Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review this manuscript.

This randomized study compared two patterns of replacing sedentary behavior with light-intensity physical activity (LIPA), intermittent bouts triggered by prolonged sitting versus one continuous daily bout, in 28 community-dwelling older women over 8 weeks. The authors assessed 30-second sit-to-stand (30STS) performance, individual repetition duration (a novel temporal decomposition of the test), and lower-limb muscle morphology/tissue quality via ultrasound, including the ultrasound sarcopenia index (USI). Both LIPA patterns improved 30STS repetitions and reduced mean repetition duration, with no between-pattern difference. USI changed in opposite directions between groups (decreasing with intermittent, increasing with continuous LIPA), and one exploratory correlation (distal gastrocnemius echo intensity with repetition 7–8 fatigability) survived correction only in the intermittent group.

Comments to the Authors

The description of the intermittent-LIPA prescription contains an internal inconsistency in the maximum achievable daily dose. The Abstract states intermittent participants could accumulate "up to 48 min·day⁻¹," while the Methods section describing the intervention in detail states "approximately 44 min·day⁻¹." This is a minor discrepancy, but since this figure is used as a direct point of comparison against the continuous group's fixed 45–50 min bout, a comparison central to the paper's framing of the two conditions as roughly dose-equivalent, the authors should reconcile this figure and confirm which value is correct.

The absence of a non-intervention control group substantially limits causal interpretation, and this should be reflected more prominently than in the Limitations paragraph alone. The manuscript appropriately lists this as a limitation, but given that the study's central claims rest on pre–post and time-course changes in a population that completed a familiarization phase and underwent repeated testing (0, 4, and 8 weeks), test-retest or learning effects remain a plausible alternative explanation for at least part of the observed 30STS improvement. The familiarization data reported (n = 8, ICC = 0.87) address short-term reliability but do not rule out a longer-term practice effect across three testing occasions eight weeks apart. I would ask the authors to discuss explicitly, in the Discussion rather than only the Limitations, how much of the observed improvement could plausibly be attributable to repeated testing exposure alone.

The multiplicity of statistical approaches applied to overlapping outcomes (split-plot ANOVA, ANCOVA, Friedman/Wilcoxon, "average internal change," and "trajectory shape" comparisons) makes the overall analytical strategy difficult to follow and could benefit from a summary table. The Methods section introduces several non-standard composite metrics (mean internal change, trajectory shape) specific to this study's time-course design, which is a reasonable approach to a genuinely novel analytical problem, but the reader must track, for each outcome, which combination of tests was applied and why. A single summary table mapping each outcome variable to its applicable test(s), sample size, and correction procedure would materially improve the Results section's readability, particularly given how many different subsample sizes (n = 28, 24, 22, 19) are already in play.

The missing-data pattern across outcomes is substantial and unevenly distributed, which affects how the headline results should be interpreted. The full sample (n = 28) was used only for the basic pre-post 30STS comparison; the time-course analysis used n = 22; repetition-duration and ultrasound outcomes used n = 24; and the three-time-point repetition-duration analysis used n = 19 (intermittent: 12, continuous: 7). This is a reduction of up to 32% from the original sample in the most data-intensive analyses, and the continuous-LIPA group is reduced disproportionately (14 to 7, a 50% loss) in the final time-course subsample. The authors should report, even briefly, whether participants with missing data differed systematically from those with complete data on key baseline characteristics, since this directly affects confidence in the time-course findings presented as a primary contribution of the paper.

The USI group × time interaction is the most striking finding in the paper, and its interpretation would benefit from closer scrutiny of the baseline group difference. Table 1 shows that the intermittent-LIPA group had 0% participants classified as pre-sarcopenic at baseline versus 10% in the continuous group, and Table 3 shows baseline USI already differed numerically between groups (3.38 vs. 3.72). Although the ANCOVA approach appropriately adjusts for baseline when a significant baseline difference is detected, the manuscript does not report whether this baseline USI difference between groups was itself tested and found significant or non-significant before the ANCOVA was applied. I would ask the authors to state explicitly whether this baseline imbalance was tested and how it was handled, given how much interpretive weight is placed on this single interaction effect in a sample where 96% of participants were non-sarcopenic to begin with.

