FarmDay: A Gamified Virtual Reality Neurorehabilitation Application for Upper Limb Based on Activities of Daily Living

Citation: Rojo, A.; Santos-Paz, J.Á.; Sánchez-Picot, Á.; Raya, R.; García-Carmona, R. FarmDay: A Gamified Virtual Reality Neurorehabilitation Application for Upper Limb Based on Activities of Daily Living. Appl. Sci. 2022,12, 7068. https://doi.org/10.3390/app12147068 Academic Editor: Federica Pallavicini Received: 9 June 2022 Accepted: 11 July 2022 Published: 13 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). applied sciences Article FarmDay: A Gamified Virtual Reality Neurorehabilitation Application for Upper Limb Based on Activities of Daily Living Ana Rojo 1,2,*,† , Jose Ángel Santos-Paz 1,† , Álvaro Sánchez-Picot 1, Rafael Raya 1and Rodrigo García-Carmona 1,† 1Departamento de Tecnologías de la Información, Escuela Politécnica Superior, Universidad San Pablo-CEU, CEU Universities, 28668 Madrid, Spain; [email protected] (J.Á.S.-P.); [email protected] (Á.S.-P.); [email protected] (R.R.); [email protected] (R.G.-C.) 2Neural Rehabilitation Group, Cajal Institute, Spanish National Research Council, 28002 Madrid, Spain *Correspondence: ana.r[email protected] † These authors contributed equally to this work. Abstract: Patients with upper limb disorders are limited in their activities of daily living and impose an important healthcare burden due to the repetitive rehabilitation they require. A way to reduce this burden is through home-based therapy using virtual reality solutions, since they are readily available, provide immersion, and enable accurate motion tracking, and custom applications can be developed for them. However, there is lack of guidelines for the design of effective VR rehabilitation applications in the literature, particularly for bimanual training. This work introduces a VR telerehabilitation system that uses off-the-shelf hardware, a real-time remote setup, and a bimanual training application that aims to improve upper extremity motor function. It is made of six activities and was evaluated by five physiotherapists specialised in (2) neuromotor disorders and (3) functional rehabilitation and occupational therapy. A descriptive analysis of the results obtained from the System Usability Scale test of the application and a collection of qualitative assessments of each game have been carried out. The application obtained a mean score of 86.25 ( ± 8.96 SD) in the System Usability Scale, and the experts concluded that it accurately reproduces activities of daily living movements except for wrist and finger movements. They also offer a set of design guidelines. Keywords: activities of daily living; neurorehabilitation; real-time; remote; telerehabilitation; upper limb; bimanual training; virtual reality 1. Introduction 1.1. Rehabilitation of Upper Limb Disorders Upper limb disorders (ULD) represent a major concern for healthcare systems because of the considerable economic burden they generate [ 1 ]. Most patients with ULD are limited in their activities of daily living (ADL) and require a continuous rehabilitation process [ 2 ], whose aim is to restore the lost capabilities and range of motion. Due to the complex nature of this type of injury [ 3 ], there are discrepancies about the most effective intervention therapies for ailment. However, most physical intervention methodologies agree that the patient must perform strength and repetition tasks [ 4 – 6 ]. Such tasks enable the patient to work on various parts of the body in a structured and separate manner. However, strength and repetition tasks, by their own nature, do not train the patient in the complications inherent in the organization of whole limb movements. This fact hinders functional improvement in ADL and delays the eventual return of the patient to a productive and fulfilling life. One of the major concerns involved in this type of rehabilitation is that the patients need to experience enough repetitions to induce the underlying neuroplastic adaptations necessary for their improvement [ 6 ]. For many patients, such a volume of therapy is economically unfeasible when it must be done in specialised centers and under the supervision Appl. Sci. 2022,12, 7068. https://doi.org/10.3390/app12147068 https://www.mdpi.com/journal/applsci Appl. Sci. 2022,12, 7068 2 of 17 of trained physicians. This is why conventional home-based therapy has become an alternative to extend the practice hours outside the clinic sessions and helps to establish a steady regime. However, most home-based therapy programs are monotonous and repetitive, resulting in a lack of motivation and reduced commitment from the patients [ 7 ]. This causes low adherence to treatment, which is crucial for achieving patient recovery. On top of that, such programs also lack the supervision of a therapist that can properly ensure that the exercises are correctly performed. Put together, these two facts are the reason that most home-based programs fail to influence the rehabilitation results in a noticeable way [8]. To try to mitigate this problem, several telerehabilitation solutions have been proposed. However, most are limited to offline monitoring by the therapist, telephone calls, or in some cases, videoconferencing [ 9 – 11 ]. There are more elaborate approaches that involve the installation of equipment in the patient’s home [ 12 ], designed and custom built specifically for this purpose, and they are therefore, expensive. To avoid this high cost, some authors have tried to use off-the-shelf products, such as video game consoles and peripherals. These solutions, due to their origin in gaming, were expected to increase the patient’s engagement. However, they are less than ideal for rehabilitation tasks, since commercial games and their peripherals have not been initially designed for the specific movements that the patient must perform [ 13 , 14 ] and are not yet sufficiently engaging for all patients [ 13 , 15 ]. In some cases, this gap cannot be bridged, due to the inability to develop custom software solutions or modify already available games for proprietary systems, such as game consoles. On top of that, these games are difficult to operate for patients [16]. On the other hand, the use of virtual reality (VR) systems used as complementing tools for rehabilitation and motor retraining have proven successful in promoting patient adherence to therapy and optimising therapeutic gains [ 17 ]. Indeed, virtual reality promotes adherence to physical activity (PA), whether commercial or customisable games are used. One study [ 18 ] pointed out that the adoption of home-based virtual rehabilitation at home for patients with neuromotor disabilities could be enhanced by using commercial games, but only if these detect compensatory movements, integrate social platforms, provide kinematic reports, and track the patient’s progress. However, the development of purpose-built VR games allows one to provide task-oriented exercises, and visual and auditory feedback regarding the performance of the patient’s PA [ 19 ], which could lead to neuromuscular reeducation and functional improvement [ 20 ]. The studies of Wu et al. (2019) [ 21 ] and Tarakci, E. et al. (2019) [ 22 ] evaluated the effectiveness and feasibility of their VR solutions for hand and upper extremity rehabilitation, respectively, using Leap Motion, a commercial device that enables hand recognition. Their findings pointed out that movements learned in VR environments can be transferred to real-world equivalent tasks in most cases, and that VR engages the player to increase the rehabilitation intensity. Taking all these facts into account, the benefits that VR telerehabilitation solutions can provide are usually dampened by the use of expensive equipment and/or the need to rely on commercial games. Therefore, it is necessary to build solutions that (a) use off-the-self low-cost hardware VR devices instead of costly and custom equipment, and (b) employ software applications specifically designed for the rehabilitation tasks instead of commercial games. The main novelty of this work is that it objectively defines the actions and ranges of movement that must be achieved in each VR game for upper limb rehabilitation of bimanual ADL movements. This clarity in the design represents a guideline not found to date in the literature for the construction of virtual environments (VEs) for functional rehabilitation. Additionally, of course, this VR application is supported by a real-time remote system using a novel feasible methodology for video compression. 1.2. Hardware Selection Considerations Concerning the hardware, most existing game-based therapies focus on two fundamental features: to induce as much immersion as possible and to accurately track the movements of the patient. The former improves the user’s engagement in a task that Appl. Sci. 2022,12, 7068 3 of 17 is eminently physical (increases the adherence to treatment), whereas the latter is necessary for assessing if the movements have been properly performed (reduces the need for supervision by a therapist). To accurately capture the movements of the patient during the rehabilitation session, it is desirable to use sensors with six degrees of freedom (movement and rotation in the three axes). This is why the Kinect ™ device