Relationship between pushing force and improvement in total A-ROM when training with a finger extensor facilitation training device “iPARKO”

Relationship between pushing force and improvement in total A-ROM when training with a finger extensor facilitation training device “iPARKO” | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Relationship between pushing force and improvement in total A-ROM when training with a finger extensor facilitation training device “iPARKO” Shota Ishigaki, Reika Yokoyama, Yoshifumi Morita, Hirofumi Tanabe This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5406511/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract We observed that when the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints of the fingers are in maximum extension and the metacarpophalangeal (MP) joints are in hyperextension, applying an external resistance from the fingertips to the MP joints increases extensor muscle activity, even unintentionally, and opens the hand. Based on this phenomenon, a finger extensor facilitation technique conducted by therapists was developed as training for hand extension for chronic stroke survivors. In previous studies, we developed iPARKO, a finger extensor facilitation training device that imitates this technique. In this study, we developed a new version of the device, iPARKO-2, that can be used for chronic stroke survivors with strong spasticity. Five chronic stroke survivors were trained with iPARKO-2 using three different pushing forces. To evaluate whether chronic stroke survivors can voluntarily perform movements, we measured the active range of motion (A-ROM). The results showed that the improvement in the total A-ROM tended to increase as the pushing force during training increased. Additionally, extensor muscle activity increased as the pushing force increased. Based on this, we conclude that the greater the pushing force, the greater the muscle activity, and that the amount of muscle activity influences the improvement in the total A-ROM. Chronic hemiplegic Finger extensor muscle Hand rehabilitation Maximum voluntary contraction Muscle activity Rehabilitation device Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 1. Introduction According to the World Health Organization (WHO), stroke is a global public health problem that causes severe disabilities [ 1 ]. As the population ages, the number of chronic stroke survivors is expected to increase [ 2 ]. After a stroke, motor function may be impaired owing to an after-effect called spasticity, a condition wherein the hands and feet are constantly stretched and flexed owing to excessive tension in the muscles [ 3 ]. Prolonged abnormal postural conditions due to spasticity can cause contractures that stiffen the muscles and joints [ 3 ]. Our previous study focused on the hand, which is the most difficult to restore motor function for. However, treatment of a hemiplegic hand is difficult because the finger joints have 23 degrees of freedom [ 4 ]. In addition, the restoration of hand motor functions is essential for chronic stroke survivors to perform daily activities that require fine finger movements and to return to society while maintaining a high quality of life [ 5 , 6 ]. Therefore, rehabilitation is often used to restore hand motor functions in chronic stroke survivors. Several studies have been conducted on rehabilitation therapy for the upper extremities, such as constraint-induced movement therapy, which encourages chronic stroke survivors to use the paralyzed upper extremity [ 7 – 9 ]; mirror therapy, which uses mirrors to produce a reflective image of the paralyzed upper extremity [ 10 – 12 ]; and bilateral arm training (BAT), which involves repetitive practice of bilateral arm movements in symmetrical or alternating patterns [ 13 , 14 ]. Moreover, repetitive facilitated exercise (RFE) has also been studied [ 15 , 16 ]. RFE is a form of rehabilitation in which a chronic stroke survivor is given the stimulation necessary to achieve the intended movement in the affected area. This stimulation can be achieved by tapping or rubbing the muscle, quickly and passively stretching the muscle, or applying slight resistance to the intended movement. Intensive stimulation is provided to chronic stroke survivors who cannot move their fingers on their own to induce spontaneous movement and restore hand motor function [ 15 ]. For the hand-opening motor function to be restored, the extensor muscles, which are the muscles that open the hand, must be strengthened. Repetitive hand-opening movements are necessary to strengthen extensor muscles. However, chronic stroke survivors cannot train their extensor muscles because they cannot open their hands voluntarily. Thus, a manual technique called the finger extensor facilitation technique (hereafter referred to as manual therapy) was developed to increase hand voluntariness of chronic stroke survivors [ 17 , 18 ]. To explain manual therapy, we first briefly describe the bone and joint structure of the human hand, as shown in Fig. 1 . Each finger typically has three phalanges: proximal, intermediate, and distal. The exception is the thumb, which has only two phalanges: the proximal and distal. Proximal phalanges are bones located near the palm of the hand, intermediate phalanges are not present in the thumb but only in the other fingers, and distal phalanges are bones located at the tips of the fingers. In addition, interphalangeal joints connect the bones of the fingers and include the proximal interphalangeal (PIP), distal interphalangeal (DIP), and metacarpophalangeal joints (MP). The PIP, DIP, and MP joints are the joints between the proximal and intermediate phalanges, intermediate and distal phalanges, and intermediate and proximal phalanges, respectively. Manual therapy is illustrated in Fig. 2 . Manual therapy enables chronic stroke survivors to increase hand voluntariness without requiring hand-opening movements. A therapist holds the proximal, intermediate, and distal phalanges of the paralyzed finger, maintaining the maximum extension of the DIP and PIP joints and hyperextension of the MP joint. While the chronic stroke survivor voluntarily moves the paralyzed hand forward, the therapist applies resistance to the MP joints from the fingertips. This resistance induces a stretch reflex in the extensor muscles [ 19 ]. The stretch reflex causes the extensor muscles to contract, thereby increasing the muscle activity. During manual therapy, the four fingers are held in hyperextension and the extensor muscles are relaxed to facilitate contraction. In contrast, the flexor muscles are stretched, making contraction difficult. Applying a force from the fingertips to the MP joint in this state increases extensor muscle activity while suppressing flexor muscle activity [ 20 ]. However, this manual therapy does not provide adequate rehabilitation treatment because of the long treatment period and physical burden on the therapist. Therefore, a device or robot that reduces the physical burden on therapists and restores hand-opening function in chronic stroke survivors is required. Based on this background, devices and robots for rehabilitating paralyzed hands have been developed, such as HandCARE [ 21 ], which assists the chronic stroke survivor’s opening and closing movements and can be adapted to various hand shapes and finger sizes; the AMADEO [ 22 ], which simulates natural movements for hemiplegic hand conditions; and the exoskeleton robotic hand [ 23 ], which is actively driven by its own muscle signals; and HANDEXOS [ 24 ], which is a wearable exoskeleton device and rehabilitation device using parallel link mechanisms [ 25 ]. Additionally, a functional recovery training device that imitates RFEs has been developed [ 26 ]. These conventional devices often aim to restore hand motor function by increasing the extensor muscle strength through repeated finger flexion and extension. However, chronic stroke survivors are unable to open their hands by themselves. Therefore, before the device is used, training should be provided to increase the voluntariness of the extensor muscles. To the best of our knowledge, no device thus far can train chronic stroke survivors to increase the voluntariness of extensor muscles other than hand flexion while suppressing abnormal tension in the flexor muscles. Therefore, we developed a device that simulates manual therapy to improve the voluntariness of extensor muscles in chronic stroke survivors. In a previous study, iPARKO, which simulates manual therapy, was developed and validated using three healthy participants [ 27 ]. Subsequently, the effectiveness of iPARKO was tested in six chronic stroke survivors. In all participants, training with iPARKO resulted in an improvement in the active range of motion (A-ROM), confirming that hand voluntariness improved [ 28 ]. In this study, we developed iPARKO-2, a modified version of the conventional iPARKO, as shown in Fig. 3 . The conventional iPARKO has the following two problems: First, it may not be applicable to chronic stroke survivors with strong fingertip spasticity. In training with the conventional iPARKO, the chronic stroke survivor 's fingertips are fixed to