Skip to main content
PLOS Digital Health logoLink to PLOS Digital Health
. 2023 Nov 22;2(11):e0000262. doi: 10.1371/journal.pdig.0000262

Test-retest reliability of the six-minute walking distance measurements using FeetMe insoles by completely unassisted healthy adults in their homes

Andrey Mostovov 1,*, Damien Jacobs 1, Leila Farid 1, Paul Dhellin 1, Guillaume Baille 2
Editor: Haleh Ayatollahi3
PMCID: PMC10664940  PMID: 37992015

Abstract

Wearable technology provides an opportunity for new ways of monitoring patient gait remotely, through at-home self-administered six-minute walk tests (6MWTs). The purpose of this study was to evaluate the test-retest reliability of FeetMe insoles, a wearable gait assessment device, for measuring the six-minute walking distance (6MWD) during tests conducted with a one-week interval by completely unassisted healthy adults in their homes. Participants (n = 21) performed two 6MWTs at home while wearing the FeetMe insoles, and two 6MWTs at hospital while wearing FeetMe insoles and being assessed by a rater. All assessments were performed with a one-week interval between tests, no assistance was provided to the participants at home. The agreement between the 6MWD measurements made at baseline and at Week 1 was good for all test configurations and was highest for the at-home FeetMe measurements, with an intraclass correlation coefficient (ICC) of 0.95, standard error of the measurement (SEM) of 15.02 m and coefficient of variation (CV) of 3.33%, compared to ICCs of 0.79 and 0.78, SEMs of 25.65 and 26.65 and CVs of 6.24% and 6.10% for the rater and FeetMe measurements at hospital, respectively. Our work demonstrates that the FeetMe system could provide a reliable solution allowing individuals to self-administer 6MWTs independently at home.

Author summary

At-home patients monitoring using wearable tools presents numerous advantages for regular care and clinical studies. Patients benefit from the convenience of not having to travel to a clinic for assessments, which is particularly helpful for those in remote areas or with mobility issues. Besides, at-home monitoring allows for more frequent assessments, leading to more accurate clinical decision-making and timely intervention, which ultimately results in enhanced patient care. For the same reasons, it can improve patients recruitment and retention in clinical studies. The six-minute walk test (6MWT) is a commonly used standardized assessment of functional capacity in patients with various diseases. We evaluated the test-retest reliability of FeetMe insoles, a wearable gait assessment device, for measuring the six-minute walking distance (6MWD) at home. Our analysis of the data from 21 healthy volunteers showed that the FeetMe insoles were as reliable at home as they were in the standard clinical setting and as a conventional way of assessing the 6MWD. In addition, the insoles provided extensive gait analysis, which may allow for more precise conclusions regarding the patient’s state and its evolution than the 6MWD alone. We conclude that the FeetMe device is an excellent candidate tool for at-home patients monitoring.

Introduction

Gait is considered as a reliable indicator of overall health status. A range of conditions, such as neurological diseases, can lead to gait impairment including a slow gait speed, gait asymmetry, and an unbalanced center of gravity [1,2]. Several tests have been developed to evaluate these parameters, such as the two-minute walking test (2MWT) [3], the six-minute walking test (6MWT) [4], and the twelve-minute walking test (12MWT) [5]. Among these tests, the 6MWT is the most widely used assessment and has emerged as the “go-to” gait evaluation test in clinical practice. It is easy to administer and well tolerated, and has been found to provide a better reflection of a patient’s capacity for daily physical activity than other tests [4]. The test involves measuring the distance walked by a patient during a 6-minute time frame (i.e., the six-minute walking distance; 6MWD). It has been used conclusively in many clinical investigations. The test-retest reliability of the 6MWT has been found to be excellent, with reported intraclass correlation coefficients (ICCs) of 0.91–0.98 and inter- and intra-rater reliability ICCs of 0.86–0.96 [68].

Despite its many advantages, the 6MWT does have some limitations that need to be addressed. First, the test is typically carried out and monitored manually by a rater, which may lead to inconsistences in the assessment. Most notably, words of encouragement [9] or variations in the instructions provided by the rater [10] could impact the patient’s performance. Second, the test only evaluates a single gait parameter (the average gait speed over 6 minutes); whereas other gait parameters, such as stride length or stance time, have been shown to be useful for evaluating patient health status. Indeed, such gait parameters have been shown to be valuable indicators of fatigue in patients with multiple sclerosis [11].

Given the widespread use of the 6MWT in clinical practice for evaluating the functional capacity of patients with a range of diseases, there is great interest in developing technical solutions that could help to streamline the evaluation process, allowing tests to be conducted more frequently and provide more detailed follow-up data and improved care. This demand aligns with the advancements of wearable technology, which present new opportunities for improving patient care and monitoring through innovative means. In particular, exploring whether wearable devices could be used to allow gait assessments to be conducted at home could be highly beneficial for patients. Self-administering gait tests at home could eliminate the patient burden associated with commuting to clinical facilities. At-home monitoring would also allow for repeated tests to be conducted over an extended period of time, allowing physicians to gather more longitudinal data and improve patient follow-up. Several research groups have proposed ways to assess gait parameters in the comfort of the patient’s own home and have evaluated the interest of such solutions. In one of the early studies, Alison et al. highlighted the interest of performing the 6MWT at home in survivors of critical illness [12]. However, in this study the 6MWTs were still administered in the conventional manner, with the rater being dispatched to the patient’s home to administer the test, something that is seldomly possible outside of a clinical study. Studies testing the reliability of an accelerometer-based quantification program [13] and a wearable guided 6MWT device [14] to measure gait speed in patients with cardiovascular conditions have obtained promising results, with the at-home distances measured with these devices being consistent with those obtained manually with clinical guidance. Such tools designed for at-home use are therefore likely to play an increasingly important role in the follow-up of patients with gait disorders. Still, only a few of these studies have involved devices that could provide a complete solution, allowing patients to conduct 6MWTs independently, without supervision by a healthcare professional, and provide estimates of the 6MWD without any assumptions or a priori information.