The rationale for analyzing only the first 10 repetitions, while methodologically justified, creates an asymmetry with the primary 30STS outcome that deserves explicit acknowledgment. The Methods justify this choice by noting the baseline range was 11–22 repetitions, ensuring all participants contributed data to all 10 repetition-duration slots. However, this means that for participants completing substantially more than 10 repetitions, the repetition-duration analysis characterizes only the first third to half of their total performance, potentially missing fatigue-related changes that manifest later in the set, which is precisely the functional endurance construct the Introduction motivates this analysis around. The Discussion's observation that only the repetition 7–8 difference changed significantly, with no change in overall fatigability metrics, could partly reflect this truncation rather than genuine absence of a training effect on later-set fatigue resistance. This should be noted as a specific limitation of the repetition-duration method, distinct from the more general limitations already listed.

The self-reported adherence data for the two groups are not directly comparable, which complicates the interpretation of "equivalent effectiveness" between patterns. The intermittent group's adherence metric (number of compliant prompts, decreasing from 9±12 to 6±8 across the intervention) and the continuous group's metric (days complying with a single daily bout, stable at 7±1–2 out of 7) measure fundamentally different constructs: one tracks degree of compliance with a variable, uncapped number of daily opportunities, while the other tracks binary daily compliance with a fixed single bout. The declining trend in the intermittent group's compliant-prompt count, which the authors note approached significance, could indicate declining adherence over the 8 weeks, a finding with direct relevance to the "equivalent effectiveness" conclusion driving the paper's practical recommendation that patterns can be prescribed "flexibly according to preference." I would ask the authors to discuss whether this declining adherence trend in the intermittent group is consistent with, or in tension with, the conclusion that both patterns are equally feasible long-term.

The exploratory correlation surviving Bonferroni correction (echo intensity and repetition 7–8 duration difference, intermittent group only) is presented with appropriate caution in the Discussion, but the Abstract does not convey this caution. The Abstract states "a positive association was found between the change in proximal GL echo intensity and the change in the repetition 7 vs. 8 difference in the intermittent group only," without any qualifying language, whereas the Discussion correctly notes this "should be viewed as hypothesis-generating" given the small subsample (n = 12) and the number of correlations tested. A reader encountering only the Abstract would not appreciate that this is a single surviving association out of a larger exploratory correlation matrix in a 12-person subgroup. I would suggest adding a brief qualifier directly in the Abstract.

 

Author Response

R1_Q1: The description of the intermittent-LIPA prescription contains an internal inconsistency in the maximum achievable daily dose. The Abstract states intermittent participants could accumulate "up to 48 min·day⁻¹," while the Methods section describing the intervention in detail states "approximately 44 min·day⁻¹." This is a minor discrepancy, but since this figure is used as a direct point of comparison against the continuous group's fixed 45–50 min bout, a comparison central to the paper's framing of the two conditions as roughly dose-equivalent, the authors should reconcile this figure and confirm which value is correct.

R1_Q1_Response:

We thank the reviewer for identifying this inconsistency. On rechecking the event-contingent prescription, the intermittent-LIPA group was not prescribed a fixed number of daily bouts. Participants performed 2 minutes of LIPA whenever 30 minutes of uninterrupted sedentary behaviour occurred between 09:00 and 21:00. Allowing for the time occupied by each activity bout, this permitted the accumulation of approximately 44 min·day⁻¹ under a maximally sedentary pattern. We have therefore corrected the Abstract, Methods and intervention-summary table and have avoided describing the two conditions as precisely dose-equivalent.

Please see page 1 lines 23-25 in the revised manuscript.

Please see page 24 lines 513-517 in the revised manuscript.

R1_Q2: The absence of a non-intervention control group substantially limits causal interpretation, and this should be reflected more prominently than in the Limitations paragraph alone. The manuscript appropriately lists this as a limitation, but given that the study's central claims rest on pre–post and time-course changes in a population that completed a familiarization phase and underwent repeated testing (0, 4, and 8 weeks), test-retest or learning effects remain a plausible alternative explanation for at least part of the observed 30STS improvement. The familiarization data reported (n = 8, ICC = 0.87) address short-term reliability but do not rule out a longer-term practice effect across three testing occasions eight weeks apart. I would ask the authors to discuss explicitly, in the Discussion rather than only the Limitations, how much of the observed improvement could plausibly be attributable to repeated testing exposure alone.

