Usability of the novel ankle training equipment with spring resistance-based plantar press exercises in the standing position: A focus on chronic stroke patients with hemiplegic gait

Abstract

BACKGROUND:

To improve gait disability in patients with chronic stroke, ankle muscle strengthening and calf muscle stretching exercises are required. However, currently available ankle training equipment limit ankle exercises based on the position. Recently developed ankle training equipment enables spring resistance-based plantar press exercises to be performed in the standing position with weight support.

OBJECTIVE:

To conduct a usability test of the ankle training equipment in the standing position by stroke patients with hemiplegic gait and verify its effects on ankle movements.

METHODS:

The ankle training equipment was applied to five patients with chronic stroke and hemiplegic gait. In the standing position, the patients performed forefoot and rearfoot press exercises in the affected side with a day’s interval at 20 repetitions maximum (RM). During the exercises, surface electromyography (sEMG) was used to measure the maximum voluntary isometric contraction (%MVIC) of the leg muscles. The System Usability Scale (SUS) was used to assess the ankle training equipment. Wilcoxon signed-rank test was used to evaluate the differences in muscle activity between the two exercises.

RESULTS:

Forefoot and rearfoot press exercises increased the %MVIC in the biceps femoris. Additionally, the tibialis anterior and medial gastrocnemius activity was significantly different between the two exercises. The SUS was 78.75% (SD 12.7).

CONCLUSION:

The usability test of the passive-control foot press trainer (PFPT) that with improvements in the structure and functions for convenience, it could be commercialized. PFPT could be an alternative to the ankle rehabilitation robot that necessitates a sitting position.

Keywords

Chronic stroke standing position ankle training equipment usability test muscle activity

1. Introduction

Stroke is a common cerebrovascular disease characterized by chronic neurological deficits arising due to brain tissue destruction [1]. It is the third most frequent cause of death in countries belonging to the Organization for Economic Cooperation and Development and commonly leads to various disabilities [2]. Stroke limits all physical activities, including movements of the upper and lower limbs, posing a challenge to performing activities of daily living and consequently reducing the quality of life [2]. With the advancements in healthcare technology, the survival of patients with stroke is steadily increasing. Currently, Furthermore, due to the declining incidence of stroke, there is a concurrent reduction in the post-stroke survival period [3].

For the rehabilitation of stroke patients, interventions traditionally administered by physical therapists and occupational therapists are now being executed through the utilization of machines or robotic systems. However, while these systems are making strides in assisting with walking and upper limb movements, they are not yet capable of replicating the full spectrum of therapeutic interventions provided by human therapists, motivating active research efforts in this domain [4].

Post-stroke disability affects a wide spectrum of functions from muscle tension to balance, weight shift and support, and motor control abilities according to the area of brain damage. Based on the cause, post-stroke disability can include defects in the perception, muscle strength and tension, sensation, and motor control. Patients with ankle disability, such as foot drop due to reduced muscle strength on the paretic side, presents with a partial or complete loss of motor function, making it difficult to maintain independent ankle range of motion (ROM). The reduced ankle ROM causes muscular atrophy and contraction-induced ankle stiffness, which is the main cause of gait disability [5]. In foot drop, the impulse is reduced in the stance phase and forefoot clearance is reduced in the swing phase, causing dragging of the foot and toes. Foot drop is seen in several brain and spine diseases, including stroke, polio, Charcot-Marie-Tooth disease, multiple sclerosis, and cerebral palsy [3, 5, 6, 7, 8].

The level of recovery of gait is a key predictor of post-stroke disability and a top-priority in post-stroke rehabilitation [6, 9]. The Robot-based Ankle Foot Orthosis and Functional Electrical Stimulation (FES) enhance the gait in patients with post-stroke hemiplegia, by effectively improving the gait cycle, gait speed, and muscle strength. A combination of FES and the newly developed muscle synergy-based stimulation algorithm contribute to normalizing gait and effectively improving it in patients with chronic deficits [10].

