Salbutamol is a classic asthma treatment. Its administration via inhalation stimulates the beta-2 receptors of the bronchial walls, dilating the bronchiae and thus allowing for greater respiratory capacity.

Its  use as a doping product is currently under review. An Inserm team headed by Samuel Vergès (Inserm Unit 1042 “Hypoxia and cardiovascular and respiratory physiopathology”) attempted to discover whether its inhalation could increase contractility in certain peripheral muscles, reduce fatigue and improve recovery after exercise for endurance athletes.

Eleven non-asthmatic athletes, presenting with high levels of endurance, were recruited for comparison in a two-level double-blind dosage of salbutamol (200 and 800 µg), administered through inhalation, in comparison with a placebo prior to a muscle strain test of the leg muscles.

The athletes then performed a progressive exercise routine consisting in stages of 10 intermittent contractions of increasing intensity of their quadriceps muscles. They were required at the outset to contract their muscles at about 20% of maximum capacity, then to increase the contraction strength by 10% and in 10% stages until exhaustion (when the subject was no longer capable of producing the level of strength demanded of him).

The mechanical and electromyographical responses to magnetic stimulation of the femoral nerve were recorded during and after the voluntary muscular contractions. These records make it possible to assess neuromuscular fatigue after each stage of the strength test and after 10 minutes and 30 minutes of recovery.

According to the results obtained by the Inserm researchers, the muscle responses did not change with the inhalation of salbutamol. 

Nevertheless, the total number of contractions performed before attaining muscular exhaustion increased significantly with Salbutamol intake

(an average of 72 contractions using the placebo as against 78 with 200 µg and 82 contractions with 800 µg).

For the researchers, although the muscle responses remained unchanged, supra-therapeutic  inhaled doses (i.e. doses above any therapeutic dose prescribed by a doctor) of ß2-agonists increased quadriceps muscle endurance during progressive strain and could have an ergogenic (doping) effect in an athlete. More studies are needed to clarify the underlying mechanisms.

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