R1_Q2_Response: We thank the reviewer for their feedback. We agree that the possibility of a test-retest/ learning effect explaining some of the observed change, is an important consideration and worthy of a more in-depth discussion. We agree that repeated-testing effects cannot be excluded in the absence of a non-intervention control group. Available evidence suggests that learning effects in STS tests may be modest following familiarisation; however, these studies used related rather than identical protocols and do not eliminate the possibility of a longer-term practice effect in the present study. We have therefore expanded the Discussion and tempered the causal interpretation of the findings.

Please see page 22 lines 801-805 in the revised manuscript.

Please see page 25 lines 958-963 in the revised manuscript.

R1_Q3: The multiplicity of statistical approaches applied to overlapping outcomes (split-plot ANOVA, ANCOVA, Friedman/Wilcoxon, "average internal change," and "trajectory shape" comparisons) makes the overall analytical strategy difficult to follow and could benefit from a summary table.

The Methods section introduces several non-standard composite metrics (mean internal change, trajectory shape) specific to this study's time-course design, which is a reasonable approach to a genuinely novel analytical problem, but the reader must track, for each outcome, which combination of tests was applied and why. A single summary table mapping each outcome variable to its applicable test(s), sample size, and correction procedure would materially improve the Results section's readability, particularly given how many different subsample sizes (n = 28, 24, 22, 19) are already in play.

R1_Q3_Response: We thank the reviewer for their feedback. We appreciate the positive feedback regarding the reasonability of our approach to solve a novel analytical problem using non-standard composite metrics. A summary table which summarises the overall analytical and statistical strategy has now been provided as a supplementary table.

Please see file ‘Supplementary material_round 1 revisions_231026’

R1_Q4: The missing-data pattern across outcomes is substantial and unevenly distributed, which affects how the headline results should be interpreted. The full sample (n = 28) was used only for the basic pre-post 30STS comparison; the time-course analysis used n = 22; repetition-duration and ultrasound outcomes used n = 24; and the three-time-point repetition-duration analysis used n = 19 (intermittent: 12, continuous: 7). This is a reduction of up to 32% from the original sample in the most data-intensive analyses, and the continuous-LIPA group is reduced disproportionately (14 to 7, a 50% loss) in the final time-course subsample. The authors should report, even briefly, whether participants with missing data differed systematically from those with complete data on key baseline characteristics, since this directly affects confidence in the time-course findings presented as a primary contribution of the paper.

R1_Q4_Response: We thank the reviewer for highlighting this issue. We compared baseline characteristics between participants with complete and incomplete data for each subsample and examined baseline differences between intervention groups within each subsample. Participants with complete data differed from those with missing data only in waist-to-height ratio in the n = 22 and n = 19 subsamples. Baseline 30STS performance also differed between intervention groups within the n = 22, n = 24 and n = 19 subsamples. These findings and the unequal reduction in group sizes have now been reported and acknowledged as limitations.

Please see page 14 lines 541-546 in the revised manuscript.

Please see page 16 lines 627-649 in the revised manuscript.

Please see page 25 lines 940-958 in the revised manuscript.

R1_Q5: The USI group × time interaction is the most striking finding in the paper, and its interpretation would benefit from closer scrutiny of the baseline group difference. Table 1 shows that the intermittent-LIPA group had 0% participants classified as pre-sarcopenic at baseline versus 10% in the continuous group, and Table 3 shows baseline USI already differed numerically between groups (3.38 vs. 3.72). Although the ANCOVA approach appropriately adjusts for baseline when a significant baseline difference is detected, the manuscript does not report whether this baseline USI difference between groups was itself tested and found significant or non-significant before the ANCOVA was applied. I would ask the authors to state explicitly whether this baseline imbalance was tested and how it was handled, given how much interpretive weight is placed on this single interaction effect in a sample where 96% of participants were non-sarcopenic to begin with.

R1_Q5_Response: We thank the reviewer for their feedback. Baseline USI differed significantly between the intermittent- and continuous-LIPA groups (t(₂₂) = −2.47, p = 0.022). Baseline USI was therefore included as a covariate in the analysis. This has now been reported explicitly in the Results, and the Discussion clarifies that, because 96% of the subsample was non-sarcopenic at baseline, the physiological and clinical significance of the interaction remains uncertain.

Please see page 20 lines 754-757 in the revised manuscript.

Please see page 23 lines 884-889 in the revised manuscript.

