eJamar: A Novel Exergame Controller for Upper Limb Motor Rehabilitation

Abstract

This work presents the design of a new game controller device and the development of two exergames (Peter Jumper and Andromeda) for upper limb rehabilitation. The eJamar controller is a novel electromechanical device designed to measure wrist and hand movements, such as pronation/supination, flexion/extension, and ulnar/radial deviation, enabling users to perform control actions in the exergames. One of eJamar’s most significant features is its ability to measure hand grip strength, a function not available in commercial gaming controllers. The exergame Peter Jumper involves a character jumping over obstacles in various environments, promoting hand grip exercises. The exergame Andromeda involves shooting enemy ships, promoting coordination between hand movements and grip strength, making it suitable for different rehabilitation techniques. A testing protocol was applied with eight healthy participants (5F and 3M), who completed a survey evaluating gameplay, usability, and satisfaction of the system. The results demonstrated that the developed exergames are intuitive and easy to play, with participants reporting that a therapist’s presence is not required for gameplay. Hence, it suggests that the developed system can improve the rehabilitation process, promoting wrist–arm movements and grasping actions.

1. Introduction

Stroke stands as a leading cause of impaired limb mobility globally, and its prevalence is on the rise [1]. Addressing this pressing issue necessitates significant efforts to implement rehabilitation systems that can enhance the daily lives of affected patients. In this line, several studies have shown that exergaming can effectively support rehabilitation in terms of physical health and quality of life [2]. Exergaming refers to an experiential activity involving playing exergames or any videogames that require physical exertion or movements that are more than sedentary activities and also include strength, balance, and flexibility activities [3].

Commercial exergames are widely available tools that could support physical rehabilitation in terms of more general physical health and quality of life. While these platforms were not initially designed for rehabilitation purposes, several studies have innovated in the design of rehabilitation protocols based on physical activity using commercial platforms, such as Nintendo Wii [4,5,6], Xbox Kinect [7,8,9], Oculus [10,11,12], HTC Vive [13], and Sony Play Station [14]. Consequently, the field of rehabilitation systems utilizing exergames has seen significant development since 1999, experiencing a notable surge in 2009 to address this urgent need [15]. Conversely, specific rehabilitation platforms like Rapael [16,17], Armeo [18,19], Bright Arm [20,21], and Neuroball [22,23] and specialized devices like Arm Band [24,25] and Leap Motion Controller [26,27] have been instrumental in targeted research efforts [28]. Notably, these systems often prove expensive and are primarily accessible within rehabilitation centers, posing challenges for individual patient acquisition.

Furthermore, there exist prototype systems tailored to address unique needs, encompassing aspects such as comfort, utility, operability, movement, and affordability. In this domain, devices have emerged to control gaming interfaces, such as the Bright Brainer Grasp [29], a therapeutic controller adept at sensing hand grasp and various hand movements crucial for rehabilitation. Another innovation includes a motion-tracking device [30] capable of monitoring hand movements, albeit without measuring grasp force. Additionally, the Arm Assist, functioning as a robotic system and game controller (GC), facilitates rehabilitation via hand movements [31]. Moreover, the Smart Elbow Bracelet, a two-degrees-of-freedom exoskeleton system, has been devised explicitly for rehabilitation in conjunction with exergames [32].

In this context, this article describes the development of a novel therapeutic controller engineered according to specialized video game guidelines specifically for upper extremity rehabilitation denoted as eJamar. This device stands out by accurately measuring hand grasp, pronation–supination, flexion–extension, and ulnar–radial deviation movements of the hand. These distinct capabilities endow it with exceptional versatility for administering rehabilitation therapies effectively. The specialized eJamar technology aims to cover two purposes: (1) a rehabilitation tool serving as a GC to promote UL motor activity, and (2) an evaluation instrument of hand grip strength. The capability of the eJamar device to interact with exergames allows measuring various user parameters, such as isometric hand grip strength, pronation–supination angles, and linear movement acceleration in three axes, applicable to movements of the hand, arm, or forearm, depending on the type of exergame implemented. The remainder of this article is organized as follows. Section 2 presents a summary of related work. Section 3 describes the system architecture, the design process, and the main features of the proposed electromechanical device. Section 4 presents the results of the preliminary usability trials. Finally, the discussion and conclusions can be found in Section 5.