FeetMe insoles are among the recently developed wearable devices that have the capability to allow gait assessments to be self-administered remotely in the patient’s own home. These insoles were designed to assess many gait parameters, including stride length, velocity, stance, swing, step, single and double support durations, and cadence and their reliability have already been proven by independent studies. Test-retest reliability of gait parameters was confirmed in older adults [15] and the insoles were found to be as reliable as the GAITRite clinical walkway system for walking tests conducted in clinical settings in patients with multiple sclerosis [16] and Parkinson’s disease [17]. Other studies in patients with post-stroke [18] and in healthy volunteers [19] came to similar conclusion. The FeetMe insoles have also already been found to be a valid and accurate solution for measuring the 6MWD in hospital settings when compared to the ground truth measured by a surveyor’s wheel and estimates made by a rater [20]. The aim of the current study was to probe the test-retest reliability of FeetMe insoles in estimating the 6MWDs in a home environment. This was accomplished by assessing the repeatability of the 6MWTs completed by unassisted healthy volunteers in their homes with a one-week interval between the tests.

Materials and methods

Study design

This single-center, prospective study was conducted between October 2021 and August 2022 by investigators working at the Delafontaine Hospital Center (Saint-Denis, France). The study was approved by a French ethics committee, CPP EST I, and complied with the Declaration of Helsinki and all subsequent amendments (registration number, ID-RCB: 2021-A00037-34).

The primary aim of the study was to assess the reliability of 6MWD measured using connected insoles in a remote home setting along a 10-meter track. Additionally, the study aimed to compare the reliability of this remote measurement to the reliability of the conventional assessment conducted in a hospital setting, where both the insoles and a rater measured the 6MWD simultaneously also along a 10-meter track.

Inclusion

All healthy volunteers aged between 18 and 80 years old, who were able to walk 100 m unaided, had no gait disorders, and who were accustomed to using a smartphone, were eligible to participate in the study. Volunteers who had undergone surgery that could potentially impact gait in the previous 3 months (e.g., orthopedic surgery, an intervention for trauma of the lower limbs or spine, gynecological or urological surgery, or brain or spinal cord surgery) and those with a chronic disease affecting walking (e.g., rheumatological, orthopedic, pain, or neurological disorders) were excluded. The participants were recruited using study posters displayed in the relevant areas (e.g. universities for the younger age groups, typical associations for older age groups). The volunteers were provided with information about the study by phone or e-mail prior to the study start, and were given the opportunity to ask any the questions. All volunteers provided signed consent prior to the study start.

Instrumentation

The study used size 35 to 46 FeetMe insoles (FeetMe SAS, Paris, France), a Class Im CE(93/42/EC) and Class I FDA 510(k) exempt medical device (Fig 1). The technical characteristics of the insoles have been described previously [19]. The FeetMe insoles were used together with the FeetMe Evaluation smartphone application (Class Im CE(93/42/EC) and Class I FDA 510(k) exempt medical device) to administer the 6MWT. Data collected by the FeetMe insoles were transferred to the smartphone application via a Bluetooth Low Energy (BLE) emitter in the insoles, allowing information on plantar pressure, gait parameters and walking distance to be received in real time. Users selected and launched the 6MWT through the smartphone application. Once the 6MWT had been launched, the application collected and recorded the user’s gait parameters for each of their steps over the entire duration of the test, and then automatically stopped recording after 6 minutes and informed the user that the test had been completed. The data then were automatically sent to a medical service-certified secure server and test results could be displayed in the application or on the associated web platform, the FeetMe Mobility Dashboard. The access to the data and to the test results is fully restricted to authorized persons only. The data was handled in accordance with the French data protection authority’s (CNIL) reference methodology MR-003 as well as in accordance with the requirements of the European Union General Data Protection Regulation (GDPR).

Fig 1. A pair of FeetMe Insoles.

Fig 1

For the 6MWTs performed at home, participants were provided with simple equipment—two hoops (diameter: 0.5 m) attached together with a 10-m string—to allow them to define a 10-m track in their home surroundings.

Intervention

Prior to the intervention, all volunteers were given a 5 to 10 minutes training on the use of the FeetMe insoles and FeetMe Evaluation smartphone application so that they could use the system independently, without any support from a nurse or other healthcare professional. The investigator also helped selecting the insoles size and insured that they fit well participants’ shoes. The healthy volunteers then wore the insoles while carrying out 6MWTs at two hospital visits (baseline: day 0, and Week 1: day 8) and on two occasions at home (baseline: day 1, and Week 1: day 7). In hospital, the participants were evaluated by a rater (a medical doctor or an engineer) trained to administer the 6MWT according to the study protocol.

For the two tests conducted at the hospital, data were analyzed for each participant as they performed the 6MWTs walking at a comfortable speed on a 10-m track, while wearing the FeetMe insoles and being simultaneously assessed by a rater. Contrary to the official test guidelines [21], no signs of encouragement were provided by the rater during the test. The rater only informed the participant of the time remaining every minute, then 30 seconds and 10 seconds before the end of the test.

For the two tests conducted at home, volunteers were provided with the insoles, a smartphone with the FeetMe Evaluation application, and the track equipment. They were asked to perform the 6MWTs while wearing the insoles on a 10-m track made using the equipment provided. The test could be performed in a quiet place either indoors or outdoors (undercover if required by weather conditions), but required a flat and hard surface, with few or no passages and, ideally, no obstacles.

Outcomes

The main outcome was the test-retest reliability of the FeetMe 6MWD measurements from tests performed by the participants at home without any assistance. The test-retest reliability of the 6MWD measurements made by the rater in hospital and by FeetMe in hospital in the same population was used as a reference level of repeatability.

Statistical analysis

The normality of the 6MWD data was assessed using Q–Q plots and Shapiro-Wilk normality tests. The mean and standard deviation (SD) of the recorded 6MWDs were calculated for the rater at hospital, FeetMe at hospital and FeetMe at home at baseline and Week 1. The bias (i.e., systematic error), the 95% confidence interval (CI) of differences (i.e., limits of agreement), Pearson correlation coefficient, ICC (2,1), coefficient of determination, standard error of the measurement (SEM) and coefficient of variation (CV) were calculated to compare baseline test results with test results obtained at Week 1 for each of the three test configurations. A Levene test was used to assess significant differences between the SDs of the test results at baseline and at Week 1.

The repeatability of the test results obtained at the two timepoints was analyzed using Bland-Altman and linear regression plots for all three configurations: rater at hospital, FeetMe at hospital and FeetMe at home.

