Previously the investigators have found that adolescent elite swimmers, who have been involved in competitive swimming for only a few years, have not developed respiratory symptoms, signs of airway inflammation or airway hyperresponsiveness exept for a slight increase in airway responsiveness to eucapnic voluntary hyperpnea. In the current study, the investigators will be doing a 3-year follow-up study on the swimmers studied previously.

Even though studies suggest that elite sport can cause AHR and airway inflammation, more studies are needed to elucidate how and when AHR and airway inflammation develop; and there is a lack of follow-up studies. The present study will give us a chance to do a follow-up study to register changes in AHR and airway inflammation in athletes without any significant airway changes at baseline.

Inclusion Criteria:

• Age 15-19 years
• Part of the Danish National Swimming Association's talent program for young swimmers at the baseline study
• Informed consent

Exclusion Criteria:

• Upper respiratory tract infection in the previous 4 weeks (visits will be postponed)

Participants were all elite swimmers and part of the Danish National Swimming Association's talent program for young swimmers at the baseline study.