R1_Q6: The rationale for analyzing only the first 10 repetitions, while methodologically justified, creates an asymmetry with the primary 30STS outcome that deserves explicit acknowledgment. The Methods justify this choice by noting the baseline range was 11–22 repetitions, ensuring all participants contributed data to all 10 repetition-duration slots. However, this means that for participants completing substantially more than 10 repetitions, the repetition-duration analysis characterizes only the first third to half of their total performance, potentially missing fatigue-related changes that manifest later in the set, which is precisely the functional endurance construct the Introduction motivates this analysis around. The Discussion's observation that only the repetition 7–8 difference changed significantly, with no change in overall fatigability metrics, could partly reflect this truncation rather than genuine absence of a training effect on later-set fatigue resistance. This should be noted as a specific limitation of the repetition-duration method, distinct from the more general limitations already listed.

R1_Q6_Response: We thank the reviewer for this observation. The first 10 repetitions were selected because all participants completed at least 10 repetitions at baseline, thereby retaining the full analysis sample and permitting repetition-matched comparisons across assessment points. We acknowledge, however, that this approach characterises only the earlier portion of the 30STS and may not capture fatigability emerging later in the test, particularly among higher-performing participants. This limitation has now been added to the manuscript. Future studies should analyse the complete task or compare normalised early, middle and late phases of each participant’s performance.

Please see page 25, lines 976–971.

R1_Q7: The self-reported adherence data for the two groups are not directly comparable, which complicates the interpretation of "equivalent effectiveness" between patterns. The intermittent group's adherence metric (number of compliant prompts, decreasing from 9±12 to 6±8 across the intervention) and the continuous group's metric (days complying with a single daily bout, stable at 7±1–2 out of 7) measure fundamentally different constructs: one tracks degree of compliance with a variable, uncapped number of daily opportunities, while the other tracks binary daily compliance with a fixed single bout.

The declining trend in the intermittent group's compliant-prompt count, which the authors note approached significance, could indicate declining adherence over the 8 weeks, a finding with direct relevance to the "equivalent effectiveness" conclusion driving the paper's practical recommendation that patterns can be prescribed "flexibly according to preference." I would ask the authors to discuss whether this declining adherence trend in the intermittent group is consistent with, or in tension with, the conclusion that both patterns are equally feasible long-term.

R1_Q7_Response: We thank the reviewer for highlighting this distinction. We agree that the diary-based adherence outcomes are not directly comparable because they reflect fundamentally different prescriptions: compliance with event-contingent prompts in the intermittent group versus completion of one prescribed daily bout in the continuous group. However, this does not prevent comparison of objectively measured physical-behaviour changes or functional outcomes between the intervention patterns. 

We also agree that the declining number of complied prompts requires careful interpretation. This reduction occurred alongside a reduction in the total number of prompts and shorter average sedentary-bout duration, suggesting that participants may have generated fewer prompts by interrupting sedentary behaviour before the device was activated. Accordingly, the raw number of complied prompts alone cannot distinguish declining adherence from a reduction in qualifying sedentary bouts. We have clarified this interpretation and tempered our conclusions regarding comparative feasibility.

Please see page 24 lines 930-939 in the revised manuscript.

R1_Q8: The exploratory correlation surviving Bonferroni correction (echo intensity and repetition 7–8 duration difference, intermittent group only) is presented with appropriate caution in the Discussion, but the Abstract does not convey this caution. The Abstract states "a positive association was found between the change in proximal GL echo intensity and the change in the repetition 7 vs. 8 difference in the intermittent group only," without any qualifying language, whereas the Discussion correctly notes this "should be viewed as hypothesis-generating" given the small subsample (n = 12) and the number of correlations tested. A reader encountering only the Abstract would not appreciate that this is a single surviving association out of a larger exploratory correlation matrix in a 12-person subgroup. I would suggest adding a brief qualifier directly in the Abstract.

R1_Q8_Response: We thank the reviewer for this observation. The Abstract has been revised to identify this finding explicitly as an exploratory, subgroup-specific association and the only association that survived multiplicity correction. The small subsample is also now reported.

Please see pages 1-2 lines 41-45 in the revised manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript entitled “Time course and muscular correlates of sit-to-stand adaptations following intermittent or continuous light-intensity activity in older adults” was reviewed. The article provides interesting information on the topic; however, adjustments need to be made so that the article can continue the path to publication. I kindly ask if all changes made to the text be highlighted in yellow or a different color in the text.

