The Effect of Inhaled Salbutamol on Sprint Performance During and After Submaximal Endurance Exercise in Non-asthmatic Athletes

Theoretical background:

The use of beta2-agonists in sports is restricted due to possible performance enhancing effects. The World Anti-Doping Agency's (WADA) prohibited list from January the 1st 2020 prohibits all use of beta2-agonists except inhaled salbutamol (maximum 1600 micrograms over 24 hours in divided doses not to exceed 800 micrograms over 12 hours starting from any dose), inhaled formoterol (maximum delivered dose of 54 micrograms over 24 hours) and inhaled salmeterol (maximum 200 micrograms over 24 hours).

Asthmatic athletes have consistently outperformed non-asthmatic athletes during the Olympic Games, and the use of inhaled beta2-agonists by athletes is surrounded by controversy, which have been highlighted in recent beta2-agonist anti-doping investigations involving world-class athletes. In 2020, Riiser et al. completed two systematic reviews with meta-analysis targeting the effect from beta2-agonists on aerobic (accepted in BSJM March 2020) and anaerobic (currently in review) performance. No effect was detected on aerobic performance, however an effect on anaerobic performance was reported. However, these meta-analyses separate the effects in either aerobic or anaerobic performance, while many sports requires both a high aerobic and anaerobic performance to succeed. For example, the development of endurance sports - such as cycling and cross-country skiing - has gone in a direction where anaerobic abilities are gaining importance, such as during sprints at the final stage of a race, closing gaps and during break away.

If beta2-agonists might improve performance in endurance sports through its effect on anaerobic performance, studies that better simulate this aspect of an endurance competitions is warranted. To the best of the present researcher's knowledge only three studies have investigated this aspect and they yielded conflicting results. In 1988, Bedi et al. found that competitive cyclists sprinted longer (196 sec vs 159 sec) after 60 min of cycling with a single inhalation of salbutamol pre-ride as compared to placebo. Furthermore, higher fatigue levels were reported during the final sprints after inhaling salbutamol, that may indicate a better ability to perform all-out anaerobic effort. However, Altarawneh et al. (2016) found no ergogenic effect of 1000 ug inhaled salbutamol on either continuous high-intensity (90 s at 130 % V̇O2max) performance or multiple sprint performance (3 sets of 5x4 s sprint with 20 s break between sprints and 4.5 min serial break) in recreationally active men. Fitness level has been suggested to confound the effect of beta2- agonists on physical performance, and to the best of our knowledge no study has investigated the effect of a WADA approved dose of inhaled salbutamol on measures of repeated bouts of anaerobic performance measured during prolonged submaximal exercise in well trained athletes. Therefore, because of the potential ergogenic effect of inhaled beta2-agonists on anaerobic performance combined with the potential reduced VO2 during submaximal work reported by Bedi et al. (1988), the combination of anaerobic performance and prolonged sub-maximal endurance exercise should be further investigated.

Materials and methods: