# An Agile Approach to Improve the Usability of a Physical Telechabilitation Platform
## 1 Introduction  
Usability refers to the degree to which a product can be used to achieve specific goals in a specific context of use [1]. The standard ISO/IEC 25000 defines the usability of a software product as the ability to beunderstood, learned, used, and be attractive to the user under specific conditions of use. These definitions suggest the possibility of using specific protocols and instruments to measure the usability level [2]. Currently, there are multiple efforts underway to improve the security, performance, and reliability of software products [3; 4; 5], but less attention has been given to addressing usability problems in any type of software, including those intended for medical assistance such as telerehabilitation platforms [6; 7]. These platforms propose the use and practice of focused rehabilitation services for those patients who cannot go to a rehabilitation centre because they have limited mobility or should avoid mobilization [8]. Usability problems can lead to a failure to complete the determined tasks on the part of the user [9]. A software product that has not gone through a usability evaluation process will not guarantee that users take advantage of the qualities and benefits of the application. To avoid user abandonment of telerehabilitation platforms, it is necessary to carry out extensive usability evaluations. The project \"Telerehabilitation system for education of patients after a hip replacement surgery (ePHoRT)\" provides a telerehabilitation platform for patients who have undergone arthroplasty surgery. Hip fracture has a great worldwide incidence, mainly in people over 65 years old, as a result of degenerative joint disease or progressive wear of the joint. In 1990, hip fractures occurred in 1.66 million elderly patients. However, there are studies that estimate that hip arthroplasty for fracture and joint replacement will surpass six million in 2050 [10; 11]. It is important to proceed with such replacements whilst anticipating potential fractures which have a high incidence of mortality because of the sepsis risks. The ePHoRT platform allows hip arthroplasty patients recovering from fracture or joint replacement to carry out part of the rehabilitation treatment at home and communicate the evolution of the recovery process to the physiotherapist [8]. The ePHoRT platform makes use of the controller for Kinect games, which is a device that is capable of capturing the movement of the human skeleton, recognizing it, and positioning it using a set of components: a depth sensor, infrared sensor (transmitter and receiver), camera RGB, and an array of microphones. The ePHoRT platform has a 'practice module' organized into three stages that are significant for the patient's recovery process. These stages are characterized by an increasing level in the intensity of the exercises. Stage 1 takes place during the week that follows the surgery, and it is mainly constituted by exercises performed in a lying-down position. The standing-up rehabilitation movements start in stage 2 (the 2 nd week after the surgery). Finally, stage 3 is characterized by functional exercises, which consist of preparing the patient to return to regular walking [12]. The ePHoRT platform is in the design stage and follows an agile and collaborative development process focused on the user. In this context, a formative evaluation is the most appropriate [13]. Published research recommended the combination of two inspection methods for usability assessment: heuristic evaluation and cognitive walkthrough [14; 15; 16; 17]. In this study, an exploratory prototype of the ePHoRT platform was used to perform the usability evaluation. An exploratory prototype is an initial version of a software product that is used to validate requirements, demonstrate concepts, try out design options, and check the usability level of the product being designed according to the stakeholders' needs [18; 19].