2. Related Work

Although there are numerous studies that incorporate exergames as part of rehabilitation treatments, around 26% utilize specialized controllers for this purpose [33]. Among the GC designed for exergames, three categories can be distinguished based on the interaction mode: active, wearable, and standard. Active interaction controllers involve the user making natural movements in front of a camera without direct contact with a device, such as the Kinect [34], Leap Motion Controller (LMC) [35], and webcams [36]. Wearable controllers are attached to a part of the limb using straps, for example, glove-type controllers [16], wristbands [37], head-mounted devices [38], and exoskeletons [39]. Standard controllers are handheld, such as end-effector robots [40], GC platforms [41], a mouse [42], and various prototype controllers. GCs use different sensors, such as accelerometers, IMUs, encoders, force, pressure, and EMG, to detect the user’s movements, strength, or speed in the upper limb, measuring tilt or motion in the hand or forearm [33].

Over the past decade, various specialized controllers have been developed and used for exergames, primarily falling into the wearable and standard categories. For example, the RAPAEL Smart Glove allows independent movements of the fingers and hand, and has been used to rehabilitate stroke patients [16,17]. The Bright Brainer Grasp is a controller that uses force sensors to measure hand strength and incorporates several aspects of comfort for hand and forearm movements, making it one of the few to do so [43]. Another specialized controller is the Arm Assist [31], a robotic device designed for comfortable hand and wrist movements, with ergonomic considerations. Lin B. et al. developed a cylindrical-shaped controller equipped with an IMU sensor that detects pronation and supination movements of the forearm, transmitting data via Bluetooth [30]. These devices have been developed to meet the need for accurately measuring hand strength and movement, something that most commercial platform controllers do not offer.

3. Materials and Method

The architecture of the proposed system is presented in Figure 1, where the main actors are the player, the eJamar game controller, and the exergame. The eJamar serves as an interface facilitating the transmission of commands to the gaming system and, thereby, enables users to command the exergame actions effectively. The eJamar can identify the arm movement and grasping actions, which are mapped with specific actions in the exergame. For this study, two exergames were designed to encourage the game–user interaction based on movements needed to perform activities of daily living. The eJamar controller connects to the computer program running the games through a Bluetooth wireless interface.

To establish this wireless connection, the computer’s Bluetooth module must first be activated. Subsequently, the onboard Bluetooth module of the eJamar device must be linked with the computer where the exergames will be executed. It should be noted that each eJamar unit is assigned a unique identifier and it allows to connect two eJamar devices to play, and promote bimanual training. During game initialization, the program connects the exergame to the eJamar controller, identifying which exergame is currently running. The eJamar controller is compatible not only with the two exergames developed for this study in the Unity game engine, but also with other ones.

The modalities and functions of the proposed exergames encourage the player to perform various hand and wrist movements, as well as repetitive and sustained grips. The aim of these game control functions is to replicate exercises commonly performed in hand and wrist rehabilitation sessions. In order to develop effective systems, it necessitates ergonomic design and should accommodate a wide range of user mobility [44]. Thus, a preliminary usability study with healthy volunteers serves as a step toward validating the controller with actual patients.

3.1. The eJamar GC

The novel exergame controller denoted as eJamar is presented in Figure 2a. The development of the eJamar controller followed design principles such as usability, physical specifications, and player experience [45]. These principles emphasize player ergonomics and comfort. For this reason, a commercial casing designed for hand exercise was used, featuring a grip handle with grooves that conform to the shape of the hand. Additionally, it includes a knob to adjust the hand grip distance, allowing for ease of use tailored to hand size and enhancing player comfort. The eJamar stands as a wireless controller specially engineered to relay commands to interactive serious games. Notably, it possesses the capability to gauge the hand grasp, making it invaluable for conducting hand rehabilitation exercises. Additionally, it integrates an inertial measurement system (IMU) capable of discerning the user’s hand movements. Complementing these features, it incorporates a haptic feedback system employing internal vibration actuators. Finally, its user interface comprises a button and two LED status indicator lights, streamlining user interaction. The electronic system architecture is presented in Figure 2b.

