Inhaled Beta₂-Agonist Increases Power Output and Glycolysis during Sprinting in Men.

PURPOSE: The aim of the present study was to investigate the effects of the beta₂-agonist terbutaline (TER) on power output and muscle metabolism during maximal sprint cycling. METHODS: In a randomized double-blind cross-over design, nine moderately trained men (...O_2max = 4.6 ± 0.2 L⋅min^-1) conducted a 10-s cycle sprint after inhalation of either 15 mg of TER or placebo (PLA). A muscle biopsy sample was collected before and G10 s after the sprint and was analyzed for metabolites. RESULTS: The mean power and peak power during the sprint were 8.3% ± 1.1% and 7.8% ± 2.5% higher (P < 0.05) with TER than with PLA, respectively. Moreover, the net rates of glycogenolysis (6.5 ± 0.8 vs 3.1 ± 0.7 mmol glucosyl units⋅kg dry weight^-1s^-1 and glycolysis (2.4 ± 0.2 vs 1.6 ± 0.2 mmol glucosyl unitsIkg dry weight^-1⋅s^-1) were higher (P < 0.05) with TER than with PLA. After the sprint, adenosine triphosphate (ATP) was reduced with PLA (P < 0.05) but not with TER. During the sprint, there was no difference in the breakdown of phosphocreatine (PCr) between treatments. Estimated anaerobic ATP utilization was 9.2% ± 4.0% higher (P < 0.05) with TER than with PLA. After the sprint, ATP in Type II fibers was lowered (P < 0.05) by 25.7% ± 7.3% with PLA but was not reduced with TER. Before the sprint, PCr in Type II fibers was 24.5% ± 7.2% lower (P < 0.05) with TER than with PLA. With PLA, breakdown of PCr was 50.2% ± 24.8% higher (P < 0.05) in Type II fibers (vs Type I fibers), whereas no difference was observed between fiber types with TER. CONCLUSION: The present study shows that a TER-induced increase in power output is associated with increased rates of glycogenolysis and glycolysis in skeletal muscles. Furthermore, as TER counteracts a reduction in ATP in Type II fibers, TER may postpone fatigue development in these fibers.