Changes in intracellular pH during repeated exercise.

The rates of change in intracellular pH during repeated exercise sessions with rest periods was determined by 31 phosphorus-nuclear magnetic resonance spectroscopy (31P-MRS). Five long-distance runners and six healthy male subjects as controls performed a 2-min femoral flexion at 20 kg.m.min-1 in a 2.1 T superconducting magnet with a 67-cm bore and repeated this exercise four times with 2-min rest periods intervening. In all cases during exercise the inorganic phosphate (Pi) peak split into two, the earlier increased rapidly (high-pH Pi) and the later (low-pH Pi) increased more slowly. The Pi peaks were separated by a fitting procedure using the least square mean method. The high-pH Pi area during exercise decreased as the number of repeated exercise periods increased, while the low-pH Pi area gradually increased. Although the total Pi area decreased exponentially during the recovery period, the high-pH Pi area decreased first and then the low-pH Pi area reduced gradually. The pH values were estimated from the chemical shift between the phosphocreatine peak and each split peak in the Pi. The high-pH in pooled data ranged from 6.6 to 7.0 during exercise and recovery, while the low pH decreased to 6.2 during exercise. As the number of exercise periods increased, each pH value gradually became less acidic, although there was a tendency to more acidity in the control subjects than in the long-distance runners.(ABSTRACT TRUNCATED AT 250 WORDS)