The purpose of the present study was to examine the relationship of plasma potassium (K+) and minute ventilation (VE) during incremental cycling (20 W/2 min) under conditions of beta-adrenergic blockade (80 mg of propranolol) and placebo in six untrained male subjects. No significant differences existed between treatments in O2 uptake, CO2 production, blood lactate, pH, or VE during the submaximal work stages of incremental exercise common to both treatments (20–220 W). During exercise with beta-blockade, plasma K+ concentrations were found to be significantly elevated compared with control levels at every work stage except 20 W. Significant positive correlations between VE and plasma K+ were found during both beta-blockade (r = 0.99) and control conditions (r = 1.00). Although the high correlation between VE and K+ was not altered with beta-blockade, propranolol treatment resulted in a significant reduction in the slope of this relationship during incremental exercise (P < 0.01). These findings suggest that 1) beta-blockade decreases the VE-K+ relationship observed during exercise and 2) K+ stimulation of muscle afferents is not an important signal in the control of exercise ventilation.
Group III and IV muscle afferents differentially affect the motor cortex and motoneurones in humans