The conventional rehabilitation training for the recovery of lower limb motor function in patients with post-stroke hemiplegia includes a high-intensity exercise program. The exercise program consists of stepwise contractions and passive, assistive, active or active resistance exercises. As the frequency and duration of these exercises directly affect the level of recovery, the training program should be repeatedly offered; however, this is physically demanding for therapists [11, 12, 13, 14]. To address this issue, various training equipment and robots have been developed and applied.

For the recovery of lower limb motor function, eccentric strengthening exercises are superior to concentric exercises; eccentric exercises stimulate collagen synthesis in the muscle and tendon and promote muscle cell growth and generation. Thus, the Eccentron (BTE Technologies Inc., Hanover, MD, USA) was developed to allow eccentric lower limb exercises in a seated position. However, it cannot be applied to certain regions due to the limitation of the stepper-type multi-joint exercise methods [15]. Conventional ankle rehabilitation relies on the experience of physical therapists and induces physical burnout in those who are required to hold the patient’s ankle toward contraction during ankle movements. To overcome these issues, platform-based ankle rehabilitation equipment and robots have been developed, focusing on ankle dorsiflexion strengthening in a seated position in lieu of therapists. However, ankle training in a seated position eliminates the effect of gravity, and the protocol does not incorporate tailored trainings [16, 17, 18]. As an alternative to the conventional high-cost ankle rehabilitation robots (Stewart’s platform or powered exoskeleton), the Motorized Ankle Stretcher (MAS) was developed to increase the ankle dorsiflexion and adaptability through active and gradual stretching of the lower calf muscles in the standing position. However, the MAS was limited in allowing active muscle strengthening [19]. A 360^∘ anterior pedaling exercise while standing leads to high ankle torque and gastrocnemius activity as the pedal on the paretic side approaches 180^∘, which is the farthest point with increased exposure to gravity. However, performing this exercise in a seated position with little exposure to gravity leads to higher gastrocnemius activity as the pedal approaches the closest point [20].

Based on the training equipment developed and evaluated in previous studies, we developed a passive-control foot press trainer (PFPT) as an ankle training. Forefoot and rearfoot press exercises can be performed using the PFPT and a spring resistance-based pedal in the standing position with exposure to gravity. Improving lower limb motor function is the key to the recovery of motor function. The novel equipment allows for repeated trainings of gait simulation in the standing position. We aimed to assess the usability of the PFPT ankle training equipment in patients with post-stroke hemiplegic gait in combination with spring resistance-based plantar press exercises in the standing position.

2. Methods

2.1 Device development

The PFPT ankle-training equipment is a device that allows the user to perform forefoot and rearfoot press exercises while controlling the contraction intensity. The device comprises a plate on which the user can perform the exercises. There are handles on either side of the plate for the user to maintain stable postures during exercise. The center of the plate has a spring that can be replaced with a spring of a different elasticity level to control the resistance and contraction intensity during plantar press exercises. The pedal-based forefoot and rearfoot press exercises depict anterior and posterior rotations in the ankle joint, respectively. The novel equipment was developed to allow forefoot and rearfoot press exercises with motions simulating gait patterns.

2.2 Participants

In a study conducted by Virzi [21], it was determined that the optimal number of subjects for usability evaluation is between 5 and 8 people, as up to 90% of usability-related issues can be identified within this range. Therefore, the study utilized a sample size of 5 participants for analysis, in accordance with this finding. Five community-dwelling patients with post-stroke hemiplegia participated in the study. The inclusion criteria were as follows: 1) hemiplegia caused by a cerebrovascular event, cerebral hemorrhage, or infarction; 2) stroke $\geqslant$ 6 months ago; 3) Functional Ambulatory Category (FAC) $>$ 3; 4) male or female aged $\geqslant$ 19 years; and 5) normal or only a slight increase in muscle tension in the ankle joint (Modified Ashworth Scale $<$ 3). The exclusion criteria were as follows: 1) orthopedic-related disability; 2) cognitive impairment or mental disorder; 3) quadriplegia, peripheral paresthesia, or a history of bilateral or brainstem lesions; 4) neurological disorder other than a stroke; and 5) minimum muscle strength ( $\geqslant$ trace) during ankle dorsi- and plantar-flexion. Some of the enrolled participants were using antihypertensive medications; however, there was no discernible evidence suggesting that antihypertensive drugs had any impact on the questionnaire or surface electromyography (sEMG) variables, which constituted the focal points of analysis in this study. Therefore, the potential influence of medication on the study results was systematically ruled out.