Below are the reviewer's considerations to be adjusted in the manuscript.

Title:
1. Include the type of study in the title.

Abstract:

2. Please create separate sections for "Background" and "Objectives."
3. Present the sociodemographic and anthropometric profile of the older women.
4. It is unclear what type of exercise the older women performed and how intensity was controlled. Please provide this information.
5. Please specify the study design and the statistical analyses performed, as well as the significance level adopted.
6. In the results section, it is important that the outcomes of the statistical analyses are described in greater detail.
7. Please provide a more assertive conclusion that directly addresses the proposed objectives.

Introduction:

8. It would be important to mention which metabolic pathway is assessed by the 30-second sit-to-stand test and its clinical relevance for the assessment of older adults.
9. When addressing the topic of falls, please present global data on their occurrence, as well as their economic consequences and impact on the autonomy of older adults.
10. Please explain the main physiological reasons why older adults fall.
11. You mention low-intensity physical activity in the introduction, but it is not clear what this means in terms of intensity, duration, and frequency, nor how it is measured. Please clarify these points.
12. The objectives presented at the end of the introduction should also be stated in the abstract.
13. Please try to shorten the introduction; it is currently too long and tends to become unfocused. My suggestion is to keep it to no more than two double-spaced pages.

Materials and Methods:

14. Begin the methods section by stating the study design and the location where data collection took place.
15. Please provide the detailed information used to arrive at the sample size of 28 participants for this study.
16. Please create a separate subsection presenting the inclusion and exclusion criteria for participants.
17. Since you conducted an intervention with older adults, the study must have been registered as a clinical trial. Did you register it? If so, please provide the registration link, number, and date. If it was not registered, please do so.
18. Please include a study flow diagram so that readers can see how many participants were recruited, how many were excluded, and how many remained for the analyses.
19. Please create a graphical figure (timeline/schedule) so that readers can follow the dynamics of the study, including the intervention periods and the data collection time points.
20. Regarding the age factor, was there any age cutoff for participant enrollment?
21. Please detail how randomization was performed. Were the principal researchers involved in this process, or were they blinded? Explain the blinding procedure, if any.
22. Why did you choose to assess the quadriceps and gastrocnemius muscles by ultrasound, and only the vastus lateralis? Please justify this choice.
23. Why did you assess the older adults only with the 30-second sit-to-stand test, rather than using additional protocols to cover all health-related physical fitness components? Please justify.
24. Please create a table presenting the training protocols performed by each group in a clearer, more didactic format.
25. Please make the description of the statistical analyses more objective. It is also necessary to include information on how the data were presented (parametric vs. non-parametric), as well as effect sizes and confidence intervals (these two must appear here and in the results section).

Results:

26. Table 1 is missing the between-group comparisons for the variables, so that readers can determine whether participants were similar or different at baseline. Please present the p value, the name of the statistical test, the effect size, and the confidence interval.
27. In Table 2, two black boxes appear to be displayed. If you decide to keep this table, please remove this information and include the details of the statistical analyses in the table instead. My other suggestion is to convert the significant results into figures and present the non-significant results only in the text. This would make the information more attractive to readers.
28. In Figure 2, the legends are making the information somewhat confusing. I suggest removing them and using only symbols to indicate the differences. Another suggestion is to convert the graph into a line graph, which provides readers with a more adequate temporal view of the data. Please follow these guidelines for the remaining figures.
29. Regarding Table 3, I suggest moving all results that did not reach statistical significance to the text and presenting the significant results as figures.

 Discussion:

30. The discussion does not clearly address the absence of a control group (no LIPA intervention). Part of the improvement in the 30STS may reflect a learning/familiarization effect with the test itself, since the same test was repeated at all assessment time points. Please discuss this possibility and justify why the improvements can be attributed to the intervention.
31. The statement that adaptations in repetition duration "may precede" the increase in the total number of repetitions is based on a comparison that was not statistically significant after correction (p = 0.076). Please temper this interpretation in the discussion, making explicit that this is a trend and not a confirmed finding, and avoid building conclusions on it.
32. The divergent response of the ultrasound-based sarcopenia index between groups (a decrease with intermittent LIPA and an increase with continuous LIPA) is described, but the discussion does not offer plausible physiological explanations for this opposite behavior. Please discuss possible mechanisms and acknowledge that, given the sample size, this result may be spurious.
33. The exploratory correlation (rs = 0.82) was calculated in a small subsample (n = 12) and in only one group, apparently without correction for multiple correlations. Please report how many correlations were tested, discuss these findings with greater caution, and avoid the physiological overinterpretation of a single association.
34. Please discuss the clinical meaning of the observed changes. How many additional repetitions in the 30STS are considered clinically relevant for older adults? Without this reference, it is difficult for readers to judge whether the improvement after 8 weeks matters in practice.
35. The discussion should address the generalizability of the findings: the sample included only older women, within a narrow age range, and with a specific LIPA dose. Please make explicit to which populations the results can and cannot be extended.