3.1.1. Electronic System

A microprocessor-based system, based on a 32-bit SAMD21 processor (Microchip Technology Inc., Chandler, AZ, USA), manages the different sub-systems of the device, such as IMU, force sensor, push button, haptic feedback, indicator LEDs, and wireless communication. Processor management within the eJamar controller is orchestrated through the following key components and functionalities:

IMU Motion Sensor (LSM6DS3): This sensor, equipped with 9 degrees of freedom, predominantly utilizes 3 degrees corresponding to the accelerometer’s response along the X-, Y-, and Z-axes. During exergame execution, the controller identifies the specific game being played. Consequently, the microprocessor system selectively transmits solely the pertinent data required by that particular game. This strategic approach avoids superfluous readings, ensuring swifter data transmission.

Force reading system: Continuous communication between the processor and the HX711 driver linked to the strain gauge enables force assessment. Implementing a software averaging filter helps diminish reading noise, complementing the filtering stage already integrated into the driver library. This system accurately gauges the force exerted by the player on the controller, facilitating rehabilitation exercises and enhancing hand grip for patients undergoing rehabilitation.

Push Button: The controller integrates a push button mechanism facilitating the activation or deactivation of the exergame pause mode. Additionally, it serves to rouse the controller from sleep mode. The latter mode automatically activates after 5 min of inactivity, conserving energy while not in use.

Haptic Feedback: Incorporated within the system is a vibration motor generating tactile feedback during exergame execution, triggered by in-game events such as impacts, or specific actions as defined within each game. This feature offers users real-time tactile cues, enhancing their gaming experience. Furthermore, this feature is customizable and can be disabled through individual game configurations.

Visual Indicators: The controller integrates two LEDs (a red and a green indicator). The red LED illuminates when the pause mode is activated using the push button or when the system enters sleep mode. To revert to normal operation, a press of the push button is required. Meanwhile, the green LED sporadically lights up during gameplay, signaling to the user that the system is functioning correctly.

Bluetooth Communication: The eJamar employs a NINA-W-102 device for seamless communication via Bluetooth, enabling data transmission between nodes. The microprocessor transmits data to the NINA device responsible for relaying this information. Simultaneously, the game interface transmits configuration data to the controller, received by the NINA and forwarded to the processor. This bidirectional communication involves the controller sending grip force values and accelerometer data (X, Y, and/or Z axis), while receiving configuration commands defining game types, modes, and haptic feedback activation. This wireless capability empowers users with increased freedom of movement during gameplay.

Time Management and Sleep Functionality: Firmware within the system manages time-related operations and sleep functionality. It orchestrates the processing sequence of various elements within the GC and includes a timer mechanism to activate the sleep mode when necessary. Referencing Figure 3, the firmware’s flowchart visually delineates the program’s processing and management sequence, ensuring efficient utilization of resources and timely activation of sleep mode to conserve energy.

3.1.2. Grasping Force Detection and Calibration

The eJamar controller measures grip strength using a strain gauge with a range of 0–100 kgf. A spring transmits the force from the hand grip to the gauge. The original spring in the housing was replaced with one that allows a measurement range of up to 25 kgf, which increases the range of finger motion during grip and reduces the stiffness of the hand holder, making it more suitable for elderly users and patients with hand motor impairments. The hand grip opening position can be adjusted using the knob, shown in the previous Figure 2a. It enables customization based on the user’s hand size and comfort preferences; however, this adaptation does not alter the spring tension. The signal from the strain gauge is processed by the HX711 24-bit ADC for weight scales, which sends the data to the microcontroller via serial communication protocol. The output 24 bits of data contain the gauge readings amplified with a gain of 128. The microcontroller processes the data and transmits them via Bluetooth to the computer.

The spring-based mechanical model of the eJamar device is presented in Figure 4a, where the main components are the spring, the gauges, and the A/D converter. A calibration procedure was performed to identify empirically the spring elastic constant. For that purpose, several loads within the usable range of 0–25 kgf were attached to the eJamar hand grip. The output of the HX711 ADC was used to measure the spring elongation $\Delta x$ for each case. Thus, the spring constant k can be obtained using Hooke’s law.

According to Hooke’s law, the graph of the applied force $F_s$ as a function of the displacement $\Delta x$ will be a straight line passing through the origin, whose slope is k. Thus, applying linear regression to the output provided by the HX7711 ADC and the force applied to the hand grip, the results shows the linear behavior of the mechanical model described in Equation (1):

$$F_s=k·\Delta x-ϵ$$

(1)

where k is the spring constant and $ϵ$ is the error term that captures all other factors which influence the measured force $F_s$ other than the spring elongation $\Delta x$. From the empirical calibration, the results were $k=0.0197$ and $\Delta x=0.0632$.