is one of the most widely-used systems for motion capture in the field of physiological therapy [23,24]. Virtual reality devices, by their own nature, are capable of very accurate motion capture, since precise tracking of the user’s head and hand movements is required for an immersive simulation, which is precisely the other criterion listed before. Therefore, VR provides reliable and precise data about the hands and head motions, and at the same time, produces an immersive simulation. On top of that, unlike other commercial closed solutions, such as video game consoles, it is easy to develop and distribute custom software for most VR devices. Although VR headsets have their drawbacks (for instance, they may be challenging to use for some stroke survivors and cerebral palsy patients [ 25 ]), rehabilitation solutions based on immersive environments are more effective than traditional [26] because they: • Improve the engagement of the patient: Exergames increase the energy expenditure of the patient and involve both cognitive and physiologicaly rewarding tasks [ 27 ], improving the adherence to treatment. • Provide physical fidelity to real movements: The patient performs motions similar to those needed for analogous daily life situations. • Provide cognitive fidelity to a real situation: The patient completes activities inside an environment designed to be similar to the real world. Therefore, it is expected that an immersive VR solution for telerehabilitation will increase the patient’s adherence to treatment and improve the fidelity of the movements performed. However, such a solution requires not only the use of a VR head-mounted display (HMD), but also a high-performance computer that renders the virtual experience and sends the movement and session information to the therapist. Such a computer could be a considerable expense—an economic barrier to access that limits this solution. 1.3. Designing Gamified Virtual Reality Content For Rehabilitation Despite there being currently no standardised criteria for the selection of commercial games for rehabilitation, some literature reviews have succeeded in establishing general guidelines to support the selection of systems [ 28 ] and games based on therapist and patient needs [ 5 , 18 ]. These guidelines are designed to evaluate how well existing VR commercial games can be adapted to a rehabilitation scenario; these frameworks focus on characterising the degree to which software and task parameters can be controlled so the therapeutic goals are achieved. As such, they do not aim to guide the design of newly developed VR applications for rehabilitation. However, the aspects they focus on offer valuable lessons that must be taken into account. This is especially important when we consider that clear strategies for the development of home-based rehabilitation therapies based on VR technologies have yet to be determined. Taking these lessons into account, we can see that VR scenarios must implement motivational strategies based on self-determination and task-oriented challenges [ 19 , 29 ]. Such strategies stimulate the self-improvement of the individual and increase the patient’s autonomy [ 30 , 31 ] during the practice. Game mechanics based on them have shown that increasing the user’s engagement leads to more practice and also to higher quality practice [18]. Concrete guidelines for the design of effective rehabilitation games that go further than that are still not present in the literature. This lack of guidelines in the design of VR and augmented reality (AR) content has also been pointed out in the field of physical exercise for the older population [ 32 ]. Moreover, many rehabilitation solutions present in the literature that use the term “VR” are non-immersive applications in which the user sees Appl. Sci. 2022,12, 7068 4 of 17 a representation of their own body on a computer monitor [ 26 , 27 , 33 – 35 ]. This terminology problem is exacerbated when looking for design guidelines for what is now being called "fully-immersive VR" in the literature, since these solutions are not thoroughly explored in the field of functional rehabilitation. On top of that, the VR-based solutions present in the literature are not focused on bimanual training. This is especially important for this work, since most ADL tasks typically involve asymmetrical bimanual movement [ 36 ]. There was an study [ 37 ] that focused on bimanual training, but again, not with a VR solution. Game design approaches for bimanual rehabilitation systems in VR are still unexplored, and there is a lack of guidelines that can guide their development. This work introduces a VR