This study complied with the principles of the Declaration of Helsinki and was approved by the Institutional Review Board of the National Rehabilitation Center Rehabilitation Hospital (No. NRC-2022-07-055; date 8 November 2022). Informed consent was obtained from each participant for voluntary participation in the study. The participants’ baseline general characteristics, including age, affected side, height, weight, body mass index (BMI) and FAC are summarized in Table 1.

Table 1
General characteristics of participants ( $n=$ 5)

	Age (years)	Affected side (left/right, %)	FAC score	Height (cm)	Weight	BMI (kg/m²)
Mean
OR ratio (%)	67.4	80/20	4.6	158.7	68.6	27.3
SD	7.7974355		0.5	9.7	9.2	2.9
Range	60–80		4–5	144–170	55.6–77.6	23.9–32.0

SD: Standard deviation.

2.3 Experimental protocol

First, this study was structured as a single-group, cross-sectional investigation with a singular measurement, and it did not incorporate any randomization procedures. Second, sEMG was used to measure the maximum voluntary isometric contraction (MVIC) of the target lower limb muscle on the paretic side. Subsequently, each participant performed the forefoot and rearfoot press exercises using the PFPT ankle training equipment at 20 repetition maximum (RM) in set time intervals, with a metronome set to 60 bpm to maintain identical exercise speed. During the exercises, the activity levels of the tibialis anterior, medial and lateral gastrocnemius heads, rectus femoris, and biceps femoris were measured using the five channels of the sEMG. The %MVIC values were compared. At the end of the test, the System Usability Scale (SUS) was applied to the participants to evaluate the usability of the PFPT.

2.4 Measurements

First, the manual muscle test (MMT) was performed and the passive ROM (dorsi- and plantar-flexion) of the affected ankle was measured. The MMT comprises six grades from 0 to 5: 0 (Zero), indicates no palpable or visible muscle contraction; 1 (Trace), indicates palpable muscle contraction without motion; 2 (Poor), indicates motion upon reduced or eliminated gravity; 3 (Fair), indicates motion against gravity; 4 (Good), indicates complete motion against moderate resistance and gravity; and 5 (Normal), indicates complete motion against maximum resistance and gravity. The passive ankle ROM was measured using a goniometer; triplicate measurements were obtained and the mean was used in the analysis.

The muscle activity levels of the tibialis anterior, medial and lateral gastrocnemius heads, rectus femoris, and biceps femoris were measured during the forefoot and rearfoot press exercises using a wireless sEMG device (Delsys Trigno Wireless EMG Surface Electrodes; Delsys Incorporated, Boston, MA, USA). To ensure accurate measurements, the electrodes were attached to the target muscles on both lower limbs, parallel to the direction of the muscle fibers. To minimize resistance, the skin of the target sites and electrodes were wiped with alcohol prior to attachment. The electrode attachment sites were determined via palpitation according to the SENIAM guidelines (www.seniam.org). EMG signals were detected at each channel in the five muscles. The sampling rate of the EMG signal was set at 1,259 Hz. The amplified waveforms were filtered through 20–45 Hz band pass filters. The signals collected during muscle contraction were processed by Root Mean Square (RMS). For use as the normalization criteria, the %MVIC was derived from the MVIC measured after resampling at 1,000 Hz. The MVIC was measured before the exercise, just as in a previous study. The participants were instructed to perform ankle and knee joint flexion and extension in the standing and seated positions. The ankle ROM was recorded three times, with each motion held at the maximum force for 5 s. There was a 30 s period of rest between each measurement. The 3-s mean muscle activity, by excluding the first and last s, were recorded as the result.

Table 2
System Usability Scale questionnaire

Items	Statement
1. Utility	I think that I would like to use this system frequently.
2. Complexity	I found the system unnecessarily complex.
3. Simplicity	I thought the system was easy to use.
4. Professionalism (technician support)	I think that I would need the support of a technical person to be able to use this
	system.
5. Integration	I found the various functions in the system were well integrated.
6. Unity	I thought there was too much inconsistency in this system.
7. Learnability	I would imagine that most people would learn to use this system very quickly.
8. Convenience	I found the system very cumbersome to use.
9. Satisfaction	I felt very confident using the system.
10. Professionalism (prior learning)	I needed to learn a lot of things before I could get going with this system.

