Influence of a beta2-agonist on physical performance at low temperature in elite athletes.
Beta2-agonists are frequently used by elite cross-country skiers, a group of athletes with a high prevalence of asthma. It has been claimed that beta2-agonists have a positive effect on physical performance. The aim of the present study was to investigate whether inhalation of a beta2-agonist increases physical performance at low temperature in healthy, nonasthmatic athletes with normal bronchial responsiveness. Twenty elite male athletes (cyclists, cross-country skiers, middle and long distance runners) with no history of allergy or airway disease and who had normal spirometry and methacholine bronchial provocation tests performed a maximal exercise test on a treadmill in a climate chamber at approximately 10 degrees C on two subsequent days. Before exercise they inhaled terbutaline (3 mg from MDI) or placebo in a randomized, single blind manner. After 10-min warm-up on the treadmill, a submaximal work preceded a stepwise increase of the workload until exhaustion. Lung function, ventilation, oxygen uptake, and heart rate were determined and blood samples for lactate and potassium analyses were drawn before, during, and after exercise. Terbutaline induced a significant bronchodilatation; FEV1 increased from 4.8 (4.4-5.1) L to 5.0 (4.6-5.4) L, mean (95% CI). There were no significant differences between the two treatments with regard to exercise time, 25.1 (24.3-25.8) min vs 24.9 (24.1-25.6) min, oxygen uptake and ventilation during exercise, or heart rate at maximal workload. Terbutaline induced an increase in serum lactate concentration but did not influence the lactate response to exercise. The serum potassium increase was attenuated at low workload but not at maximal work. The postexercise decrease in serum potassium concentration was significantly greater after terbutaline (-0.52 (-0.29 to -0.76) mmol x L-1) than after placebo (-0.13 (0.06 to -0.32) mmol x L-1 (P < 0.001). We conclude that inhalation of a beta2-agonist (terbutaline) in a dose that yields significant bronchodilatation does not influence physical performance at low temperature in healthy athletes. Acute inhalation of the beta2-agonist amplified the postexercise hypokalemia, a finding of unclear significance. Although there is a slight bronchodilatation and potential negative airways effect of cold air inhalation, a beta2-agonist does not increase physical performance in top athletes.