Conclusions:

36. Please rewrite this section so that it directly answers the objectives presented at the end of the introduction. Avoid statements that go beyond the data (for example, the recommendation that LIPA "can be prescribed flexibly" should be conditional on the limitations discussed) and briefly acknowledge the main limitations (absence of a control group, small sample, women only).

 

Author Response

R2_Q1: Include the type of study in the title.

R2_Q1_Response: We thank the reviewer for this suggestion. The title has been amended to identify the study as a two-arm quasi-randomised trial.

Please see page 1 line 4 in the revised manuscript.

R2_Q2: Please create separate sections for "Background" and "Objectives."

R2_Q2_Response: We thank the reviewer for their feedback. Separate sections have now been added into the abstract for "Background" and "Objectives."

Please see page 1 lines 16 &18 in the revised manuscript.

R2_Q3: Present the sociodemographic and anthropometric profile of the older women.

R2_Q3_Response: We thank the reviewer for their feedback. The average BMI and waist:height ratio of the original sample has now been added into the abstract alongside pre-existing information on age and gender.

Please see page 1 lines 22-23 in the revised manuscript.

R2_Q4: It is unclear what type of exercise the older women performed and how intensity was controlled. Please provide this information.

R2_Q4_Response: We thank the reviewer for their feedback. The type of physical activity prescribed was light intensity physical activity (LIPA), appropriately abbreviated throughout the abstract considering its frequent use. We have now provided additional clarity on the type of physical activity performed in each group by clarifying the amount, pattern of LIPA prescribed to each group, as well as clarified how intensity was controlled through acknowledging that compliance was objectively assessed using accelerometery at three separate time points.

Please see page 1 lines 23-25 in the revised manuscript.

However, we do not feel it is necessary to provide such detail in the abstract, considering the limited word count limit.

R2_Q5: Please specify the study design and the statistical analyses performed, as well as the significance level adopted.

R2_Q5_Response: We thank the reviewer for this suggestion.  The Abstract has been revised to state the study design, principal statistical approaches, significance threshold and multiplicity correction applied to the exploratory correlation analyses

Please see page 1 lines 29-32 in the revised manuscript.

R2_Q6: In the results section, it is important that the outcomes of the statistical analyses are described in greater detail.

R2_Q6_Response: We thank the reviewer for this suggestion.

The Abstract Results have been expanded to report the principal within-participant changes, between-pattern comparisons and group × time interaction, together with the corresponding p-values. Given the abstract word limit and the number of outcome-specific analyses, full test statistics are presented in the main Results section.

Please see page 1 lines 31,35,36,37,40, 44 & 45 in the revised manuscript.

R2_Q7: Please provide a more assertive conclusion that directly addresses the proposed objectives.

R2_Q7_Response: We thank the reviewer for their feedback. The Abstract conclusion has been revised to address directly the effects of both LIPA patterns on STS performance, the observed time course of adaptation and the ultrasound-derived findings.

Please see page 2 lines 46-52 in the revised manuscript.

R2_Q8: It would be important to mention which metabolic pathway is assessed by the 30-second sit-to-stand test and its clinical relevance for the assessment of older adults.

R2_Q8_Response: We thank the reviewer for this suggestion. The Introduction has been revised to clarify the contributions of phosphagen, glycolytic and oxidative metabolism to repeated STS performance, while noting that the 30STS is a functional test rather than a direct assessment of an individual metabolic pathway. Its clinical relevance to lower-limb function and independence in older adults has also been clarified.

Please see page 2 lines 62-82 in the revised manuscript.

R2_Q9: When addressing the topic of falls, please present global data on their occurrence, as well as their economic consequences and impact on the autonomy of older adults.