the resistance-providing part, and force is applied from the fingertips to the MP joint via the fingers. However, some chronic stroke survivors have significant fingertip spasticity, which complicates fixing their fingertips to the resistance-providing part. Even if they were able to fix their fingertips to the device, the fingertips, which had strong spasticity, occasionally move off the resistance-providing part during training. Second, a large burden is placed on chronic stroke survivors when fixing their fingers to iPARKO. The conventional iPARKO requires the fingers of a paralyzed hand to be individually fixed to the device. Fixing each spastic finger to a device is inconvenient and time-consuming for chronic stroke survivors. In this study, we developed iPARKO-2, which solves the above problems, and examined the relationship between pushing force and improvement in hand voluntariness during training with iPARKO-2. Specifically, we conducted iPARKO-2 training with five chronic stroke survivors using different pushing forces. We measured changes in the A-ROM of the four fingers before and after training to examine whether chronic stroke survivors could voluntarily perform movements. A-ROM refers to the range of motion that a chronic stroke survivor can achieve using their own muscle strength without any external assistance. In addition, we measured extensor muscle activity during training and analyzed the relationship between changes in A-ROM and extensor muscle activity. 2. Materials and methods 2.1 Development of iPARKO-2 iPARKO had two main problems. (1) Because the fingertips are fixed and force is applied from the fingertips to the MP joint, chronic stroke survivors with strong fingertip spasticity are occasionally unable to wear iPARKO. (2) Chronic stroke survivors must fix each finger individually, which places a heavy burden on them. To solve problem 1, we changed the design to fix the PIP joint instead of the fingertips and applied force from the PIP joint to the MP joint. In addition, to solve Problem 2, we changed the design to one that could fix four fingers simultaneously. iPARKO-2, as shown in Fig. 3 , consists of training, biofeedback, and data acquisition components, similar to iPARKO [ 27 ]. In this study, the term "fingers" refers to the four fingers, excluding the thumb. 2.2 Training component The training component consists of finger-fixing part 1, finger-fixing part 2, and a wrist-fixing part, as shown in Fig. 4 . Figure 5 shows only finger-fixing part 1, with the other training components removed. As shown in Fig. 5 , finger-fixing part 1 was fabricated from thermoplastic resin and was attached from the PIP joint to the fingertip. Unlike iPARKO, which requires fixation of one fingertip at a time on a rubber band, the fingertips from the PIP joints of four fingers can be fixed simultaneously. In addition, because finger-fixing part 1 is bent in the direction of hand extension, it plays the same role as the finger sack of iPARKO, and the PIP and DIP joints can be maintained at maximum extension, which is the same condition as in manual therapy. Figure 6 shows only finger-fixing part 2, with the other training components removed. Finger-fixing part 2 was fabricated from thermoplastic resin and consists of two plates. The PIP joints of the index, middle, ring, and little fingers were pinched from above and below, as shown in Fig. 6 . Therefore, the PIP joints of the four fingers are fixed simultaneously instead of individually. In this state, resistance can be applied to the MP joint, which is directly connected to the PIP joint, by pushing the hand forward. Unlike iPARKO, which applies a force from the fingertips of the four fingers, this device applies force from the PIP joint, enabling force to be applied to the hands of chronic stroke survivors with strong fingertip spasticity. As described earlier, finger-fixing 1 and 2 can fix four fingers simultaneously. Therefore, the burden on chronic stroke survivors caused by fixing one finger at a time (problem 2) could be reduced. The wrist-fixing part is attached to the chronic stroke survivor's wrist and maintains the MP joint during hyperextension. A six-axis force/torque sensor (FFS055F251M8R0A6S; Leptrino Co., Ltd.) is attached to the lower part of finger-fixing part 2 to measure the force applied to the PIP joint and the MP joint directly connected to it. Finger-fixing part 1, finger-fixing part 2, and the six-axis force/torque sensor are fixed on a slide rail (FBW3590XRUU + 300L; THK Co., Ltd.), enabling a chronic stroke survivor to smoothly move his or her hand forward. A sponge is attached to the tip of the slide rail to absorb the shock when a chronic stroke survivor pushes forward, as shown in Fig. 4 . The firmness of the sponge was adjusted such that finger-fixing part 1, finger-fixing part 2, and the six-axis force/torque sensor move approximately 5 mm on the slide rail when the chronic stroke survivor pushes forward. 2.3 Biofeedback and data acquisition components iPARKO-2 measures extensor muscle activity during training using a portable electromyography (EMG) sensor (OPE-2; Unique Medical Co., Ltd.), similar to iPARKO. This EMG sensor consists primarily of a surface electrode and a preamplifier. By attaching a surface electrode to the skin over any muscle, the action potentials of the muscle can be summed and displayed as a diagram. The six-axis force/torque sensor was used to measure the pushing force. The data acquisition component consisted of an EMG sensor, the six-axis force/torque sensor, data acquisition system (USB6211; National Instruments Corp.), and personal computer. The sampling frequency of the measurements was 1000 Hz. The measurement data collected by the data acquisition systems were displayed on a monitor screen, as shown in Fig. 7 . 3. Experiments 3.1 Purpose This study aimed to compare improvements in hand voluntariness among five chronic stroke survivors before and after training with iPARKO-2 using different pushing forces. The A-ROM was used to evaluate hand voluntariness, and the change in the A-ROM before and after training was used to improve hand voluntariness. Information on the participants is presented in Table 1 . The passive range of motion (P-ROM) is the range of motion of a joint obtained by moving the joint using an external force or the hands of another person. The P-ROM was measured in advance by a therapist using a goniometer. All participants were paralyzed in their left hand. All the participants provided informed consent before participating in the study. The study was conducted in accordance with a protocol approved by the Ethics Committee of the Nagoya Institute of Technology (Approval number 2020-001). Table 1 Information of the five participants Participant No. Sex Age Dominant hand Paralyzed hand 1 F 59 R L 2 M 69 R L 3 M 56 R L 4 F 69 R L 5 M 66 R L Mean ± SD M:3, F:1 63.8 ± 5.3 R:5, L:0 R:0, L:5 Participant No. P-ROM [°] Maximum pushing force [N] Period of onset [Years] Remarks 1 15 40 10 Lacunar infarction 2 20 80 8 Lacunar infarction 3 65 60 13 Cerebral hemorrhage 4 40 28 13 Cerebral hemorrhage 5 53 40 17 Cerebral infarction Mean ± SD 38.6 ± 19.0 49.6 ± 18.3 12.2 ± 3.1 - 3.2 Method The experimental procedure is depicted in Fig. 8 . First, the participants underwent a maximum pushing force test as a preliminary experiment. Each participant was then trained with iPARKO-2 using three different pushing forces. An A-ROM test was performed before and after each training session. A maximum pushing force test was conducted at the beginning of the experiment. Because muscle strength differed among participants, the maximum pushing force was defined as the maximum force at which the participant could push without experiencing pain, and this was measured. The measurement was performed in the same posture as that used during training with iPARKO-2, as described below. In this posture, the participants were requested to push their hands forward with the maximum force they could exert without feeling pain for 3 s, beginning from the supervisor's cue, and the maximum force during these 3 s was defined as the maximum pushing force. The maximum pushing forces for each participant are listed in Table 1 . A six-axis force/torque sensor was used to measure the pushing force in this study. The training with iPARKO-2 is described next. At the beginning of the training with three different pushing forces, the therapist attached the surface electrodes of the EMG sensor to a participant's left arm to measure the extensor muscle activity. The surface electrodes were left attached during the three training sessions to prevent variations in the data due to differences in their attachment positions of the surface electrodes. Subsequently, the wrist-fixing part was attached to each participant's wrist to fix the wrist angle. The PIP joint of the left hand was fixed to finger-fixing part 2, and the fingertips were fixed to finger-fixing part 1. Under these conditions, training with iPARKO-2 was conducted at three pushing forces: 20%, 50%, and 80% of the maximum pushing force for each participant. To account for sequential effects, training was performed in the order of 80%, 50%, and 20% force for participants 1, 2, and 3, and 20%, 50%, and 80% force for participants 4 and 5. As shown in Fig. 8 , one training session consisted of an initial 3 s waiting period and 10 sets of pushing. Each set consisted of 2 s of pushing and 2 s of relaxation for a total of 4 s. A metronome was used to indicate a timing of 2 s and a sampling time of 0.001 s. The indicated pushing force was 20%, 50%, or 80% of the maximum force. During training, the participants pushed their hands forward to achieve the indicated pushing force while observing the force on the monitor screen. Three-minute rest periods were given between three training sessions. During the rest period, the participant's hand was removed from iPARKO-2. 