-->PONE-D-25-62280-->-->Does asymmetry in the activity of the upper trapezius muscles contribute to neck pain during work?-->-->PLOS One

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Reviewer #1: Partly

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

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Reviewer #1: the asymmetry in upper trapezius active as a source of neck pain is an interesting hypothesis

General comments:

the paper is well written. the effort to combine and extract asymmetry information form a very large data set is commendable. However, This reviewer, like the authors, has a doubt on the conclusion "that

asymmetry in the very low levels of muscle activity (muscular rest and static activities) may.increase neck pain intensity". In several instances the authors , apparently, provide information relative to other studies or within their own results that asymmetry may not be the issue and that other factors may be masked, rendering the statistical analysis difficult to interpret since causality may not be as hypothesized. Hence, asymmetry may be too strongly emphasized.

As several of the authors have already provided ample support to the relationship between sustained low level of muscle activity and pain and the alleviation of pain by intermittent higher levels of muscle activity then it may be suspected that these phenomena are likely the major underlying mechanisms leading to pain and not so much asymmetry. It would be important to reflect mode adequately the title "Does asymmetry..." to attenuate the responsibility of asymmetry or to provide stronger evidence concerning "asymmetry"

minor comments:

L105-6 strange syntax "was anonymized accessed"

L212 "Participants had" suggestion: the average age of .......

in this study, is the description of population a real results or a part inherent to the methods??

L215 the sentence is missing something or " respectively" is not sin the correct place. Suggestion : On average participants rated neck pain intensity xx and YY in X-sec and in Long. studies, respectively

L217. the average (is it an overall average over all participants

L219 in relation to "their respective" MVIC

L217-20 considering the noise in signals (even after reduction process) and noise in the motor drive, are the differences a reliable indication of asymmetry (see general comments)

l263 "our"study" /present study; and "was with values" ( awkward form)

L264 same remark as before about syntax and use of respectively (something missing)

L267-70. this hypothesis should not be proposed since it has no basis of support. (IF").

L277 after manual task may add ref to strength support of argument

L277 "day spent in .. muscle activity" syntax please

L280 "the study calculated" certainly not, but YOU did

L282 "center" may not be appropriate word

L284 since study included diverse populations this can be added to strengthen argument (as indicated by the authors latter on)

L291 "Paradoxical" it may not be a paradox since data suggest that higher activity as opposed to static low level has a beneficial effect on(it has been suggested that disruption of monotonic activity by higher activity ( change in recruitment) is beneficial.

L298 this send back to comment about asymmetry (may be sustained low level not appearing in asymmetry computation)

L297-302 see comments about asymmetry ( as presented it may be misleading/biased)

L310. confounding factors. _indeed agreed so see comment about prudence concerning asymmetric assertion. the 2 paragraphs may come late since they contribute to cast some doubt and weaken the proposed conclusion

L 377. indeed the VAS transformation may have biased pain intensity measure

L402 the authors recommend caution but not strongly enough since conclusion does not

Reviewer #2: Does asymmetry in the activity of the upper trapezius muscles contribute to neck pain during work?

This manuscript investigates the association between asymmetric activation of the upper trapezius muscles during the workday and neck pain intensity using pooled electromyography (EMG) data from several Scandinavian research institutes. The study includes cross-sectional (n = 530) and longitudinal (n = 256) analyses and evaluates asymmetry across different muscle activation levels relative to maximal voluntary isometric contraction (MVIC).

The study addresses an interesting and underexplored question regarding bilateral muscle activation patterns in occupational settings. The dataset is relatively large and includes diverse occupational groups with full-day EMG recordings. Overall, the manuscript is well written and clearly structured.

Below are some suggestions that may help improve the manuscript.

Abstract

Your study is largely cross-sectional with limited predictive power. The following claim may therefore be too strong: “asymmetry in the higher levels of muscle activity appears to be protective against neck pain.” Please consider using more cautious language, such as “may be associated with.”

Given the limitations of the study, you may also consider adding a sentence such as:

“However, the explained variance of the models was small, and the results should therefore be interpreted with caution.”

Introduction

Is the difference between asymmetry and co-activation clearly explained for the reader?

At the end of the introduction, please consider clarifying your hypothesis. For example:

“We hypothesized that asymmetry …”

Methods You combine datasets from seven institutes. While this is a strength, it may also introduce heterogeneity. Please consider providing more information on whether the measurement protocols were identical across sites and whether potential study-level differences were accounted for in the analyses.

You also converted different scales into VAS values. Since ordinal scales do not necessarily represent equal intervals, please consider adding a short justification for this decision.

Results Statistical significance is reported, but the effect sizes are not interpreted. For example, the β and R² values appear small. Although you acknowledge that the explained variances were minimal, this should also be more clearly highlighted in the Results section.

In addition, the Results could more clearly distinguish between cross-sectional and longitudinal findings. The longitudinal results appear weaker and could be emphasized as such.

Discussion You propose that asymmetry during higher activity levels may be beneficial. While this is an interesting interpretation, it remains speculative. Please consider adding a clearer caution, for example: “These interpretations remain speculative and should be confirmed in future experimental studies.”

You correctly discuss the possibility of reverse causality. However, given its importance, it might be useful to introduce this limitation earlier in the discussion.

You report that smoking had a negative association with neck pain. This is a somewhat surprising finding and may warrant a more thorough discussion.

Although you acknowledge that the explained variances were minimal, this limitation could be discussed more explicitly.

Conclusion The current conclusion “asymmetry in higher activity appears protective against neck pain”—may be too strong given the low explained variance, mixed results, and the design of the study. Please consider softening this statement.

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Reviewer #1: No

Reviewer #2: No

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Is asymmetric upper trapezius muscle activation during work associated with neck pain? A cross-sectional and longitudinal analysis.

PONE-D-25-62280R1

Dear Dr. Koch,

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Kind regards,

Gianpiero Greco

Academic Editor

PLOS One

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