1. Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council (CSIC), 28002 Madrid, Spain
2. Department of Automation and Systems Engineering, Carlos III University, 28911 Madrid, Spain
3. Legs and Walking AbilityLab, Shirley Ryan AbilityLab, Chicago, IL 60611, USA
4. Department of Physical Medicine and Rehabilitation, Feinberg School of Medicine, Northwestern University, Evanston, IL 60208, USA
5. Department of Biomedical Engineering, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, USA
6. Department of Mechanical Engineering, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, USA