R2_Q9_Response: We thank the reviewer for their feedback. Global data concerning falls prevalence, temporal trends, consequences for autonomy and economic burden have now been added to the introduction.

Please see page 3 lines 89-93 in the revised manuscript.

R2_Q10: Please explain the main physiological reasons why older adults fall.

R2_Q10_Response: We thank the reviewer for their feedback. The Introduction has been revised to summarise the interacting musculoskeletal, sensory and nervous-system impairments that contribute to falls in older adults.  

Please see pages 2&3 lines 85-89 in the revised manuscript.

R2_Q11: You mention low-intensity physical activity in the introduction, but it is not clear what this means in terms of intensity, duration, and frequency, nor how it is measured. Please clarify these points.

R2_Q11_Response: We thank the reviewer for their feedback. The Introduction now provides the operational definition of LIPA used in the present study, based on the older-adult validation study underpinning the thigh-mounted accelerometer algorithm (Wullems et al, 2017). The Methods and intervention-summary tables provide the prescribed intensity, duration, frequency and accumulation pattern for each intervention, together with the accelerometery and diary procedures used to quantify physical behaviour and adherence.

 

Please see page 4 lines 144-148 in the revised manuscript and Table 2.

R2_Q12: The objectives presented at the end of the introduction should also be stated in the abstract.

R2_Q12_Response: Thank you. The study objectives are now stated in a dedicated Objectives subsection of the Abstract and aligned with those presented at the end of the Introduction.

Please see page 1 lines 18-22 in the revised manuscript.

R2_Q13: Please try to shorten the introduction; it is currently too long and tends to become unfocused. My suggestion is to keep it to no more than two double-spaced pages.

R2_Q13_Response:  Thank you. We appreciate the recommendation to maintain a focused Introduction. However, the revised Introduction has necessarily increased from approximately 1464 to 1721 words because it now incorporates the additional background requested in Responses R2_Q8–R2_Q11. Reducing it to approximately 800 words (two double-spaced pages, 10pt) would require removing much of this requested context and potentially weaken the rationale for the study. We have therefore retained the necessary detail while reviewing the section carefully for any remaining repetition or material that can be removed without compromising clarity.

R2_Q14: Begin the methods section by stating the study design and the location where data collection took place.

R2_Q14_Response: Thank you. The Methods section now begins by stating the study design and location of data collection.

Please see page 6 lines 203-205 in the revised manuscript.

R2_Q15: Please provide the detailed information used to arrive at the sample size of 28 participants for this study.

R2_Q15_Response: Thank you. The Sample Size subsection has been revised to report the a priori calculation, including its evidential basis, statistical assumptions, estimated sample requirement and allowance for attrition.

Please see page 6 lines 207-220 in the revised manuscript.

R2_Q16: Please create a separate subsection presenting the inclusion and exclusion criteria for participants.

R2_Q16_Response: We thank the reviewer for their feedback. A separate subsection has now been created presenting the inclusion and exclusion criteria for participants.

Please see page 8 lines 279-299 in the revised manuscript.

R2_Q17: Since you conducted an intervention with older adults, the study must have been registered as a clinical trial. Did you register it? If so, please provide the registration link, number, and date. If it was not registered, please do so.

R2_Q17_Response:

Thank you. This study was not prospectively registered. At the time of commencement, it was classified and ethically approved institutionally as a non-clinical behavioural intervention, and trial registration was not stipulated as a condition of approval. We acknowledge that broader contemporary definitions of clinical trials may encompass behavioural interventions of this nature. As retrospective registration cannot provide the transparency afforded by prospective registration, we have stated the absence of registration explicitly in the manuscript and will prospectively register future studies of this type.

Please see page 6 lines 231-232.

R2_Q18: Please include a study flow diagram so that readers can see how many participants were recruited, how many were excluded, and how many remained for the analyses.

R2_Q18_Response: We thank the reviewer for their feedback. A study flow diagram has now been added detailing recruitment, exclusions, and participants remaining for each analyses and subsamples.

Please see page 7 in the revised manuscript.

R2_Q19: Please create a graphical figure (timeline/schedule) so that readers can follow the dynamics of the study, including the intervention periods and the data collection time points.

R2_Q19_Response: We thank the reviewer for their feedback. A graphical figure which outlines the study dynamics including intervention period and data collection time points has now been added.

Please see page 9 lines 328-337 in the revised manuscript.

