Dynamic phosphorus-31 magnetic resonance spectroscopy of the quadriceps muscle - Effects of age and sex on spectroscopic results

RATIONALE AND OBJECTIVES. Phosphorus-31 (P-31) magnetic resonance spectrosc opy (MRS) is used to assess the influence of sex and age on quadriceps musc le metabolism before and after exercise. METHODS. Fifty-four healthy volunteers and 56 patients with an arterial occ lusive disease were examined by dynamic P-31 MRS. In the magnet, the quadri ceps muscle was stressed by an isometric and an isotonic form of exercise u ntil exhaustion, RESULTS. Older subjects showed a significantly larger ratio of inorganic ph osphate (P-i) to phosphocreatine (PCr) than younger subjects (r = 0.52, P = 8 x 10(-9)). With subjects' increasing age, the ratio of adenosine triphos phate (beta-ATP) to total phosphate decreased (r = -0.36, P = 5 x 10(-5)). The ratio of phosphomonoester to beta-ATP and phosphodiester (PDE) to beta- ATP showed a strong age dependence (r = 0.71 and 0.69, P = 3 x 10(-17) and 4 x 10(-15), respectively). The pH was the only one of the evaluated spectr oscopic parameters that showed a sex dependence. Female subjects had a sign ificantly lower pH (7.03 a +/- 0.03) than male subjects (7.05 +/- 0.03) (P = 6 x 10(-4)). With increasing age, the maxima of P-i to PCr were less extr eme during both of the exercises (r = -0.51, P = 3 x 10(-16)). Likewise, th e exercise-induced acidosis was less severe with increasing age (r = -0.51, P = 7 x 10(-16)). After the exercises ended, the times of half recovery of P-i to PCr and the pH neither correlated with the subjects' age nor with s ex or the cross-sectional area of the quadriceps muscle. CONCLUSIONS. The sex and age of volunteers or patients may affect spectrosc opic results in a significant way. This influence has to be considered in t he interpretation of spectroscopic studies. According to the recovery rates of P-i to PCr and the pH, an age-related deterioration of muscular metabol ism seems to be avoidable by appropriate physical activity.