Assessing Balance Loss and Stability Control in Older Adults Exposed to Gait Perturbations under Different Environmental Conditions: A Feasibility Study
Round 1
Reviewer 1 Report
Thank you for giving me the opportunity to read and review this manuscript. The manuscript is generally well written, however a challenge to read. All information is there, but hard to find. A major revision of how results are displayed is necessary.
Specific comments:
Title: describes the study well
Abstract: Well written
Introduction: Ref 1 on page 1, line 30 concerns older persons with mental problems. I suggest using a reference addressing a general older population.
Page 1, line 36-37: “There is a need to physically prepare the population at high risk of falling ……” . What does this sentence mean? I think you mean that the risk an unexpected mechanical disturbance means for persons at high risk at falling needs to be addressed.
Page 3, line 104-108: this is method and should be moved to the method section.
Aim: Clear
Method: Page 3, line 127: Please specify if other tests than the six minutes walk test and TUG was used as inclusion criteria.
Page 4, line 142: please provide diary number of the ethical approval.
Page 5, line 166: I think you mean zero, not cero?
Page 6, line 200: The NASA task load index needs to be described in more detailed, max sum scores etc. MOCA test and FSS also needs to be described in the method.
Page 6, line 216-231: To determine feasibility, acceptability, practicality, and safety was used. However, only acceptability and safety are mentioned in the aim and displayed in the results.
Results: Acceptability is a heading, but both acceptability and safety is displayed in the paragraph. I suggest changing the heading to “Feasiblity” and also include practicality, if you decide to include that in the aim.
The results would be easier to follow if they were displayed in the same order as in method. Results about validity is missing (comparison between assessor and video).
Discussion: Easy to read and well displayed!
Conclusion: In the conclusion, practicality is mentioned. If this is included in the conclusion, results about practicality needs to be shown. How about safety?
Tables and figures:
Table 1: there seems to be two headings, one above and one below the table. Explain all abbreviations used in the table.
References: As mentioned above, reference 1 concerns only older persons with mental problems.
Author Response
Reviewer 1.
- Ref 1 on page 1, line 30 concerns older persons with mental problems. I suggest using a reference addressing a general older population.
Response: we thank the reviewer for the recommendation. Now, we modified the reference citing an article that addressed general older population.
- Page 1, line 36-37: “There is a need to physically prepare the population at high risk of falling ……” . What does this sentence mean? I think you mean that the risk an unexpected mechanical disturbance means for persons at high risk at falling needs to be addressed.
Response: We thank the reviewer for the recommendation. Now, we modified the sentence and the final lines of the first paragraph of the introduction reads as follow: “Therefore, it is essential to prepare the population at high risk of falling for situations where unexpected postural disturbance may occur”.
- Page 3, line 104-108: this is method and should be moved to the method section.
Response: According to the reviewer comment, we moved this sentence to the method section.
- Method: Page 3, line 127: Please specify if other tests than the six minutes walk test and TUG was used as inclusion criteria.
Response: As inclusion criteria, we included the six-minutes walking test (capability to finish the test) and Timed Up and Go (score < 13.5 s). Additionally, the Montreal Cognitive Assessment Scale (MOCA) was used as inclusion criteria for cognitive skills. According to the reviewer´s comment, we added more details in this section. Now the paragraph reads as follow: “Participants were excluded in any of the following medical issues occurs at baseline measurements: Heart rate > 85% of age-predicted maximal heart rate (HR max), Systolic blood pressure (SBP) > 165mmHg and/or diastolic blood pressure (DBP) > 110 mmHg during resting, oxygen saturation (measured by pulse oximeter) during resting < 93%, and short of breath during the walking tests included in the baseline assessment protocol. Individuals were also excluded if they reported any neurological, musculoskeletal, or other systemic disorders that would affect the subject’s postural control and/or gait functions. Finally, participants were asked about their medical history and if they were under a particular or permanent medical treatment. In this context, participants on sedative drugs, psychotropic medications such as benzodiazepines, antidepressants, pain killer medications like morphine and oxycodone were also excluded. These exclusion criteria were established for safety (ability to safely follow instructions and complete the study). Additionally, the NASA task load index (NASA TLX), a clinical tool for measuring subjective mental workload and the Fatigue severity scale (FSS), A 9-item scale which measures the severity of fatigue and its effect on person´s activities, were used during the proposed protocol.”