3.3 Experimental Posture The posture during the experiment is shown in Fig. 9 . The participant sat in a chair adjusted so that the ankle joint was at 0° flexion and the knee joint was at 90° flexion. Both legs were placed shoulder width apart, with the soles of feet grounded on the floor. The shoulder joint was maintained without elevation. The training component of iPARKO-2 was placed next to the participant's body. The participants were also instructed to place their elbows on the upper limb stand, keep their posture straight, and avoid twisting their trunks. The monitor screen was placed in front of the participant and the height was adjusted so that the participant could easily see the screen. The upper limb is represented by the four-joint link model shown in Fig. 10 . Let the flexion angle of the shoulder joint be \(\:{\theta\:}_{1}\) , the flexion angle of the elbow joint be \(\:{\theta\:}_{2}\) , the extension angle of the wrist joint be \(\:{\theta\:}_{3}\) , and the extension angle of the MP joint be \(\:{\theta\:}_{4}\) . In addition, for all joint angles, the counterclockwise direction was positive. The following relationship exists between these angles: $$\:\begin{array}{c}\:{\theta\:}_{1}+\:{\theta\:}_{2}+\:{\theta\:}_{3}\:+\:{\theta\:}_{4}\:=\:90^\circ\:\#\left(1\right)\end{array}$$ We assumed \(\:{\theta\:}_{1}\) = 80°, \(\:{\theta\:}_{2}\) = 0°, and \(\:{\theta\:}_{4}\:\) is the P-ROM of each participant. \(\:{\theta\:}_{3}\) is uniquely determined from Eq. (1). Throughout the experiment, the participants moved their hands, which were placed on the training component, forward. The distance traveled was approximately 5 mm. As the forearm moves, the angles of the shoulder, elbow, and wrist changed. The change in the angle of the shoulder was the largest, extending by approximately 5°. In comparison, the elongation of the elbow and wrist was small. 3.4 Evaluation method The A-ROM was measured before and after training. Twelve points were measured at the MP, DIP, and PIP joints of the four fingers of a participant's paralyzed hand, excluding the thumb. Measurements were performed by a therapist using a goniometer. The angles were as shown in Fig. 11 , where the fully extended position was 0°, the angle in the extension direction was positive, and the angle in the flexion direction was negative with respect to the fully extended position. To evaluate whether chronic stroke survivors could voluntarily perform movements, we calculated the sum of the joint angles at 12 locations as the total A-ROM. Thereafter, the total A-ROM was used as an indicator of voluntariness. Additionally, the change in the total A-ROM before and after training was defined as an improvement in the total A-ROM. In other words, the larger the improvement in the total A-ROM, the greater the improvement in voluntariness. The extensor muscle activity was measured during training using an EMG sensor. The muscle activity was defined as the average of 10 sets, where the absolute average value of 1 s, excluding the first and last 0.5 s of the 2-s period of pushing, was the muscle activity of 1 set. The first and last 0.5 s of 1 s were excluded to reduce errors caused by different timing of pushing between participants. Generally, because the amount of muscle activity varies from individual to individual, each muscle activity was normalized using the maximum voluntary contraction (MVC). However, measuring the MVC in chronic stroke survivors is difficult because of the narrow range of movement of the wrist joints and individual differences in the degree of paralysis. Therefore, normalization was not performed in this study. 4. Results and discussion 4.1 Relationship between pushing force and A-ROM The total A-ROM before and after training, as well as the improvement in the total A-ROM for each of the five participants at 20%, 50%, and 80% of the maximum pushing force, are shown in Fig. 12 . The Friedman test was used to compare the improvement in the total A-ROM at the three pushing forces. The mean values of improvement in total A-ROM for the five participants in training at 20%, 50%, and 80% of maximum pushing force were 67.0 ± 45.8°, 134.0 ± 102.7°, and 183 ± 117.8°, respectively. The improvement in the total A-ROM tended to increase significantly with increasing pushing force (*p < 0.05 ). This indicated the effectiveness of training with pushing forces close to the maximum pushing force. At 50% of the maximum pushing force, the improvement in the total A-ROM was greater than that at 20% for all four participants except participant 1. At 80% pushing force, the improvement in the total A-ROM was greater than that at 20% and 50% for all participants. During the training, the participants adjusted their pushing force to match the target value, which may have resulted in individual differences in the actual pushing force. The target and measured pushing forces for the three training sessions (20%, 50%, and 80% of the maximum pushing force) for each participant are shown in Fig. 13 . As with muscle activity, each measured pushing force is the average of 10 sets of absolute average values for 1 s, excluding the first and last 0.5 s of the 2-s period, where one set of pushing force was defined as the average of the 10 sets of pushing force. As shown in Fig. 13 , the ability to adjust the pushing force to the target value varies among individuals. Participant 3 could be considered to have a high adjustment capability because the pushing force is close to the target value. In contrast, Participants 1, 2, 4, and 5 tended to exhibit higher actual pushing forces as the target value increased. However, when the target value was large, the error and variation increased. This indicated that their adjustment capability for large forces was inferior. In particular, participant 5 was considered to have an inferior adjustment capability for both small and large pushing forces. Therefore, as shown in Fig. 14 , the relationship between the measured pushing force and improvement in the total A-ROM is represented by a scatter plot. Figure 14 shows the linear approximation curve. The correlation coefficients between the measured pushing force and improvement in the total A-ROM for the five participants were 0.23, 0.96, 1.00, 0.99, and 1.00. Figure 14 shows that, except for participant 1, the improvement in the total A-ROM increased as the pushing force increased. 4.2 Relationship between pushing force and muscle activity The relationship between the measured pushing force and extensor muscle activity was examined. A scatter plot, as well as a linear approximation curve, representing the relationship between the measured pushing force and extensor muscle activity during training for the five participants is shown in Fig. 15 . The correlation coefficients between the measured pushing force and extensor muscle activity for the five participants were 0.58, 0.84, 0.91, 0.95, and − 0.07, respectively. As shown in Fig. 15 , except for participants 1 and 5, the extensor muscle activity increased as the measured pushing force increased. Based on these results, we consider that muscle activity tended to increase as the pushing force increased, and the amount of muscle activity affected the improvement in the total A-ROM. 4.3 Effectiveness of iPARKO-2 The newly developed iPARKO-2 was used in this experiment. The participants’ fingertips did not come off the iPARKO-2 during training. Additionally, the time required, compared with the conventional iPARKO, was reduced by 60%, from approximately 5 min to approximately 2 min on average. Based on these results, we believe that iPARKO-2 successfully addressed the problems in the conventional iPARKO. 