Squat Lifting Imposes Higher Peak Joint and Muscle Loading Compared to Stoop Lifting

Round 1

Reviewer 1 Report

Authors presented a good study on differences between two primary methods of lifting, i.e., squat and stoop lifting.  The draft is well-written with a clear description of the method/analysis.  The main concern is about the lack of depth in the discussion section and the message that this draft would convey. Authors, in the Introduction section, discussed the compression and shear forces; however, the topic was not really followed through the rest of the manuscript. It is essential to discuss the differences in compression/shear forces between the two methods.  Moreover, considering the maximum moment as an important measure, it is expected to have an extensive discussion and include the findings of many other studies in the field. Authors briefly acknowledged the contrast of findings in the current study with the body of literature.  Since there is almost a consensus in the literature about the differences between the effects of stoop vs. squat lifting on low-back; the reported contrast is surprising, thus need substantial discussion for clarification purposes.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the authors investigated the effect of squat and stoop lifting technique on musculoskeletal loading. To satisfy the requirement for publication, some improvements of the paper should be made.

Major comments:

First, since the comparison of kinematics and kinetics of squat lifting and stoop lifting has already been made in some existing studies, the authors give more clearer description of the novelty and contribution of this paper in the Abstract and the last paragraph of Introduction.

Second, in this paper, the authors defined squat lifting as “performed with fully flexed knees and heel lift-off”. Is this definition of squat lifting widely accepted? Is there a reference? As I know, the definition of squat lifting in reference [10] is "the one in which the knee joints are fully flexed and the trunk is held as vertical as possible", where vertical trunk posture (i.e. small hip joint movement) is emphasized. Performing squat lifting with different ways may result in bias results with previous studies.

Third, why did the authors select 40% ALST as the other weight apart from 10 kg for test? The average value of 40% ALST was 12+/-4kg, which was quite close to 10 kg. For some subjects, these two weight might be very similar, which makes the comparison of the results with different load weights unconvincing. It is better to select two weights such as 20% ALST and 40% ALST, or 10 kg and 15 kg.

Minor comments:

1) Line 38 and line 107, “more specific” should be revised as “more specifically”.

2) Line 43, I think “0.2 lifts per minute” should be revised as “0.2 lifts per second”. Please have a check.

3) Line 134-135, why 0.25m/s is used as the threshold to determine the start and the end of lifting and lowering phase? Is there any reason?

4) Line 138-139, more details about the metrics used for evaluating lifting movement should be given. It is unclear how these metrics are calculated.

5) For figure 2 and figure 3, it is better to plot the average results of all the subjects rather than a representative subject. Because it is unknown whether descriptions of the results of the representative subject in line 147-156 also works for other subjects. In addition, when the authors described the results, it is better to cite corresponding subfigure, which makes it easier for readers to follow.

6) Apart from joint moments and powers, joint angles should also be reported.

7) For Figure 4 to 7, the authors should explain what the error bars denote.

8) The texts in figure 7 are too small to read.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors have addressed some of my concerns. However, I still have some comments.

1) Since the authors have already report the results of 40% ALST trials, what is the meaning of reporting the results of the 10kg trials? It is better to give more explanations. Otherwise, it will make the readers confusing.

2) There are several figures in Appendix B. The authors should describe it more clearly which figures are exactly cited, instead of simply referring to Appendix B.

3) In the second paragraph of Section 3.1, “Weight of the box only affected the L5S1, hip and elbow moment during stoop lifting (Appendix B)”. This conclusion is not convincing, because the authors did not compare the results using several boxes with obvious differences in weight. I suggest the authors to add experiments with 20% ALST.

4) Although the authors have checked the "0.2 lifts per minute" issues, I still think it is necessary to double check it on other references. Because "0.2 lifts per minute" means it takes 5 minutes to finish one lift, which is unreasonable.

5) For Figure 2, Figure 3, and the figure in Appendix A, it looks better if the black curves covering the shade regions are removed.

Author Response

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Author Response File: Author Response.pdf

Round 3

Reviewer 2 Report

I have no other comments.