Dose response of inhaled salbutamol on exercise performance and urine concentrations.

PURPOSE

This study determined the dose-response effects of inhaled salbutamol (SAL) on time-trial performance and urine concentrations of SAL (cSAL).

METHODS

Nonasthmatic, trained male cyclists and triathletes (N = 37) were studied. Day 1 consisted of screening for airway hyperresponsiveness, using a eucapnic voluntary hyperpnea test (EVH), followed by an incremental exercise test to determine V O 2max and peak power (P max). On days 2-5, athletes performed a 20-km time trial 15 min after inhalation (PI) of placebo, 200 microg (D2), 400 microg (D4), or 800 microg (D8) of SAL. At 60 min PI, urine samples were provided. All conditions were randomized and double blinded, with repeated-measures ANOVA used to determine effects of dose. Post hoc analysis was done with Tukey's HSD test.

RESULTS

Seven subjects had positive responses to the EVH test, resulting in a 19% incidence within this sample; they were excluded from further participation in this study. The remaining subjects (N = 30) had a V O 2max of 67.1 (4.3) mL x kg(-1) x min(-1) and Pmax of 457 (31) W (W). There was no effect of dose on completion time (P > 0.05), mean power (P > 0.05), or mean heart rate (P > 0.05). Similarly, SAL had no effect on any metabolic or ventilatory parameters (P > 0.05). Urine cSAL increased with dose and was highly variable, with the peak value observed being 831 ng x mL(-1) after a dose of 800 microg. Moderate but significant correlations were noted between cSAL and urine specific gravity at higher doses (D4, r = 0.42; D8, r = 0.37).

CONCLUSIONS

These findings suggest that inhaled SAL does not enhance time-trial performance, regardless of dose, and that urine cSAL after exercise is related to dose, demonstrates high variability, and is partially related to hydration status.