Changes in Body Composition and Functional Capacity of Antarctic Expedition Participants

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors must be congratulated on a well presented and clearly written manuscript.  I thank them for the opportunity to review this article.

Major

Novel and Import Contribution: please clearly identify this article's contribution to the body of knowledge in this field.

Sample size and statistical power: the total cohort (n = 34) and BMI‑stratified subgroups (n = 10–14) are relatively small. While this is understandable given the logistical constraints of Antarctic research, the limited statistical power should be more explicitly acknowledged in the Discussion.

Body composition assessment using bioelectrical impedance: body composition was assessed using bioelectrical impedance analysis (TANITA RD‑545). Whilst BIA benefits from ease-of-use it has many disadvantages.  More detail is required on the validation of the BIA system, and discussing how these were mitigated for, e.g. hydration status, sensor contact, etc.

On-Ice Activity: no information is given on the change of physical or habitual activity changes between free-living (home) conditions and the on-ice period.

Timing of post‑expedition measurements: post‑expedition measurements were obtained within 7 days of return. This time window may capture acute recovery or travel‑related effects rather than stable physiological adaptations. Please clarify the typical timing of post‑return testing and discuss how acute fatigue, recovery, or detraining could have influenced results.

Minor:

Typos/Consistency

Consistency in mean ± SD and p‑values throughout the text and tables.  In Table 1,  “1190 ± 12.2 mmHg,” 

Sex distribution

The cohort is predominantly male (28:6), this imbalance should be acknowledged as a limitation given known sex differences in body composition and cardiovascular responses.

Terminology and clarity

• Please define “short‑term” explicitly (e.g., 30‑day summer expedition) at first mention.
• Definition of HR3 in the Introduction for non exercise specialist.

Presentation 

The manuscript is heavily table driven, perhaps investigate alternative methods of displaying the data.

 

 

 

Author Response

We, the authors of the manuscript entitled “Changes in Body Composition and Functional Capacity of Antarctic Expedition Participants”, would like to thank the reviewers for their comments and the time spent reviewing the manuscript. They helped us to improve the quality of our manuscript significantly.

All reviewers' comments have been taken into consideration in the revised version.

Detailed responses to reviewers' comments are provided below:

Point-by-Point Response to Reviewer 1

Major

Comment 1: Novel and Import Contribution: please clearly identify this article's contribution to the body of knowledge in this field.

Response 1: We thank the reviewer for this important comment. In the revised manuscript, we have clarified the novelty and scientific contribution of the study. Specifically, the present work contributes to the current body of knowledge by providing new evidence on the short-term physiological adaptations to Antarctic conditions in expedition members stratified by their BMI. Despite the growing number of personnel participating in Antarctic expeditions, data on short-term physiological adaptations to the Antarctic environment remain limited, particularly with respect to differences related to body weight status. Most previous studies have focused on general physiological responses to polar conditions, while comparatively little attention has been paid to how body composition and BMI may influence adaptive responses during expeditions. The present study addresses this gap by examining changes in body composition, cardiovascular parameters, and physical working capacity in expedition members before and after a one-month stay in Antarctica, with participants stratified according to BMI categories. By exploring potential differences in adaptation among normal-weight, overweight, and obese individuals, this study provides additional insight into the role of body weight status in functional adaptation to extreme environments and may inform health monitoring and preparation strategies for personnel involved in polar missions.

The corresponding text is added:

Page 2, Lines 67-84 (in the version without track changes): “Despite the growing number of personnel participating in Antarctic expeditions, data on short-term physiological adaptations to the Antarctic environment remain limited, particularly with respect to differences related to their body weight status. This study aimed to examine the effect of a short-term (30-day) summer stay in Antarctica on the body composition and functional capacity of participants in the 32nd Bulgarian polar expedition, divided into three body mass index (BMI) categories. BMI was used as the primary grouping criterion, as it is generally associated with similar patterns of physical activity, dietary habits, and health status. By comparing changes in body composition, cardiovascular parameters, and physical working capacity across BMI categories, this study may contribute to a better understanding of how body weight status may influence functional adaptation to the extreme Antarctic environment and workload. These findings could provide valuable insights for enhancing performance and safeguarding the health of expedition members, particularly in remote environments with limited medical support. The results may also contribute to the development of more effective health-monitoring protocols and tailored nutritional and physical training programs for personnel preparing to participate in polar expeditions. Moreover, the findings enrich the broader field of polar medicine and research on human adaptation to extreme conditions.”

Comment 2: Sample size and statistical power: the total cohort (n = 34) and BMI‑stratified subgroups (n = 10–14) are relatively small. While this is understandable given the logistical constraints of Antarctic research, the limited statistical power should be more explicitly acknowledged in the Discussion.

Response 2: We thank the reviewer for this important observation. We acknowledge that the sample size and resulting BMI-stratified subgroups are relatively small, which limits the statistical power of some analyses and the generalizability of the findings. This limitation has now been explicitly discussed in the Discussion section. We have added a statement highlighting that, while the study provides valuable preliminary insights into BMI-related physiological adaptations in Antarctic expeditions, the results should be interpreted with caution and confirmed in larger cohorts where feasible. A paragraph has been added to the Discussion section.

Page 6, Lines 187–192 (in the version without track changes): „Given the different, but always limited number of participants in the polar expeditions, further stratification by additional variables (such as age, sex, profession, etc.) would have resulted in a reduction of the statistical power of the study and may affect the generalizability of the findings. Nevertheless, the study provides valuable preliminary insights into the influence of body weight status on physiological adaptations during short-term (30-day) polar expedition.“

Comment 3: Body composition assessment using bioelectrical impedance: body composition was assessed using bioelectrical impedance analysis (TANITA RD‑545). Whilst BIA benefits from ease-of-use it has many disadvantages.  More detail is required on the validation of the BIA system, and discussing how these were mitigated for, e.g. hydration status, sensor contact, etc.

