Effects of Obesity on Adaptation Transfer from Treadmill to Over-Ground Walking

Round 1

Reviewer 1 Report

This is valuable work with an interestingly planned experiment. Your work could facilitate rehabilitation for people with obesity.

Comments for author File: Comments.pdf

Author Response

I have attached a pdf of my responses to your comments below.

Author Response File: Author Response.pdf

Reviewer 2 Report

Overall
Thank you to the authors for submitting this study, I enjoyed reading and reviewing your work. The study presented in this manuscript is a significant contribution to the literature, is novel, and tries to address an issue about understanding our ability to adapt gait of people who are obese to improve physical activity. The overall readability and flow are good, the larger problem reduces to a couple of questions with good hypotheses, there were sound methods, well-presented results, and a good discussion. I think there are major and minor issues to address in each section but nothing that disqualifies the manuscript or requires further collection of results to publish. Below are my major and minor issues per section with suggestions and justifications for correction.
Introduction Major
I think the introduction is good overall, but I think the theoretical foundation could be strengthened by addressing the issues below.
Lines 36-37: I do not think the gait characteristics presented (shorter and wider steps, maybe slower) increases susceptibility to falls but actually are ways of improving stability. Gait may be changed in response to obese people feeling less stable, having a smaller margin of safety, or being more likely to fall but those characteristics are not increasing risk. Also, the link or causation you try to draw from fall susceptibility to interfering with daily activities to decreased independence are too much. If obese people have activities that include frequent sedentary behavior and level walking, they probably can do them. Depending on financial means, they most likely can transport themselves around where they want to go. All of this to say, they may limit themselves to be more active and do harder tasks, and in severe circumstances have difficulty traveling, but interference with daily activities and independence is not well supported by the current writing.
Lines 49-50 “Taken together…require walking” is a sentence that needs softening, related to my comment above. I think obese people may have difficulty with new activities and more strenuous activities, but if they have developed sedentary behavior, then daily activities are probably fine. If you are talking about people who are morbidly obese or have obesity that is a clinical problem, they have difficulty with activities like prolonged walking to do groceries, but that is a different walking activity than short bouts of walking which are most common for everyone. Maybe providing examples of walking activities that would be difficulty would strengthen your argument.
Line 65-66: Populations with neurologic asymmetry (stroke) and structural asymmetry (amputation) and general neurologic issues (Parkinson’s) are mentioned but are these the best comparisons to obese people. Obese people do not necessarily have those issues, trying to avoid them before occurring with a PA intervention, so maybe there is other literature that makes a better connection to obese people.
Lines 71-79: Not an issue, I liked this paragraph how you distilled your argument down and present how your work in novel by looking at transfer/washout to over-ground walking.
Introduction Minor
Lines 33-34: This is an issue repeatedly through the manuscript, using “i.e.,” or that is in parentheses when what it is can be stated directly. I would delete “weight-bearing activity” and say walking, because there are many weight bearing activities, walking is one of them, but I do not think you are referencing other weight-bearing activities.
Line 34: Delete “One” and start with “Common characteristics”
Line 35: Delete “atypical walking with” and say “obesity are slow, shorter, and wide steps”
Line 40: Remove “novel” and replace with another word or just remove, because surfaces with obstacles (e.g., curbs) or slopes are not novel for most. Hiking uneven terrain with significant elevation change may be novel to them.
Line 42: Delete “serious” because based on the example you give afterwards about greater toe clearance, I do not think that is serious, more of an energetic consequence that avoids a toe hitting an object and therefore avoiding a more severe consequence, so they did adapt a safe pattern in the cited study
Line 45: Delete “their” to avoid possessiveness when possible
Line 47: “aftereffects” is vague, what is happening? Do patterns persist, like maintaining a greater stride frequency after fast metronome or does is reverse to slower?
Line 59: provide a citation for sentence that ends with “…faster than the other.”
Line 65: This is a personal preference, but I would not say patients, because to be a patient you need to be under someone’s care, but individuals/people have characteristics that we want to change/adapt even when not a patient.
Lines 82-83: “adapt both spatial and temporal walking patterns” is vague, we all adapt patterns, but what is changing that makes it different than a preferred walking pattern
Methods Major
Well written and overall strong methods, with a few issues that if addressed, could strengthen the paper. I also present questions that I had when reading it a couple of times, that if clarified, could help inform the reader of your thought process.
Lines 102-103: Why did you have participants do the conditions barefoot? Why not wear daily use athletic shoes? This is a perturbation for most people because we wear shoes for daily tasks, and some wear them in the house too, and it may exacerbate changes to walking
patterns and be uncomfortable for 40 minutes of walking on a hard surface (and yes, the Bertec split-belt TM, is hard). Please clarify and expand why you choose this for the reader.
Lines 105-110: Please clarify instructions for preferred walking speed determination, did you ask them to walk at a comfortable speed? A preferred speed? Instructions will influence what pattern they choose and cite a study that uses this method if applicable.
