Provided is at least one chemical entity chosen from compounds of Formula I and compounds of Formula II: ##STR00001## and pharmaceutically acceptable salts thereof, compositions thereof, and methods for their use in modulating of one or more of skeletal myosin, skeletal actin, skeletal tropomyosin, skeletal troponin C, skeletal troponin I, skeletal troponin T, skeletal muscle, and skeletal sarcomere.