Functional magnetic resonance imaging of muscle.

Muscle functional magnetic resonance imaging (MRI) is used to compare the relative involvement of different muscles recruited during exercise. The method relies on the activity-induced increase in the nuclear magnetic resonance transverse relaxation time (T2) of muscle water, which is caused by osmotically driven shifts of fluid into the myofibrillar space. In addition to imaging of whole muscle recruitment, muscle MRI may reveal changes in motor unit organization during disease.