Dynamic (31)phosphorus magnetic resonance spectroscopy of the quadriceps muscle: Metabolic changes resulting from two different forms of exercise.

Purpose: The aim of the present investigation was to examine the metabolism of the quadriceps muscles of normal young individuals using dynamic (31)phosphorus magnetic resonance spectroscopy. Methods: 22 normal individuals were examined in a 1.5 T-MRT using a 6 cm surface coil. The metabolic changes in the quadriceps muscle as shown by the phosphorus spectrum were evaluated during rest, exercise (isometric and isotonic exercise) and during a 36-second period of recovery. Results: The P-i/PCr quotient rose from its resting value of 0.11 +/- 0.02 following exercise to a maximum of 0.83 +/- 0.47 (isometric) or 1.40 +/- 0.59 (isotonic) (difference p=0.0001). Half-time recovery of P-i/PCr was 35 +/- 11 s or 31 +/- 10 s, respectively (p=0.13). During the recovery phase P-i/ PCr fell briefly but significantly below its rest value. Following an initial rise in pH, there was a continual fall. Minimum pH (6.68 +/- 0.21 and 6.53 +/- 0.27 respectively; p=0.01) occurred in the early recovery phase. The recovery process of pH values lasted longer following isotonic than after isometric exercise (half-value recovery time 229 +/- 72 s and 146 +/- 55 s, respectively; p=0.001). Conclusion: Compared with isometric exercise, isotonic stress is more expensive in terms of metabolism. Dynamic (31)phosphorus MRT spectroscopy can differentiate changes in muscle metabolism during different forms of exercise.