Bloem, A., M. Veltkamp, M. A. Spruit, J. W. Custers, E. W. Bakker, H. M. Dolk, and J. C. Grutters. “Validation of 4-Meter-Gait-Speed Test and 5-Repetitions-Sit-to-Stand Test in Patients With Pulmonary Fibrosis: A Clinimetric Validation Study”. Sarcoidosis Vasculitis and Diffuse Lung Disease, Vol. 35, no. 4, Nov. 2018, pp. 317-26, http://mattioli1885journals.com/index.php/sarcoidosis/article/view/7035.