Skeletal muscle dysfunction is a common feature in chronic obstructive pulmonary disease (COPD) which is associated with intrinsic muscular abnormalities. One of the most consistently reported alterations is a I to II fibre type shift in the vastus lateralis of these patients. Surprisingly, the relationship between this shift and COPD severity and phenotype remains unclear. This study was conducted to address the question whether vastus lateralis muscle fibre type proportions are associated with COPD disease severity and to provide reference values for vastus lateralis fibre type proportions in COPD. A systematic review and a meta-analysis were conducted for which muscle fibre type data and markers of disease severity were collected from the literature. The forced expired volume in one second (FEV1), the FEV1/forced vital capacity and the body mass index were positively associated with fibre type I proportion in COPD. A proportion of 51% for vastus lateralis fibre type I and 13% for fibre type IIX were calculated from the combined data as normal values for the typical GOLD stage III-IV COPD range of 60-70 years. Based on these reference values a fibre type I proportion below 27% and a fibre type IIX proportion above 29% were defined as pathologically abnormal. This review sheds new light on the relationship between skeletal muscle abnormalities and important hallmarks of the disease in severe COPD and identifies absence of data in GOLD I-II. In addition, for diagnostic purposes this review provides a frame of reference on fibre type composition in COPD. AD - Department of Respiratory Medicine / NUTRIM, University of Maastricht, Netherlands.