Table 3

System Usability Scale score classification

Grade scale	Range	Percentile range	Adjective rating	Acceptance level	Recommendation
A $+$	84.1–100	96–100	Best imaginable	Acceptable	Recommendable
A	80.8–84.0	90–95	Excellent
A $-$	78.9–80.7	85–89
B $+$	77.2–78.8	80–84			Neutral
B	74.1–77.1	70–79
B $-$	72.6–74.0	65–69
C $+$	71.1–72.5	60–64	Good
C	65.0–71.0	41–59		Nearly acceptable
C $-$	62.7–64.9	35–40
D	51.7–62.6	15–34	Fair		Unrecommendable

The SUS is a simple, practical, and reliable questionnaire, consisting of 10 questions, that were used to evaluate the usability of various products and services. The tool can detect a problem associated with usability in various digital products and services. Each of the 10 items are rated on a 5-point Likert scale (1 $=$ Strongly disagree, 5 $=$ Strongly agree). Among the 10 items, the odd ones are positive questions with higher scores indicating higher system performance. The even items are negative questions with lower scores indicating higher system performance. The SUS items and statements are summarized in Table 3. The total SUS score was 100. For the odd items 5 was subtracted from the total score (X), while for the even items 25 was subtracted from the total score (Y). The sum of X and Y was multiplied by 2.5 to obtain the total SUS score. Finally, the total SUS score was classified according to the percentile range, adjective rating, acceptance level, and recommendation (Table 3).

2.5 Data analysis

The participants’ general and functional characteristics were expressed as mean $\pm$ standard deviation (SD) or percentage (%). Wilcoxon’s signed-rank test was used to compare the %MVIC of the lower limb muscles between the two exercises. Statistical analyses were performed using SPSS (version 24.0; IBM SPSS Inc., Armonk, NY, USA). Statistical significance was set at $p<$ 0.05.

Table 4
Functional characteristics

	ROM		MMT
	Dorsi flexion	Plantar flexion	Dorsi flexion	Plantar flexion
Mean	8	27	2.3	2.7
SD	10.9	8.3	1.5	1.2
Range	0–20	15–35	1–4	1.5–4

ROM: Range of motion, MMT: Manual Muscle Testing, SD: Standard deviation.

Table 5

System Usability Scale evaluation results ( $N=$ 5, Unit:point)

Item	Min	Max	M $\pm$ SD	Scaled M $\pm$ SD
Total	–	–	3.93 $\pm$ 0.63	78.75 $\pm$ 12.67
Utility	2.00	4.00	3.50 $\pm$ 1.00	70.00 $\pm$ 20.00
Complexity	2.00	4.00	3.25 $\pm$ 0.95	65.00 $\pm$ 19.15
Simplicity	1.00	3.00	2.50 $\pm$ 1.00	50.00 $\pm$ 20.00
Professionalism (technician support)	3.00	4.00	3.25 $\pm$ 0.50	65.00 $\pm$ 10.00
Integration	2.00	4.00	3.00 $\pm$ 0.81	60.00 $\pm$ 16.33
Unity	3.00	4.00	3.50 $\pm$ 0.57	70.00 $\pm$ 11.55
Learnability	2.00	4.00	2.75 $\pm$ 0.95	55.00 $\pm$ 19.15
Convenience	0.00	4.00	2.25 $\pm$ 2.06	45.00 $\pm$ 41.23
Satisfaction	3.00	4.00	3.75 $\pm$ 0.50	75.00 $\pm$ 10.00
Professionalism (prior learning)	3.00	4.00	3.75 $\pm$ 0.50	75.00 $\pm$ 10.00

M: Mean, SD: Standard deviation.

Figure 1.

The developed passive-control foot press trainer.

Figure 2.

Measuring muscle activity of tibialis anterior, medial and lateral gastrocnemius, rectus femoris, biceps femoris. (a) Forefoot press exercise, (b) Rearfoot press exercise.