Hence, the previous linear model was programmed in the microprocessor to estimate the hand grip forces, given in newtons, N. This model is independent of the user or external factors different of the spring characteristics, so calibration is only required once. The measurement resolution is 0.1 kgf. The performance of the linear model was tested using different loads applied at the hand grip, and the model response is presented in Figure 4b. It can be seen that the force estimation fits a linear model (black dashed line) with 2% full-scale error.

3.2. GC Functioning

This section details the use mode of the eJamar device as an exergame controller, that is, a device that allows controlling actions in a videogame. The eJamar system is designed to promote the performing of grasping gestures and arm movements to command specific actions in an exergame.

The movements measurable with the eJamar GC are illustrated in Figure 5, where grasping is represented by the orange arrow along the X-axis. In Figure 5a, radial/ulnar movement is shown by the green arrow rotating around the Y-axis. Pronation/supination movement is indicated by the red arrow around the X-axis. In Figure 5b, the horizontal usage mode is displayed, where flexion/extension movement occurs around the Z-axis.

It should be noted that the eJamar can be used in a sitting or standing position. When sitting, the movements can be performed with the arm resting on a table or other support, focusing the training on the wrist. However, using the eJamar by standing allows to target a large interjoint coordinated arm motion that involves the elbow and shoulder. The following section describes two video games designed to engage patients in a variety of repetitive grasping and wrist movements.

3.2.1. Peter Jumper Game

Peter Jumper (PJ) is a 2D game set within a 3D environment where the character navigates a pathway amidst an array of obstacles like boxes, towers, and fences. Figure 6 illustrates the second level of gameplay and the customization screen. Peter must leap to avoid these obstacles; failure results in a life being lost. Adhering to exergame development guidelines [44], the game offers customizable features allowing users to adjust game parameters such as duration, difficulty levels, speed, haptic feedback intensity, effects activation, audio volume, and game modes. PJ encompasses two distinct game modes. In the gripper squeeze mode, the user must exert force on the eJamar’s gripper. When the applied force surpasses the preset threshold for that level, the character executes a jump. In the controller movement mode, the user moves the eJamar vertically upwards, employing radial/ulnar deviation movements in the vertical sub-mode and flexion/extension in the horizontal sub-mode. The previous Figure 5 illustrates the hand–wrist movements corresponding to the various working modes used in the PJ game.

Prior to gameplay, the system measures the user’s maximum force (MAX) either through force or controller movement. Subsequently, thresholds for all levels are calibrated based on this value, incrementing with each progressive level. Additionally, the character can collect coins and hearts; every 5 coins or each heart acquired adds a life. Colliding with obstacles deducts a life and triggers vibration feedback via the eJamar. If all lives are lost, users can restart the level at that point.

Table 1. Peter Jumper game details.

Level	Name	Details	Incentive	Obstacles	Threshold
1	Rural Fantasy	It is a rural environment with pastel colors. The environment has classic houses and nature.	Coins	Boxes, cylinders, and fences	10% MAX
2	Capital City	It is a city with a cold climate with streets, houses, and buildings of the main city.	Coins and hearts	Big boxes, Medium boxes, and fire boxes	15% MAX
3	Amazonas	It is the jungle, with mountains, rivers, lakes, flora, and fauna typical of the flora and fauna of the zone	Coins and hearts	Big boxes, Medium boxes, and fire boxes	20% MAX

details the specific attributes of each PJ level, outlining their unique characteristics and challenges.

By engaging users in these game modes with varying movement patterns and challenges, the rehabilitation system promotes targeted exercises and entertainment while aiding in the recovery of hand and wrist mobility.

The aim of this game is to engage users in active participation in rehabilitation exercises, specifically targeting the enhancement of hand grip strength and wrist movements involving flexion, extension, and lateral deviations. Upon completion of the three levels, played within a specified time frame, all grip strength and movement data recorded by the eJamar are meticulously stored. This comprehensive data collection allows for a comprehensive understanding of the user’s entire exercise regimen. Analyzing this data across multiple rehabilitation sessions enables a comparative analysis, facilitating a detailed assessment of the patient’s progression over time.

