Dynamic Phosphorus-31 Magnetic Resonance Spectroscopy of the Quadriceps Muscle

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Abstract
Phosphorus-31 (31P) magnetic resonance spectroscopy (MRS) is used to assess the influence of sex and age on quadriceps muscle metabolism before and after exercise. Fifty-four healthy volunteers and 56 patients with an arterial occlusive disease were examined by dynamic 31P MRS. In the magnet, the quadriceps muscle was stressed by an isometric and an isotonic form of exercise until exhaustion. Older subjects showed a significantly larger ratio of inorganic phosphate (Pi) to phosphocreatine (PCr) than younger subjects (r = 0.52, P = 8 × 10−9). With subjects' increasing age, the ratio of adenosine triphosphate (β-ATP) to total phosphate decreased (r = −0.36, P = 5 × 10−5). The ratio of phosphomonoester to β-ATP and phosphodiester (PDE) to β-ATP showed a strong age dependence (r = 0.71 and 0.69, P = 3 × 10−17 and 4 × 10−15, respectively). The pH was the only one of the evaluated spectroscopic parameters that showed a sex dependence. Female subjects had a significantly lower pH (7.03 ± 0.02) than male subjects (7.05 ± 0.03) (P = 6 × 10−4). With increasing age, the maxima of Pi to PCr were less extreme during both of the exercises (r = −0.51, P = 3 × 10−16). Likewise, the exercise-induced acidosis was less severe with increasing age (r = −0.51, P = 7 × 10−16). After the exercises ended, the times of half recovery of Pi to PCr and the pH neither correlated with the subjects' age nor with sex or the cross-sectional area of the quadriceps muscle. The sex and age of volunteers or patients may affect spectroscopic results in a significant way. This influence has to be considered in the interpretation of spectroscopic studies. According to the recovery rates of Pi to PCr and the pH, an age-related deterioration of muscular metabolism seems to be avoidable by appropriate physical activity.