the forces and displacements that underly every movement. An additional interest is how altered environments such as in spaceflight and pathologies, such as atrophy impact the normal execution of movement. Most recent work has been in collaboration with Dr. Shantanu Sinha in the Department of Radiology at UCSD (http://radiology.ucsd.edu/about-us/people/faculty/shantanu-sinha) and with Professor J.S. Chen in the Department of Civil Engineering at UCLA (http://www.cee.ucla.edu/faculty/chen/profile). We are investigating how intramuscular structure impacts whole muscle force and displacement. MRI imaging is used to provide muscle structure data and also a pixel-resolution map of intramuscular displacements. Finite element computational models of 'generic' muscles have been used to simulate muscle contractions and the intramuscular deformations compared with experimental observations. These efforts indicate that intramuscular morphology, such as fiber pennation angle and elastic properties of intramuscular passive materials have a significant impact on muscle performance. Furthermore, our results suggest specific properties of intramuscular passive materials which will be investigated in the future. We are currently developing a database of subject-specific muscle morphologies using several MRI techniques to image intramuscular fat, connective tissue, muscle fiber pennation angles and intramuscular dynamics of muscle contractions. Parallel efforts are being made to convert the data into subject-specific, image-based computational models in which simulated contractions can be compared with observations of real muscles contracting. Previously document variability in muscle structure will allow us to determine the impact of intramuscular structure on muscle performance. An additional interest is in the degree to which the changes in structure wrought by muscle atrophy contribute to the disproportionate loss of function relative to the loss of muscle mass or cross sectional area. We hope to approach this by conducting studies on muscles before, after and during recovery from atrophy artificially induced by muscle disuse.