Right atrial monophasic action potential and effective refractory periods in relation to physical training and maximal heart rate

The monophasic action potential (MAP) and the effective refractory period (ERP) of the right atrium were determined in eight healthy volunteers before and after hard physical training. The duration and amplitude of the MAP increased in seven individuals after training. ERP showed no consistent changes. One possible explanation of the findings is an accumulation of intracellular potassium. The duration of the MAP was well correlated to maximal heart rate.