Response 3: We thank the reviewer for this insightful comment. To mitigate some confounding factors, all participants were instructed to avoid vigorous physical activity, alcohol, and caffeine for at least 12 hours prior to assessment, and measurements were performed under standardized conditions (e.g., morning hours, after voiding, barefoot, and in light clothing). Also, Tanita uses a potentiometric method that minimizes the influence of resistance between the electrodes and the skin. These details have now been added to the Methods section.

Pages 9-10, Lines: 325-330 (in the version without track changes): “To minimize variability related to hydration, recent activity, and sensor contact, participants were measured in the morning (8–9 a.m.) after voiding, in light clothing, and barefoot. Participants were also instructed to avoid vigorous exercise, alcohol, and caffeine for at least 12 hours prior to assessment. The TANITA RD 545 uses a potentiometric method that minimizes the influence of resistance between the electrodes and the skin. “

Comment 4: On-Ice Activity: no information is given on the change of physical or habitual activity changes between free-living (home) conditions and the on-ice period.

Response 4: We thank the reviewer for this important observation. We acknowledge that the study did not include direct measurements of participants’ physical activity during the Antarctic expedition or compare it to their physical or habitual activity at home. We have now added a statement in the Materials and Methods section to acknowledge this limitation and clarify that the observed changes in body composition and functional parameters reflect the combined effects of environmental exposure, work-related activity, and other lifestyle factors encountered during the expedition. A sentence has been added to the Materials and Methods.

Page 9, Lines 314–318 (in the version without track changes): “Monitoring the participants’ physical activity and dietary patterns during their stay at the Antarctic base was outside the scope of the present study. The observed changes in body composition, cardiovascular function, and physical working capacity likely reflected the combined influence of environmental exposure, occupational workload, and lifestyle factors encountered during the expedition.”

Comment 5: Timing of post‑expedition measurements: post‑expedition measurements were obtained within 7 days of return. This time window may capture acute recovery or travel‑related effects rather than stable physiological adaptations. Please clarify the typical timing of post‑return testing and discuss how acute fatigue, recovery, or detraining could have influenced results.

Response 5: The recovery trajectory following long-distance travel across multiple time zones is variable and depends largely on the re-establishment of the sleep–wake cycle. In individual cases, the recovery period can range from 3 to 11 days, typically lasting around one week (Herxheimer, 2008; Benito et al., 2026). For this reason, we conducted our post-expedition assessments within 7 days of return. Functional assessments were performed on a cycle ergometer with gas analysis and ECG monitoring, which required a specific test duration for each participant. Therefore, the participants were scheduled in groups of eight per day and attended the laboratory at designated times. Over 90% of participants (30 individuals) were tested between the 5th and 7th day after return, while two participants were assessed on the 4th day, and only 1 on the 3rd day due to various circumstances.

Benito, A.; Boppre, G.; Lopes, A.; Cruz, D.; Moreira-Gonçalves, D.; Pyne, D.B.; Baptista, L.C.; Zacca, R. Do Long-Haul Travel and Jet Lag Affect Athletes’ Physiological, Humoral and Performance Outcomes? A Systematic Narrative Review. Sports 2026, 14, 93. https://doi.org/10.3390/sports14030093

Herxheimer, A. Jet lag. BMJ Clin. Evid. 2008, 2008, 2303.

A sentence has been added to the Materials and Methods:

Page 9, Lines 304–313 (in the version without track changes): “The time frame of 7 days after returning was selected to assess physiological adaptations in the participants rather than travel-related post-expedition effects. The recovery trajectory following long-distance travel across multiple time zones is variable and largely depends on the re-establishment of the sleep–wake cycle. In individual cases, the recovery period may range from 3 to 11 days, typically lasting around one week [46,47]. Participants were not assessed simultaneously, as the stress test required a variable amount of time to complete. Consequently, they were scheduled in groups of 10–12 per day to attend the laboratory. Over 90% of participants (31 individuals) were tested between the 5th and 7th day after return, while two participants were assessed on the 4th day, and only one on the 3rd day due to various circumstances.”

Minor:

Comment 6: Typos/Consistency: Consistency in mean ± SD and p‑values throughout the text and tables.  In Table 1,  “1190 ± 12.2 mmHg,” 

Response 6: Thank you for pointing out this inconsistency. We carefully reviewed the manuscript and tables to ensure consistent formatting of numerical data. The typographical error in Table 1 (“1190 ± 12.2 mmHg”) has been corrected to “119.0 ± 12.2 mmHg.”

Change in the revised manuscript:

Page 3, Line 110 (in the version without track changes), Table 1: The formatting of mean ± SD and p-values has been revised throughout the manuscript, and the error in Table 1 has been corrected.

Comment 7: Sex distribution. The cohort is predominantly male (28:6), this imbalance should be acknowledged as a limitation given known sex differences in body composition and cardiovascular responses.

Response 7: The number of participants in Antarctic expeditions is limited by the accommodation capacity of research stations. In addition, scientists conducting field research in Antarctica are typically accompanied by logistics personnel, who constitute a substantial proportion of the station’s staff and often remain for much longer periods. As a result, the pool of eligible participants further narrows due to the experimental design of the present study, based on a one-month stay. This constraint limits the possibility of studying larger samples and of stratifying participants according to a greater number of relevant characteristics because of reduction of the statistical power of the study. The following sentence has been added in the manuscript.

