Emerging opportunities with NMR.

Several nuclear magnetic resonance (NMR) methods with potential as tools for the study of neuromuscular fatigue are described briefly. 13C MR spectroscopy (MRS) is presented as a means of studying the regulation of substrate (fuel) flux into the citric acid cycle. 23Na and 39K MRS can be used to study the distribution of sodium and potassium ions across the cell membrane. 1H MR imaging (MRI) takes advantage of the relationship between the environment of water 1H and the mechanisms of nuclear spin relaxation to make static and cine images which present spatial (anatomical) information that can be tied to essential physiological, biochemical, or biophysical phenomena of fatiguing muscle.