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some spelling errors, typos

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sentences are sometimes too long

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stick with one "order", e.g. you speak about "relation between PA and frailty", then don't switch to speaking about "association between frailty and PA"

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frailty assesment part: get more directly to the point :-)

PA-part: reduce info to advantages, provide references only, not repeating results from studies

Intro in general a bit long

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less abreviations

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(gait performance, - function, - capacity)

ambulation vs. gait?

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Roter Faden not visible

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a bit jumping between thoughts in Intro

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Not sure if I over-read it, but I did not quite understand how your clusters were defined and why you use them

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make it fit to readership

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Material section - I did not immediately understand which measurements you use and what you measure how. Maybe state them all shortly more clear ?

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Could be clearer what's the benefit of knowing the relation between self-reported frailty and objective PA. What can we do (better) with it?

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writing style/language: somtimes long sentences, unnessecary use of words like "Additionally","Therefore"

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I had to read over your hypothesis a few times - maybe you can make them more clear?

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The match between aim, hypotheses, methods, results, discussion was only partially clear; I couldnt easily find whether key hypothesis were confirmed or rejected, questions answered

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Sometimes I believe your paper would profit from more explanation, maybe even simpler explanation, less abbreviations. As a non-specialist in that field I believe some things were hard to understand.

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frailty assessment introduction might be a bit to detailed

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frailty assessment introduction might be a bit to detailed

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I liked the writing style

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Good use of academic language and terms.