Lines 129-133: “During treadmill…felt unbalanced.” This passage could go after line 112 ending in “Figure 1).” for chronological order with treadmill instructions.
Methods Minor
Lines 94-95: “having no hip…past 90 days.” When you say most, did you quantify this or just ask about most days and let the participants report, because 46 out of 90 days without pain is most but significant. Improve vagueness for clarification.
Line 119: Consider usage of “limping” here and below, because it is usually associated with injury. Maybe say “visible inter-limb difference” or something similar.
Lines 135-136: Instead of describing the spatial and temporal coordination tasks in parentheses, maybe say what they are doing (what is in the parentheses) and put “spatial coordination” and “temporal coordination” in parentheses.
Line 148: delete “a” in “indicates a perfect symmetry.”
Line 150-155: Is this transfer index new? If not, cite a study that used it or provided inspiration for it.
Lines 179-181: cite a study(ies) that create these definitions for effect sizes, because how large of effect something has is defined differently, for example Cohen versus Sawilowsky 2009
Results Major
The results are interesting, well-written, and have a little feedback in regards to corrections/suggestions.
Figure 2: The light gray lines in the figure do not come out well on the screen or when printed with a color printer, change the shade for visibility. What do you think about how obese people having a faster rate of adaptation towards DST symmetry in both the initial adaptation and then re-adaptation conditions? Based on the data presented, it looks like they get there faster, maybe because it is more uncomfortable for them to walk with DST asymmetry.
Comment/question on data in figure 2 and 3: What is the effect of the spread on the data for obese participants with BLo and EWo? Are there outliers or a lot of variability?
Comment on figure 3 and transfer index in general: I have read this section 3+ times and cannot wrap my head around the transfer index and keep that in my mind with some of the questions
that follow. In general though, if it is not clear with multiple readings on my end, it may need clarification for future audience of this paper.
Results Minor
Line 235: You could indicate shading of color as well in the paratheses with left and right to reinforce the legend.
Figure 3: You frequently present DST before SL, including in figure 2, for continuity, I would present DST on the left in figure 3. One less thing for the reader to think about.
Discussion Major
Overall, the discussion is good, and your passages are well founded by the results.
Lines 262-263: “The adaptation…with normal weight.” Doesn’t this passage contradict Figure 3? Please clarify this statement and delineate it from the transfer index.
Lines 263-267: “This provides…strategy.” I do think your results support previous findings, but I do not think you can make the connection that the changes are necessary unless you perform some measure that validates the changes. For example, weight loss or increased PA after making these changes.
Lines 275-277: “Therefore, this…with obesity.” Contrary to my previous comments, I think this statement is well founded and supported by the results and previous literature.
Lines 287-292: I think you need to expand on your idea about enforced absolute speed versus preferred gait speed. If you enforce absolute speed, then you have a speed effect/perturbation in addition to adaption to split-belt conditions. In special populations, providing multiple deviations from preferred adds complexity and difficulty with interpretation. I was wondering if a training paradigm with velocity manipulation alone could help with PA and gait changes that are closer to normal-weight gait.
Lines 298-302: “Considering that…treadmill walking.” I think this passage is spot on.
Line 304: Are legs moved passively by the split-belt, more accurate to say treadmill powers/moves legs, something Sanchez and Finely discuss in their paper about using the belts to lower metabolic costs.
Lines 305-306: Rough transition from one paragraph to the other
Lines 306-309: Get to the point that you make in “In other word,…treadmill walking” faster rather than introducing it with previous sentences. I understand that you are trying to build it up with previous evidence, but it is choppy.
Lines 311-315: “However, altered…gait parameter).” I think this is a rough/less-founded connection by your previous statements. This paragraph in general was the roughest read for me. I think there are good points, but it could be connected better.
Lines 316-324: General comment about idea split-belt treadmills in rehabilitation, and something I have thought about before, are split-belt treadmills realistic and viably in most clinic settings someday?
Lines 327-329: I think that your results are less generalizable to obese people with multiple conditions, but it is also a strength of your study that people did not have those issues and therefore could have had more confounding variables to explain the differences between groups.
Lines 329-330: Please expand why the difference in male versus female participants is a limitation, how might have this affected your data/findings?
Discussion Minor
Line 282: provide a citation for sentence ending “…gait symmetry.”
Lines 292-295: Wording is confusing, “initial” at the beginning of the sentence but then stating “entire testing conditions” at the end, it seems you are referencing two separate pieces of the results.
Line 296: provide a citation for sentence ending “…with previous findings.”
Line 320-321: Re-write to say more directly, like this “In the current study, participants reduced step asymmetry in both treadmill…”
Conclusions Major
Lines 334-337: If I read the first two sentences and not the entire article, which many readers initially do before investing time to read the entire abstract, I would be confused by your findings. They seem like to contradictory statements, even though you are stating your results, but that would not be clear to readers who do not read the entire paper.

