1H-MRS evaluation of the Phosphocreatine-Creatine (PCr/Cr) pool in human muscle

Phosphocreatine (PCr) has been shown to effectively buffer ATP levels at high work rates in skeletal muscles. Our main goal was to assess whether or not the pool of PCr and Cr (Crtot) is the same in different metabolic states. Twelve healthy power trained (PWR) athletes (V02max 48 ± 1.9 ml/kg/min) and 12 healthy endurance trained (END) athletes (V02max 69.9 ± 1.5 ml/kg/min) completed a plantar flexion of the right foot against an increasing load until volitional fatigue. This was performed while lying supine in a 3 Tesla superconducting magnet with the gastrocnemius medialis (m. gastrocnemius), centered in a circumscribing coil. Total work production was calculated for the entire activity. Immediately following exhaustion a pressure cuff was inflated for 5 min (>350 mmHg superior to the knee) to allow collection of spectra prior to PCr resynthesis. A PRESS (Point Resolved Spectroscopy) sequence was used to resolve the 1H-visible Cr/PCr peak (3.02 ppm) during rest and ischemic fatigue. Standardized echo time (TE) of 100ms for 164 averages was used in collecting data from a 4.5 cm3 volume of interest (VOI) in the m. gastrocnemius. Upon removal of the cuff, recovery of Crtot was assessed for 10 min. Comparisons of rest vs. ischemic fatigue states in both groups indicated at least a 140% increase in the iH-MRS visible pool of Crtot. After 10 min of recovery the Crtot pool returned to within 27% of its resting state. These results suggest that there is a separate pool of Cr in the muscle which may be unavailable to creatine kinase until the onset of intense exercise. It is interesting to note that while both the transverse relaxation time (T2) for Crtot and the choline/carnitine/taurine peak (3.1 ppm) decreased by 65% and 26% respectively, the T2 of water was unchanged.Science, Faculty ofZoology, Department ofGraduat