- Page 4, line 142: please provide diary number of the ethical approval.
Response: In the manuscript version with author details we provided all the information regarding IRB approval.
- Page 5, line 166: I think you mean zero, not cero?
Response: Thank you for noticing this typo error. We fixed this error in the current version of the manuscript.
- Page 6, line 200: The NASA task load index needs to be described in more detailed, max sum scores etc. MOCA test and FSS also needs to be described in the method.
Response: According to the reviewer suggestion, now we included the description of the mentioned scales in the method section. Now the paragraph reads as follow: “Twenty-one healthy older adults (> 65 years) (12 females and 9 males) participated in this study. Participants were included if they passed a cognitive test (>26/30 on Montreal Cognitive Assessment Scale) and mobility tests such as the six-minutes walking test (able to finish the test) [31], and Timed Up and Go (TUG) (score <13.5 s) [32] to ensure that they were all independent ambulators without cognitive, balance, and gait impairments. Individuals were excluded if they reported any neurological, musculoskeletal, or other systemic disorders that would affect the subject’s postural control and/or gait functions. Participants were also asked about their medical history and if they were under a particular or permanent medical treatment. In this context, participants on sedative drugs, psychotropic medications such as benzodiazepines, antidepressants, pain killer medications like morphine and oxycodone were excluded. These exclusion criteria were established for safety (ability to safely follow instructions and complete the study). Additionally, the NASA task load index (NASA TLX), a clinical tool for measuring subjective mental workload and the Fatigue severity scale (FSS), A 9-item scale which measures the severity of fatigue and its effect on person´s activities, were used during the proposed protocol (Table 1). Demographic details and baseline clinical assessments are presented in Table 1.”
- Page 6, line 216-231: To determine feasibility, acceptability, practicality, and safety was used. However, only acceptability and safety are mentioned in the aim and displayed in the results. Results: Acceptability is a heading, but both acceptability and safety is displayed in the paragraph. I suggest changing the heading to “Feasiblity” and also include practicality, if you decide to include that in the aim.
Response: According to the reviewer´s comment, we included practicality in our first aim. Now the paragraphs of aims reads as follow: “The first aim of this study was to examine the feasibility, assessing acceptability, practicality, and safety, of the presented perturbation-based balance protocol to induce balance loss from perturbations under various environmental conditions in healthy older adults. We hypothesized that this overground perturbation-based balance protocol would be well accepted by the participants, and capable of inducing loss of balance in a safe environment. A second aim of this study was to test the validity of this novel perturbation-based balance protocol, comparing stability values and behavioral strategies used for the participants for each experimental condition included in this perturbation-based protocol”. Additionally, according to the reviewer´s comment, we changed the heading to “Feasibility” in our results section and included practicality in the same section.
- The results would be easier to follow if they were displayed in the same order as in method. Results about validity is missing (comparison between assessor and video).
Response: According to the reviewer’s suggestion, we now organized the results section in the same order as the method section. Now the heading of the outcomes in the method and result sections are presented in the following order: feasibility, behavioral outcomes, validity (biomechanical outcomes). “For validity, now we specified that we compared the behavioral outcomes with biomechanical outcomes. The paragraph reads as follow: Using the behavioral classification (no loss of balance or loss of balance) conducted by comparing the trial record sheet filled out during the experiment with the video recordings of each trial, biomechanical outcome measures (margin of stability, step length, and maximum trunk angle) were compared between natural walking trials, no loss of balance trials, and loss of balance trials”. Regarding the discussion, the comment from the reviewer was: “Discussion: Easy to read and well displayed!”. We got similar comments for the others reviewers. For that reason, we decided to maintain the organization of the discussion section, and discuses behavioral and biomechanical outcomes together.