Author Response

I have attached a pdf of my responses to your comments below.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments for Editors:

Overall, the study is interesting and well conducted and well written. In addition, it has possible implication for further and deeper studies in the field of obesity treatment. However, the methodology needs to be better explained to allow reproducing the study. Conclusions should agree between the abstract and the text.

Comments and suggestions for Authors:

Brief summary:

This study deals with the gait adaptation and tranfer from treadmill walking to over-ground walking for both obese and normal weight people. A protocol consisting of a combination of walking on the ground and walking on a treadmill with the two feet at the same speed or at different speeds was performed. The step length symmetry, double-support time symmetry and tranfer index were evaluated. A comparison between the two groups (obese and normal weight) was done to assess weight effect. A comparison between different protocol stages was done to assess the degree of adaptation, test storage and test memory. Results showed that both groups had temporal adaptation; in particular, both groups: (i) had perturbed walk when the belts were first split, (ii) had aftereffects, (iii) had smaller errors in the re-adaptation period. However, comparing the groups differences were found: (i) greater double-limb support time symmetry was found for obese compared to normal weight in the washout period (when the perturbation is removed), (ii) transfer index for double-limb support time symmetry was less in obese adults than in normal weight adults.

Broad comments:

Title and abstract

The abstract is informative about the study since briefly reports the research question, methodology, results and conclusion. Takling about the transfer of aftereffects (line 17), the term ”greater” is correct or should be ”less”?

The title should be more specific concerning the topic of the study (transfer walking adaptation from treadmill to over-ground walking).

Introduction

The introduction is overall clear, since it guides the reader towards the research question. A good use of the existing literature is done in order to present the background of the study and to introduce the aim. However, when altered walking characteristic of obese individuals are reported to support their risk of falls, other than spatio-temporal characteristics also altered joint kinematics (with respect to normal weight people) can be mentioned. For example the following studies can be reffered:

• DeVita, P., & Hortobágyi, T. (2003). Obesity is not associated with increased knee joint torque and power during level walking. Journal of biomechanics, 36(9), 1355-1362.
• Agostini, V., Gastaldi, L., Rosso, V., Knaflitz, M., & Tadano, S. (2017). A wearable magneto-inertial system for gait analysis (H-Gait): Validation on normal weight and overweight/obese young healthy adults. Sensors, 17(10), 2406.

The research question is clearly declared: if adaptations to split-belt treadmill walking and tranferring its effects to over-ground walking is showed also in obese people. However, references to support the hypotheses should be indicated. For example, do the hypotheses based on nomo weigh adults results?

Materials and Methods

Concerning the methods some aspects should be clarified as reported in the following comments to allow to replicate the study.

The equipment description should be more specific. Was the pressure-sensitive gait carpet used fot the over-ground walking? In addition, information about what was collected with the two acquisitions systems for the ground and treadmill walking should be indicated (Force? Pressure?).

In the experimental protocol, during the over-ground walking, did the participants walk on the carpet only once or back and forth more times until they received the prompt ”stop”? This should be specified.