5. Conclusion In this study, we developed a new finger extensor facilitation training device, iPARKO-2, which can be applied to chronic stroke survivors with strong spasticity. In addition, the relationship between the pushing force during training and improvement in the total A-ROM was examined in five chronic stroke survivors. The results showed that the greater the pushing force during training, the greater the muscle activity, and the amount of muscle activity affected the total A-ROM improvement. Future studies should examine the effects of other manual therapy conditions on improving hand voluntariness to explore training methods that can further enhance hand function in chronic stroke survivors. Furthermore, although immediate effects were verified in this study, we aim to verify the long-term effects and explore more effective training methods to improve the overall treatment efficacy. Abbreviations DIP Distal interphalangeal PIP Proximal interphalangeal MP Metacarpophalangeal P-ROM Passive range of motion A-ROM Active range of motion MVC Maximum voluntary contraction EMG Electromyography Declarations Competing interests The authors declare that they have not competing interests. Authors' Contributions All authors proposed the concept about iPARKO-2. SI and RY developed new devices. All authors performed the experiments. SI and RY performed data analysis. All authors read and approved of the final manuscript. Ethics declarations This study was approved by the ethics committee of the Nagoya Institute of Technology: 2020-001. All participants provided written informed consent before the measurements. Competing interests The authors declare that they have no competing interests. Acknowledgements We would like to thank Editage (www.editage.com) for the English language editing. Funding This research was supported by the JSPS Grant-in-Aid for Scientific Research (19K12878). References World Health Organization (2014) Global status report on noncommunicable diseases 2014 Katan M, Luft A (2018) Global burden of stroke. Semin Neurol 38:208–211. https://doi.org/10.1055/s-0038-1649503 Feldman RG, Young RR, Koella WP (1980) Spasticity, disordered motor control. Year book medical. 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Robomech J 10. https://doi.org/10.1186/s40648-023-00248-w Yokoyama R, Nakamura A, Morita Y, Tanabe H (2023) Verification of immediate effect of finger extension using a finger extensor facilitation training device iPARKO. IEEJ Trans EIS C 143–12:1099–1105. https://doi.org/10.1541/ieejeiss.143.1099 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5406511","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":381206872,"identity":"eef94778-b041-429b-908b-9794660533c9","order_by":0,"name":"Shota Ishigaki","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEUlEQVRIie2RwUrDQBBAZ1kYL2O9tuSQX1gpeKr6KwmBHkuglxxqCSxsfiGhoL8SCcRLsB/Qk/gDhQXx4MExeijIJlfBfbAsDPN2ZnYAPJ4/icglKICphLP3KFsAckxCf40rMD12S0AcVfoETuczq0zTJ8uh9DCX2qbpXTgrAObU7VeTUD/aFCYrl6JqYYJSPV3u+OWEssMaEZOgBFw7FRBGkmrFPSsNdYfYIF1JAoxzZ2NCW1ZuWRH63DyzcvE2qEAt8oDUJubGpKhM/VUFBxXV8Cyk6qTSwsCxS1hZzjniniUsildLH9vrct+0EGU38YNuXixlrfPHflbA6+CdnlZvI6fyzfZXZDOmeDwez//hE8l4TAush1sxAAAAAElFTkSuQmCC","orcid":"","institution":"Nagoya Institute of Technology","correspondingAuthor":true,"prefix":"","firstName":"Shota","middleName":"","lastName":"Ishigaki","suffix":""},{"id":381206873,"identity":"1fef215c-ff47-4594-94e5-50a9eb4cbe62","order_by":1,"name":"Reika Yokoyama","email":"","orcid":"","institution":"Nagoya Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Reika","middleName":"","lastName":"Yokoyama","suffix":""},{"id":381206875,"identity":"e8c4edac-58ba-4481-9a86-fb7e804e6706","order_by":2,"name":"Yoshifumi Morita","email":"","orcid":"","institution":"Nagoya Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yoshifumi","middleName":"","lastName":"Morita","suffix":""},{"id":381206876,"identity":"297ea4a8-26c2-4910-b562-102d211dbbbf","order_by":3,"name":"Hirofumi Tanabe","email":"","orcid":"","institution":"Shonan University of Medical Sciences","correspondingAuthor":false,"prefix":"","firstName":"Hirofumi","middleName":"","lastName":"Tanabe","suffix":""}],"badges":[],"createdAt":"2024-11-07 03:53:35","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5406511/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5406511/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":70102344,"identity":"1a2f86f4-e330-4718-af5d-d7e08267114e","added_by":"auto","created_at":"2024-11-28 10:45:25","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":407460,"visible":true,"origin":"","legend":"\u003cp\u003eBones and joints of the hand\u003c/p\u003e","description":"","filename":"floatimage179.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/6054a6ff1ac9fb5adc7c0c43.png"},{"id":70101085,"identity":"4630bfcf-295c-458f-a4a8-3de4a1961530","added_by":"auto","created_at":"2024-11-28 10:37:25","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":246175,"visible":true,"origin":"","legend":"\u003cp\u003eFinger extensor facilitation technique\u003c/p\u003e","description":"","filename":"floatimage260.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/a778ce0008b5ba8117a44c77.png"},{"id":70100722,"identity":"d1055681-d2e2-4045-9189-6b8dfa261f02","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":590152,"visible":true,"origin":"","legend":"\u003cp\u003eFinger extensor facilitation training device “iPARKO-2”\u003c/p\u003e","description":"","filename":"floatimage354.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/bc4538712cf49bf29047c86d.png"},{"id":70100712,"identity":"5dab3c8b-2ed0-45ba-85ed-b90de15c033a","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":454613,"visible":true,"origin":"","legend":"\u003cp\u003eTraining components of iPARKO-2\u003c/p\u003e","description":"","filename":"floatimage440.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/74e1ad59d739ed178ecdc7a2.png"},{"id":70100718,"identity":"c837b59d-ba32-49a6-ba1e-0028ef657163","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":576516,"visible":true,"origin":"","legend":"\u003cp\u003eFinger-fixing part 1\u003c/p\u003e","description":"","filename":"floatimage531.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/b9e28917d67f56f554c15231.png"},{"id":70100715,"identity":"5dd3e889-8bb9-470b-b163-12b1d36b55ad","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":543074,"visible":true,"origin":"","legend":"\u003cp\u003eFinger-fixing part 2\u003c/p\u003e","description":"","filename":"floatimage621.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/1e78b8d32fe7562599294601.png"},{"id":70100713,"identity":"e3a4a797-009e-4451-8331-841786aa1f99","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":226073,"visible":true,"origin":"","legend":"\u003cp\u003eMonitoring of the biofeedback component\u003c/p\u003e","description":"","filename":"floatimage712.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/2f2af9ee8da2280c488e4b9b.png"},{"id":70101091,"identity":"5ff8d014-78ef-466a-b59d-a2488c8d6127","added_by":"auto","created_at":"2024-11-28 10:37:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":100391,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental procedure\u003c/p\u003e","description":"","filename":"floatimage85.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/c0640dd86eb2ca350868bf49.png"},{"id":70102343,"identity":"806331c7-354a-4613-8a26-bbcae8cb7600","added_by":"auto","created_at":"2024-11-28 10:45:25","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":558456,"visible":true,"origin":"","legend":"\u003cp\u003eExperimental posture\u003c/p\u003e","description":"","filename":"floatimage95.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/7eba15b6b9ed09a9bcd2529e.png"},{"id":70102770,"identity":"6716ff9e-1e4c-4042-84b0-fdfc6e0b8d88","added_by":"auto","created_at":"2024-11-28 10:53:32","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":76839,"visible":true,"origin":"","legend":"\u003cp\u003eUpper limb four-joint link model\u003c/p\u003e","description":"","filename":"floatimage101.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/ea2e4a7b944711cbf83c18f0.png"},{"id":70101092,"identity":"95999fb4-dac0-494a-affd-802dbb036212","added_by":"auto","created_at":"2024-11-28 10:37:25","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":931740,"visible":true,"origin":"","legend":"\u003cp\u003eAngle of each joint\u003c/p\u003e","description":"","filename":"floatimage113.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/1b86d9f4b60c21757f3e4851.png"},{"id":70101088,"identity":"a8623c56-2afc-46ad-9049-71834f91b2b4","added_by":"auto","created_at":"2024-11-28 10:37:25","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":64614,"visible":true,"origin":"","legend":"\u003cp\u003eTotal A-ROM of each participant\u003c/p\u003e","description":"","filename":"floatimage122.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/ae0cf7f4de0631968d8a03bc.png"},{"id":70101093,"identity":"964356e6-11fa-4d47-9088-5953e9a27797","added_by":"auto","created_at":"2024-11-28 10:37:26","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":116489,"visible":true,"origin":"","legend":"\u003cp\u003eTarget and measured pushing force of each participant\u003c/p\u003e","description":"","filename":"floatimage131.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/dc0e0faa722ad10bbfef953d.png"},{"id":70100725,"identity":"1418288c-0a96-47fd-95c7-b3d4c276223c","added_by":"auto","created_at":"2024-11-28 10:29:25","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":122749,"visible":true,"origin":"","legend":"\u003cp\u003eScatterplot of the relationship between the measured pushing force and improvement in the total A-ROM\u003c/p\u003e","description":"","filename":"floatimage141.