Effects of training on potassium homeostasis during exercise

Potassium release from contracting skeletal muscle cells facilitates ongoing muscle contraction but may also lead to muscular fatigue. This review focuses on the effects of altered physical activity on K+ regulation during exercise, with special emphasis on K+ regulation in humans. Endurance and sprint training specifically enhance prolonged and high intensity exercise performance, respectively. Both forms of training reduce the exercise-induced rise in plasma [K+] at the same absolute exercise work rate and duration and increase the total concentration of Na+,K+ pumps in trained human muscle by approximately 15%. However, the increased pump density has not been proven to account directly for either the reduced hyperkalaemia or the improved exercise performance after training. The most likely factor accounting for the improved K+ regulation after training is an increased activation of Na+,K+ pumps during exercise, but this is not due to increased circulating catecholamine concentrations after training. A chronic reduction in physical activity reduces the muscle Na+K+ pump concentration in animal models, with an augmented exercise-induced rise in plasma [K+]. Thus, physical training enhances, whilst inactivity impairs K+ regulation during exercise, consistent with the improved exercise performance after physical training and the impaired performance with inactivity.