- Conclusion: In the conclusion, practicality is mentioned. If this is included in the conclusion, results about practicality needs to be shown. How about safety?
Response: According to the reviewer’s suggestion, we now included practicality in our method section in the subsection “feasibility”. Additionally, we included comments about safety in the conclusion.
- Tables and figures: Table 1: there seems to be two headings, one above and one below the table. Explain all abbreviations used in the table.
Response: According to the reviewer’s suggestion, we now included all the abbreviation for table 1. Additionally, the information that was included in Table 1, now, in the new version of the manuscript, was separated in two tables (Table 1 and 3).
Author Response File: 
Author Response.pdf
Reviewer 2 Report
biomechanics-1775099
Assessing balance loss and stability control in older adults exposed to gait perturbations under different environmental conditions: A feasibility study
General Comments:
The paper is well written and provides a proof of concept for an already developed perturbation treadmill, but with novel environmental conditions.
The introduction is well written and cites appropriate literature. Please add NCOA statistics on fall rates in elderly, in addition to what has been already provided from a paper. Additionally, including the financial cost of such falls also from NCOA can further emphasize the problem statement in the introduction.
Was leg dominance established and used as a factor for slip and trip perturbations?
Results are well presented and extremely valuable to the scientific community researching fall prevention.
Specific Comments:
Abstract: Please add, “twenty apparently healthy older adults” in the abstract and if the abstract word limit allows, please add the participant age, height, weight, in Mean ± SD format in the abstract. (the Table 1 in the manuscript is good).
Introduction:
Suggest re-writing the line 57 - Reactive balance control involves feedback as well as feedforward mechanisms, as “postural control responses involves both feedback (compensatory postural responses - CPR) and feedforward (anticipatory postural responses – APR)”, since the word reactive used in the start of the sentence is emphasizing more feedback responses. Suggest similar change on line 86. The proactive balance terms used later in the manuscript as appropriate.
2.2. – Line 149 – Typo. I am assuming custom-made rather than costume-made.
Figure 1. Is the multisensory gait perturbation training as pre-built module in the Surefooted trainer?
Line 200 – NASA TLX and describe earlier in Table 1, which I think it first appears.
Line 223. – Same as above comment and Typo written as TXL rather than TLX
Table 2 – verify and re-write values as there is overlap of numbers on TripOBFoam.
I did see the Surefooted LLC had a prior STTR, but no funding received is mentioned for this manuscript. Just wanted to double check, if this specific project did not receive any funding from STTR (I do realize that this was few years back).
APPLAUD THE RESEARCHERS. VERY WELL DONE. THANK YOU.
Author Response
Responses to Reviewer 2.
- The introduction is well written and cites appropriate literature. Please add NCOA statistics on fall rates in elderly, in addition to what has been already provided from a paper. Additionally, including the financial cost of such falls also from NCOA can further emphasize the problem statement in the introduction.
Response: We thank the reviewer for this suggestion, now, we added NCOA data on fall rates in elderly in the first paragraph of the introduction section.
- Was leg dominance established and used as a factor for slip and trip perturbations?
Response: No, leg dominance was not established as a factor for postural disturbances. Now, we added this information in the method section.
- Abstract: Please add, “twenty apparently healthy older adults” in the abstract and if the abstract word limit allows, please add the participant age, height, weight, in Mean ± SD format in the abstract. (the Table 1 in the manuscript is good).
Response: We thank the reviewer for this suggestion, we included the sentence “twenty apparently healthy older adults” in the abstract. Additionally, according to the reviewer´s suggestion, we included demographics data of the participants.
- Suggest re-writing the line 57 - Reactive balance control involves feedback as well as feedforward mechanisms, as “postural control responses involves both feedback (compensatory postural responses - CPR) and feedforward (anticipatory postural responses – APR)”, since the word reactive used in the start of the sentence is emphasizing more feedback responses. Suggest similar change on line 86. The proactive balance terms used later in the manuscript as appropriate.