Page 7, Line 187-191 (in the version without track changes): “Given the limited number of participants in the polar expeditions, further stratification by additional variables (such as age, sex, profession, physical activity, etc.) would have resulted in a reduction of the statistical power of the study and may affect the generalizability of the findings.”

Comment 8: Terminology and clarity

• Please define “short‑term” explicitly (e.g., 30‑day summer expedition) at first mention.
• Definition of HR3 in the Introduction for non exercise specialist.

Response 8: We thank the reviewer for these suggestions. To improve clarity, we have now explicitly defined “short-term” at its first mention as a 30-day Antarctic expedition (Page 1, line 15). In addition, a brief explanation of the HR3’ parameter has been added to make the terminology clearer for readers who are not specialists in exercise physiology (Page 7 lines 247-251).

Changes in the revised manuscript (in the version without track changes):

Page 1, Line 15: “…aimed to evaluate the impact of a short-term (30-day) expedition …”

Page 1, Lines 21-22: “… and heart rate measured at the third minute after exercise completion (HR3’) used as an indicator of cardiovascular recovery.”

Comment 9: Presentation. The manuscript is heavily table driven, perhaps investigate alternative methods of displaying the data.

Response 9: We thank the reviewer for this suggestion. We agree that graphical presentation may improve the readability of key findings. Therefore, we have revised the manuscript by adding graphical representations (Figure 1) of the main outcomes (significant differences between groups, before and after the expedition) while retaining the tables to provide the complete dataset.

Page 6, Figure 1

Making the above-mentioned revisions, we believe that the manuscript has been substantially improved and is now more complete. We hope that it now meets the requirements of the journal and will be accepted for publication.

Sincerely yours

Prof. Albena Alexandrova

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses an interesting topic related to physiological responses to Antarctic expeditions and explores differences according to BMI categories. The study design, based on pre- and post-expedition measurements, provides potentially valuable information about functional adaptations in this environment. Nevertheless, several aspects of the manuscript should be improved to enhance clarity and scientific rigor. In particular:

- The introduction provides a general overview of physiological challenges in Antarctic environments and cites relevant literature on polar expeditions and human adaptation. However, the research gap is not clearly articulated. The authors state that few studies exist on short-term expeditions but do not clearly explain what is novel about analyzing BMI groups.

- The total sample size is further divided into three BMI groups, which substantially reduces statistical power and may limit the reliability of between-group comparisons. This limitation should be more clearly acknowledged and discussed in the manuscript

- BIA measurements are sensitive to hydration status, recent physical activity, and environmental conditions. Changes in hydration and physical workload could influence impedance-derived estimates of fat mass and muscle mass. This limitation is particularly relevant considering that participants were not assessed simultaneously, but within a 7-day period after returning from the expedition, when testing conditions could have differed.

- The estimation of aerobic capacity may be limited due to inter-individual variability in the HR-VO₂ relationship and the known error associated with age-predicted maximal HR equations. This limitation should be acknowledged and discussed when interpreting changes in predicted VO2max.

- Although the incremental protocol on the cycle ergometer is described, important procedural details are missing. For example, cadence control and environmental testing conditions are not reported.

- The study does not report key factors that could strongly influence physiological responses during the expedition, such as physical workload, daily physical activity, dietary intake, or environmental exposure. In my opinion, this is an important aspect, especially since throughout the manuscript the authors speculate that some of the observed changes may be explained by these factors.

- The Results section could be written in a more concise and fluid way. I suggest avoiding duplication of data that are already presented in the tables. The authors compare pre- and post-expedition values within each BMI group, and they mention using ANOVA or equivalent tests depending on the distribution. In this context, one would expect the authors to determine whether BMI category actually affected the variables studied. If BMI had no significant effect, reporting overall pre- and post-expedition mean values might have been sufficient and would help streamline the Results section. In addition, it is unclear why the authors did not compare the changes (Δ values) between groups. This comparison could be more informative than comparing only baseline and post values, as groups may start with different absolute values but show similar changes.

- The manuscript interprets reductions in HR3’ as improvements in cardiovascular recovery. While this is plausible, the interpretation would benefit from citing literature specifically related to heart rate recovery as a marker of autonomic function or cardiorespiratory fitness. In addition, HR recovery is influenced by multiple factors, including fitness level, environmental stress, hydration status, and fatigue. Considering the expedition environment, these factors could influence HR recovery independently of training adaptation.

- Considering that the duration of the expedition was approximately one month, substantial improvements in maximal aerobic capacity may be unlikely unless participants were exposed to a structured and sufficiently intense training stimulus. If the authors collected HR responses at the different workload stages of the test, reporting these values (Figure) could provide additional insight into potential changes in submaximal physiological responses, such as improved exercise efficiency. Such information could be more informative than focusing exclusively on predicted VO2max values.

- Although some limitations are implicitly acknowledged, the manuscript would benefit from a clearer statement addressing sample size, observational design, and lack of control over environmental and behavioral variables during the expedition.

- The discussion and conclusions would benefit from a more cautious interpretation of the results.

- The meaning of the column labeled “Distribution” in Tables 1-3 is not clearly explained. If it refers to the result of the normality test, this should be explicitly stated. In addition, some values presented in the tables appear inconsistent or may contain typographical errors (e.g., the SBP value reported as “1190 mmHg” in Table 1). These issues should be carefully checked and corrected to ensure accuracy of the reported results.