3.2.2. Andromeda Game

This game presents a 2D environment where the player take control of a spaceship tasked with firing projectiles to thwart enemy ships or asteroids from advancing towards its position across the screen. Throughout the game, users have the opportunity to collect coins and hearts, each offering unique benefits. Accumulating 5 coins grants an additional life and awards 30 extra projectiles, while obtaining a heart adds one life and supplies 50 more projectiles. Figure 7 presents the two Andromeda modes, vertical (Mode V) and horizontal (Mode H), each comprising two difficulty levels.

In Mode V, as depicted in Figure 7a, the player’s spaceship resides at the bottom of the screen, while enemies approach from the top. Users hold the eJamar vertically and maneuver the spaceship horizontally by executing prono-supination movements of the hand–arm, as is shown in Figure 5a. Firing projectiles requires squeezing the hand gripper, triggering the spacecraft to shoot when surpassing the predetermined threshold. In Mode H the player’s craft appears on the left side of the screen, and adversaries emerge from the right, as is shown in Figure 7b. Movement of the spaceship vertically involves radial/ulnar deflection movements, as is shown in Figure 5a, while firing projectiles is achieved by pressing the hand gripper. Both modes entail random appearances of enemy ships and asteroids at slower speeds in Level 1. Level 2 introduces larger ships capable of firing projectiles, exhibiting higher speeds. If an enemy ship breaches the player’s position, a life is lost, and the eJamar vibrates accordingly. In the event of losing all lives, players can restart the level from that particular moment.

Refer to

Table 2. Andromeda game settings.

Mode	Movements	Level	Details	Incentive	Enemies	Threshold
Vertical	Pronation/supination (to move the spaceship laterally)	1	The user appears at the bottom of the screen and enemies appear randomly appear at the top of the screen	Coins and projectiles	Little ships and asteroids	10% MAX
		2	The user appears at the bottom of the screen and enemies appear randomly at the top of the screen	Coins, hearts, and projectiles	Big ships, asteroids, and projectiles	15% MAX
Horizontal	Radial and cubital wrist deviations (to move the spaceship vertically)	1	The user is on the left side of the screen and enemies appear randomly from the right	Coins and projectiles	Little ships and asteroids	10% MAX
		2	The user is on the left side of the screen and enemies appear randomly from the right	Coins, hearts, and projectiles	Big ships, asteroids, and projectiles	15% MAX

for a summary detailing the unique attributes of each Andromeda mode and level. This gameplay dynamic challenges users with varied spatial configurations and movements, promoting engagement while targeting specific hand–arm exercises for rehabilitation.

3.3. Requirements for Operation

3.3.1. System Requirements

The computer running the game must have Bluetooth connectivity and meet the following minimum specifications: Windows 7 SP1+ (64-bit) or macOS 10.12+, Intel Core i3-2100 processor or equivalent, Intel HD Graphics 4000 or similar GPU (Intel, Santa Clara, CA, USA), 4 GB of RAM, at least 1 GB of free disk space, a resolution of 1280 × 720, and DirectX Version 11.

3.3.2. Bluetooth Connection

To connect the eJamar controller to the computer, first, power on the controller. Then, in the Windows Settings window, select the Bluetooth device labeled “AC_BT_0X”, where X can range from 1 to 9. Once the controller is paired with Windows, launch the exergame, which will automatically recognize the eJamar. The controller will emit a vibration signal to confirm that it is successfully linked to the game.

3.3.3. Measurement Ranges

The eJamar device measures grip strength from 0 to 25 kgf with a resolution of 0.1 kgf, requiring a minimum of 1 kgf for proper functionality. It also measures motion angles from 0 to 90 degrees with a resolution of 1 degree, requiring a minimum initial range of ±20 degrees. Participants must meet these strength and motion requirements, which can be evaluated using the eJamar device through its calibration window.

4. Preliminary System Validation

The feasibility of the proposed eJamar as a game controller device was evaluated through various preliminary trials in the laboratory with healthy volunteers. The main goals of the trial were to validate the effectiveness of the eJamar to control the Peter Jumper and Andromeda exergames using grasping and hand actions, and preliminarily evaluate the system usability and user experience.