In the split-belt condition, explain why was chosen the belt under the right (and not the one under the left) lower limbs was moved slower.

How were defined the duration of the wash out tield-belt condition (5 minutes) to recover the symmetric walking and the duration of the second split-belt condition (5 minutes) to verify the re-adapt time? Is there a reference as for the duration of the first split-belt condition?

Specify how much time was required to adapt (reduce or increase) velocity of the right split-belt in the split-belt condition.

Did the participants also receive instruction on the upper limbs movements during the test?

Data analysis in the present form is slightly confusing. Firstly, clearly indicated which variables were used to assess spatial coordination and which for temporal coordination (list the variables). Then, describe how each variable was calculated from acquired data (or refer to a previous study in which it was already described) and how indexes were calcualted based on variables. Finally, stated which variables and indexes were calculated for the different walking conditions, such as ground/treadmill, tield-belt/split-belt, and early/late.

Results

Results are overall presented appropriately avoiding information repetition between the text and the figures. In addition, it is clearly indicated the practical significance of the results.

Walking speed should be moved from table 1 to the results section.

To increase the figures readibility, in the captions report what ”*” and ”**” stand for. Move the figures and the table 1 along the text instead of in a separate paragraph.

Discussion

Overall, the results and their implications have been discussed in comparison with the existing literature. However, additional comparison with the existing literature (also on healty adults) could be done when suggestion for future use of treadmill is reported (lengthen or quicken stepping movements or manage new constraints) because it is the main point of the study.

An interesting discussion was done on the initial double-limb support times of slow (right) leg and fast (left) leg was done; however, nothing was reported concerning these variables in the results.

The authors investigates and described two possible limitations for the study, which allow to look for further studies. Concerning the limitations, do the authors expect a difference in transfer and adaptation due to the gender?

The conclusion should briefly sum up the main aspects of the study, then report the main findings (both similarities and differences) and implication. Similar conclusion should be found in the text and in the abstract.

Specific comments:

• Page 2, lines 56-59: ” Previous research on split-belt treadmill walking adaptation in healthy adults has demonstrated that step length and double-limb support time are asymmetric during an initial adaptation period when belt speed is changed so that one belt moves faster than the other.” add a reference. Do lines 56-62 refer to the studies [15-16]?
• Page 2, lines 81-82: ”both groups (normal and obese BMI groups)” simply report: ”normal and obese people” because it has not been said that in this study there are two groups yet.
• Page 2, lines 89-91: ”Spatiotemporal walking data were collected at the Motor Development Lab and the Human Adaptation Lab in Sargent College, Boston University, from July 2019 through November 2019.” should be moved in the ”experimental protocol”.
• Page 3, lines 137-139: ” The primary measurements were step length and double-limb support time for both legs, which were expected to change robustly when exposed to the split-belt perturbation [15].” should be moved in the discussion.
• Page 3, lines 139-141: The step width was calculated but then no analysis was done with this variable and results are not reported.
• Page 4, lines 173-178: this part should be moved in data analysis.
• Page 8, lines 263-267: should be moved towards the conclusion.
• Page 8, lines 295-298: ”This finding suggests that temporal gait is affected by obesity, consistent with previous findings” add references.
• In table 1, why waist circumference is indicated since it has not been used in the study?

Author Response

I have attached a pdf of my responses to your comments below.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Please see attached PDF for my comments.

Comments for author File: Comments.pdf

Author Response

I have attached the second response letter to reviewer 2.

Author Response File: Author Response.docx

Reviewer 3 Report

Specific comments

Page 2, line 64: Change “walkers exhibit aftereffects[16,17].” with “walkers exhibit aftereffects [16,17].”

Page 2, lines 84-88: It would be clearer for the reader if the hypotheses are directly supported by the references. Since you said that the hypotheses are based on references 12-14, add them to the text.

Page 3, line 115: Specify that within each of the four treadmill walking condition the speed of the treadmill was constant; thus, the transition phases between tied-belt and split-belt (and vice versa) were discarded for the analysis.

Page 4, lines 145-147: Report in the text how center of pressure, heel strike, and toe-off were calculated for over-ground and treadmill walking.

 

Author Response

I have attached the second response letter to reviewer 3.

Author Response File: Author Response.docx