1 Department of Life, Health and Environmental Sciences, University of L'Aquila, L'Aquila, Italy.
2 San Raffaele Institute of Sulmona, Sulmona, Italy.
3 Department of Health Sciences and Technology, Sensory-Motor Systems Lab, Institute of Robotics and Intelligent Systems, ETH Zurich, Zurich, Switzerland.
4 Spinal Cord Injury Center, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
5 Department of Electrical and Information Engineering, Politecnico di Bari, Bari, Italy.
6 The BioRobotics Institute, Scuola Superiore Sant'Anna, Pisa, Italy.