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/4eead40902dbb8eb436ed301.png"},{"id":70101086,"identity":"873c1ba5-0e97-44ae-9a1f-8dadd8c6c36c","added_by":"auto","created_at":"2024-11-28 10:37:25","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":114486,"visible":true,"origin":"","legend":"\u003cp\u003eScatterplot of the relationship between the measured pushing force and extensor muscle activity\u003c/p\u003e","description":"","filename":"floatimage15.png","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/9d224fe456d9148fa1700b7d.png"},{"id":88567543,"identity":"e1615251-6579-401d-b4b6-a8e85b03c1c4","added_by":"auto","created_at":"2025-08-07 20:31:35","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6756595,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5406511/v1/d179dea4-1e3d-418d-9440-fb14b162c79b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Relationship between pushing force and improvement in total A-ROM when training with a finger extensor facilitation training device “iPARKO”","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eAccording to the World Health Organization (WHO), stroke is a global public health problem that causes severe disabilities [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. As the population ages, the number of chronic stroke survivors is expected to increase [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. After a stroke, motor function may be impaired owing to an after-effect called spasticity, a condition wherein the hands and feet are constantly stretched and flexed owing to excessive tension in the muscles [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Prolonged abnormal postural conditions due to spasticity can cause contractures that stiffen the muscles and joints [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Our previous study focused on the hand, which is the most difficult to restore motor function for. However, treatment of a hemiplegic hand is difficult because the finger joints have 23 degrees of freedom [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. In addition, the restoration of hand motor functions is essential for chronic stroke survivors to perform daily activities that require fine finger movements and to return to society while maintaining a high quality of life [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Therefore, rehabilitation is often used to restore hand motor functions in chronic stroke survivors.\u003c/p\u003e \u003cp\u003eSeveral studies have been conducted on rehabilitation therapy for the upper extremities, such as constraint-induced movement therapy, which encourages chronic stroke survivors to use the paralyzed upper extremity [\u003cspan additionalcitationids=\"CR8\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]; mirror therapy, which uses mirrors to produce a reflective image of the paralyzed upper extremity [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]; and bilateral arm training (BAT), which involves repetitive practice of bilateral arm movements in symmetrical or alternating patterns [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Moreover, repetitive facilitated exercise (RFE) has also been studied [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. RFE is a form of rehabilitation in which a chronic stroke survivor is given the stimulation necessary to achieve the intended movement in the affected area. This stimulation can be achieved by tapping or rubbing the muscle, quickly and passively stretching the muscle, or applying slight resistance to the intended movement. Intensive stimulation is provided to chronic stroke survivors who cannot move their fingers on their own to induce spontaneous movement and restore hand motor function [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFor the hand-opening motor function to be restored, the extensor muscles, which are the muscles that open the hand, must be strengthened. Repetitive hand-opening movements are necessary to strengthen extensor muscles. However, chronic stroke survivors cannot train their extensor muscles because they cannot open their hands voluntarily. Thus, a manual technique called the finger extensor facilitation technique (hereafter referred to as manual therapy) was developed to increase hand voluntariness of chronic stroke survivors [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eTo explain manual therapy, we first briefly describe the bone and joint structure of the human hand, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. Each finger typically has three phalanges: proximal, intermediate, and distal. The exception is the thumb, which has only two phalanges: the proximal and distal. Proximal phalanges are bones located near the palm of the hand, intermediate phalanges are not present in the thumb but only in the other fingers, and distal phalanges are bones located at the tips of the fingers. In addition, interphalangeal joints connect the bones of the fingers and include the proximal interphalangeal (PIP), distal interphalangeal (DIP), and metacarpophalangeal joints (MP). The PIP, DIP, and MP joints are the joints between the proximal and intermediate phalanges, intermediate and distal phalanges, and intermediate and proximal phalanges, respectively.\u003c/p\u003e \u003cp\u003eManual therapy is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Manual therapy enables chronic stroke survivors to increase hand voluntariness without requiring hand-opening movements. A therapist holds the proximal, intermediate, and distal phalanges of the paralyzed finger, maintaining the maximum extension of the DIP and PIP joints and hyperextension of the MP joint. While the chronic stroke survivor voluntarily moves the paralyzed hand forward, the therapist applies resistance to the MP joints from the fingertips. This resistance induces a stretch reflex in the extensor muscles [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. The stretch reflex causes the extensor muscles to contract, thereby increasing the muscle activity. During manual therapy, the four fingers are held in hyperextension and the extensor muscles are relaxed to facilitate contraction. In contrast, the flexor muscles are stretched, making contraction difficult. Applying a force from the fingertips to the MP joint in this state increases extensor muscle activity while suppressing flexor muscle activity [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. However, this manual therapy does not provide adequate rehabilitation treatment because of the long treatment period and physical burden on the therapist. Therefore, a device or robot that reduces the physical burden on therapists and restores hand-opening function in chronic stroke survivors is required.\u003c/p\u003e \u003cp\u003eBased on this background, devices and robots for rehabilitating paralyzed hands have been developed, such as HandCARE [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], which assists the chronic stroke survivor\u0026rsquo;s opening and closing movements and can be adapted to various hand shapes and finger sizes; the AMADEO [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e], which simulates natural movements for hemiplegic hand conditions; and the exoskeleton robotic hand [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], which is actively driven by its own muscle signals; and HANDEXOS [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], which is a wearable exoskeleton device and rehabilitation device using parallel link mechanisms [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Additionally, a functional recovery training device that imitates RFEs has been developed [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. These conventional devices often aim to restore hand motor function by increasing the extensor muscle strength through repeated finger flexion and extension. However, chronic stroke survivors are unable to open their hands by themselves. Therefore, before the device is used, training should be provided to increase the voluntariness of the extensor muscles. To the best of our knowledge, no device thus far can train chronic stroke survivors to increase the voluntariness of extensor muscles other than hand flexion while suppressing abnormal tension in the flexor muscles. Therefore, we developed a device that simulates manual therapy to improve the voluntariness of extensor muscles in chronic stroke survivors.\u003c/p\u003e \u003cp\u003eIn a previous study, iPARKO, which simulates manual therapy, was developed and validated using three healthy participants [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Subsequently, the effectiveness of iPARKO was tested in six chronic stroke survivors. In all participants, training with iPARKO resulted in an improvement in the active range of motion (A-ROM), confirming that hand voluntariness improved [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, we developed iPARKO-2, a modified version of the conventional iPARKO, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The conventional iPARKO has the following two problems: First, it may not be applicable to chronic stroke survivors with strong fingertip spasticity. In training with the conventional iPARKO, the chronic stroke survivor 's fingertips are fixed to the resistance-providing part, and force is applied from the fingertips to the MP joint via the fingers. However, some chronic stroke survivors have significant fingertip spasticity, which complicates fixing their fingertips to the resistance-providing part. Even if they were able to fix their fingertips to the device, the fingertips, which had strong spasticity, occasionally move off the resistance-providing part during training. Second, a large burden is placed on chronic stroke survivors when fixing their fingers to iPARKO. The conventional iPARKO requires the fingers of a paralyzed hand to be individually fixed to the device. Fixing each spastic finger to a device is inconvenient and time-consuming for chronic stroke survivors.