Effects of β2-adrenergic stimulation on exercise capacity in normal subjects

β2-Adrenergic receptor agonists are believed to present with ergogenic properties. However, how combined respiratory, cardiovascular and muscular effects of these drugs might affect exercise capacity remain incompletely understood. The effects of salbutamol were investigated in 23 healthy subjects. The study was randomised, placebo-controlled in double-blind and followed a cross-over design. Salbutamol was given at the dose of 10 μg/min in 11 subjects and 20 μg/min iv in the other 12 subjects. Measurements included muscle sympathetic nerve activity (MSNA), ventilatory responses to hyperoxic hypercapnia (7% CO₂ in O_2, central chemoreflex), isocapnic hypoxia (10% O₂ in N₂, peripheral chemoreflex) and isometric muscle contraction followed by a local circulatory arrest (metaboreflex), cardiopulmonary exercise test (CPET) variables and isokinetic muscle strength. Salbutamol 10 μg/min increased heart rate and blood pressure, while MSNA burst frequency remained unchanged. Peripheral chemosensitivity increased, as evidenced by an increased ventilatory response to hypoxia, but ventilatory responses to hypercapnia or muscle ischaemia remained unchanged. The effects of salbutamol 20 μg/min were similar. Both doses of salbutamol did not affect CPET. Only the higher dose of salbutamol decreased the anaerobic threshold, but this was not associated with a change in VO₂ max. Salbutamol increased the slopes of ventilation as a function of VO₂ (P < 0.05) and VCO₂ (P < 0.001) during CPET. Maximal isokinetic muscle strength was not affected by salbutamol. In conclusion, the acute administration of either low or high dose salbutamol does not affect exercise capacity in normal subjects, in spite of an earlier anaerobic threshold and increased chemosensitivity.