%0 Journal Article %A D Langer %A R Gosselink %A R Sena %A C Burtin %A M Decramer %A T Troosters %T Validation of two activity monitors in patients with COPD %D 2009 %R 10.1136/thx.2008.112102 %J Thorax %P 641-642 %V 64 %N 7 %U https://thorax.bmj.com/content/thoraxjnl/64/7/641.full.pdf