A Study on the Intersection of Ground Reaction Forces during Overground Walking in Down Syndrome: Effects of the Pathology and Left–Right Asymmetry

Round 1

Reviewer 1 Report

The intersection of ground reaction forces during walking is affected by Down syndrome condition but not by side during overground walking

This paper presented an important study of ground force reaction in Down Syndrome patients. The authors obtained an important finding that the virtual pivot point during walking in down syndrome is more anteriorly compared with healthy people. The study method is well presented and the paper is well organized. I have the following suggestion to improve this paper

 

1. The title is a full sentence, which sounds strange. I would suggest the title be changed to “A study of ….”

2. Figure 1 fonts are blurred, please fix them.

3. It will be great if the authors could provide more references for gait analysis for down syndrome in the introduction, which is not limited by GRFs.

Author Response

1. Yes, you are right. We have changed it to the following title: “A study on the intersection of ground reaction forces during overground walking in Down syndrome: effects of the pathology and left-right asymmetry”. 2. Thanks for the hint. There was a problem with the format of the figure and its conversion. This should now be fixed. 3. You are right, that would make the introduction stronger. The group of Manuela Galli and colleagues made significant efforts in studying gait of DS populations. This is not a widely diffused topic of research, but we mentioned a recent systematic review which should cover the main findings on the topic and added other references (e.g. reference 10).

Reviewer 2 Report

The goal of this study aiming to use the virtual pendulum model to unveil dynamic features typical of the pathological condition, as well as inherent potential bilateral asymmetries. Therefore, this was a very interesting investigation, but several problems remain:

1.      What’s difference between V irtual Pivot Point COM-COP inclination angle?

2.      Line 47-49. Not clear. Please confirm and revise the sentence.

3.      Line 70-71. “although there is not much literature about the GRFs in DS”. I disagree.

https://scholar.google.com.tw/scholar?hl=zh-TW&as_sdt=0%2C5&q=down+syndrome+gait&oq=Down+Syndrome%2C+ga

4.      Line 91. Figure 1. In force plate is not clear.

5.      Line 98. The participant’s years is wide range. Please explain the purpose?

6.      Line 124 How much is sample rate about force plates?

7.      Line 132-141. In this study have two force plate need to depiction more detail about setting. More detail about symmetry angle, such as force plate 1 heel strike and toe off in symmetry angle.

8.      Line 144 Why not control the gait speed? The walking speed 0.7 and 1.5 m·s-1 is wide range. Will this affect the purpose of the experiment?

9.      Line264-275. Is there any literature to support the argument of this paper?

10.   Line243-246. But in this study did not calculate moments.

11.   Line272-289. Discussion should add more narrative.

12.   Line272-290. Research limitations?

13.   Line315-317. Need deled

14.   Line319-323. Need deled

Author Response

1. Thank you for the question. In contrast to the VPP, the CoM-CoP inclination angle does not consider the ground reaction forces. For the VPP calculation, we use a CoM-centered coordinate system. Here, we consider (for each instant of measurement) a) the ground-reaction-force-vector (GRF) starting at the (CoM-centered) CoP. Additionally, we compute a point (the VPP), where the distance to each GRF vector as calculated in a) is minimal for the whole measurement time. Then, we calculate b) the angle between the GRF and the vector, that points to the VPP, both starting at the CoP (in a CoM-centered coordinate system). The vectors of a) and b) are illustrated in figure 1. We hope that explained the difference sufficiently. 2. You are right, the sentence was difficult to read. Now it reads: “In clinical gait analysis, models and specific variables that describe important walking characteristics can help to identify critical impairments that are often hidden within general behavior; the impairments are hardly appraisable under the “overwhelming amount of available motion data” [12,13].” 3. Thank you for your suggestion of more literature. Unfortunately, neither in our previous intensive research nor via your suggested link did we find (English-language) papers that provide information on the ground reaction forces during walking of DS patients. We would be very pleased if you could provide us with concrete papers, because we would be happy to use this information to improve our paper. 4. Thank you for the hint. The format of figure 1 is now changed, there was probably during the conversion of the file. We hope that this has solved the problem. 5. Thank you for the question. In our study, we evaluated data from previous measurements that included this age range. Such an age span is wide, as noticed by the Reviewer. However, we included just a single patient aged 6 years (who met the inclusion criteria), and only 5 aged less than 10 years. In fact, the DS group was 2 years older than healthy controls; this also compensates in a way the delayed development of people with DS. However, we changed the description-section of the participants that this will be also clear to the reader. We included subjects with different ages (and from a wide age range) because we estimate the influence of age on VPP to be small, since body proportions are taken into account in the CoM calculation here. Rather, we saw an advantage in studying as large a sample of subjects as possible. Nevertheless, we have included this objection in the limitations. 6. We added the sample rate in l.126 as follows in the manuscript: “One complete gait cycle (comprising one right and one left step, i.e., from an heel strike to the subsequent heel strike for each leg) per patient was detected by means of two force plates (sampling frequency: 1000 Hz; Kistler, Switzerland) positioned halfway down the walkway and embedded on the floor.” 7. We added some details about the laboratory setting. However, there’s no particular relationship between the symmetry angle and the order of heel strikes. 8. The Reviewer is correct, gait speed in principle could alter results. That is why we considered gait speed as a covariate in the statistical model we applied – see l. 160. We found no significant speed effect (Table 2). 9. Thank you for the question, now we have added literature to support this argument (l. 264). 10. Yes, you are right. However, we refer here to the connection between the forces and the moments reported in the literature, which we had pointed out in the introduction with the following sentence: “Additionally, this reduced peak plantar flexion leads to a lower second peak in the horizontal (x) and vertical (y) GRFs [27,28]. These lower forces have actually been reported specifically for DS patients (horizontal GRFs [9], vertical GRFs [29,30]),[…]” 11. We appreciate your suggestion to add more narrative to the discussion section. We took your comment into consideration as we revised our manuscript, providing a more comprehensive explanation of our findings and their implications in the context of previous research and current knowledge. 12. We already have a small section concerning limitations in the discussion section 4.1. (l. 250-257) However, we have now added more general limitations in the Conclusions section: “A limitation of the study concerns the comparison of the different groups. Here, factors such as step length, frequency, duty factor and age could have an influence on the VPP, which were not controlled in detail. Additionally, the sample size is relatively small and the results should be validated in subsequent studies with larger samples.“ 13. Done, thank you for the hint. 14. Done, thank you for the hint.