\u003c/p\u003e \u003cp\u003eIn this study, we developed iPARKO-2, which solves the above problems, and examined the relationship between pushing force and improvement in hand voluntariness during training with iPARKO-2. Specifically, we conducted iPARKO-2 training with five chronic stroke survivors using different pushing forces. We measured changes in the A-ROM of the four fingers before and after training to examine whether chronic stroke survivors could voluntarily perform movements. A-ROM refers to the range of motion that a chronic stroke survivor can achieve using their own muscle strength without any external assistance. In addition, we measured extensor muscle activity during training and analyzed the relationship between changes in A-ROM and extensor muscle activity.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Development of iPARKO-2\u003c/h2\u003e \u003cp\u003eiPARKO had two main problems.\u003c/p\u003e \u003cp\u003e(1) Because the fingertips are fixed and force is applied from the fingertips to the MP joint, chronic stroke survivors with strong fingertip spasticity are occasionally unable to wear iPARKO.\u003c/p\u003e \u003cp\u003e(2) Chronic stroke survivors must fix each finger individually, which places a heavy burden on them.\u003c/p\u003e \u003cp\u003eTo solve problem 1, we changed the design to fix the PIP joint instead of the fingertips and applied force from the PIP joint to the MP joint. In addition, to solve Problem 2, we changed the design to one that could fix four fingers simultaneously.\u003c/p\u003e \u003cp\u003eiPARKO-2, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, consists of training, biofeedback, and data acquisition components, similar to iPARKO [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. In this study, the term \"fingers\" refers to the four fingers, excluding the thumb.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Training component\u003c/h2\u003e \u003cp\u003eThe training component consists of finger-fixing part 1, finger-fixing part 2, and a wrist-fixing part, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e shows only finger-fixing part 1, with the other training components removed. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, finger-fixing part 1 was fabricated from thermoplastic resin and was attached from the PIP joint to the fingertip. Unlike iPARKO, which requires fixation of one fingertip at a time on a rubber band, the fingertips from the PIP joints of four fingers can be fixed simultaneously. In addition, because finger-fixing part 1 is bent in the direction of hand extension, it plays the same role as the finger sack of iPARKO, and the PIP and DIP joints can be maintained at maximum extension, which is the same condition as in manual therapy.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows only finger-fixing part 2, with the other training components removed. Finger-fixing part 2 was fabricated from thermoplastic resin and consists of two plates. The PIP joints of the index, middle, ring, and little fingers were pinched from above and below, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Therefore, the PIP joints of the four fingers are fixed simultaneously instead of individually. In this state, resistance can be applied to the MP joint, which is directly connected to the PIP joint, by pushing the hand forward. Unlike iPARKO, which applies a force from the fingertips of the four fingers, this device applies force from the PIP joint, enabling force to be applied to the hands of chronic stroke survivors with strong fingertip spasticity. As described earlier, finger-fixing 1 and 2 can fix four fingers simultaneously. Therefore, the burden on chronic stroke survivors caused by fixing one finger at a time (problem 2) could be reduced.\u003c/p\u003e \u003cp\u003eThe wrist-fixing part is attached to the chronic stroke survivor's wrist and maintains the MP joint during hyperextension. A six-axis force/torque sensor (FFS055F251M8R0A6S; Leptrino Co., Ltd.) is attached to the lower part of finger-fixing part 2 to measure the force applied to the PIP joint and the MP joint directly connected to it. Finger-fixing part 1, finger-fixing part 2, and the six-axis force/torque sensor are fixed on a slide rail (FBW3590XRUU\u0026thinsp;+\u0026thinsp;300L; THK Co., Ltd.), enabling a chronic stroke survivor to smoothly move his or her hand forward. A sponge is attached to the tip of the slide rail to absorb the shock when a chronic stroke survivor pushes forward, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. The firmness of the sponge was adjusted such that finger-fixing part 1, finger-fixing part 2, and the six-axis force/torque sensor move approximately 5 mm on the slide rail when the chronic stroke survivor pushes forward.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Biofeedback and data acquisition components\u003c/h2\u003e \u003cp\u003eiPARKO-2 measures extensor muscle activity during training using a portable electromyography (EMG) sensor (OPE-2; Unique Medical Co., Ltd.), similar to iPARKO. This EMG sensor consists primarily of a surface electrode and a preamplifier. By attaching a surface electrode to the skin over any muscle, the action potentials of the muscle can be summed and displayed as a diagram. The six-axis force/torque sensor was used to measure the pushing force.\u003c/p\u003e \u003cp\u003eThe data acquisition component consisted of an EMG sensor, the six-axis force/torque sensor, data acquisition system (USB6211; National Instruments Corp.), and personal computer. The sampling frequency of the measurements was 1000 Hz. The measurement data collected by the data acquisition systems were displayed on a monitor screen, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Experiments","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Purpose\u003c/h2\u003e \u003cp\u003eThis study aimed to compare improvements in hand voluntariness among five chronic stroke survivors before and after training with iPARKO-2 using different pushing forces. The A-ROM was used to evaluate hand voluntariness, and the change in the A-ROM before and after training was used to improve hand voluntariness. Information on the participants is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The passive range of motion (P-ROM) is the range of motion of a joint obtained by moving the joint using an external force or the hands of another person. The P-ROM was measured in advance by a therapist using a goniometer. All participants were paralyzed in their left hand. All the participants provided informed consent before participating in the study. The study was conducted in accordance with a protocol approved by the Ethics Committee of the Nagoya Institute of Technology (Approval number 2020-001).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eInformation of the five participants\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParticipant No.\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSex\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAge\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDominant hand\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eParalyzed hand\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eL\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eM:3, F:1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e63.8\u0026thinsp;\u0026plusmn;\u0026thinsp;5.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR:5, L:0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eR:0, L:5\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eParticipant No.\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003eP-ROM [\u0026deg;]\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003eMaximum pushing\u003c/b\u003e\u003c/p\u003e \u003cp\u003e\u003cb\u003eforce [N]\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003ePeriod of onset [Years]\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003eRemarks\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLacunar infarction\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLacunar infarction\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCerebral hemorrhage\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCerebral hemorrhage\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCerebral infarction\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e38.6\u0026thinsp;\u0026plusmn;\u0026thinsp;19.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e49.6\u0026thinsp;\u0026plusmn;\u0026thinsp;18.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e12.2\u0026thinsp;\u0026plusmn;\u0026thinsp;3.