MATERIALS AND METHODS
exacerbations
COLD
The Flow diagram. Fifty of 137 contacted patients met the eligibility criteria and entered the training-free run-in period. At training start, allocation concealment was ensured by an external block randomization for group allocation and concealed medical gas sources by locked away gas cylinders; a hidden gas distributing system was provided from the gas supplier. Although 16 patients could not be evaluated after the training intervention, no differences in dropout rates were observed between both samples. Only two patients opted out during the training period, at a very early stage of the intervention. Other withdrawals were because of comorbidities, exacerbations during the cold winter months, and no available MRI data. The exercise training intervention was conducted at the University Institute of Sports Medicine, Prevention and Rehabilitation of the Paracelsus Medical University of Salzburg (Austria).