Response: We thank the reviewer for this suggestion, now, according with the reviewer´s suggestion, we modified the paragraph, and it reads as follow: “Postural control involves both feedback (compensatory) and feedforward (anticipatory) responses [16] which are required to trigger modification of the base of support (BOS) and/or counter rotation of segments around the body’s center of mass (COM) [17], to maintain postural stability during challenging conditions (e.g., perturbations) [18,19]. Error feedback information acquired from external perturbations is used to predictively adapt the locomotion to persisting or recurring perturbations in a feedforward manner [18,19]. However, such gait adaptation mechanisms may be less effective when participants are exposed to balance perturbations with high components of unpredictability [15], which is what usually happens before everyday falls.”
- Line 149 – Typo. I am assuming custom-made rather than costume-made.
Response: We thank the reviewer for noticing this typo error. Now the typo error was corrected.
- Line 200 – NASA TLX and describe earlier in Table 1, which I think it first appears. Line 223. – Same as above comment and Typo written as TXL rather than TLX.
Response: We thank the reviewer for noticing this typo error. Now the typo error was corrected.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear authors,
Despite the clarity of the introduction section, it is very long. Thus, reduce the information to the minimal necessary.
Please, provide a sample size calculation based on previous similar studies.
Was the sample balanced? Any homogeneity calculation?
I'm not sure about adherence. You need to provide more background concerning previous adherence protocols. In my experience, one session would not be able to provide this type of analysis. And if so, the authors shoulde make a statement about the bias interpreting data from a single session to conclude about adherence.
The statistical section is to large. Please, split in data synthesis (or data extraction), and statistical analysis. Also, make a statement concerning the asumption checks.
The results must show the actual acquired values (the graphic is not ideal for that). I suggest using the text for that (and keep the graphics). Also, the graphics are too small, so it is difficult to understand the significance. Please, correct for the next version.
Please, deposit the raw data in an online open repository to ensure transparency. As you do have many inferences from your results, this would be very recommendable.
Regards.
Author Response
Responses to Reviewer 3.
- Despite the clarity of the introduction section, it is very long. Thus, reduce the information to the minimal necessary.
Response: According to the reviewer´s comment, we reduced the extension of the introduction in order to improve clarity and make it easier to follow.
- Please, provide a sample size calculation based on previous similar studies.
Response: As Margin of stability is one of the principal outcome measures, we used this variable to estimate the optimal sample size. Using data from Patel et 2018 [21], in which the changes in stability values observed after the intervention showed a large effect size (0.80), the sample size was calculated with an acceptable alpha risk of 0.05, an acceptable beta risk of less than 0.8 and estimated loss of 5 % of participants. Thus, it was found that 20 participants were needed to achieve the aims proposed for this study.
- I'm not sure about adherence. You need to provide more background concerning previous adherence protocols. In my experience, one session would not be able to provide this type of analysis. And if so, the authors should make a statement about the bias interpreting data from a single session to conclude about adherence.
Response: We agree with the reviewer. We decided to make a statement about the bias interpreting data from a single session to conclude about adherence. We added this information in the limitation section. The paragraph in the limitation section reads as follow: “Another limitation of this study was that we reported data from adherence to the protocol, however it should be considered that the proposed experimental design included a single-session protocol. Among this line, there is a potential bias interpreting data from a single session to conclude about adherence. Similarly, our protocol only included healthy individuals. Future work should extend these initial findings to a larger group, including individuals who suffer from recurrent falls and/or neurological diseases.”
- The statistical section is to large. Please, split in data synthesis (or data extraction), and statistical analysis. Also, make a statement concerning the asumption checks.
Response: According to the reviewer´s comment, we split the statistical analysis section in two, data synthesis and statistical analysis. In addition, we reduced the extension of this section.