Figure 3.

Comparison of EMG activity between forefoot and rearfoot exercises. %MVIC: Maximum Voluntary Isometric Contraction.

3. Results

The mean MMT and passive ROM values of the paretic ankle are presented in Table 4.

The biceps femoris muscle showed the highest activity during the forefoot and rearfoot press exercises, followed by the medial gastrocnemius, lateral gastrocnemius, rectus femoris and tibialis anterior muscles. The %MVIC of the tibialis anterior and medial gastrocnemius were significantly different between the two exercises ( $p<$ 0.05) (Fig. 3).

The mean SUS score was 78.75, indicating a B $+$ grade on the scoring scale. The items exhibiting a lower score than the mean were simplicity (Q3), integration (Q5), learnability (Q7) and convenience (Q8) [22, 23].

4. Discussion

The PFPT, an ankle training equipment, was developed in this study to strengthen the foot and ankle muscles for the recovery of lower limb motor function and gait. The novel equipment allowed forefoot and rearfoot press exercises to be performed in the standing position with exposure to gravity and use of a spring resistance-based pedal. An advantage of this system is the possibility of repeated gait training simulations in the standing position. We conducted a usability test on the PFPT training equipment in patients with post-stroke hemiplegic gait for spring resistance-based plantar-press exercises in a standing position.

The mean SUS score in our study was 78.75; Excellent for adjective ratings, acceptable for acceptance level, and neutral for recommendations, implied an overall high level of satisfaction with the PFPT ankle training equipment developed in this study. Based on previous studies [22, 23], the structure and function of the equipment was improved for convenience, with a focus on the items showing scores lower than the mean (simplicity, integration, learnability and convenience). Improvement of these parameters could allow PFPT to become commercialized and satisfy consumer demands. However, formative and summative usability tests should continue to be performed to determine improvement, which is critical in developing effective equipment [24]. Further studies that repeatedly conduct usability tests for PFPT are required to ensure systematic improvements.

The differences in muscle activity levels were comparatively analyzed based on the %MVIC; the biceps femoris muscle had the highest muscle activity level during the foot press exercises, followed by the medial gastrocnemius, lateral gastrocnemius, rectus femoris and tibialis anterior. The high biceps femoris activity may be attributed to the high use of biceps femoris to efficiently create exercise motions against gravity in the standing position, to compensate for the inadequate passive ROM and MMT. The passive ROM was 8^∘ (Dorsiflexion normal range: 20^∘) and 27^∘ (Plantarflexion normal range: 50^∘) for dorsiflexion and plantarflexion, respectively. The MMT was 2.3 and 2.7 for dorsiflexion and plantarflexion, respectively [25]. reported an increase in the biceps femoris activity in response to an increase in the weight load. In our study, the medial and lateral heads of the gastrocnemius muscle showed high activity during the forefoot and rearfoot press exercises, which concur with the results of a previous study [20, 26]. Brown et al. stated that the ankle torque and gastrocnemius activity was highest as the pedal on the paretic side approached the farthest point, with increased exposure to gravity during exercises in the standing position.

The forefoot press exercise led to significantly higher activity levels in the tibialis anterior and medial gastrocnemius muscle than the rearfoot press exercises did. As patients with stroke pedaled, the tibialis anterior activity significantly varied [27]. Likewise, the tibialis anterior activity was higher in the forefoot press exercise than in the rearfoot press exercise in our study. Our findings indicate that the forefoot press exercise in the standing position could be used as an alternative to the conventional dorsiflexion exercise using an ankle rehabilitation robot for strengthening the tibialis anterior and medial gastrocnemius muscles [16, 17, 18].