The following criteria were used to assess the degree of correlation [22]: <0.30 negligible, 0.30–0.50 low, 0.50–0.70 moderate, 0.70–0.90 good, and 0.90–1.00 excellent. The same criteria were used for the coefficients of determination. For the ICCs, values below 0.50 were deemed to indicate poor validity, values between 0.50 and 0.75 to indicate moderate validity, values between 0.75 and 0.90 to indicate good validity and values greater than 0.90 to indicate excellent validity (as described previously [23]). A priori significance levels (α) were set at 0.05 for all analyses. All data and statistical analyses were performed using Python software (version 3.8).

Results

Demographics and population distribution

A total of 33 healthy volunteers, 15 females and 18 males, were included in the study. Participants ranged in age from 23 to 73 years, with a mean of 42 years. The average height and weight of the population were 173.9 ± 9.3 cm and 70.9 ± 10.9 kg, respectively.

Results of the tests

Overall, 30 out of the 33 participants completed all the tests in the hospital setting (Fig 2). Among these 30 participants, one participant performed no tests at home and four performed the test at home on only one out of the two days required or performed an incorrect type of test on one of the days. In addition, three of the participants carried out tests that were shorter than 6 minutes, and a technical issue (application crash) prevented data from being recorded in one case. Data from all of these participants were excluded from the analysis and therefore the final analysis population consisted of 21 healthy volunteers.

Fig 2. Flowchart of participant enrolment and data exclusion.

Fig 2

Abbreviation: 6MWT, six-minute walking test.

Q-Q plots evaluating the normality of the data for each test configuration (rater at hospital, FeetMe at hospital and FeetMe at home) both at baseline and at Week 1, indicated that the distribution of the data was close to normal in all cases (Fig 3). The Shapiro-Wilk tests yielded p-values greater than 0.05 for the data collected at baseline for all three configurations. However, Shapiro-Wilk p-values for the data collected at Week 1 by the rater and by FeetMe at home were equal to or below 0.05 (Table 1).

Fig 3. Q-Q plots for the 6MWDs evaluated at baseline and Week 1 by a rater at hospital, and by FeetMe at hospital and at home.

Fig 3

Table 1. Mean and standard deviation of the 6MWD measurements obtained at baseline and at Week 1 by the rater and FeetMe at hospital and by FeetMe at home.

Test
configuration
n 6MWD at baseline 6MWD at Week 1 Shapiro-Wilk
p-values*
Levene test
p-values**
Mean [m] SD [m] Mean [m] SD [m] Baseline Week 1
Rater at hospital 21 410.86 52.60 425.43 57.87 0.09 0.05 0.82
FeetMe at hospital 21 436.93 52.14 453.20 61.09 0.07 0.06 0.77
FeetMe at home 21 453.02 67.18 450.87 67.02 0.09 0.004 0.98

*The Shapiro-Wilk test was used to assess the normality of the data obtained from the three configurations at baseline and at Week 1.

**The Levene test p-values were obtained from comparisons between the SDs of the test results at baseline and Week 1. Abbreviations: 6MWD, six-minute walking distance; n, number of participants; SD, standard deviation.

Repeatability assessments

The mean and SD of the 6MWDs measured at baseline were very similar to those estimated at Week 1 for the FeetMe evaluations conducted at home. On the contrary, when comparing the measurements taken during the initial hospital visit with those of the second visit, we noted a notable disparity in both the mean and SD estimators (Table 1). This observation held true for both the rater assessments and the FeetMe assessments. The results of the Levene test showed that there were no significant differences in the SDs of the distance estimates made at baseline and Week 1 for all three test configurations (Table 1).

The FeetMe at home measurements showed a very low test-retest bias of 2.15 m, which was less than 0.5% of the total distance measured at both time points (Table 2). In comparison, the equivalent bias for the rater assessment was -14.57 m. The results of the linear regression analysis between the two visits for each test configuration (rater at hospital, FeetMe at hospital and FeetMe at home) are shown in Fig 4. It is noticeable that for FeetMe at home estimates, the regression line was very close to the ideal reference. This observation was further confirmed by the coefficient of determination value of 0.90 and the Pearson correlation coefficient value of 0.95 indicating an excellent level of correlation between the 6MWDs measured at the two timepoints (Table 2). In addition, the 95% CIs of the ICC (0.88–0.98) for the at-home FeetMe measurements indicated a very good to excellent intraclass correlation between the distances measured by the device at the two timepoints. By contrast, the coefficient of determination value of 0.66 and the Pearson correlation coefficient value of 0.81 indicated that the measurements made by the rater showed a moderate to good correlation between the two timepoints, and the 95% CIs of the ICC (0.54–0.91) indicated a moderate to excellent intraclass correlation for the rater measurements. The SEM and the CV values were also lower for the measurements made during the FeetMe at-home assessments than for those made during the rater assessments at hospital: 15.02 m and 3.33% for FeetMe at home versus 25.65 m and 6.24% for the rater, respectively. Analysis of the Bland-Altman plots (Fig 5) confirmed these conclusions: in addition to showing much lower bias, the FeetMe at home estimates showed substantially narrower limits of agreement compared to those for the two in-hospital test configurations.

Table 2. Analysis of the test–retest reliability of the 6MWD measurements at baseline and Week 1 by the rater, and by FeetMe at hospital and FeetMe at home.

Test
configuration
n Bias
[m]
Limits of agreement
[m]
Coefficient of determination Pearson
Correlation
ICC
[lower–upper 95% CI]
SEM
[m]
CV
[%]
Rater at hospital 21 -14.57 [-81.83–52.69] 0.66 0.81 0.79 [0.54–0.91] 25.65 6.24
FeetMe at hospital 21 -16.27 [-85.29–52.74] 0.67 0.82 0.78 [0.53–0.91] 26.65 6.10
FeetMe at home 21 2.15 [-40.24–44.54] 0.90 0.95 0.95 [0.88–0.98] 15.02 3.33

Abbreviations: CI, confidence interval; CV, coefficient of variation; ICC, intraclass correlation coefficient; SEM, standard error of the measurement.

Fig 4. Linear regression plots between the 6MWD evaluated at baseline and Week 1 by the rater at hospital, and by FeetMe at hospital and at home.

Fig 4

Red lines denote the linear regression, and dashed blue lines indicate the line of ideal match between the Baseline and Week 1 measurements.

Fig 5. Bland-Altman plots between the 6MWD estimated at baseline and at Week 1 by the rater at hospital, and by FeetMe at hospital and at home.

