MO-FG-CAMPUS-IeP3-05: A Novel Model for Evaluating Exercise Induced Skeletal Muscle Metabolism with Phosphorus MRS

Abstract

Purpose: The phosphocreatine (PCr) recovery rate after exercise is used an index of mitochondrial function in muscle 31P-MRS. We tested the hypothesis that the initial rate of PCr recovery after exercise reflects the equilibrium mitochondrial ATP production rate required to balance ATP requirements during exercise. Methods: Exercise data is often analyzed by fitting the PCr recovery curve to the Levenberg-Marquardt algorithm to determine the rate constant, k. In this study, the initial rates of change for PCr and inorganic phosphate (Pi) were examined at the beginning and after the end of exercise in the vastus lateralis. We applied a linear model to the first five data points and the slope plus the baseline [PCr] were used to determine initial rates of change in mM/s. Data from a 3T Siemens scanner in age-matched subjects with normal glucose tolerance (NGT, N=11) and type 2 diabetes mellitus (T2DM, N=9) were analyzed. Results: In NGT subjects, the initial depletion rate of PCr was significantly correlated with the recovery rate of PCr (r = 0.69, p = 0.02). The initial recovery rate of PCr was also significantly correlated with the initial rise (r = −0.42, p = 0.04) and decrease of Pi (r = −0.78, p = 0.005). For T2DM subjects, there is a breakdown between the relationship of the initial rates of change of [PCr] and the recovery of PCr as well as the relationship to the initial increase and decrease of Pi. Only the relationship between the rise and recovery of Pi remains. Conclusion: A novel method for analyzing data obtained from MRS exercise protocols is presented. Analysis of the initial depletion and recovery rates of PCr and Pi, during and after exercise, reveal associations that may be related to the uncoupling of metabolic processes at the cellular level in subjects with T2DM.