The Association Between β

β-Blockers (BBs) have been associated with a reduced cardiorespiratory fitness (CRF). This is possibly caused by inhibition of β2-receptors in the airways. However, there are limited data available on β-receptor selectivity and CRF. We therefore aimed to assess the association between BB use and CRF and to assess the association between β-receptor selectivity and CRF. Participants in the Maastricht Study were aged between 40 and 75 years. Exposure to BB use was determined by use of pharmacy records. General linear models were used to obtain adjusted means of 2 proxies for CRF: covered distance during the 6-minute walk test (6MWT) and estimated maximum power output adjusted for body mass (Wmax kg？1) during the submaximal cycle ergometer test. Adjusted means were compared between current, past, and never BB users. Current users were subsequently stratified by β-receptor selectivity and dose. Compared to never use, current use was associated with a lower CRF, based on the 6MWT (current use: 569.7 m; never use: 580.4 m [P = .010]), but not based on the cycling test (current use: 2.14 W kg？1; never use: 2.13 W kg？1 [P = .690]). There was no difference between current selective and current nonselective BB use. β-Blockers use was associated with CRF based on the 6MWT but not the cycling test. There was no difference between current selective and nonselective BB users, possibly due to the small number of nonselective BB users, differential underlying diseases, other pharmacological properties, and limitations related to the proxies of the outcome