Fig 5

The solid lines indicate the bias (mean difference) values, and the dashed lines indicate the upper and lower limits of agreement (95% confidence intervals).

Discussion

This study evaluated the potential of FeetMe insoles, a connected wearable gait assessment device, to provide a solution allowing 6MWTs to be self-administered, independently and accurately, by individuals in their own home. The test-retest reliability of the 6MWDs measured by the FeetMe insoles during two at-home 6MWTs performed within a one-week of interval by unsassisted healthy participants was compared with that for measurements obtained in hospital by a rater and using the FeetMe insoles. Our study demonstrated that, while there was good agreement between the test-retest measurements for all three test configurations, the 6MWD measurements made by the FeetMe insoles at home had higher ICC and coefficient of determination values, and lower bias, SEM and CV% values than those obtained for the in-hospital FeetMe and rater measurements. Furthermore, the learning effect [24], which was evident in the in-hospital measurements, was not observed in the measurements conducted at home. This difference suggests that the FeetMe insoles facilitate consistent and unbiased assessments during at-home testing, unaffected by the learning curve observed in the hospital setting. Thus, at-home self-administered 6MWTs using the FeetMe technology were found to be at least, if not more, reliable than rater assessments conducted in a hospital setting, providing evidence that the FeetMe insoles could deliver an easy-to-use, reliable, and accurate solution allowing patients to conduct 6MWTs at home.

The performance of FeetMe insoles in this study was assessed in a population of 21 healthy volunteers, aged between 23 and 73 years old. The age range of the study population was therefore wide enough to cover various levels of physical performance. The excellent test-retest ICC value obtained in our study for the at-home FeetMe measurements (0.95, 95% CI: [0.88–0.98]) was similar to the ICC values reported previously in the literature for repeated 6MWTs conducted in controlled settings with conventional assessment of the 6MWD by a rater (e.g. 0.98, 95% CI: [0.97–0.99] [6] and 0.93 [25]). In contrast, the ICC values obtained for the measurements made by the rater (0.79, 95% CI: [0.54–0.91]) and by the FeetMe device in hospital (0.78, 95% CI: [0.53–0.91]) were lower than those reported previously. The CV% values obtained in our study were lower than those reported previously (e.g., 8% [26]) for all three test configurations studied. This difference might be explained by the fact that previous studies involved different populations (frail older adults with dementia [6], patients with chronic obstructive pulmonary disease, COPD [7] or patients with osteoarthritis [26]) with different age ranges from those used in our study, or conducted the assessments on tracks with different lengths, following the official test guidelines. Indeed, the track length of 10 m used in our study was optimized to allow for the test to be conducted in all home environments with minimal equipment. However, the same space constraints may also occur in hospital settings where use of the 30-m track recommended in the official test guidelines is not always feasible. Our study therefore also provides strong evidence validating the use of shorter track lengths in all settings, which should be considered in any future revisions of 6MWT guidelines.

Besides, it is of interest to compare our findings with the results reported in previously published research. A few of the solutions assessed in previous studies used accelerometer signals to measure gait and focused only on the number of steps taken [13,14,27,28]. These studies either did not include any assessment of the 6MWD, or tried to derive the distance walked based on a priori information such as patient height or average stride length at baseline. However, these derived estimates are prone to error as stride length has been shown to vary over time in patients with pathologies such as stroke, cerebral ataxia or Parkinson’s disease, especially after the patient has received physical therapy [2931].

In a preliminary study conducted in a laboratory setting, Smith-Turchyn et al. evaluated the potential of the EasyMeasure application as an aid for self-administering 6MWTs at home [32]. As part of the experimental design, the participants were responsible for timing the test and had to manually count the laps walked. Although this study was carried out using a healthy population of 20 young university student volunteers, the reported accuracy of the tests conducted using the application was low, and 80% of the participants were found to have deviated from the test instructions (i.e., lost count of the number of laps, did not measure the distance walked, or did not walk at their maximum speed). Thus, given the extent of the test deviations reported in this healthy population, the technology-based method assessed in this study appears unlikely to be suitable for use by elderly people or patients with cognitive difficulties, highlighting the need for a more automated and easy-to-use tool.

The results of the test-retest analyses of the FeetMe at home measurements can be compared to those reported for other systems that have been evaluated for self-administering the 6MWT. Brooks et al. [28] evaluated the performance of a smartphone-based application for assessing 6MWTs conducted at home by 19 participants, including patients with congestive heart failure or pulmonary hypertension, and healthy controls. At least three tests with a two-week interval were performed by each participant. Analyses of the results revealed a CV value of 4.7% for the smartphone application, compared to the lower CV value of 3.33% obtained for the FeetMe device used at home in the current study. One of the most promising previous studies evaluating a solution for carrying out 6MWTs remotely was that by Wevers et al. [33]. This study investigated the use of a global positioning system (GPS) by investigators administering 6MWTs to 27 patients with chronic stroke outdoors in the patients’ own neighborhoods [33]. A measuring wheel was also used by the investigators as a reference and the official 6MWT guidelines were followed as closely as possible, including the use of a 30-m track. The results obtained for the reproducibility of the GPS-estimated 6MWDs were very good, with an ICC of 0.96 and an SEM of 18.1 m. Remarkably, the values obtained for the FeetMe device at home in the current study were slightly better for the SEM (15.02 m) and very similar for the ICC (0.95). In addition, although the GPS appeared to provide a well suited and accurate solution for conducting 6MWTs remotely, unlike the FeetMe system, the GPS cannot be used to conduct the tests indoors.

Study limitations

The current study provided the first assessment of the test-retest reliability of FeetMe insoles for measuring 6MWDs during tests conducted independently by the participants at home and compared it to the reliability of the evaluation in hospital settings. However, this study also had some limitations. In particular, this study was carried out using in-hospital tests conducted at a single center in a single country and involved healthy volunteers rather than patients with pathological gait. Besides, some of the authors of this work were affiliated with FeetMe company. Future studies by an independent group of researchers are therefore required to replicate these results in a larger sample population, including both healthy volunteers and those with gait anomalies, with in-hospital tests conducted at multiple centers and in multiple countries. In addition, the learning effect between repeated 6MWTs at home should be further studied and compared to that in hospital settings [24].

