Advancements in medical and engineering approaches to the treatment of musculoskeletal disorders are dependent on accurate characterization of normal and diseased muscle function. The goals of this project are to develop and validate techniques for directly and noninvasively measuring musculoskeletal motion in normal and diseased muscle and to test the new methods in two in vivo experiments. the development and validation effort will include extension and adaptation of phase contrast magnetic resonance data acquisition and analysis methods for two- and three- dimensional motion. These methods will provide direct in vivo measurement of the motion of every selected point within a muscle and will characterize muscle contraction (deformation, rotation, and translation) using velocity encoded image sets. Numerical data on tensile and shear strains in muscle tissue will be compared to the amount of force developed by the muscle. The data acquisition methods will be validated by using data from motion phantoms (devices which simulate muscle motion). As an evaluation of clinical application, muscle motion will be imaged in patients undergoing muscle- tendon transfers in the forearm. Pre-surgical scans will be compared with post-surgical scans made at three fixed intervals during muscle adaptation and retraining, and then correlated with clinical outcome. In the second in vivo experiment, muscle contraction and myotendinous strain will be measured in an isolated muscle, the soleus, and compared to the force developed by that muscle working against different external loads. these images will be compared to images of functional musculoskeletal recovery in patients who have experienced soleus muscle disuse after wearing a leg cast for at least eight weeks. The success of this work will lead to a readily transportable, clinically useful, noninvasive, and accurate technique for evaluating musculoskeletal motion and deformation in three dimensions and to the future development of improved surgical and rehabilitative treatment of patients with impaired muscle function.