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Method\u003c/h2\u003e \u003cp\u003eThe experimental procedure is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. First, the participants underwent a maximum pushing force test as a preliminary experiment. Each participant was then trained with iPARKO-2 using three different pushing forces. An A-ROM test was performed before and after each training session.\u003c/p\u003e \u003cp\u003eA maximum pushing force test was conducted at the beginning of the experiment. Because muscle strength differed among participants, the maximum pushing force was defined as the maximum force at which the participant could push without experiencing pain, and this was measured. The measurement was performed in the same posture as that used during training with iPARKO-2, as described below. In this posture, the participants were requested to push their hands forward with the maximum force they could exert without feeling pain for 3 s, beginning from the supervisor's cue, and the maximum force during these 3 s was defined as the maximum pushing force. The maximum pushing forces for each participant are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A six-axis force/torque sensor was used to measure the pushing force in this study.\u003c/p\u003e \u003cp\u003eThe training with iPARKO-2 is described next. At the beginning of the training with three different pushing forces, the therapist attached the surface electrodes of the EMG sensor to a participant's left arm to measure the extensor muscle activity. The surface electrodes were left attached during the three training sessions to prevent variations in the data due to differences in their attachment positions of the surface electrodes. Subsequently, the wrist-fixing part was attached to each participant's wrist to fix the wrist angle. The PIP joint of the left hand was fixed to finger-fixing part 2, and the fingertips were fixed to finger-fixing part 1.\u003c/p\u003e \u003cp\u003eUnder these conditions, training with iPARKO-2 was conducted at three pushing forces: 20%, 50%, and 80% of the maximum pushing force for each participant. To account for sequential effects, training was performed in the order of 80%, 50%, and 20% force for participants 1, 2, and 3, and 20%, 50%, and 80% force for participants 4 and 5.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, one training session consisted of an initial 3 s waiting period and 10 sets of pushing. Each set consisted of 2 s of pushing and 2 s of relaxation for a total of 4 s. A metronome was used to indicate a timing of 2 s and a sampling time of 0.001 s. The indicated pushing force was 20%, 50%, or 80% of the maximum force. During training, the participants pushed their hands forward to achieve the indicated pushing force while observing the force on the monitor screen. Three-minute rest periods were given between three training sessions. During the rest period, the participant's hand was removed from iPARKO-2.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Experimental Posture\u003c/h2\u003e \u003cp\u003eThe posture during the experiment is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. The participant sat in a chair adjusted so that the ankle joint was at 0\u0026deg; flexion and the knee joint was at 90\u0026deg; flexion. Both legs were placed shoulder width apart, with the soles of feet grounded on the floor. The shoulder joint was maintained without elevation. The training component of iPARKO-2 was placed next to the participant's body. The participants were also instructed to place their elbows on the upper limb stand, keep their posture straight, and avoid twisting their trunks. The monitor screen was placed in front of the participant and the height was adjusted so that the participant could easily see the screen.\u003c/p\u003e \u003cp\u003eThe upper limb is represented by the four-joint link model shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e. Let the flexion angle of the shoulder joint be \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e, the flexion angle of the elbow joint be \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{2}\\)\u003c/span\u003e\u003c/span\u003e, the extension angle of the wrist joint be \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{3}\\)\u003c/span\u003e\u003c/span\u003e, and the extension angle of the MP joint be \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{4}\\)\u003c/span\u003e\u003c/span\u003e. In addition, for all joint angles, the counterclockwise direction was positive. The following relationship exists between these angles:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:\\begin{array}{c}\\:{\\theta\\:}_{1}+\\:{\\theta\\:}_{2}+\\:{\\theta\\:}_{3}\\:+\\:{\\theta\\:}_{4}\\:=\\:90^\\circ\\:\\#\\left(1\\right)\\end{array}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWe assumed \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{1}\\)\u003c/span\u003e\u003c/span\u003e = 80\u0026deg;, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{2}\\)\u003c/span\u003e\u003c/span\u003e = 0\u0026deg;, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{4}\\:\\)\u003c/span\u003e\u003c/span\u003eis the P-ROM of each participant. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{\\theta\\:}_{3}\\)\u003c/span\u003e\u003c/span\u003e is uniquely determined from Eq.\u0026nbsp;(1). Throughout the experiment, the participants moved their hands, which were placed on the training component, forward. The distance traveled was approximately 5 mm. As the forearm moves, the angles of the shoulder, elbow, and wrist changed. The change in the angle of the shoulder was the largest, extending by approximately 5\u0026deg;. In comparison, the elongation of the elbow and wrist was small.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Evaluation method\u003c/h2\u003e \u003cp\u003eThe A-ROM was measured before and after training. Twelve points were measured at the MP, DIP, and PIP joints of the four fingers of a participant's paralyzed hand, excluding the thumb. Measurements were performed by a therapist using a goniometer. The angles were as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, where the fully extended position was 0\u0026deg;, the angle in the extension direction was positive, and the angle in the flexion direction was negative with respect to the fully extended position. To evaluate whether chronic stroke survivors could voluntarily perform movements, we calculated the sum of the joint angles at 12 locations as the total A-ROM. Thereafter, the total A-ROM was used as an indicator of voluntariness. Additionally, the change in the total A-ROM before and after training was defined as an improvement in the total A-ROM. In other words, the larger the improvement in the total A-ROM, the greater the improvement in voluntariness.\u003c/p\u003e \u003cp\u003eThe extensor muscle activity was measured during training using an EMG sensor. The muscle activity was defined as the average of 10 sets, where the absolute average value of 1 s, excluding the first and last 0.5 s of the 2-s period of pushing, was the muscle activity of 1 set. The first and last 0.5 s of 1 s were excluded to reduce errors caused by different timing of pushing between participants. Generally, because the amount of muscle activity varies from individual to individual, each muscle activity was normalized using the maximum voluntary contraction (MVC). However, measuring the MVC in chronic stroke survivors is difficult because of the narrow range of movement of the wrist joints and individual differences in the degree of paralysis. Therefore, normalization was not performed in this study.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Results and discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Relationship between pushing force and A-ROM\u003c/h2\u003e \u003cp\u003eThe total A-ROM before and after training, as well as the improvement in the total A-ROM for each of the five participants at 20%, 50%, and 80% of the maximum pushing force, are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. The Friedman test was used to compare the improvement in the total A-ROM at the three pushing forces. The mean values of improvement in total A-ROM for the five participants in training at 20%, 50%, and 80% of maximum pushing force were 67.0\u0026thinsp;\u0026plusmn;\u0026thinsp;45.8\u0026deg;, 134.0\u0026thinsp;\u0026plusmn;\u0026thinsp;102.7\u0026deg;, and 183\u0026thinsp;\u0026plusmn;\u0026thinsp;117.8\u0026deg;, respectively. The improvement in the total A-ROM tended to increase significantly with increasing pushing force (*p\u0026thinsp;\u0026lt;\u0026thinsp;0.05 ). This indicated the effectiveness of training with pushing forces close to the maximum pushing force. At 50% of the maximum pushing force, the improvement in the total A-ROM was greater than that at 20% for all four participants except participant 1. At 80% pushing force, the improvement in the total A-ROM was greater than that at 20% and 50% for all participants.