A MODEL FOR PHOSPHOCREATINE RESYNTHESIS

A model for phosphocreatine (PCr) resynthesis is proposed based on a s imple electric circuit, where the PCr store in muscle is likened to th e stored charge on the capacitor. The solution to the second-order dif ferential equation that describes the potential around the circuit sug gests the model for PCr resynthesis is given by PCr(t) = R - [d(1) . e xp(-k(1) . t) +/- d(2) . exp(-k(2) . t)], where R is PCr concentration at rest, d(1), d(2), k(1), and k(2) are constants, and t is time. By using nonlinear least squares regression, this double-exponential mode l was shown to fit the PCr recovery data taken from two studies involv ing maximal exercise accurately. In study 1, when the muscle was elect rically stimulated while occluded, PCr concentrations rose during the recovery phase to a level above that observed at rest. In study 2, aft er intensive dynamic exercise, PCr recovered monotonically to resting concentrations. The second exponential term in the double-exponential model was found to make a significant additional contribution to the q uality of fit in both study 1 (P < 0.05) and study 2 (P < 0.01).