- Minor grammatical and stylistic revisions would improve readability. For example, some sentences are relatively long and could be simplified.

Author Response

We, the authors of the manuscript entitled “Changes in Body Composition and Functional Capacity of Antarctic Expedition Participants”, would like to thank the reviewers for their comments and the time spent reviewing the manuscript. They helped us to significantly improve the quality of our manuscript.

All reviewers' comments have been taken into consideration in the revised version.

Detailed responses to reviewers' comments are provided below:

Point-by-Point Response to Reviewer 2

Comment 1: The introduction provides a general overview of physiological challenges in Antarctic environments and cites relevant literature on polar expeditions and human adaptation. However, the research gap is not clearly articulated. The authors state that few studies exist on short-term expeditions, but do not clearly explain what is novel about analyzing BMI groups.

Response 1: We thank the reviewer for this important comment. To better highlight the contribution of the present study, we have revised the final paragraph of the Introduction to more clearly state the novelty and relevance of our findings.

The following text has been added to the manuscript:

Page 2, Lines 72-84 (in the version without track changes): “BMI was used as the primary grouping criterion, as it is generally associated with similar patterns of physical activity, dietary habits, and health status. By comparing changes in body composition, cardiovascular parameters, and physical working capacity across BMI categories, this study may contribute to a better understanding of how body weight status may influence functional adaptation to the extreme Antarctic environment and workload. These findings could provide valuable insights for enhancing performance and safeguarding the health of expedition members, particularly in remote environments with limited medical support. The results may also contribute to the development of more effective health-monitoring protocols and tailored nutritional and physical training programs for personnel preparing to participate in polar expeditions. Moreover, the findings enrich the broader field of polar medicine and research on human adaptation to extreme conditions.”

Comment 2:  The total sample size is further divided into three BMI groups, which substantially reduces statistical power and may limit the reliability of between-group comparisons. This limitation should be more clearly acknowledged and discussed in the manuscript

Response 2: We thank the reviewer for this observation. We acknowledge that the sample size and resulting BMI-stratified subgroups are relatively small, which limits the statistical power of some analyses and the generalizability of the findings. The expedition participants represented a heterogeneous group in terms of sex, profession, physical activity, body composition, and other characteristics. At the same time, their limited number did not allow for stratification according to all these variables. We therefore chose to group participants based on BMI, as this measure largely reflects differences in physical activity (likely related to profession), dietary habits, lifestyle behaviors, health risk, and other relevant factors. This limitation has now been explicitly discussed in the Discussion section.

Page 6, Lines 187–192 (in the version without track changes): „Given the limited number of participants in the polar expeditions, further stratification by additional variables (such as age, sex, physical activity, etc.) would have resulted in a reduction of the statistical power of the study and may affect the generalizability of the findings. Nevertheless, the study provides valuable preliminary insights into the influence of body weight status on physiological adaptations during short-term polar expeditions.“

Comment 3: BIA measurements are sensitive to hydration status, recent physical activity, and environmental conditions. Changes in hydration and physical workload could influence impedance-derived estimates of fat mass and muscle mass. This limitation is particularly relevant considering that participants were not assessed simultaneously, but within a 7-day period after returning from the expedition, when testing conditions could have differed.

Response 3: We thank the reviewer for this insightful comment. To mitigate some confounding factors, all participants were instructed to avoid vigorous physical activity, alcohol, and caffeine for at least 12 hours prior to assessment, and measurements were performed under standardized conditions (e.g., morning hours, after voiding, barefoot, and in light clothing). Also, Tanita uses a potentiometric method that minimizes the influence of resistance between the electrodes and the skin. These details have now been added to the Methods section.

Pages 9-10, Lines: 325-330 (in the version without track changes): “To minimize variability related to hydration, recent activity, and sensor contact, participants were measured in the morning (8–9 a.m.) after voiding, in light clothing, and barefoot. Participants were also instructed to avoid vigorous exercise, alcohol, and caffeine for at least 12 hours prior to assessment. The TANITA RD 545 uses a potentiometric method that minimizes the influence of resistance between the electrodes and the skin. “

Regarding the remark that participants were not assessed simultaneously but within a 7-day period after returning from the expedition, we would like to note that the functional tests were conducted on a cycle ergometer with gas analysis and ECG monitoring, with each test performed until participants reached 85% of their predicted maximal heart rate (HR85%). The duration of each assessment varied according to individual physical status. Consequently, participants were scheduled in groups of 10–12 per day to attend the laboratory. This information has been added to the manuscript.

Page 9, Lines: 309-313 (in the version without track changes): “Participants were not assessed simultaneously, as the stress test required a variable amount of time to complete. Consequently, they were scheduled in groups of 10–12 per day to attend the laboratory. Over 90% of participants (31 individuals) were tested between the 5th and 7th day after return, while two participants were assessed on the 4th day, and only one on the 3rd day due to various circumstances.”

Comment 4:  The estimation of aerobic capacity may be limited due to inter-individual variability in the HR-VO₂ relationship and the known error associated with age-predicted maximal HR equations. This limitation should be acknowledged and discussed when interpreting changes in predicted VO2max.

Response 4: We thank the reviewer for this important point. The participants’ physical fitness and morphological characteristics did not allow the completion of a maximal aerobic test to exhaustion. During the submaximal test, in addition to monitoring heart rate via ECG, we performed gas exchange analysis using CPET. This allowed us to objectively determine oxygen consumption at a workload corresponding to 85% of the predicted maximal heart rate (HR85’), which provides a close approximation of VO₂max with relatively small error. This approach is particularly suitable for repeated pre- and post-expedition comparisons. The obtained values were then compared before and after the expedition using a paired-samples approach.

