Dynamic hyperinflation restricts volume expansion during exercise and is suspected as a primary mechanism of dyspnea. The dissociation between drive or muscular effort to breathe and the mechanical response to increased volume (as reflected by an increased Pes/PImax: VT/predicted VC ratio) correlates well with the intensity of inspiratory difficulty during exercise in COPD. It was hypothesised that reduced Borg ratings at a standardized exercise level after tiotropium would correlate strongly with reduced restricted volume expansion during exercise (i.e., increased VT/IC and EILV/TLC ratios, and decreased IC and IRV). In other words, dyspnea and its predominant qualitative dimensions (i.e., inspiratory difficulty) result from patients being forced by DH to breathe at a high lung volume, at or above predicted TLC.