Toward Clinically Feasible Assessment of Muscle Mass: Validation of a Seated Bioelectrical Impedance Device Against Dual-Energy X-Ray Absorptiometry (DXA) in Older Adults

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The Authors presented a very interesting and important study from the perspective of clinical practice.

They demonstrated that seated bioelectrical impedance analysis (BIA) provides clinically acceptable estimates of appendicular skeletal muscle mass (ASMM) in older adults.

In my opinion, however, a fundamental flaw in this study is the analysis of results for the total group ( regardless of gender). Presenting mean values ​​in Table 2 (height, weight, BMI, etc.) for a combined group of women and men is inappropriate, given the known existence of significant sex-related differences across most parameters. Although the female-to-male ratio was maintained when comparing healthy and sarcopenic participants, it remains unclear whether the same level of agreement between BIA and ASMM results would be observed in both women and men.

The Authors provided different cut-off points for low chair stand strength, handgrip strength, and low muscle quantity for women and men in Table 1, confirming the existence of significant, sex-dependent differences. However, further analyses were conducted jointly. I believe that the analysis should be adjusted for sex and age, as the age range was very wide (60.37–94.29 years). It seems also worthwhile to verify whether the Kyle or Sergi's equations yield similar results in women and men.

Furthermore, the group is relatively small and diverse in terms of age and gender, which may influence the results.

The Authors did not make full use of the relevant literature in the ‘Introduction’ and ‘Discussion’ sections.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

An interesting study, but in my opinion, it is more suitable for a medical journal rather than a technical one, since no new methods of measuring or analyzing data were proposed here, just a comparison of two devices and statistical processing of the information obtained. There were also several questions and comments about the text:

1) In section 2.3 Assessments and measurements, - Then, body composition was assessed using DXA with the STRATOS dR densitometer (DMS Imaging), a non-invasive imaging technique associated with very low radiation exposure. I would like to see more technical details about this method, why it is considered a reference, but not very convenient to use.

2) The measure of Appendicular Skeletal Muscle Mass from the DEXA in kg (ASMM DEXA) and Appendicular Skeletal Muscle Index in kg/m2 (ASMI DEXA) was then used in the analysis - as far as I understand, it was these two parameters that were later compared when using two devices, and this is the whole point of the study, the question arises, what is the scientific novelty of such a study in the context of the topics of the journal Sensors?

3) BIA was performed using the Biody XpertZM 3 device. This non-invasive system is equipped with four integrated electrodes and allows measurements to be conducted in a seated position, with electrodes placed on the fingers and the heel, just below the malleolus, enabling whole-body assessment. - I would also like to see more technical details about the device used. This raises many questions about the quality of the recorded signals if embedded electrodes are used, since the quality of the recorded signals directly depends on the quality of the electrode-skin contact, while the skin condition in elderly patients may also vary greatly.

4)  During measurement, a current of 0.035 mA is applied through the electrodes and travels between the hand and foot. This current is well below the sensory threshold of the nervous system [16], making the procedure painless and safe - If we are talking about the amplitude of the current, it would be nice to specify its frequency.

5) Concerning concordance analysis, for ASMM, the Sergi equation demonstrated higher concordance with DXA (CCC = 0.942) than the Kyle equation (CCC = 0.898) (Table 3). For ASMI, a similar pattern was observed, with higher concordance for the Sergi equation (CCC = 0.865) compared with the Kyle equation (CCC = 0.796) (Table 3). - from the context, it is not very clear how good these results are, whether they are enough to replace DXA with BiodyXpert device.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the detailed answers to all my questions, there are no substantive comments left, except for inconsistencies with the topics of the journal, if this does not contradict the policy of the editorial board, I have no other objections.

Author Response

Comments 1: [Thank you for the detailed answers to all my questions, there are no substantive comments left, except for inconsistencies with the topics of the journal, if this does not contradict the policy of the editorial board, I have no other objections.]

Response 1: [ We sincerely thank the reviewer for the positive evaluation of the revised manuscript and for acknowledging that the scientific concerns have been satisfactorily addressed. We understand the remaining concern regarding the fit with the scope of Sensors.

We respectfully believe that the present study is well aligned with several areas of the journal, particularly Biomedical sensors and Sensor devices. Rather than simply comparing DXA and BIA, our work focuses on the validation of a novel bioelectrical impedance sensor device designed for use in a seated position with integrated electrodes. The study evaluates the performance of this sensing technology in a clinically relevant configuration, examines how the prediction models implemented within the device influence the sensor output, and investigates the clinical utility of the sensor-derived phase angle. Together, these aspects address the validation and practical implementation of a biomedical sensing system for routine geriatric assessment.]