Page 10, Lines 345-348 (in the version without track changes): “The test was conducted under continuous: gas analysis (Quark CPET, COSMED, Italy), electrocardiographic monitoring (ECG), and automatic blood pressure measurement based on Korotkoff sounds. All procedures followed the requirements for conducting the Exercise Stress Test [40].”

Comment 5:  Although the incremental protocol on the cycle ergometer is described, important procedural details are missing. For example, cadence control and environmental testing conditions are not reported.

Response 5: We thank the reviewer for this observation. To clarify, all participants were instructed to maintain a pedaling cadence of 60 revolutions per minute during the stress test, which is considered the most economical for the majority of individuals and ensures better comparability across participants. The cycle ergometer (Ergoline ErgoSelect VIAsprint 150P) maintained a constant workload regardless of cadence, allowing accurate control of exercise intensity. All tests were conducted in the same laboratory under standardized conditions, with the room temperature maintained at 25°C. These measures were implemented to minimize variability related to cadence and environmental factors and to improve the reliability and reproducibility of the functional test results.

The Methods section has been revised to include:

Page 10, Lines 338-344 (in the version without track changes): “To determine the functional capabilities of the expedition participants, an exercise stress test was performed on a bicycle ergometer (Ergoline ErgoSelect VIAsprint 150P, Ergoline GmbH, Germany) in a laboratory with the temperature maintained at 25°C, to ensure standardized environmental conditions and comparability of results. The initial workload was set at 30 W, increasing by 30 W every 1.5 minutes until the heart rate reached 85% (HR85%) of the maximum predicted heart rate (MPHR = 220 – age) [48]. Participants were instructed to maintain a pedaling cadence of 60 revolutions per minute.”

Comment 6: The study does not report key factors that could strongly influence physiological responses during the expedition, such as physical workload, daily physical activity, dietary intake, or environmental exposure. In my opinion, this is an important aspect, especially since throughout the manuscript the authors speculate that some of the observed changes may be explained by these factors.

Response 6: The authors of this article were not participants in the 32nd Bulgarian Antarctic Expedition and therefore did not have direct observations or measurements of the participants’ physical workload, daily physical activity, dietary intake, or environmental exposure during the expedition. The results presented in this study reflect the changes in body composition and functional status of the participants based on a comparison of data obtained before departure and after their return. The observed changes in body composition, cardiovascular function, and physical working capacity likely reflect the combined influence of environmental exposure, occupational workload, and lifestyle factors experienced during the expedition. We acknowledge this limitation of the present study and intend to address it in future research by monitoring physical activity using inertial sensors and by collecting information on dietary intake and physical workload, including field activities, through daily questionnaire records.

Comment 7: The Results section could be written in a more concise and fluid way. I suggest avoiding duplication of data that are already presented in the tables. The authors compare pre- and post-expedition values within each BMI group, and they mention using ANOVA or equivalent tests depending on the distribution. In this context, one would expect the authors to determine whether BMI category actually affected the variables studied. If BMI had no significant effect, reporting overall pre- and post-expedition mean values might have been sufficient and would help streamline the Results section. In addition, it is unclear why the authors did not compare the changes (Δ values) between groups. This comparison could be more informative than comparing only baseline and post values, as groups may start with different absolute values but show similar changes.

Response 7: We thank the reviewer for this thoughtful suggestion. In response, we have revised the Results section to improve clarity and reduce duplication of numerical values already presented in the tables.

Regarding the role of BMI categories, the primary aim of our study was to examine potential differences in physiological responses among participants stratified by BMI. For this reason, pre- and post-expedition comparisons were presented within each BMI group.

Although comparing the magnitude of changes (Δ values) between BMI groups could provide additional insight, the relatively small sample size and variability within the groups limit the statistical power of such comparisons. Therefore, the results are primarily interpreted based on within-group pre–post changes.

Despite the limited statistical power to detect between-group differences, stratification by BMI was retained because body mass index is a widely used indicator associated with differences in body composition, physical fitness, and cardiovascular risk. This approach allowed exploratory assessment of whether individuals with different weight status might exhibit distinct patterns of physiological response to the expedition.

Comment 8: The manuscript interprets reductions in HR3’ as improvements in cardiovascular recovery. While this is plausible, the interpretation would benefit from citing literature specifically related to heart rate recovery as a marker of autonomic function or cardiorespiratory fitness. In addition, HR recovery is influenced by multiple factors, including fitness level, environmental stress, hydration status, and fatigue. Considering the expedition environment, these factors could influence HR recovery independently of training adaptation.

Response 8: We thank the reviewer for this important observation. In response to this comment, we have added appropriate references supporting the use of heart rate recovery as a marker of autonomic regulation and cardiovascular fitness. In addition, the Discussion section has been revised to acknowledge that heart rate recovery may also be affected by factors such as physical fitness level, environmental stress, hydration status, and fatigue. Considering the specific conditions of the Antarctic expedition, these factors may have contributed to the observed changes in HR3’, and therefore the results should be interpreted with appropriate caution.

Page 8, Lines 247-255 (in the version without track changes): “Heart rate during recovery from submaximal functional exercise reflects the reactivation of the parasympathetic nervous system and serves as a reliable, sensitive, and easily applicable indicator of the functional state of the cardiovascular system and autonomic regulation. Faster heart‑rate recovery is associated with higher physical fitness and better overall health status [Dimkpa, 2009; Barak et al., 2011]. It should be mentioned that heart rate recovery can be affected by multiple factors, including physical fitness level, environmental stress, hydration status, and fatigue, especially given the specific conditions encountered during the Antarctic expedition [Akerman et al., 2017; Carteret al., 2005; Perini & Veicsteinas, 2003].”

