An Integrated Virtual Reality–Based Telerehabilitation Platform to Support Recovery and Maintenance of Functional Abilities Among Older Adults: Protocol for a Usability and Acceptability Study - Marco Benadduci; Claudia Franceschetti; Rachele Alessandra Marziali; Sebastian Frese; Peter Stephan Sándor; Valentina Tombolesi; Valentina Bozzi; Lorena Rossi (JMIR Research Protocols)