telerehabilitation system that uses off-the-shelf hardware and a newly developed application: FarmDay. This application aims to enhance the bimanual upper extremity motor function of patients with ULD. Its design, due to the aforementioned gap in the literature, was guided by the expert opinions of practicioners and evaluated by them. This way, a set of design principles for the development of VR-based rehabilitation solutions and a collection of valuable lessons learned can begin to form. 2. Material and Methods The solution developed for this work (named FarmDay) addresses the need to integrate VR exercises with a functional component inside an existing rehabilitation programme, currently performed in a clinic by therapists. It is hoped that these VR exercises will enable a telerehabilitation setup that the patients can use to increase their volumes of work without needing to leave their houses. This rehabilitation programme focuses on patients that have suffered a stroke or other neurological damage. Various research studies have confirmed that exercises aimed at improving ADL have greater acceptance among adults, increase motivation, and improve adherence to the treatment [ 38 – 40 ]. Therefore, the exercises developed must have an intentional goal that makes the user perform one or more of the functional movements present in ADL. 2.1. VR Real-Time Remote System As previously stated, one the main drawbacks of a VR solution is the need for an expensive high-performance computer that renders the VE and relays the session’s information to the therapist. To avoid this problem, the FarmDay application was designed to run on top of a real-time, remote VR system. The details of this system are out of the scope of this document, but its architecture can be explained briefly. In this real-time, remote VR system, the VR application runs on a remote high-powered cloud computer (the server), from which the rendered environment is encoded and streamed to a less powerful computer at the patient’s home (the client), which in turn is connected to the VR HMD and controllers. This is possible through the use of an elastic down-sampling video compression codec [41]. This architecture relies on the continuous transmission of HMD and controller positions and interaction events from the client to the server. This way, the results of the interactions can be computed on the server and the video image relayed to the client. Figure 1shows the architecture of this real-time, remote VR system. The FarmDay application is, therefore, run in the cloud server but used by the patient at their home. This way, the cost of running this setup for the user is greatly reduced. Appl. Sci. 2022,12, 7068 5 of 17 Figure 1. Diagram of the the real-time, remote VR system architecture. Every VR application designed to use this system must use the OpenVR libraries, since it must use four custom components developed for it: • A client inputs process that captures the HMD and controllers inputs and sends them to the server. • A server virtual inputs driver that receives the input data from the client and feeds them to the actual VR application running in the server (in this case, FarmDay). • A server video encoding driver that captures the rendered VE product of these interactions, encodes it, and sends it to the client. • A client video decoding process that receives the encoded video, decodes it, and shows it in the client’s HMD. 2.2. VR Application The FarmDay application was developed using the Unity3D game engine v.2019.2.13f, mainly using the collection of scripts and predefined elements of the Virtual Reality ToolKit (VRTK) v.3.3.0 framework. This open source toolkit was used to implement the virtual space locomotion, object grasping interactions, object interaction via pointers, 3D button interactions, and 3D body physics within the virtual space. (i) VR framework and platform As stated before, and due to the custom real-time remoting system developed in OpenVR, it was consequently determined that the VR application should be built for systems compatible with the OpenVR platform. Then, FarmDay was designed for the OpenVR SDK (Software Development Kit), so the real-time remote system can be used. The VR application was developed entirely as a single Unity scenario. In this 3D scenario, six activities are distributed through specific areas of the environment. For interactive actions and locomotion control, the VRTK prefab module was used. The VR solution generated supports the HTC Vive ™ and Oculus Rift ™ platforms’ controllers, which are used for the interactions. (ii) Gamification elements The gamification strategy of the activities