Dimkpa, U. Post‑exercise heart rate recovery: An index of cardiovascular fitness. J. Exerc. Physiol. Online 2009, 12, 10–22.

Barak, O.F.; Ovcin, Z.B.; Jakovljevic, D.G.; Lozanov‑Crvenkovic, Z.; Brodie, D.A.; Grujic, N.G. Heart rate recovery after submaximal exercise: Relationship with oxidative stress and antioxidant capacity in young healthy males. J. Sports Sci. Med. 2011, 10, 261–266.

Akerman AP, Lucas SJE, Katare R, Cotter JD. Heat and Dehydration Additively Enhance Cardiovascular Outcomes following Orthostatically-Stressful Calisthenics Exercise. Front Physiol. 2017;8:756. Published 2017 Oct 9. doi:10.3389/fphys.2017.00756

Carter, R.; Cheuvront, S.N.; Wray, D.W.; Kolka, M.A.; Stephenson, L.A.; Sawka, M.N. The influence of hydration status on heart rate variability after exercise heat stress. J. Therm. Biol. 2005, 30, 495–502. https://doi.org/10.1016/j.jtherbio.2005.05.006

Perini, R.; Veicsteinas, A. Heart rate variability and autonomic activity at rest and during exercise in various physiological conditions. Eur. J. Appl. Physiol. 2003, 90, 317–325. https://doi.org/10.1007/s00421-003-0953-9

Comment 9:  Considering that the duration of the expedition was approximately one month, substantial improvements in maximal aerobic capacity may be unlikely unless participants were exposed to a structured and sufficiently intense training stimulus. If the authors collected HR responses at the different workload stages of the test, reporting these values (Figure) could provide additional insight into potential changes in submaximal physiological responses, such as improved exercise efficiency. Such information could be more informative than focusing exclusively on predicted VO2max values.

Response 9: In the original version of the manuscript, we did not explicitly indicate the use of gas‑analysis equipment. This omission has been corrected in the revised manuscript, where the instrumentation is now clearly described in the Materials and Methods section. Because heart rate at each stage of a submaximal exercise test is strongly age‑dependent, we continuously monitored oxygen consumption throughout the protocol to ensure accurate physiological characterization.

To quantify functional capacity, we used the oxygen consumption measured at HR85% of the age‑predicted maximal heart rate (220 − age, the most widely applied formula). This value was subsequently approximated to a VO₂max‑equivalent metric. Given this approach, we consider that our assessment of functional capacity is only minimally influenced by the inherent limitations of submaximal exercise testing.

Page 10, Lines 338-338 (in the version without track changes):”To determine the functional capabilities of the expedition participants, an exercise stress test was performed on a bicycle ergometer (Ergoline ErgoSelect VIAsprint 150P, Ergoline GmbH, Germany) in a laboratory with the temperature maintained at 25°C, to ensure standardized environmental conditions and comparability of results. The initial workload was set at 30 W, increasing by 30 W every 1.5 minutes until the heart rate reached 85% (HR85%) of the maximum predicted heart rate (MPHR = 220 – age) [48]. “

Comment 10: Although some limitations are implicitly acknowledged, the manuscript would benefit from a clearer statement addressing sample size, observational design, and lack of control over environmental and behavioral variables during the expedition.

Response 10: We thank the reviewer for this suggestion. We have now added data about the environmental conditions at the base and acknowledged the limitations of our study in the manuscript.

Data on meteorological conditions during the austral summer on Livingston Island have been added to the manuscript.

Page 9, Lines 293–297 (in the version without track changes): During the austral summer on Livingston Island, temperatures fluctuated near freezing with a mean around 0°C, relative humidity remained consistently high between 90% and 100%, and wind speeds ranged from 15 to 45 km/h, occasionally reaching up to 80 km/h [https://www.meteoblue.com/en/weather/historyclimate/weatherarchive/livingston-island_antarctica].

Page 9, Lines 314–318 (in the version without track changes): “Monitoring the participants’ physical activity and dietary patterns during their stay at the Antarctic base was outside the scope of the present study. The observed changes in body composition, cardiovascular function, and physical working capacity reflected the combined influence of environmental exposure, occupational workload, and lifestyle factors encountered during the expedition.”

Comment 11:  The discussion and conclusions would benefit from a more cautious interpretation of the results.

Response 11: We thank the reviewer for this suggestion. We have revised the Discussion and Conclusions sections to adopt a more cautious and balanced interpretation of our findings. Statements regarding improvements in cardiovascular function, body composition, and aerobic capacity have been tempered to reflect the exploratory nature of the study and the potential influence of confounding factors such as travel-related effects and lifestyle variations during the expedition.

Comment 12:  1) The meaning of the column labeled “Distribution” in Tables 1-3 is not clearly explained. If it refers to the result of the normality test, this should be explicitly stated. 2) In addition, some values presented in the tables appear inconsistent or may contain typographical errors (e.g., the SBP value reported as “1190 mmHg” in Table 1). These issues should be carefully checked and corrected to ensure accuracy of the reported results.

Response 12: 1) We thank the reviewer for pointing this out. The “Distribution” column in Tables 1–3 indicates the results of the normality test for each variable. To clarify, we have revised the tables to explicitly state in the footnote that this column denotes whether the data followed a normal distribution, as determined by the Shapiro–Wilk test.