- The graphics are too small, so it is difficult to understand the significance. Please, correct for the next version.
Response: Thank you for the recommendation, for this version of the manuscript, we increased the size and font of the graphs to make them easier to understand.
- Please, deposit the raw data in an online open repository to ensure transparency. As you do have many inferences from your results, this would be very recommendable.
Response: Thank you for the recommendation, we will follow the journal instruction to do that, and make the raw data available for the readers.
Author Response File: Author Response.pdf
Reviewer 4 Report
Thank you for submitting your paper. If this paper is intended to show the validity of the equiptment and methods, it may be beneficial to cover some more detail on the construction of the system. Or if that has been published elsewhere, refer to that publication. This might also be helpful as detail supplementary information provided online.
The format of table 1, as well as it's location is a bit questionable. I generally don't expect to see demographics and results in the methods section. Also breaking it into pre-and post with a single point in time intervention doesn't make sense.
It is a bit unclear if the order of the 7 conditions were randomized.
The sentence: "Specifically, the perturbation onset was at the second 2.30 after participants start walking." is unclear and suggest that the timing / variation of the perturbation was NOT randomized.
I believe "the Surefooted trainer recognizes as time [z]ero (gait start) the moment of separation between two load cells located at the beginning of the safety rail and at the top of the participant's harness" some additional description would be helpful here as well. Do you mean "A load cell was used to detect when the carriage for the safety moved from it's initial position, this was also used to set the start time for the Surefoot trainer" or similar?
The description of the conditions is poor and unclear (for example, both condition 4 and 7 seem very similar). Perhaps a tabling showing the different hazards used in each condition?
The process and rationale for normalization of the MOS is unclear.
Whitespace between text in page 8 seems very inconsistent.
There is some error in Table 2 where the results for "TripOBFoam" are not legible.
Why isn't step length for trip trails presented?
Similarly, why isn't trunk angle presented for slip trials?
The swapping between 'forward platform perturbation' and 'slip' is confusing. I would suggest defining the 'slip' early on and using that.
Seems like a limitation if the maximum 'trip' displacement wasn't able to produce a loss of stability. Or if the rate of loss of stability for 'trip' is considered sufficient, maybe a lower magnitude of displacement for slip should be used.
Besides a few sections, the paper is well written overall. It is a bit verbose, and editing to reduce the overall length (without significant reduction in content) is suggested.
Author Response
Reviewer 4.
- Thank you for submitting your paper. If this paper is intended to show the validity of the equiptment and methods, it may be beneficial to cover some more detail on the construction of the system. Or if that has been published elsewhere, refer to that publication. This might also be helpful as detail supplementary information provided online.
Response: We thank the reviewer for the suggestion. Now we added more details regarding the interventional device. The paragraph regarding the interventional device reads as follow: “In this study, we utilized an overground moveable computer-controlled platform called the Surefooted Trainer, capable of inducing backward and forward perturbations on regular, slippery and foam surfaces with and without overlying obstacles with the aim of implementing a novel perturbation-based balance protocol in various environmental context (Figure 1). Participants were asked to walk over a 4 by 2 m costoume-made overground computer-controlled movable platform (the Surefooted Trainer), at their regular speed (Figure 1). Platform displacements were induced by the device software that moves the platform 33 cm forward and backward at 0.36 m/s seconds with an acceleration of 7.2 m/s2. The movable platform is placed over a 5 by 3 m static base (not movable platform). Note the platform allows two displacement settings 16 and 33 cm. To assess responses at the highest intensity we used 33 cm displacement for the study. For more details regarding the interventional device visit surefootedtech.com.”
- The format of table 1, as well as its location is a bit questionable. I generally don't expect to see demographics and results in the methods section. Also breaking it into pre-and post with a single point in time intervention doesn't make sense.
Response: We thank the reviewer for the suggestion. According to the reviewer comment, now we separated the Table 1 in two tables avoiding to mix demographics data with results. The information that was included in Table 1, no can be found in Table 1 and 3.