In this study, we conducted an evaluation focusing on exercise movements involving the pressing of the forefoot and hindfoot in a standing position. However, as part of our ongoing research, we intend to develop an expanded range of applications beyond these two simple movements. Our specific goal is to conduct a comprehensive usability assessment that considers the distinct traits of patients with central nervous system diseases. We will primarily focus on aligning the device’s functions with therapeutic standards and differentiating it from existing commercial lower extremity exercise devices [28]. Through these efforts, we anticipate potential enhancements to the device’s functionalities based on the insights gained from our research. If such improvements are realized, they could lead to advancements in existing device design. It’s worth noting that while this study employed EMG measurements using a similar design, future investigations will require additional considerations. Both needle electromyography (EMG) and surface electromyography (sEMG) quantify motor unit activation through muscle electrical signals. Consequently, Manual Muscle Testing (MMT) yields numeric strength measurements that exhibit a correlation with EMG [29] but are limited to the ordinal grading scale. This limitation arises from the inherent constraints of an evaluation method reliant on maximal muscle strength as the benchmark, in line with Maximum Voluntary Contraction (MVC) and Reference Voluntary Contraction (RVC), which serve as the primary means for interpreting EMG signals. Therefore, while our device is designed for use by a broad spectrum of individuals, from the general public to patients with central nervous system diseases, follow-up research is imperative to separately assess usability and design refinements, while validating the device’s appropriate utilization.

5. Conclusions

With improvements on the structure and functions for convenience of use, the PFPT ankle training equipment developed in this study could be commercialized to satisfy the consumer demand, as suggested by the results of the usability test in our study. Furthermore, the forefoot press exercise in the standing position using the PFPT could be an alternative to the conventional dorsiflexion exercise in the seated position using an ankle rehabilitation robot, as confirmed by our comparative analysis of the muscle activity.

Nevertheless, there was a limitation in analyzing the characteristics of the forefoot and rearfoot press exercises and defining the method of use; it is difficult to apply the PFPT in a standing position in participants with abnormal ROMs and low muscle strengths. Further studies are required to verify the effects of the equipment by conducting usability tests in a wider population with varying levels of physical function. This will aid in applying PFPT in exercises tailored to each patient’s characteristics, improving the electric motor control-based PFPT, and establishing guidelines for its use for suitable exercise intensity application.

Footnotes

Conflict of interest

The authors declare that they have no conflict of interest.

Funding

This study was supported by the Translational Research Project for Rehabilitation Robots, National Rehabilitation Center, Ministry of Health and Welfare, South Korea (#NRCTR-IN23006).

References

National Heart

, and Blood Institute. What Is a Stroke?: National Heart, Lung, and Blood Institute; 2023 [cited 2023 9-14]. Available from: https://www.nhlbi.nih.gov/health/stroke.

Feigin

Stark

Johnson

Roth

Bisignano

Abady

, et al. Global, regional, and national burden of stroke and its risk factors, 1990–2019: A systematic analysis for the Global Burden of Disease Study 2019. The Lancet Neurology. 2021; 20(10): 795-820.

Islam

SMS

Maddison

Uddin

Ball

Livingstone

Khan

, et al. The burden and trend of diseases and their risk factors in Australia, 1990–2019: A systematic analysis for the Global Burden of Disease Study 2019. The Lancet Public Health. 2023; 8(8): e585-e99.

Kim

D-H

T-S

Jung

K-S

. Effects of robot-assisted trunk control training on trunk control ability and balance in patients with stroke: A randomized controlled trial. Technology and Health Care. 2022; 30(2): 413-22.

Bae

Lee

B-h

. Effect of an EMG – FES Interface on Ankle Joint Training Combined with Real-Time Feedback on Balance and Gait in Patients with Stroke Hemiparesis. 2020.

Chow

Stokic

. The contribution of walking speed versus recent stroke to temporospatial gait variability. Gait & Posture. 2023; 100: 216-21.

Gilleard

Brown

. Structure and function of the abdominal muscles in primigravid subjects during pregnancy and the immediate postbirth period. Physical therapy. 1996; 76(7): 750-62.

Cameron

Wagner

. Gait abnormalities in multiple sclerosis: Pathogenesis, evaluation, and advances in treatment. Current Neurology and Neuroscience Reports. 2011; 11: 507-15.

Ali

HME

Amaravadi

. Effect of aerobic and resistance exercise training on balance, strength, functional capacity, and pulmonary function in post-stroke patients: A systematic review. Critical ReviewsTM in Physical and Rehabilitation Medicine. 2023; 35(3).

10.