\u003c/p\u003e \u003cp\u003eDuring the training, the participants adjusted their pushing force to match the target value, which may have resulted in individual differences in the actual pushing force. The target and measured pushing forces for the three training sessions (20%, 50%, and 80% of the maximum pushing force) for each participant are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e. As with muscle activity, each measured pushing force is the average of 10 sets of absolute average values for 1 s, excluding the first and last 0.5 s of the 2-s period, where one set of pushing force was defined as the average of the 10 sets of pushing force. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e, the ability to adjust the pushing force to the target value varies among individuals. Participant 3 could be considered to have a high adjustment capability because the pushing force is close to the target value. In contrast, Participants 1, 2, 4, and 5 tended to exhibit higher actual pushing forces as the target value increased. However, when the target value was large, the error and variation increased. This indicated that their adjustment capability for large forces was inferior. In particular, participant 5 was considered to have an inferior adjustment capability for both small and large pushing forces.\u003c/p\u003e \u003cp\u003eTherefore, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e, the relationship between the measured pushing force and improvement in the total A-ROM is represented by a scatter plot. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e shows the linear approximation curve. The correlation coefficients between the measured pushing force and improvement in the total A-ROM for the five participants were 0.23, 0.96, 1.00, 0.99, and 1.00. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e14\u003c/span\u003e shows that, except for participant 1, the improvement in the total A-ROM increased as the pushing force increased.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e4.2 Relationship between pushing force and muscle activity\u003c/h2\u003e \u003cp\u003eThe relationship between the measured pushing force and extensor muscle activity was examined. A scatter plot, as well as a linear approximation curve, representing the relationship between the measured pushing force and extensor muscle activity during training for the five participants is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e. The correlation coefficients between the measured pushing force and extensor muscle activity for the five participants were 0.58, 0.84, 0.91, 0.95, and \u0026minus;\u0026thinsp;0.07, respectively. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e15\u003c/span\u003e, except for participants 1 and 5, the extensor muscle activity increased as the measured pushing force increased.\u003c/p\u003e \u003cp\u003eBased on these results, we consider that muscle activity tended to increase as the pushing force increased, and the amount of muscle activity affected the improvement in the total A-ROM.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e4.3 Effectiveness of iPARKO-2\u003c/h2\u003e \u003cp\u003eThe newly developed iPARKO-2 was used in this experiment. The participants\u0026rsquo; fingertips did not come off the iPARKO-2 during training. Additionally, the time required, compared with the conventional iPARKO, was reduced by 60%, from approximately 5 min to approximately 2 min on average. Based on these results, we believe that iPARKO-2 successfully addressed the problems in the conventional iPARKO.\u003c/p\u003e \u003c/div\u003e"},{"header":"5. Conclusion","content":"\u003cp\u003eIn this study, we developed a new finger extensor facilitation training device, iPARKO-2, which can be applied to chronic stroke survivors with strong spasticity. In addition, the relationship between the pushing force during training and improvement in the total A-ROM was examined in five chronic stroke survivors. The results showed that the greater the pushing force during training, the greater the muscle activity, and the amount of muscle activity affected the total A-ROM improvement.\u003c/p\u003e \u003cp\u003eFuture studies should examine the effects of other manual therapy conditions on improving hand voluntariness to explore training methods that can further enhance hand function in chronic stroke survivors. Furthermore, although immediate effects were verified in this study, we aim to verify the long-term effects and explore more effective training methods to improve the overall treatment efficacy.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDIP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eDistal interphalangeal\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePIP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eProximal interphalangeal\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMetacarpophalangeal\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eP-ROM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePassive range of motion\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eA-ROM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eActive range of motion\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMVC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMaximum voluntary contraction\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEMG\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eElectromyography\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have not competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026apos; Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors proposed the concept about iPARKO-2.\u003c/p\u003e\n\u003cp\u003eSI and RY developed new devices.\u003c/p\u003e\n\u003cp\u003eAll authors performed the experiments.\u003c/p\u003e\n\u003cp\u003eSI and RY performed data analysis.\u003c/p\u003e\n\u003cp\u003eAll authors read and approved of the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eEthics declarations\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by the ethics committee of the Nagoya Institute of Technology: 2020-001. All participants provided written informed consent before the measurements.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to thank Editage (www.editage.com) for the English language editing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the JSPS Grant-in-Aid for Scientific Research (19K12878).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eWorld Health Organization (2014) Global status report on noncommunicable diseases 2014\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKatan M, Luft A (2018) Global burden of stroke. 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IEEJ Trans EIS C 143\u0026ndash;12:1099\u0026ndash;1105. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1541/ieejeiss.143.1099\u003c/span\u003e\u003cspan address=\"10.1541/ieejeiss.143.1099\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Chronic hemiplegic, Finger extensor muscle, Hand rehabilitation, Maximum voluntary contraction, Muscle activity, Rehabilitation device","lastPublishedDoi":"10.21203/rs.3.rs-5406511/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5406511/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eWe observed that when the distal interphalangeal (DIP) and proximal interphalangeal (PIP) joints of the fingers are in maximum extension and the metacarpophalangeal (MP) joints are in hyperextension, applying an external resistance from the fingertips to the MP joints increases extensor muscle activity, even unintentionally, and opens the hand. Based on this phenomenon, a finger extensor facilitation technique conducted by therapists was developed as training for hand extension for chronic stroke survivors. In previous studies, we developed iPARKO, a finger extensor facilitation training device that imitates this technique. In this study, we developed a new version of the device, iPARKO-2, that can be used for chronic stroke survivors with strong spasticity. Five chronic stroke survivors were trained with iPARKO-2 using three different pushing forces. To evaluate whether chronic stroke survivors can voluntarily perform movements, we measured the active range of motion (A-ROM). The results showed that the improvement in the total A-ROM tended to increase as the pushing force during training increased. Additionally, extensor muscle activity increased as the pushing force increased. Based on this, we conclude that the greater the pushing force, the greater the muscle activity, and that the amount of muscle activity influences the improvement in the total A-ROM.\u003c/p\u003e","manuscriptTitle":"Relationship between pushing force and improvement in total A-ROM when training with a finger extensor facilitation training device “iPARKO”","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-28 10:29:20","doi":"10.21203/rs.3.rs-5406511/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c758b810-18eb-4bdf-9732-7c2cb08712fb","owner":[],"postedDate":"November 28th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-08-07T20:23:24+00:00","versionOfRecord":[],"versionCreatedAt":"2024-11-28 10:29:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5406511","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5406511","identity":"rs-5406511","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}