The Effects of Inhaled Terbutaline on 3-km Running Time-Trial Performance

Terbutaline is a prohibited drug except for athletes with a therapeutic use exemption certificate; terbutaline’s effects on endurance performance are relatively unknown.

Purpose:

To investigate the effects of two therapeutic (2mg; 4mg) inhaled doses of terbutaline on 3km running time-trial performance.

Methods:

Eight males (24.3±2.4yrs; 77.6±8kg; 179.5±4.3cm) and eight females (22.4±3yrs; 58.6±6kg; 163±9.2cm) free from respiratory disease and illness provided written informed consent. Participants completed 3 km running time-trials on a non-motorised treadmill on three separate occasions following placebo, 2 mg or 4 mg inhaled terbutaline, in a single-blind, repeated-measures design. Urine samples (15mins post-exercise) were analysed for terbutaline concentration. Data were analysed using one-way repeated measures ANOVA, significance was set at p<0.05 for all analyses.

Results:

No differences were observed for completion times (1103±201; 1106±195; 1098±165s; P=0.913) for the placebo trial, the 2mg inhaled trial and the 4mg inhaled trial, respectively. Lactate values were higher (P=0.02) following 4mg terbutaline (10.7±2.3mmol·L-1) vs. placebo (8.9±1.8mmol·L-1). FEV1 values were greater following inhalation of 2mg (5.08±0.2; P=0.01) and 4mg terbutaline (5.07±0.2; P=0.02) compared to placebo (4.83±0.5L) post-inhalation. Urinary terbutaline concentrations were mean (306±288ng·mL-1; 435±410ng·mL-1; P=0.2) and peak (956ng·mL-1; 1244ng·mL-1) following 2mg and 4mg inhaled terbutaline, respectively. No differences were observed between the male and female participants.

Conclusions:

Therapeutic dosing of terbutaline does not lead to an improvement in 3 km running performance despite significantly increased FEV1. Our findings suggest that athletes using inhaled terbutaline at high therapeutic doses to treat asthma will not gain an ergogenic advantage during 3 km running performance.