Beyond bronchodilation: Illuminating the performance benefits of inhaled beta -agonists in sports.

Given the prevalent use of inhaled beta -agonists in sports, there is an ongoing debate as to whether they enhance athletic performance. Over the last decades, inhaled beta -agonists have been claimed not to enhance performance with little consideration of dose or exercise modality. In contrast, orally administered beta -agonists are perceived as being performance enhancing, predominantly on muscle strength and sprint ability, but can also induce muscle hypertrophy and slow-to-fast fiber phenotypic switching. But because inhaled beta -agonists are more efficient to achieve high systemic concentrations than oral delivery relative to dose, it follows that the inhaled route has the potential to enhance performance too. The question is at which inhaled doses such effects occur. While supratherapeutic doses of inhaled beta -agonists enhance muscle strength and short intense exercise performance, effects at low therapeutic doses are less apparent. However, even high therapeutic inhaled doses of commonly used beta -agonists have been shown to induce muscle hypertrophy and to enhance sprint performance. This is concerning from an anti-doping perspective. In this paper, we raise awareness of the circumstances under which inhaled beta -agonists can constitute a performance-enhancing benefit.