4.1. Experimental Protocol

The testing protocol was conducted with the participation of 8 healthy inexperienced individuals in a single session lasting approximately 45 min. Participants with disabilities were intentionally excluded to ensure an impartial evaluation, eliminating biases potentially associated with physical or cognitive limitations [29]. The

Table 3. Demographic information of participants.

ID	Age	Gender	Dominant Hand	Years of School	Prior Computer Usage
P1	33	F	Right	18	Yes
P2	36	F	Left	18	Yes
P3	55	F	Right	12	No
P4	62	F	Right	12	No
P5	64	M	Left	14	Yes
P6	65	M	Right	18	Yes
P7	68	F	Right	12	No
P8	71	M	Right	14	Yes

provides the demographic information of the participants.

The protocol began with a brief project introduction, where the main objective of the research was explained to the participant (1 min). Next, the exergame “Peter Jumper” was introduced, and its objective was explained (2 min). The participant then engaged in gameplay using a keyboard (2 min). This was followed by an introduction to the configuration screens and an explanation of the two game modes (3 min). A spring screw adjustment was then performed, where the screw was set to the maximum position to measure the participant’s grip strength, and the process was repeated with the screw in the medium and minimum positions (2 min). Participants proceeded to play “Peter Jumper” using the eJamar controller, with gameplay lasting 1 min per level in each of the two modes (8 min). After a 5 min break, the exergame “Andromeda” was introduced, and its objective was explained (2 min). The participant played “Andromeda” using the keyboard (2 min), followed by an introduction to its configuration screens and game modes (3 min). Participants tested the game, playing 1 min per level in both modes (6 min). The session concluded with participants completing a questionnaire available on https://forms.gle/TVCoatU3f3JgvKit9, (accessed on 2 October 2024) (4 min), followed by a farewell and appreciation (2 min).

4.2. USE Questionnaire: Usefulness, Satisfaction, and Ease of Use

The questionnaire consisted of five sections. The first section collected participant information, such as gender, age, and dominant hand. The second section, with 12 questions, evaluated the playability of the two proposed games. The third section, consisting of 7 questions, assessed the usability of the eJamar GC. The fourth section evaluated player satisfaction during the overall gameplay experience. Additionally, a suggestions section was included, where participants provided feedback on potential system improvements. The responses were recorded on a Likert scale ranging from −2 to 2, where −2 indicated “strongly disagree”, −1 “disagree”, 0 “neutral”, 1 “agree”, and 2 “strongly agree”.

Table 4. Results of usability questionnaires.

ID	Question	P1	P2	P3	P4	P5	P6	P7	P8	Mean	STD
	Playability
Q1	Was the Peter Jumper Game (PJG) friendly?	1	1	1	2	1	2	2	2	1.5	0.53
Q2	Was PJG interesting for you?	−1	0	1	2	1	0	2	1	0.63	1.19
Q3	Would you use PJG at home?	2	2	1	1	1	1	2	1	1.4	0.52
Q4	Was the graphic design of PJG adequate (player, obstacles, environment, etc.)? friendly?	1	1	2	1	1	2	2	2	1.5	0.53
Q5	Was PJG intuitive and easy to play?	2	1	1	2	2	2	1	2	1.8	0.5
Q6	Have you been able to play PJG without a therapist’s support?	2	2	2	2	1	2	2	2	1.9	0.4
Q7	Was the Andromeda Game (AG) friendly?	1	1	1	2	1	2	2	1	1.4	0.52
Q8	Was AG interesting for you?	1	1	1	2	1	2	2	1	1.4	0.52
Q9	Would you use AG at home?	2	2	2	1	1	2	2	1	1.6	0.52
Q10	Was the graphic design of AG adequate (spaceship, enemies, environment, etc.)?	1	1	0	2	2	2	2	1	1.4	0.74
Q11	Was AG intuitive and easy to play?	2	2	2	2	2	2	2	1	1.9	0.35
Q12	Have you been able to play AG without a therapist’s support?	2	2	2	2	1	2	2	1	1.8	0.46
	Usability
Q13	Have you been able to use the Game Controller (GC) easily?	2	2	1	2	2	1	2	2	1.8	0.46
Q14	In general, was it easy to control the game actions with the GC?	2	2	1	2	2	1	2	2	1.8	0.46
Q15	Was the weight of the GC suitable?	1	1	1	1	2	−1	2	1	1.0	0.93
Q16	Were elements of the GC easy to handle?	2	2	0	2	2	1	2	2	1.6	0.74
Q17	Have you felt comfort in your hand when taking the GC?	2	2	1	2	1	0	2	2	1.5	0.76
Q18	There were no disconnection issues during the session (GC and PC)	2	2	1	2	2	2	2	2	1.9	0.35
Q19	Do you find the vibration mode useful?	2	2	0	1	1	2	2	0	1.3	0.89
	Satisfaction
Q20	Have you been able to perform all the game levels successfully?	2	2	2	2	2	2	2	2	2.0	0.0
Q21	Have the games taken a lot of effort from you? (fatigue)	2	2	1	2	1	1	1	1	1.4	0.52
Q22	In general, the difficulty level of the games is adequate.	2	1	1	2	1	2	2	1	1.5	0.53
Q23	Were you able to easily calibrate the rigidity of the device?	−1	−1	−1	2	2	−1	0	2	0.25	1.49
Q24	If possible, would you like to continue using this system (GC + games)?	2	2	1	2	1	2	2	1	1.6	0.52