Conclusions

In conclusion, this study demonstrated that the FeetMe connected insoles provide a reliable solution for allowing 6MWTs to be self-administered independently at home by healthy adults. This finding makes a substantial contribution to the progress of remote patient monitoring, a crucial aspect of future clinical practice. Indeed, at-home monitoring of gait, through 6MWT for instance, would remove the patient burden associated with commuting to hospital assessment centers, and would drastically simplify the patient’s care. The home setting would also allow for more frequent assessments of the functional capacity of patients, and therefore result in better patient follow-up and, ultimately, in overall improvements in patient management.

Besides, it is important to mention, that in addition to measuring the 6MWD, the FeetMe device has the capability of collecting additional information on patient gait parameters during the test, providing complementary data, which when analyzed together with the 6MWD, can help obtain a finer understanding of a patient’s condition. This makes the FeetMe device one of the most convincing solutions for at-home gait monitoring. Therefore, further studies are endorsed to evaluate its performance across various pathologies, thereby enhancing its potential for widespread clinical application.

Acknowledgments

The authors would like to thank all volunteers who agreed to participate in this study. We also thank Margarita Arango, Ayelen Gallardo, Christelle Saulnier and prof Caroline Moreau for proofreading of this manuscript and Gilles Monneret for advising on statistical analysis. We are grateful to Cyril Basquin for data management services, and for his input on the study methodology. We would also like to thank Drs Emma Pilling and Marielle Romet (Santé Active Edition–Synergy Pharm) for medical writing assistance and language editing. We express our gratitude to FeetMe company for providing FeetMe insoles for this study.

Data Availability

The data that support the findings of this study are publicly available from Zenodo public repository with the identifier https://doi.org/10.5281/zenodo.8252988.

Funding Statement

The authors received no specific funding for this work.