included in the FarmDay experience is based on goal achievement. Thus, each activity is composed of a sequence of actions that the user Appl. Sci. 2022,12, 7068 6 of 17 must perform to complete the task. The achievement of these objectives implies that the motions of the different body segments involved in the ADL functional movements were properly performed. (iii) Design of activities Of the six activities offered by the application, three are based on real-life situations and were designed following the guidelines and advice of five physiotherapists specialised in neuromotor disorders from the Spinal Cord Injury Foundation (Fundación de Lesionado Medular, FLM) and CEU San Pablo University (Universidad San Pablo CEU, USPCEU). They are hand-washing, pouring a drink, and playing the piano. The three remaining activities were themed around farm life and designed to involve movements similar to ADL. They are animal caring, picking apples from trees, and picking vegetables up off the ground. This way, the user can perform a bigger variety of exercises, hopefully increasing their adherence, reducing the feeling of boredom, and allowing them to work on similar movements in different ways. (iv) User Interaction The FarmDay application begins by placing the user at the entrance of the farm, allowing them to explore the environment by moving around the delimited physical space, either by directly walking or by using a teleport functionality that can be activated with any of the two controllers. Additionally, game selection panels have been distributed throughout the environment. Through them, the user can teleport from one activity to another without having to physically traverse the VE. These game selection panels consist of six interactive buttons that react when pressed with the controller, moving the user to the zone of the selected activity. The zone for each activity has a floating transparent panel which shows the objective of the activity and contains a play button. When the user presses the play button (by moving their hand), this game panel fades out and the activity starts. Once the activity is completed, the game panel fades in again, allowing the user to repeat the activity as many times as desired, restoring all the environment elements to their initial positions. Design of Activities Since each of the six activities aims to make the user perform movements specific to a particular ADL, it was essential to identify such movements. It was also necessary to determine the range of motion (ROM) for each joint (neck, shoulder, elbow, and wrist) and action, to make the tasks’ movements as faithful as possible to what the user would do in a real-world ADL. A recent state-of-the art review of devices for performing physical therapy at home or assisting with ADLs identified at least 15 systems that employ VR feedback, and in most of these cases, wrist support (ROM assessment), and in a few cases grip function, was considered [ 42 ]. No further information on finger movements is given. Therefore, the definition of the virtual scenarios and the placement of the interactive virtual objects were done in such a way so the user must reach a certain ROM for each joint to actually perform the tasks. All six virtual scenarios are depicted in Figure 2. By applying inverse kinematics to the controllers’ positional and rotational data, the ROMs in the sagittal and horizontal planes of these body joints were evaluated. Tables 1–6 detail the sequence of actions to be performed in each activity, the movements of the upper limb, and the ROMs involved for each joint. Each activity is further described in detail. Appl. Sci. 2022,12, 7068 7 of 17 Figure 2. Virtual environments for the activities. ( A ) The cabin area for the hand-washing activity, consisting of a faucet, a mirror, and the interactive objects: gloves and soap. ( B ) The barn dinning area for the pouring a drink activity. ( C ) The interactive keyboard for the playing the piano activity. ( D ) The toilet cabin area for the animal caring activity. ( E ) The forest area for the picking apples from trees activity. (F) The orchard field area for the picking vegetables up off the ground activity. Table 1. Sequence of actions and the upper limb movements involved in the hand-washing activity. Action Upper Limb Movement Target ROM Turn on/off the faucet Shoulder flexion 90° Elbow extension 0° Elbow pronation 70° Wrist flexion 45° Placing hands under water Shoulder flexion 45° Elbow flexion 90° Elbow neutral position 0° Wrist neutral position 0° Soap hands elbow flexion 45° Wrist radial-ulnar rotation 15° Hand-washing activity: In this task, the user must