shows the three main sections of questionnaire and answers of participants.

In the Playability section, participants consider that both games are user-friendly (Q1 and Q7). However, Andromeda (Q8 = 1.4 ± 0.52) is considered more engaging than PJG (Q2 = 0.63 ± 1.19). This result is further supported by the suggestions section, where participants note that PJG could benefit from having more levels or improving the game environment. On the other hand, both games are found to be intuitive and easy to use (Q5 and Q11), as participants mention that they could play these exergames at home (Q3 and Q9) without the help of a therapist (Q6 and Q12).

In the Usability section, participants consider that the eJamar controller and its respective control actions for each game are easy to manage (Q13 and Q14 = 1.8 ± 0.46). The controller’s weight received the lowest rating (Q15 = 1 ± 0.93), prompting us to consider a possible reduction in the device’s weight. Participants report feeling comfortable using the eJamar (Q17 = 1.5 ± 0.76), despite having to hold the controller in mid-air without support. We believe this comfort could be further improved if participants rest their hand on a table, a modification we plan to implement during future patient trials. No Bluetooth communication disconnections were reported (Q18 = 1.9 ± 0.35). The controller’s electronic system is designed to provide feedback to the user through eJamar’s vibration, but, as shown in Table 4, question Q19, participants P3 and P8 had difficulty distinguishing the vibration from the controller.

In the Satisfaction section, it is notable that all participants were able to complete all levels of the games (Q20), which aligns with the responses from the Playability section, where the games were found to be easy to play (Q5 and Q11). Additionally, participants generally did not experience fatigue during gameplay and felt that the difficulty level of the games was appropriate (Q22 and Q23). The controller features a knob that must be manually adjusted to fit the user’s hand size and enhance comfort. However, participants found this knob difficult to calibrate due to its rigidity (Q23 = 0.25 ± 1.49). As a result, we suggest that this adjustment should be performed by a specialist prior to gameplay.

5. Discussion

This work presented the development of the eJamar GC alongside the exergames Peter Jumper and Andromeda. The results of usability tests with healthy participants were favorable, as shown in Table 4, indicating that the system provided an intuitive and user-friendly experience.

The exergame Peter Jumper primarily focuses on repetitive exercises to improve grip strength, as well as radial/ulnar and flexion/extension movements, which can be configured according to the participant’s or patient’s needs. The Andromeda exergame promotes coordination between grip strength and repetitive pronation/supination or radial/ulnar movements to aim and defeat enemy ships. Both games offer different modes and configurations, allowing the system to be tailored to the specific treatment required by a patient.

The eJamar controller, designed to measure hand grip strength and detect various hand movements, has proven to be an efficient tool for control and precision, which are important variables that have been considered in the design of the eJamar game controller [45]. The ability to adjust the hand holder via the knob and the spring adjustment has contributed to making the device comfortable to use. Additionally, the electronic system that measures different movements allows the device to be used for various hand rehabilitation treatments through exergames. The eJamar controller + exergames system promotes repetitive and intensive movements, which, according to evidence, enhances the effectiveness of rehabilitation interventions [46], a practice also applied in other systems that use exergames [9,22,27].

