NMR of glycogen in exercise

Natural-abundance C-13 NMR spectroscopy is a non-invasive technique that en ables in vivo assessments of muscle and/or liver glycogen concentrations. O ver the last several years, C-13 NMR has been developed and used to obtain information about human glycogen metabolism with diet and exercise. Since N MR is non-invasive, more data points are available over a specified time co urse, dramatically improving the time resolution. This improved time resolu tion has enabled the documentation of subtleties of muscle glycogen re-synt hesis following severe glycogen depletion that were not previously observed . Muscle and liver glycogen concentrations have been tracked in several dif ferent human populations under conditions that include: (1) muscle glycogen recovery from intense localized exercise with normal insulin and with insu lin suppressed; (2) muscle glycogen recovery in an insulin-resistant popula tion; (3) muscle glycogen depletion during prolonged low-intensity exercise ; (4) effect of a mixed meal on postprandial muscle and liver glycogen synt hesis. The present review focuses on basic C-13 NMR and gives results from selected studies.