follow the instructions shown in the mirror, step by step, to complete the action of washing their hands. The user is located in front of the toilet cabin and must move to stand in front of the sink, whose tap can be opened and closed by interacting with the yellow and blue buttons. Small shelves are placed to the left and right of the tap. On top of those shelves there are objects that must be reached: gloves and soap (see Figure 2A). The height and distance of these shelves and Appl. Sci. 2022,12, 7068 8 of 17 the buttons on the faucet are configured according to user’s position to ensure the proper shoulder extension, elbow movements, and wrist rotations (see Table 1). Table 2. Sequence of actions and the upper limb movements involved in the pouring a drink activity. Action Upper Limb Movement Target ROM Grab a bottle/glass Shoulder flexion 45° Elbow flexion 90° Elbow neutral position 0° Wrist flexion 45° Pour the liquid into the glass Shoulder flexion 45° Shoulder internal rotation 45° Elbow pronation 35° Wrist neutral 0° Take the glass to mouth Neck extension 10 ° Shoulder flexion 65° Elbow flexion 130° Wrist radial deviation 20° Pouring a drink activity: In this task, the user must follow the instructions shown on the board, step by step, to complete the actions of pouring water into a glass and drinking from it. Initially, the user is placed in front of the bar where the interactive objects (bottle, glass and wooden board) are placed (see Figure 2B). They are arranged at a comfortable height and a distance appropriate to perform the flexion movements at the elbow, shoulder, and wrist to reach the objects; and elbow pronation and wrist movements to grab the objects (see Table 2). Table 3. Sequence of actions and the upper limb movements involved in the playing piano activity. Action Upper Limb Movement Target ROM Pressing the piano keys Shoulder flexion 30° Elbow flexion 70° Elbow pronation 70° Wrist flexion 45° Playing the piano activity: In this task, the user stands in front of the piano keyboard. The height of the piano is set to allow the subject to perform the elbow, shoulder, and slight wrist flexing movements (see Figure 2C). To complete the activity, the user must follow the melody for 2 min. This involves pressing the keys shown on the score panel (see Table 3). Animal caring activity: In this task, the user must follow the instructions on the board, step by step, to complete the action of showering a sheep. Initially, the user is located in front of the bathtub (see Figure 2D). The interactive objects (buttons to activate the bathtub tap, soap bottle, and brush) are placed on the shelf of the shower or the floor, allowing the movements of flexion of the shoulder, the elbow, and the wrist, and internal rotation of the shoulder and elbow pronation to pour the soap on the sheep. Additionally, the brushing action induces elbow abduction (ABD) and adduction (ADD) movements and wrist radial-ulnar rotation movements (see Table 4). Appl. Sci. 2022,12, 7068 9 of 17 Table 4. Sequence of actions and the upper limb movements involved in the animal caring activity. Action Upper Limb Movement Target ROM Turn on/off the faucet Shoulder flexion 30° Elbow extension 0° Elbow pronation 70° Wrist flexion 45° Pour soap Shoulder flexion 45° Shoulder internal rotation 45° Elbow flexion 0° Elbow pronation 35° Wrist neutral 0° Brushing the animal Shoulder flexion 30° Shoulder ABD 45° Shoulder ADB 45° Elbow flexion 30° Elbow pronation 70° Wrist extension 20° Wrist radial deviation 15° Wrist ulnar deviation 20° Table 5. Sequence of actions and the upper limb movements involved in the picking apples from trees activity. Action Upper Limb Movement Target ROM Grab apples Shoulder flexion 100° Shoulder ABD/ADD 20°–30° Elbow flexion 0°–30° Wrist extension 20 ° Neck extension 20 ° Put apples into the basket Shoulder flexion 30° Shoulder ABD/ADD 20°–30° Elbow neutral position 0° Wrist flexion 45° Neck flexion 10° Picking apples from trees activity: This task asks the user to pick as many apples from the trees as possible in 2 min and place them in the baskets next to each tree (see Figure 2E). To do this, the user must move to each tree. The collection of the apples from the tree and the placement of these in the baskets involves movements of flexion and extension of the elbow, shoulder, and wrist. Additionally, this action induces shoulder ABD/ADD movements. On top of that, the task forces the user incline their neck tilt, for gaze redirection (see Table 5). Appl. Sci. 2022,12, 7068 16 of 17 10. Kizony, R.; Raz, L.; Katz, N.; Weingarden, H.; Weiss, P.L.T. 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