Effect of beta2 -adrenergic agonist and resistance training on maximal oxygen uptake and muscle oxidative enzymes in men

Abstract

While beta₂ -adrenoceptor stimulation has been shown to increase lean mass and to alter metabolic properties of skeletal muscle, adaptations in muscle oxidative enzymes and maximal oxygen uptake ( $\dot{V}$ O_2max ) in response to beta₂ -adrenergic agonist treatment are inadequately explored in humans, particularly in association with resistance training. Herein, we investigated beta₂ -adrenergic-induced changes in $\dot{V}$ O_2max , leg and arm composition, and muscle content of oxidative enzymes in response to treatment with the selective beta₂ -adrenergic agonist terbutaline with and without concurrent resistance training in young men. Forty-six subjects were randomized to 4 weeks of lifestyle maintenance (n = 23) or resistance training (n = 23). Within the lifestyle maintenance and resistance training group, subjects received daily terbutaline (8 × 0.5 mg) (n = 13) or placebo (n = 10) treatment. No apparent treatment by training interactions was observed during the study period. Terbutaline increased leg and arm lean mass with the intervention, whereas no treatment differences were observed in absolute $\dot{V}$ O_2max and incremental peak power output (iPPO). Treatment main effects were observed for $\dot{V}$ O₂ -reserve (P < .05), $\dot{V}$ O_2max relative to body mass (P < .05), $\dot{V}$ O_2max relative to leg lean mass (P < .01), and iPPO relative to leg lean mass, in which terbutaline had a negative effect compared with placebo. Furthermore, content of electron transport chain complex I-V decreased by 11% (P < .05) for terbutaline compared with placebo. Accordingly, chronic treatment with the selective beta₂ -adrenergic agonist terbutaline may negatively affect $\dot{V}$ O_2max and iPPO in relative terms, but not in absolute.

Keywords: beta2-agonist; doping; endurance; exercise; performance; salbutamol; strength training.