T1 measurements of 31P metabolites in resting and exercising human gastrocnemius/soleus muscle at 1.5 Tesla.

This study has measured the apparent 31P T1 times at 1.5 T in human gastrocnemius/soleus muscle groups at rest, during exercise, and during recovery from a 90-sec submaximal plantar flexion exercise. T1 times were measured with a 10-sec time resolution in 11 normally active volunteers using a surface coil with a nine-point progressive saturation technique. A two-point short repetition time technique was also used. Both techniques showed similar trends in the apparent T11 times of all the 31P metabolites at rest, during exercise, and during recovery. For the nine-point progressive saturation technique, the apparent T1 of PCr and beta-ATP decreased approximately 20% to a steadystate value (P = 0.027 and P = 0.004, respectively). The two-point short repetition time technique demonstrated a 10% reduction in the apparent T1 of PCr and beta-ATP Both techniques demonstrated an apparent T1 increase of 58% for inorganic phosphate at the beginning of exercise (P<0.0001) and a return to resting value during the 90-sec submaximal isometric contraction. Neither technique showed any significant differences between resting and exercising T1 times of the alpha-ATP and gamma-ATP resonances (P = 0.06 and P>0.40, respectively).