Estimates of Mitochondrial Capacity Derived from Phosphocreatine Recovery Kinetics in Human Calf and Thigh Muscle Differ Systematically from Published Measurements Using Invasive Methods

Elina Raja Ahmad¹, William Bimson¹, Graham Kemp²

Analysis of 31P MRS phosphocreatine recovery kinetics provides valuable information about muscle mitochondrial function in vivo. Correct analysis of the data in terms of mitochondrial capacity (a function of mitochondrial numbers, function and substrate/O2 supply) depends on the underlying physiology. We compare the results of such analysis in quadriceps and calf muscle at 60% and 90% maximum voluntary contraction force, and with estimates inferred from some published measurements by invasive methods. Results differ little between the two muscles, but systematic quantitative differences between methods of assessing mitochondrial function in vivo remain unexplained.