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 β-ATP decreased approximately 20% to a steady-state 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 β-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 α- ATP and γ-ATP resonances (P = 0.06 and P > 0.40, respectively).