BACKGROUND: A more profound investigation of respiratory muscle strength during COPD exacerbation was needed, so we investigated respiratory muscle strength and related factors in patients with COPD during and after hospitalization for COPD exacerbation. METHODS: In 19 subjects hospitalized for COPD exacerbation (12 males, mean age 67 ؎ 11 y, median percent-ofpredicted FEV 1 26% [IQR 19 -32%]) we measured lung function and respiratory and quadriceps muscle strength at admission (day 1), at discharge, and 1 month after discharge. RESULTS: At admission, 68% of the subjects had inspiratory muscle dysfunction (maximum inspiratory pressure < 70% of predicted O], P ‫؍‬ .001). Inspiratory capacity increased between discharge (1.59 ؎ 0.44 L) and 1 month after discharge (1.99 ؎ 0.54 L, P ‫؍‬ .02). There was no significant change in other lung function variables or quadriceps strength. At admission the inspiratory muscle dysfunction and reduction in inspiratory capacity (< 80% of predicted) correlated linearly (phi coefficient 0.62, P ‫؍‬ .03), whereas the expiratory muscle strength correlated inversely with FEV 1 (Spearman rho ؊0.61, P ‫؍‬ .005) and inspiratory capacity (Spearman rho ؊0.54, P ‫؍‬ .02). CONCLUSIONS: There was a high prevalence of inspiratory muscle dysfunction in patients hospitalized for COPD exacerbation. Inspiratory and expiratory muscle strength increased markedly during and after hospitalization. The degree of air-flow obstruction and hyperinflation were related to inspiratory and expiratory muscle strength.