KINETICS OF PLASMA POTASSIUM CONCENTRATIONS DURING EXHAUSTING EXERCISE IN TRAINED AND UNTRAINED MEN

The purpose of this study was to examine the time course of changes in plasma potassium concentration during high intensity exercise and rec overy in trained and untrained men. The subjects performed two exercis e protocols, an incremental test and a sprint, on a cycle ergometer. A polyethylene catheter was inserted into the antecubital vein to obtai n blood samples for the analysis of plasma electrolyte concentrations and acid-base parameters, during and after exercise. During both tests , venous plasma sodium, potassium and chloride concentrations increase d in all the subjects, although the largest relative increase was dete cted in potassium concentration - 35% and 31% over rest in the progres sive test and 61% and 37.7% in the sprint test, for cyclists and contr ols, respectively. After exercise plasma potassium concentration decre ased exponentially to below resting values. There was a linear correla tion between the amount of potassium accumulated in plasma during exer cise and the amount eliminated from plasma when the exercise ceased. W e found that, although plasma potassium accumulation occurred in both forms of exercise in the trained and nontrained subjects, the time con stant of potassium decrease following exercise was shorter in the trai ned subjects. Thus, the trained subjects exhibited a better capacity t o recover to resting concentrations of plasma potassium. We propose th at the extracellular potassium accumulation acts as a negative feedbac k signal for sarcolemma excitability depending on the muscle metabolic rate.