1. Oxford Gait Laboratory, Oxford University Hospitals NHS Foundation Trust, Oxford, Oxfordshire, UK
2. Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Oxford, Oxfordshire, UK
3. Department of Rehabilitation Medicine, VU University Medical Centre Amsterdam, Amsterdam, Noord-Holland, Netherlands
4. Department of Biomechanical Engineering, Delft University of Technology, Delft, Zuid-Holland, Netherlands
5. Centre for Population Health Sciences, Usher Institute, University of Edinburgh Division of Medical and Radiological Sciences, Edinburgh, Edinburgh, UK