References

  • 1.Mirelman A, Bonato P, Camicioli R, Ellis TD, Giladi N, Hamilton JL, et al. Gait impairments in Parkinson’s disease. Lancet Neurol. 2019. Jul;18(7):697–708. doi: 10.1016/S1474-4422(19)30044-4 [DOI] [PubMed] [Google Scholar]
  • 2.Ataullah AHM, De Jesus O. Gait Disturbances. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022. [cited 2022 Nov 29]. Available from: http://www.ncbi.nlm.nih.gov/books/NBK560610/ [Google Scholar]
  • 3.Butland RJA, Pang J, Gross ER, Woodcock AA, Geddes DM. Two-, six-, and 12-minute walking tests in respiratory disease. BMJ. 1982. May 29;284(6329):1607–8. doi: 10.1136/bmj.284.6329.1607 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Enright PL. The six-minute walk test. Respir Care. 2003. Aug;48(8):783–5. [PubMed] [Google Scholar]
  • 5.Solway S, Brooks D, Lacasse Y, Thomas S. A Qualitative Systematic Overview of the Measurement Properties of Functional Walk Tests Used in the Cardiorespiratory Domain. Chest. 2001. Jan;119(1):256–70. doi: 10.1378/chest.119.1.256 [DOI] [PubMed] [Google Scholar]
  • 6.Chan WLS, Pin TW. Reliability, validity and minimal detectable change of 2-minute walk test, 6-minute walk test and 10-meter walk test in frail older adults with dementia. Exp Gerontol. 2019. Jan;115(September 2018):9–18. doi: 10.1016/j.exger.2018.11.001 [DOI] [PubMed] [Google Scholar]
  • 7.Hansen H, Beyer N, Frølich A, Godtfredsen N, Bieler T. Intra- and inter-rater reproducibility of the 6-minute walk test and the 30-second sit-to-stand test in patients with severe and very severe COPD. Int J Chron Obstruct Pulmon Dis. 2018. Oct;Volume 13:3447–57. doi: 10.2147/COPD.S174248 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8.Cheng DK, Nelson M, Brooks D, Salbach NM. Validation of stroke-specific protocols for the 10-meter walk test and 6-minute walk test conducted using 15-meter and 30-meter walkways. Top Stroke Rehabil. 2020. May;27(4):251–61. doi: 10.1080/10749357.2019.1691815 [DOI] [PubMed] [Google Scholar]
  • 9.Guyatt GH, Pugsley SO, Sullivan MJ, Thompson PJ, Berman LB, Jones NL, et al. Effect of encouragement on walking test performance. Thorax. 1984;39(11):818–22. doi: 10.1136/thx.39.11.818 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Weir NA, Brown AW, Shlobin OA, Smith MA, Reffett T, Battle E, et al. The Influence of Alternative Instruction on 6-Min Walk Test Distance. Chest. 2013. Dec;144(6):1900–5. doi: 10.1378/chest.13-0287 [DOI] [PubMed] [Google Scholar]
  • 11.Ibrahim AA, Küderle A, Gaßner H, Klucken J, Eskofier BM, Kluge F. Inertial sensor-based gait parameters reflect patient-reported fatigue in multiple sclerosis. J NeuroEngineering Rehabil. 2020;17(1):1–9. doi: 10.1186/s12984-020-00798-9 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 12.Alison JA, Kenny P, King MT, McKinley S, Aitken LM, Leslie GD, et al. Repeatability of the Six-Minute Walk Test and Relation to Physical Function in Survivors of a Critical Illness. Phys Ther. 2012. Dec 1;92(12):1556–63. doi: 10.2522/ptj.20110410 [DOI] [PubMed] [Google Scholar]
  • 13.Jehn M, Prescher S, Koehler K, von Haehling S, Winkler S, Deckwart O, et al. Tele-accelerometry as a novel technique for assessing functional status in patients with heart failure: Feasibility, reliability and patient safety. Int J Cardiol. 2013. Oct;168(5):4723–8. doi: 10.1016/j.ijcard.2013.07.171 [DOI] [PubMed] [Google Scholar]
  • 14.Burch AE, Scherr D, Rieth A, Griffin J, Bianco NR, Odeneg T, et al. Wearable Cardioverter Defibrillator-Guided 6-Min Walk Test Performed at Home Is Accurate and Reliable: RESULTS OF THE TRENDS STUDY. J Cardiopulm Rehabil Prev. 2020. Mar;40(2):E14–7. doi: 10.1097/HCR.0000000000000441 [DOI] [PubMed] [Google Scholar]
  • 15.Lunardini F, Malavolti M, Pedrocchi ALG, Borghese NA, Ferrante S. A mobile app to transparently distinguish single- from dual-task walking for the ecological monitoring of age-related changes in daily-life gait. Gait Posture. 2021. May;86:27–32. doi: 10.1016/j.gaitpost.2021.02.028 [DOI] [PubMed] [Google Scholar]
  • 16.Granja Domínguez A, Romero Sevilla R, Alemán A, Durán C, Hochsprung A, Navarro G, et al. Study for the validation of the FeetMe integrated sensor insole system compared to GAITRite system to assess gait characteristics in patients with multiple sclerosis. Moccia M, editor. PLOS ONE. 2023. Feb 9;18(2):e0272596. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 17.Parati M, Gallotta M, Muletti M, Pirola A, Bellafà A, De Maria B, et al. Validation of Pressure-Sensing Insoles in Patients with Parkinson’s Disease during Overground Walking in Single and Cognitive Dual-Task Conditions. Sensors. 2022. Aug 25;22(17):6392. doi: 10.3390/s22176392 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Farid L, Jacobs D, Do Santos J, Simon O, Gracies JM, Hutin E. FeetMe Monitor-connected insoles are a valid and reliable alternative for the evaluation of gait speed after stroke. Top Stroke Rehabil. 2021. Feb 17;28(2):127–34. [DOI] [PubMed] [Google Scholar]
  • 19.Jacobs D, Farid L, Ferré S, Herraez K, Gracies JM, Hutin E. Evaluation of the validity and reliability of connected insoles to measure gait parameters in healthy adults. Sensors. 2021;21(19):1–14. doi: 10.3390/s21196543 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Mostovov A, Jacobs D, Farid L, Dhellin P, Baille G. Validation of the Six-Minute Walking Distance Measured by FeetMe Insoles. BMC Digital Health. 2023. Oct 3;1(1). [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 21.ATS Statement: Guidelines for the Six-Minute Walk Test. Am J Respir Crit Care Med. 2002. Jul 1;166(1):111–7. [DOI] [PubMed] [Google Scholar]
  • 22.Mukaka MM. Statistics corner: A guide to appropriate use of correlation coefficient in medical research. Malawi Med J J Med Assoc Malawi. 2012. Sep;24(3):69–71. [PMC free article] [PubMed] [Google Scholar]
  • 23.Koo TK, Li MY. A Guideline of Selecting and Reporting Intraclass Correlation Coefficients for Reliability Research. J Chiropr Med. 2016. Jun;15(2):155–63. doi: 10.1016/j.jcm.2016.02.012 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 24.Holland AE, Spruit MA, Troosters T, Puhan MA, Pepin V, Saey D, et al. An official European respiratory society/American thoracic society technical standard: Field walking tests in chronic respiratory disease. Eur Respir J. 2014;44(6):1428–46. doi: 10.1183/09031936.00150314 [DOI] [PubMed] [Google Scholar]
  • 25.Hernandes NA, Wouters EFM, Meijer K, Annegarn J, Pitta F, Spruit MA. Reproducibility of 6-minute walking test in patients with COPD. Eur Respir J. 2011. Aug 1;38(2):261–7. doi: 10.1183/09031936.00142010 [DOI] [PubMed] [Google Scholar]
  • 26.Naylor JM, Hayen A, Davidson E, Hackett D, Harris IA, Kamalasena G, et al. Minimal detectable change for mobility and patient-reported tools in people with osteoarthritis awaiting arthroplasty. BMC Musculoskelet Disord. 2014. Dec 11;15(1):235. doi: 10.1186/1471-2474-15-235 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 27.Rens N, Gandhi N, Mak J, Paul J, Bent D, Liu S, et al. Activity data from wearables as an indicator of functional capacity in patients with cardiovascular disease. Lazzeri C, editor. PLOS ONE. 2021. Mar 24;16(3):e0247834. doi: 10.1371/journal.pone.0247834 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 28.Brooks GC, Vittinghoff E, Iyer S, Tandon D, Kuhar P, Madsen KA, et al. Accuracy and Usability of a Self-Administered 6-Minute Walk Test Smartphone Application. Circ Heart Fail. 2015. Sep;8(5):905–13. doi: 10.1161/CIRCHEARTFAILURE.115.002062 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Munari D, Pedrinolla A, Smania N, Picelli A, Gandolfi M, Saltuari L, et al. High-intensity treadmill training improves gait ability, VO2peak and cost of walking in stroke survivors: preliminary results of a pilot randomized controlled trial. Eur J Phys Rehabil Med [Internet]. 2018. Jun [cited 2022 Dec 13];54(3). Available from: https://www.minervamedica.it/index2.php?show=R33Y2018N03A0408. doi: 10.23736/S1973-9087.16.04224-6 [DOI] [PubMed] [Google Scholar]
  • 30.Triegaardt J, Han TS, Sada C, Sharma S, Sharma P. The role of virtual reality on outcomes in rehabilitation of Parkinson’s disease: meta-analysis and systematic review in 1031 participants. Neurol Sci. 2020. Mar;41(3):529–36. doi: 10.1007/s10072-019-04144-3 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 31.Keller JL, Bastian AJ. A Home Balance Exercise Program Improves Walking in People With Cerebellar Ataxia. Neurorehabil Neural Repair. 2014. Oct;28(8):770–8. doi: 10.1177/1545968314522350 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 32.Smith-Turchyn J, Adams SC, Sabiston CM. Testing of a Self-administered 6-Minute Walk Test Using Technology: Usability, Reliability and Validity Study. JMIR Rehabil Assist Technol. 2021. Sep 23;8(3):e22818. doi: 10.2196/22818 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 33.Wevers L, Kwakkel G, van de Port I. Is outdoor use of the six-minute walk test with a global positioning system in stroke patients’ own neighbourhoods reproducible and valid? J Rehabil Med. 2011;43(11):1027–31. doi: 10.2340/16501977-0881 [DOI] [PubMed] [Google Scholar]
PLOS Digit Health. doi: 10.1371/journal.pdig.0000262.r001

Decision Letter 0

Haleh Ayatollahi

22 Jun 2023

PDIG-D-23-00161

Excellent test-retest reliability of the six-minute walking distance measured by FeetMe® insoles during tests conducted with a one-week interval by completely unassisted healthy adults in their homes.