Page 3, Lines 111-112, Page 4, Lines 133-134, Page 5, lines 148-149 (in the version without track changes): *Data distribution — indicates the type of probability distribution: “normal” or, if left blank, the data were considered to follow a non‑normal distribution.

2) Thank you for pointing out this inconsistency. We carefully reviewed the manuscript and tables to ensure consistent formatting of numerical data. The typographical error in Table 1 (“1190 ± 12.2 mmHg”) has been corrected to “119.0 ± 12.2 mmHg.”

Comment 13:  Minor grammatical and stylistic revisions would improve readability. For example, some sentences are relatively long and could be simplified.

Response 13: We thank the reviewer for this valuable suggestion. We have carefully revised the manuscript to improve readability, focusing on shortening long sentences, simplifying complex phrasing, and correcting minor grammatical issues throughout the text to improve overall readability.

Making the above-mentioned revisions, we believe that the manuscript has been substantially improved and is now more complete. We hope that it now meets the requirements of the journal and will be accepted for publication.

Sincerely yours

Prof. Albena Alexandrova

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the revisions. The manuscript has improved and most of the previous methodological concerns have been addressed. However, a major revision is still recommended before acceptance.

The main remaining issue is interpretative. In my opinion, the conclusions and parts of the Discussion should be more cautious, as the study did not directly assess key variables that could explain the observed changes, such as physical workload, daily physical activity, dietary intake, or environmental exposure.

Related to this point, even if these variables were not objectively measured, the manuscript would benefit from including a brief descriptive account of a typical day during the expedition (e.g., main tasks, approximate physical demands, time spent outdoors, and meal routines). This contextual information would help readers better interpret the findings and reduce the speculative nature of some statements in the Discussion.

The current analytical approach focuses primarily on absolute pre- and post-expedition values. However, given the longitudinal design of the study, the most relevant outcome is the magnitude of change within individuals. Comparing absolute values between BMI groups may be misleading, as these groups differ at baseline by definition. In contrast, analyzing the changes would provide more direct insight into whether BMI status influences the physiological response to the expedition. Therefore, I strongly recommend that the authors report, and if possible statistically compare, the changes in the main variables across groups. At minimum, descriptive Δ values should be included, as they are more physiologically meaningful than absolute values in this context. While the authors argue that the small sample size limits the statistical power for such analyses, this limitation equally applies to the current between-group comparisons of pre- and post-expedition values.

In addition, the Results section could benefit from further refinement in terms of structure and narrative clarity. The current organization, which presents results separately for each BMI group in a highly similar format, leads to a somewhat repetitive description of the findings. While this approach is clear, it tends to obscure the overall pattern of results. I would suggest considering a more integrated presentation, highlighting the main changes observed across the entire sample and then specifying any relevant differences between BMI groups. This would help emphasize the key findings and improve readability, allowing the reader to more easily identify what actually changed as a result of the expedition, rather than following parallel and repetitive descriptions for each subgroup.

Finally, to strengthen the physiological interpretation of the results, the manuscript would benefit from presenting the responses obtained during the submaximal incremental test (e.g., heart rate, workload, or and VO2 across stages) before and after the expedition. A figure illustrating these responses could provide valuable insight into potential changes in submaximal efficiency, rather than relying primarily on estimated VO2max.

Author Response

We, the authors of the manuscript entitled “Changes in Body Composition and Functional Capacity of Antarctic Expedition Participants”, would like to thank the reviewer for the comments and time spent reviewing the manuscript. They helped us to improve the quality of our manuscript significantly.

All reviewer's comments have been taken into consideration in the revised version.

Detailed responses to the reviewer’s comments are provided below:

Point-by-Point Response to Reviewer 1

Comment 1. The main remaining issue is interpretative. In my opinion, the conclusions and parts of the Discussion should be more cautious, as the study did not directly assess key variables that could explain the observed changes, such as physical workload, daily physical activity, dietary intake, or environmental exposure.

Response 1. Thank you for this comment. We agree that the interpretation of our findings should be presented with greater caution, given that key variables such as physical workload, daily physical activity, dietary intake, and environmental exposure were not directly assessed in this study. In response, we have revised the Conclusions (adding a paragraph) and relevant sections of the Discussion (some words in the text) to more explicitly acknowledge these limitations and to avoid overinterpretation of the results. The text has been modified to emphasize that the observed changes may be influenced by unmeasured factors and should therefore be interpreted with appropriate caution.

Page 12, Lines 405-422 (in the version without track changes):“In conclusion, the Antarctic expedition at the Bulgarian base was associated with group-specific physiological responses among participants, with individuals of moderate BMI (Group 2) demonstrating the most pronounced improvements in cardiovascular recovery and physical working capacity. Participants with a normal BMI (Group 1) generally maintained their baseline fitness levels, suggesting that lower adiposity may protect health metrics under extreme conditions. Participants with higher BMI (Group 3) showed limited adaptive responses, highlighting potential challenges in achieving significant cardiometabolic benefits from short-term (30-day summer) expedition load in this cohort.

These findings should be interpreted with caution, as the study did not directly assess factors that may have contributed to the observed responses, such as physical workload, daily physical activity, dietary intake, or environmental exposure. Therefore, the mechanisms underlying the group differences remain unclear.