- It is a bit unclear if the order of the 7 conditions were randomized.
Response: The training conditions were not randomized. We clarified this information in the method section of the new version of the manuscript.
- The sentence: "Specifically, the perturbation onset was at the second 2.30 after participants start walking." is unclear and suggest that the timing / variation of the perturbation was NOT randomized.
I believe "the Surefooted trainer recognizes as time [z]ero (gait start) the moment of separation between two load cells located at the beginning of the safety rail and at the top of the participant's harness" some additional description would be helpful here as well. Do you mean "A load cell was used to detect when the carriage for the safety moved from it's initial position, this was also used to set the start time for the Surefoot trainer" or similar?
Response: We thank the reviewer for the suggestion. Now, we included the reviewer´s recommendation and added additional information to improve clarity regarding the perturbation time. The paragraph reads as follow: “Specifically, the perturbation onset was at the second 2.30 after participants start walking. The software of the Surefooted trainer recognizes as time zero (gait start) the moment of separation between two load cells located at the beginning of the safety rail and at the top of the participant's harness, which mean that the load cell was used to detect when the carriage for the safety harness moved from its starting position, and used, at the same time, to set the start time for the surefooted trainer. All the participants were naive to the type of perturbations included in our experimental protocol, and no practice or familiarization trials were included. And the training condition were not randomized.”
- The description of the conditions is poor and unclear (for example, both condition 4 and 7 seem very similar). Perhaps a tabling showing the different hazards used in each condition?
Responses: We thank the reviewer for the suggestion. Now we added a table with all the details for each experimental condition used in the protocol. Please see Table 3 of the new version of the manuscript. On the other hand, condition 4 include forward platform displacement trials (slip-like perturbation trials) over a foam and condition 7 include both forward and backward platform displacement trials (slip and trip-like perturbation trials) over a foam and with obstacles (elastomeric cables).
- The swapping between 'forward platform perturbation' and 'slip' is confusing. I would suggest defining the 'slip' early on and using that.
Response: We know that it would be easier to use the terms slip and trip-like perturbation in this manuscript. However, it has been strongly recommended to use the terms backward and forward platform displacement when the perturbation training protocol use a platform to induce disturbances. Even in this review process, others reviewers suggested to avoid the terms slip and trips.
- Seems like a limitation if the maximum 'trip' displacement wasn't able to produce a loss of stability. Or if the rate of loss of stability for 'trip' is considered sufficient, maybe a lower magnitude of displacement for slip should be used.
Response: We agree with the reviewer. According to our results the “trip” perturbation induced by the interventional device was not able to produce the same amount loss of stability than the “slip-like” perturbations. Additionally, for backward platform displacement perturbation trials (“trip-like” perturbations; TripOB, TripOBFoam, SlipTripFoam and SlipTripOBFoam), the MOS values were similar between loss of balance and no loss of balance trials (Figure 3), however when we assessed trunk angle during the loss of balance trials we observed that in those trials, the maximum trunk angle was higher compared to the no loss of balance trials which can be assumed as an indicator of instability (Figure 5). Among this line, it has been well described that after experience a backward perturbation (posterior displacement of the base of support), the forward compensatory stepping strategy contribute to a counter-clockwise rotational torque that help to arrest and reduce the trunk flexion angle observed after a forward loss of balance [20]. Thus, it is possible to assume that the more trunk flexion is observed after a backward perturbation, the more postural instability. This allows us to infer that the system was able to induce losses of balance during backward platform displacement perturbation trials, however in a lower magnitude compared to the slip-perturbation conditions. For this reason, we used trunk angle as an outcome for trip-like perturbation trials.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thank you for your revised manuscript, which is much improved. The authors have addressed all my concerns and I now think the manuscript is suitable for publication.
Author Response
We thank the reviewer for all the recomendations.
Reviewer 3 Report
Dear authors
The manuscript has been improved according to our guidance.
I have no further questions.
Regards.
Author Response
We thank the reviewer for all the recomendations.