PLOS Digital Health

Dear Dr. Mostovov,

Thank you for submitting your manuscript to PLOS Digital Health. After careful consideration, we feel that it has merit but does not fully meet PLOS Digital Health's publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript within 60 days Aug 21 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at digitalhealth@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pdig/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

* A rebuttal letter that responds to each point raised by the editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

* A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

* An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

We look forward to receiving your revised manuscript.

Kind regards,

Haleh Ayatollahi

Section Editor

PLOS Digital Health

Journal Requirements:

1. Please provide separate figure files in .tif or .eps format only and remove any figures embedded in your manuscript file. Please also ensure that all files are under our size limit of 10MB.

For more information about figure files please see our guidelines:

https://journals.plos.org/digitalhealth/s/figures

https://journals.plos.org/digitalhealth/s/figures#loc-file-requirements

2. We noticed that you used unpublished data in the manuscript. We do not allow these references, as the PLOS data access policy requires that all data be either published with the manuscript or made available in a publicly accessible database. Please amend the supplementary material to include the referenced data or remove the references.

3. We do not publish any copyright or trademark symbols that usually accompany proprietary names, eg ©, ®, ™ (e.g. next to drug or reagent names). Please remove all instances of trademark/copyright symbols throughout the text, including ®.

4. Figure 1 contains screenshots. We are not permitted to publish these under our CC-BY 4.0 license; websites are usually intellectual property and are copyrighted.This includes peripheral graphics of the web browser such as the buttons. We ask that you please remove or replace it.

5. In the online submission form, you indicated that "Data available on request due to restrictions e.g. privacy or ethical". All PLOS journals now require all data underlying the findings described in their manuscript to be freely available to other researchers, either 1. In a public repository, 2. Within the manuscript itself, or 3. Uploaded as supplementary information.

This policy applies to all data except where public deposition would breach compliance with the protocol approved by your research ethics board. If your data cannot be made publicly available for ethical or legal reasons (e.g., public availability would compromise patient privacy), please explain your reasons by return email and your exemption request will be escalated to the editor for approval. Your exemption request will be handled independently and will not hold up the peer review process, but will need to be resolved should your manuscript be accepted for publication. One of the Editorial team will then be in touch if there are any issues.

Additional Editor Comments (if provided):

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does this manuscript meet PLOS Digital Health’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Yes

--------------------

2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: No

Reviewer #3: Yes

--------------------

3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #2: Yes

Reviewer #3: No

--------------------

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Digital Health does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Yes

--------------------

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Dear authors,

Your submission titled 'Excellent test-retest reliability of the six-minute walking distance measured by

FeetMe® insoles during tests conducted with a one-week interval by completely

unassisted healthy adults in their homes' was an interesting read and was an appropriate submission for PLOS Digital Health. The study evaluated the potential of a wearable smart insole to empower patients with monitoring their gait at their convenience. The results highlight the tested device's potentials in assessing conditions with gait disturbances.

However, there are some aspects that need to be addressed. While the conflict of interest have been disclosed, a majority of the authors are/have been related to the company providing the device tested, in addition of the financial support provided by the FeetMe company. This requires a measure of caution when drawing conclusions and should be further highlighted within the text, preferably in a dedicated limitations sections.

On a related note, some of the literature used to support the potentials of the solution (14, 15) included authors who were employees of the FeetMe company, hence indicating need for caution regarding conflicting interests. Deriving such potentials from independent studies would add more value to the claims.

Some clarifications on the procedures and results would also be beneficial to add to the body of literature. For example, in the Intervention section, the length of the training of the participants could have been specified. Reasons for why some patients missed taking the required test and the relevant technical issues would also be important to share.

As the use of a companion smartphone application has been made, its compliance to relevant privacy policies should be specified. The field of digital health is not focused only on the technological component but also integrates the relevant ethical, social and regulatory concerns. As the FeetMe smart insoles is a commercial product, acknowledging its compliance to relevant policies would be a recommendation for scientific publication.

While the authors compared their findings with other research in gait studies, they did not do so with other studies that analysed other smart insoles for similar purposes. There have been a number of such studies in the past 5 years or so which the authors could compare their findings to in order to provide a more objective analysis of their findings.

It could also be recommended for the authors to use more cautious language when deriving recommendations in the discussion and conclusions. This is because the participants were healthy and the generalisability of the findings can be challenging to extrapolate to patients with gait disturbances. Further limiting the generalisability is that only 4 interventions took place for each participant. Thus, it could also be recommended to rephrase the study title as a feasibility assessment or pilot to be more indicative of the study scope.

This concludes my review comments and I hope this feedback is useful for your manuscript going further.

Reviewer #2: Thank you to the authors and editors for the opportunity to review this paper. This paper describes the utility of FeetMe, an innovative technology which may help capture measurements in non-clinical settings. Although I appreciate the goal of this study and the gap in intervention it is aiming to fill, I have strong concerns regarding the methodology and conclusions of the study. I have organized my concerns by section.

Introduction:

The authors identify a clear gap in measurement and provide a thoughtful solution to help fill this gap. However, clarification is needed throughout this section.

In line 58, please specify the type of bias and explicitly state how it affects measurement.

The language used in line 81/82 is misleading, given that the authors are reporting unpublished observations. Please provide more details on this study and explicitly state in text that these results require additional testing and/or peer review.

In line 84, the authors state that they are assessing reliability and repeatability of the FeetMe. In later sections it seems that they are only assessing test-retest reliability (which can also be called repeatability). Is there another form of reliability being assessed? Additionally, in line 135 the authors state that their primary outcome was to compare the test-retest reliability of at home vs by the rater in the hospital. Please use consistent language and goals throughout the manuscript.

The hypothesis for test-retest reliability, including a targeted kappa score is not provided. This is concerning as it prevents the reader from understanding what the initial goal was and whether or not it was met.

Methods:

Thank you to the authors for the detailed information in the methods section.

Please provide details on how participants were recruited. Were all participants recruited through one clinic? This information may help readers understand the context of the study and its generalizability.

Information on who rated the 6MWT would be useful.

Thank you for providing information on the soles used. Please provide additional information on if soles were adapted for different feet types/sizes. Additionally, if the soles were ill-fitting, would this affect the results provided? Please describe.

Statistical analysis:

Thank you to the authors for the efforts made in the statistical analysis section of the paper.

The age range included in this study was quite wide. Were there any subgroup analysis made, or any noted differences included across different age ranges?

