Optimisation of the quantification of muscle phosphocreatine degradation during dynamic exercise and recovery using 31P MRS

Motivation: Measurement of muscle phosphocreatine degradation and recovery with exercise using 31P MRS provide indices of mitochondrial ATP to energy production. Goal(s): To assess the impact of 31P MRS repetition time (TR) and occlusion (OCC) and no-occlusion (NO-OCC) protocols on PCr recovery and depletion constants. Approach: 31P MRS data collected in OCC and NO-OCC protocols and downsampled to replicate longer TRs. Results: A short TR allows measurement of both PCr depletion and recovery time constants, particularly for NO-OCC where less depletion is induced resulting in faster recovery dependent on %PCr depletion. Longer TRs do not have sufficient sampling to robustly fit the depletion curve. Impact: To use 31P MRS to assess the phosphocreatine kinetics in a moving muscle during exercise, non-localised short TRs are necessary to robustly measure both depletion constants during exercise and recovery, key to the accurate quantification of contributions to energy delivery.