In terms of gameplay, both Peter Jumper and Andromeda games were found to be user-friendly and intuitive. However, Andromeda proved to be more engaging for users, which we believe is due to the nature of the game. Nevertheless, we are taking participant feedback to enhance Peter Jumper by integrating more engaging levels more and different game mechanics and not just different modes [47].

Regarding usability, the complete system demonstrated its potential for implementation in home rehabilitation settings, as participants confirmed that the game levels were easy to play and they felt capable of using the exergames without the presence of a therapist making it suitable for use in home rehabilitation therapies [22,48,49]. Unlike other exergames that implement numerous difficulty levels [20], PJ and Andromeda were developed with three difficulty levels that automatically adjust to the player’s maximum strength level. This also brings a subtle shift to the game mechanics, ensuring a pleasant experience in each session and promoting adherence to the game [47]. As previously mentioned, this feature, particularly in Peter Jumper, will be further enhanced in future work.

The wireless and portable design of the eJamar, combined with the ability to measure and store data about motor functionality and grip strength, will facilitate the integration of this system into remote rehabilitation treatments. These treatments are particularly needed by patients with neurological conditions who face challenges in attending medical centers for rehabilitation. As such, the development of new systems like this is always essential [50]. Hence, the novel eJamar can contribute to design new tele-rehabilitation strategies in complementing and enhancing the effects of conventional physical therapy.

Additionally, in the holistic context of rehabilitation, it is important to not only exercise motor function but also to assess the patients’ functional status and the effects of treatments [51]. This assessment–rehabilitation dichotomy should be considered, especially when designing tools intended for neurological rehabilitation. Thus, the proposed exergame controller could serve also for the assessment of UL motor function and hand-grip strength and provide relevant information about the patient’s evolution. For that purpose, outcome measures given by the eJamar must be correlated with the golden standard metrics (ARAT, FMA, Jamar, etc.) for clinical validation. Future studies will focus on data gathering for outcome measurement correlation, similarly to other validation studies [52,53].

Finally, we identified some areas for improvement. For instance, some participants considered the device to be somewhat heavy. To address this, we plan to modify the protocol in future studies, allowing participants to rest their arm on a table, as has been done in other studies [20,48]. Additionally, although the vibration system was designed to enhance the gaming experience and provide haptic feedback [45], participants found it difficult to detect. This suggests that the vibration system may need to be improved, or that alternative forms of haptic feedback should be explored.

In a future study, we plan to conduct trials with patients who have neurological or pathological conditions to evaluate the acceptability and effectiveness of the system in clinical settings. This will provide us with a more comprehensive understanding of the potential of the developed system in clinical rehabilitation contexts. Furthermore, we will develop additional exergames compatible with eJamar to offer a wider range of games tailored to the specific rehabilitation needs of each patient.

Limitations

The number of participants was eight, and, due to this small sample size, a more exhaustive statistical analysis of the results was not conducted. Although the questionnaire used was adapted from a standard usability questionnaire, the subjectivity of the questions may have introduced some bias into the results. Additionally, the tests were conducted in controlled environments, which may not fully capture the challenges of real-world scenarios. This study did not involve patients with UL motor impairments; however, we have initiated trials in larger groups of patients and therapists, and the results will be presented in future work. This will allow us to analyze their responses and evaluate the overall acceptability of the system by individuals with neurological or other pathological conditions. In addition, feedback from therapists will help refine the specific categories of individuals who could benefit from using this device. Furthermore, the long-term effects of the use of the system will be analyzed in a future work.

6. Conclusions

The eJamar exergame controller was successfully implemented, capable of detecting pronation/supination, ulnar/radial deviation, and flexion/extension hand movements, as well as grip strength. These features make the device a valuable tool in the field of upper limb rehabilitation through exergames. Two exergames were developed with the aim of promoting hand movements and enhancing grip strength. Both games are compatible with the eJamar controller and can be used to apply various hand rehabilitation techniques. Participants in the evaluation test confirmed that the controller was comfortable and easy to use. The control actions are simple, allowing easy manipulation of the game characters. Due to the system’s ease of use, participants expressed confidence that they would be able to perform rehabilitation exercises at home without the assistance of a therapist. Based on these promising results, we plan to conduct further trials with patients who have neurological or pathological conditions to assess the system’s acceptability and effectiveness in clinical settings.