Gil-Castillo

Alnajjar

Koutsou

Torricelli

Moreno

. Advances in neuroprosthetic management of foot drop: A review. Journal of NeuroEngineering and Rehabilitation. 2020; 17(1): 46.

11.

Alarcón

Henríquez

Peñailillo

. Effects of lower limb eccentric strength training on functional measurements in football players with cerebral palsy. European Journal of Adapted Physical Activity. 2021; 14(1): 2-14.

12.

Lee

B-c

Kim

D-h

Son

Seo

K-h

Park

Yoo

, et al. Development and assessment of a novel ankle rehabilitation system for stroke survivors. IEEE. 2017; 3773-6.

13.

Marathamuthu

Selvanayagam

Yusof

. Contralateral effects of eccentric exercise and DOMS of the plantar flexors: Evidence of central involvement. Research Quarterly for Exercise and Sport. 2020; 00(00): 1-10.

14.

Voglar

Kozinc

Šarabon

. The effects of eccentric exercise on passive hamstring muscle stiffness: Comparison of shear-wave elastography and passive knee torque outcomes. European Journal of Translational Myology. 2022; 32(2).

15.

Park

G-h

Lee

H-m

. Effect of action observation physical training for chronic stroke patients on the stairs walking ability and self-efficacy. The Journal of Korean Physical Therapy. 2021; 33(2): 53-61.

16.

Zeng

Zhu

Zhang

Xie

. Reviewing clinical effectiveness of active training strategies of platform-based ankle rehabilitation robots. Journal of healthcare engineering. 2018; 2018.

17.

Alvarez-Perez

Garcia-Murillo

Cervantes-Sánchez

. Robot-assisted ankle rehabilitation: A review. Disability and Rehabilitation: Assistive Technology. 2020; 15(4): 394-408.

18.

Dong

Zhou

Rong

Fan

Zhou

, et al. State of the art in parallel ankle rehabilitation robot: A systematic review. Journal of NeuroEngineering and Rehabilitation. 2021; 18(1): 1-15.

19.

Yamada

Okamoto

Shiraishi

Hashimoto

Akiyama

Yamada

. Machine-assisted foot stretching in the elderly: A comparison with self-stretching. Journal of Physical Therapy Science. 2021; 33(3): 179-86.

20.

Linder

Rosenfeldt

Bazyk

Koop

Ozinga

Alberts

. Improved lower extremity pedaling mechanics in individuals with stroke under maximal workloads. Topics in Stroke Rehabilitation. 2018; 25(4): 248-55.

21.

Virzi

. Refining the test phase of usability evaluation: How many subjects is enough? Human Factors. 1992; 34(4): 457-68.

22.

Sauro

. Ways to interpret a SUS score. Dipetik November. 2022; 4: 2019.

23.

Bangor

Kortum

Miller

. An empirical evaluation of the system usability scale. Intl Journal of Human-Computer Interaction. 2008; 24(6): 574-94.

24.

Kim

Bae

Y-H

Kim

Lee

. Formative Usability Evaluation of a Three-Way Digital Healthcare System for the People with Disabilities and Their Caregivers: A Cross-Sectional Study. Healthcare. 2022; 10.

25.

Kristiansen

Odderskær

Kristensen

. Effect of body weight support on muscle activation during walking on a lower body positive pressure treadmill. Journal of Electromyography and Kinesiology. 2019; 48: 9-16.

26.

Brown

Kautz

Dairaghi

. Muscle activity patterns altered during pedaling at different body orientations. Journal of Biomechanics. 1996; 29(10): 1349-56.

27.

Fujiwara

Liu

Chino

. Effect of pedaling exercise on the hemiplegic lower limb. American Journal of Physical Medicine & Rehabilitation. 2003; 82(5): 357-63.

28.

Mao

Gao

Yang

Song

. Influence of proprioceptive training based on ankle-foot robot on improving lower limbs function in patients after a stroke. Frontiers in Neurorobotics. 2022; 16: 969671.

29.

Watanabe

Kouzaki

Ogawa

Akima

Moritani

. Relationships between muscle strength and multi-channel surface EMG parameters in eighty-eight elderly. European Review of Aging and Physical Activity. 2018; 15(1): 1-10.