I appreciated the use of several statistical tests. For test-retest reliability, kappa statistics to estimate the proportion of observed agreement to the proportion of agreement expected to chance is recommended. Would it be possible to provide the kappa statistic?

Results:

Thank you to the authors for the detailed results section.

The authors mention low retest bias in line 179/180, however, the statistical analysis section does not describe how this was calculated, as the units of measurements do not correlate to the above statistical analysis section. Please clarify in the statistical analysis section how this was quantified and calculated.

Discussion:

Given the small sample size and concerns detected in the methods and statistical analysis section, the final conclusion in the discussion should be reworded. Instead of saying “strong evidence” in line 224, the authors could restate to suggest that FeetMe shows promising results for future exploration, rather than suggesting that the app can be used now.

In line 175 of the results section, the authors describe a large difference between the FeetMe measurements and clinical measurements. Please provide additional information in the discussion section on why this may have occurred. For example, does this suggest that the app does not correlate well with gold standard clinical measurements, or does it require modifications in assessment?

When describing the use of new technology in research, it is essential to describe any potential ethical concerns. The authors mention that technical details of the app have already been published, however, it is important to note where the data is stored, for how long it is stored, who has access to the data, and how healthcare professionals access the information. Please include a section discussing the potential ethical concerns of the app.

Reviewer #3: A worthwhile piece of research, I can see the application of this technology within clinical practice and how it might benefit the quality of life for patients. Many thanks for the opportunity to review.

This research could be improved in the following ways.

Structure and flow. A large part of the discussion feels like it is providing the justification for this research and therefore should set the scene for the research within the introduction (lines 227-253)

The figure 2 and figure 3 should be moved below the commentary, which explains the figure which follows next (i.e. move lines 158-160 above figure 2 and move figure 3 below lines 167-171).

I suggest a section title for the statistical analyses, provides a clear distinction from the population demographics, which starts with a short introduction to the statistical analyses section.

Table 1 should be moved lower down the section, where the results within it are described.

Results interpretation, the researchers have highlighted and explained the difference between hospital rater and the FeetMe at home tests, however, have not sufficiently explained or interpreted the results between the FeetMe at home and in hospital results. A further commentary outlining the differences in the results and exploring possible reasons for this should be expanded upon.

Clearly defined implications for future research (or similar) and learnings from this study sections, would add value to the manuscript as would a section more clearly defined as limitations.

Overall improvements could be made to structure and flow with use of headings to break up longer sections to aid readability.

--------------------

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: Yes: Shoshana Bloom

--------------------

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLOS Digit Health. doi: 10.1371/journal.pdig.0000262.r003

Decision Letter 1

Haleh Ayatollahi

12 Sep 2023

PDIG-D-23-00161R1

Excellent test-retest reliability of the six-minute walking distance measured by FeetMe insoles during tests conducted with a one-week interval by completely unassisted healthy adults in their homes.

PLOS Digital Health

Dear Dr. Mostovov,

Thank you for submitting your manuscript to PLOS Digital Health. After careful consideration, we feel that it has merit but does not fully meet PLOS Digital Health's publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript within 30 days Oct 12 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at digitalhealth@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pdig/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

* A rebuttal letter that responds to each point raised by the editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

* A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

* An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

We look forward to receiving your revised manuscript.

Kind regards,

Haleh Ayatollahi

Section Editor

PLOS Digital Health

Journal Requirements:

1. Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article's retracted status in the References list and also include a citation and full reference for the retraction notice.

2. We do not publish any copyright or trademark symbols that usually accompany proprietary names, eg ©, ®, ™ (e.g. next to drug or reagent names). Please remove all instances of trademark/copyright symbols throughout the text, including ® on page 17.

Additional Editor Comments (if provided):

The manuscript was interesting; please address the following comments in your next revision.

1- The title is a bit long. Could you please make it shorter?

2- Please follow the journal instructions for the manuscript preparation including the abstract format.

3- Please add appropriate keywords based on the MeSH terms.

4- Please ensure that the aim of the study is the same in the abstract, introduction, etc.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #3: All comments have been addressed

--------------------

2. Does this manuscript meet PLOS Digital Health’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

Reviewer #3: Yes

--------------------

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: Yes

--------------------

4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #3: Yes

--------------------

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Digital Health does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #3: Yes

--------------------

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Thank you to the authors for addressing the initial feedback. However, there are minor aspects that need to be considered further.

While the authors have specified the CE/FDA classifications regarding the use of the application, the data handling policies were not specified. Data collection is explicitly mentioned in line 125 where the relevant data handling policy that was adhered to can be specified as good practice for scientific publication.

Regarding the title, considering the limited number of interventions, lack of control groups and the focus on healthy participants (while aiming to address patients with gait issues), it would be advisable to rephrase the study title as a feasibility assessment or pilot study to be more indicative of the study scope.

Reviewer #3: All my comments have been addressed within the revised manuscript. No further comments from me at this time. Many thanks.

--------------------

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: Yes: Shoshana Bloom

--------------------

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLOS Digit Health. doi: 10.1371/journal.pdig.0000262.r005

Decision Letter 2

Haleh Ayatollahi

16 Oct 2023

Test-retest reliability of the six-minute walking distance measurements using FeetMe insoles by completely unassisted healthy adults in their homes.

PDIG-D-23-00161R2

Dear Dr Mostovov,

We are pleased to inform you that your manuscript 'Test-retest reliability of the six-minute walking distance measurements using FeetMe insoles by completely unassisted healthy adults in their homes.' has been provisionally accepted for publication in PLOS Digital Health.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow-up email from a member of our team. 

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they'll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact digitalhealth@plos.org.

Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Digital Health.

Best regards,

Haleh Ayatollahi

Section Editor

PLOS Digital Health

***********************************************************

Reviewer Comments (if any, and for reference):

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

**********

2. Does this manuscript meet PLOS Digital Health’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Digital Health does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: Dear authors,

Thank you for addressing the rounds of feedback and providing clarifications where needed. I am happy to recommend the publication of your research.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

**********

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

    Attachment

    Submitted filename: 230816-rebuttalLetter_PLOS.pdf

    Attachment

    Submitted filename: 230921-rebuttalLetter_PLOS.pdf

    Data Availability Statement

    The data that support the findings of this study are publicly available from Zenodo public repository with the identifier https://doi.org/10.5281/zenodo.8252988.


    Articles from PLOS Digital Health are provided here courtesy of PLOS

    RESOURCES