The goal of this proposal is two-fold: (1) to further develop and validate a technology, magnetic resonance elastography (MRE), for quantitatively imaging mechanical properties and tension distribution in muscle and (2) to apply the technique for in vivo evaluation of patients with four common, and clinically significant muscle disorders (spasticity, disuse atrophy, myofascial pain and a metabolic myopathy). These studies will employ a magnetic resonance imaging sequence with synchronous motion-sensitizing gradients to map propagating shear waves in the muscle. The technique will assess the mechanical properties of the muscle and its tension distribution. Specifically, the study can be divided into three specific aims. Aim 1: Optimize MRE methods of acquisition and analysis for the assessment of muscle, including electromechanical drivers, data acquisition techniques, and methods for image analysis. Advanced techniques for very rapid MRE assessment of muscle will continue to be developed. Aim 2: Validate the MRE assessment of muscle properties and tension with phantom, ex-vivo muscle, and Finite Element Modeling (FEM) techniques. Finite Element Analysis will be performed by using both phantom and bovine muscles to better correlate MRE wave-length findings as function of muscle properties, tension and fiber architecture. Aim 3: Study In Vivo Normal and Abnormal Muscle. The MRE technique will be applied in vivo to provide elastographic images of abnormal muscle with known disorders. The patient groups chosen for study are each important in their own right, and furnish unique information across the spectrum of muscular disease and dysfunction. Groups to be studied include individuals with new onset of spasticity following an ischemic, hemispheric stroke, disuse atrophy as a result of immobilization, metabolic (hyperthyroid) myopathy and myofascial pain for trigger point identification. The overall hypothesis of this work is that will bring benefits to both basic research and clinical care.