Effects of active and passive recoveries on splitting of the inorganic phosphate peak determined by 31P-nuclear magnetic resonance spectroscopy.

Six male long-distance runners performed knee flexion exercises in a 2.1 T superconducting magnet. 31P MRS was used to investigate the splitting pattern of the inorganic phosphate (Pi) peak during active and passive recovery. During exercise splitting of the Pi peak into two was observed (high and low pH) and after exercise the manner in which the Pi peak disappeared was different in passive and active recoveries. During passive recovery, in which exercise was not performed at all, the high-pH Pi peak disappeared more rapidly than the low-pH Pi peak. The low-pH Pi peak remained at a similar acidified chemical shift as during exercise, and then gradually disappeared during passive recovery. Conversely, during active recovery in which unloaded exercise was followed, the high-pH Pi peak was reduced, but remained, whereas the low-pH Pi peak returned very quickly to the pre-exercise level and then disappeared. Teh recovery rate of the low pH during active recovery (0.095 +/- 0.019 pH units/min) was significantly faster than that during passive recovery (0.014 +/- 0.019 pH units/min) (p < 0.01). The slow disappearance of the low pH Pi peak during passive recovery can be explained by the halting of glycogenolysis and an insufficient oxygen supply to resting glycolytic fibers, whereas the quick disappearance observed with active recovery would have been due to elevated sufficient oxygen supply and efficient removal of lactate as a result of the maintained blood flow. Oxy-myoglobin and hemoglobin was also measured with near infrared spectroscopy.