Factors influencing hydrogen ion concentration in muscle after intense exercise

To assess the importance of factors influencing the resolution of exercise-associated acidosis, measurements of acid-base variables were made in nine healthy subjects after 30 s of maximal exercise on an isokinetic cycle ergometer. Quadriceps muscle biopsies (n = 6) were taken at rest, immediately after exercise, and at 3.5 and 9.5 min of recovery; arterial and femoral venous blood were sampled (n = 3) over the same time. Intracellular and plasma inorganic strong ions were measured by neutron activation and ion-selective electrodes, respectively; lactate concentration (La-) was measured enzymatically, and plasma PCO2 and pH were measured by electrodes. Immediately after exercise, intracellular La- increased to 47 meq/l, almost fully accounting for a reduction in intracellular strong ion difference (SID) from 154 to 106 meq/l. At the same time, femoral venous PCO2 increased to 100 Torr and plasma La- to 9.7 meq/l; however, plasma SID did not change because of a concomitant increase in inorganic SID secondary to increases in K+, Na+, and Ca2+. During recovery, muscle La- fell to 26 meq/l by 9.5 min; SID remained low (101 and 114 meq/l at 3.5 and 9.5 min, respectively) due almost equally to the elevated La- (30 and 26 meq/l) and reductions in K+ (from 142 meq/l at rest to 123 and 128 meq/l). Femoral venous PCO2 rose to 106 Torr at 0.5 min postexercise and fell to resting values at 9.5 min.(ABSTRACT TRUNCATED AT 250 WORDS)