Nevertheless, the results suggest that individuals with obesity participating in Antarctic expeditions may be considered a distinct group requiring enhanced and more holistic medical supervision. Such supervision should include rigorous weight monitoring, structured physical activity, and a personalized nutrition plan tailored to the specific needs of individuals with obesity. These targeted measures can facilitate better individual adaptation to the expedition environment and reduce potential health risks.“

Comment 2. Related to this point, even if these variables were not objectively measured, the manuscript would benefit from including a brief descriptive account of a typical day during the expedition (e.g., main tasks, approximate physical demands, time spent outdoors, and meal routines). This contextual information would help readers better interpret the findings and reduce the speculative nature of some statements in the Discussion.

Response 2. Thank you for this suggestion. In response, we have included a brief descriptive account of a typical day during the expedition in the revised manuscript. This description outlines the main daily activities, approximate duration, and nature of physical workload, time spent outdoors depending on weather conditions, and general meal patterns and food availability at the base.

In detail, activities at the Bulgarian Antarctic Base are strongly dependent on weather conditions. Under favorable conditions, and depending on their specific expertise, researchers carry out their field tasks over a period of 6 to 8 hours, including travel to and from the sampling or study sites. In cases of extremely cold weather accompanied by strong winds, fieldwork is not conducted.

Individuals who regularly engage in physical exercise typically maintain their routines at the base, participating in activities such as morning running, yoga, aerobics, and table tennis.

Regarding diet, expedition members are free to follow their preferred dietary patterns; some consume only fish, while others adhere to vegetarian or vegan diets. The available food is diverse, with a wide variety of fruits and vegetables supplied each Antarctic season by the Bulgarian vessel. Food is continuously accessible, and there are no strictly fixed meal times.

In the Discussion section, we have added the following short text:

Page 10, Lines 297-302 (in the version without track changes): „In practice, participants generally maintained their usual diet and physical activity during the expedition. They followed preferred dietary patterns (as fish-based, vegetarian, or vegan diets), with continuous access to diverse food. Those who exercised regularly continued activities such as jogging, yoga, and aerobics. Fieldwork typically lasted 6–8 hours per day, including travel to and from sampling or study sites, but was suspended during severe weather conditions.“

Comment 3. The current analytical approach focuses primarily on absolute pre- and post-expedition values. However, given the longitudinal design of the study, the most relevant outcome is the magnitude of change within individuals. Comparing absolute values between BMI groups may be misleading, as these groups differ at baseline by definition. In contrast, analyzing the changes would provide more direct insight into whether BMI status influences the physiological response to the expedition. Therefore, I strongly recommend that the authors report, and if possible statistically compare, the changes in the main variables across groups. At minimum, descriptive Δ values should be included, as they are more physiologically meaningful than absolute values in this context. While the authors argue that the small sample size limits the statistical power for such analyses, this limitation equally applies to the current between-group comparisons of pre- and post-expedition values.

Response 3. In the Supplementary material, we provide individual data for all participants for each parameter before (Table S1) and after (Table S2) the expedition, as well as a table showing the magnitude of change for each individual (Δ values) (Table S3).

Comment 4. In addition, the Results section could benefit from further refinement in terms of structure and narrative clarity. The current organization, which presents results separately for each BMI group in a highly similar format, leads to a somewhat repetitive description of the findings. While this approach is clear, it tends to obscure the overall pattern of results. I would suggest considering a more integrated presentation, highlighting the main changes observed across the entire sample and then specifying any relevant differences between BMI groups. This would help emphasize the key findings and improve readability, allowing the reader to more easily identify what actually changed as a result of the expedition, rather than following parallel and repetitive descriptions for each subgroup.

Response 4. Thank you for this constructive comment. We agree that the structure of the Results section, organized separately by BMI groups lead to repetition. In response to your remark, the main changes observed across the entire sample are now presented first, followed by a detailed description of group differences.

Page 2, Lines 85-99 (in the version without track changes): “The primary changes observed as a result of the expedition across the entire sample concerned HR3’. In all three groups studied, this parameter decreased significantly, indicating improved heart rate recovery (i.e., a faster return to resting levels). The greatest number of statistically significant post-expedition changes were observed in the second group; in addition to HR3’, these included MM, SBP, PWC85%, and PWC85%R. In the first group, a significant increase in PWC85% was also found after the expedition. The results and a detailed description of the measured parameters for each group are presented below, along with statistically significant differences both within groups (pre- vs. post-expedition) and between groups (section 2.4). The individual data of anthropometric, physiological, and functional characteristics of participants before (Table S1) and after (Table S2) the expedition, as well as the individual differences in the tested parameters (Table S3), are given in the Supplementary material.”

Comment 5. Finally, to strengthen the physiological interpretation of the results, the manuscript would benefit from presenting the responses obtained during the submaximal incremental test (e.g., heart rate, workload, or and VO2 across stages) before and after the expedition. A figure illustrating these responses could provide valuable insight into potential changes in submaximal efficiency, rather than relying primarily on estimated VO2max.

Response 5.

Heart rate responses during the submaximal incremental test before and after the expedition are shown in Figure 2. The figure illustrates heart rate expressed as a percentage of the predicted maximal heart rate (HRmax) during the submaximal stress test, plotted against exercise intensity expressed as a percentage of the maximal power achieved in the final stage (Wmax). This approach enables comparison of cardiovascular responses across different workload levels, while accounting for age-related differences in maximal heart rate and the fact that participants completed a varying number of stages before reaching 85% of their maximal heart rate.

Page 7, Figure 2 (in the version without track changes).

 

Making the above-mentioned revisions, we believe that the manuscript has been substantially improved and is now more complete. We hope that it now meets the requirements of the journal and will be accepted for publication.

Sincerely yours

Prof. Albena Alexandrova

Author Response File: Author Response.docx