R2_Q20: Regarding the age factor, was there any age cutoff for participant enrollment?

R2_Q20_Response: We thank the reviewer for their feedback. The criteria for age was between the ages of 65-85y. This information has now been added into the manuscript along with the new section of inclusion/ exclusion criteria consistent with the previous response ‘R2_Q16_Response’.

Please see page 8 lines 279-281 in the revised manuscript.

R2_Q21: Please detail how randomization was performed. Were the principal researchers involved in this process, or were they blinded? Explain the blinding procedure, if any.

R2_Q21_Response: Thank you. Participants were allocated in a 1:1 ratio using a quasi-randomised sequence based on order of enrolment. The principal researcher was involved in implementing the allocation sequence, and no allocation concealment or blinding was employed. The Methods section has been clarified accordingly.

 

Please see page 9 lines 318-321 in the revised manuscript.

 

R2_Q22: Why did you choose to assess the quadriceps and gastrocnemius muscles by ultrasound, and only the vastus lateralis? Please justify this choice.

R2_Q22_Response: Thank you. The Methods section now explains the physiological and functional rationale for selecting the GM, GL and VL for ultrasound assessment.

 

Please see page 10 lines 367-371 & 374-380 in the revised manuscript.

 

R2_Q23: Why did you assess the older adults only with the 30-second sit-to-stand test, rather than using additional protocols to cover all health-related physical fitness components? Please justify.

R2_Q23_Response: Thank you. The study was designed specifically to examine the time course of STS adaptation rather than to assess every health-related physical-fitness component. The 30STS provides an integrated assessment of lower-limb functional strength and endurance, while repetition-level timing enabled movement speed and within-test fatigability to be examined. A broader fitness battery was not included to limit participant burden across the repeated functional and ultrasound assessments and extended accelerometer monitoring. This rationale and the resulting limitation have now been clarified in the Methods and Strengths and Limitations sections.

Please see page 1, lines 431–435 and page 24, lines 926–929.

 

R2_Q24: Please create a table presenting the training protocols performed by each group in a clearer, more didactic format.

R2_Q24_Response: We thank the reviewer for their feedback. This table (Table 2) presenting the frequency, intensity, time, type, pattern, and duration of the intervention groups has been created. This is a great addition to the paper, and we thank the reviewer for this suggestion.

Please see page 14 lines 532-536 in the revised manuscript.

 

R2_Q25: Please make the description of the statistical analyses more objective. It is also necessary to include information on how the data were presented (parametric vs. non-parametric), as well as effect sizes and confidence intervals (these two must appear here and in the results section).

R2_Q25_Response: Thank you. The Statistical Analysis section has been revised to clarify the presentation of parametric and non-parametric data, the selection of statistical tests, and the calculation and interpretation of effect sizes and 95% confidence intervals. Effect sizes and confidence intervals have also been added to the corresponding Results, and Supplementary Table S1 provides a concise summary of the analytical approach.

Please see pages 14-17, lines 541-546, 552-556, 560-563, 564-571, 592-613 in the revised manuscript

Please see highlighted yellow text on pages 16-21 for added effect sizes and confidence intervals in the revised manuscript

Please see file ‘Supplementary material_round 1 revisions_231026’

 

R2_Q26: Table 1 is missing the between-group comparisons for the variables, so that readers can determine whether participants were similar or different at baseline. Please present the p value, the name of the statistical test, the effect size, and the confidence interval.

R2_Q26_Response: We thank the reviewer for their feedback. Between group comparisons have now been added into table 1, including the name of the statistical test (independent samples t-test or Mann-Whitney U), effect size (Cohens D or Hodges-Lehmann), and confidence intervals.

Please see table 3, page 17 lines 653-657 in the revised manuscript.

R2_Q27: In Table 2, two black boxes appear to be displayed. If you decide to keep this table, please remove this information and include the details of the statistical analyses in the table instead. My other suggestion is to convert the significant results into figures and present the non-significant results only in the text. This would make the information more attractive to readers.

R2_Q27_Response: We thank the reviewer for their feedback. This table has now been removed and replaced with a line graph that covers the significant effect of time on sedentary behaviour. The remaining non-significant results have been discussed in the text.

Please see Figure 4 page 18 line 688-689 in the revised manuscript.

R2_Q28: In Figure 2, the legends are making the information somewhat confusing. I suggest removing them and using only symbols to indicate the differences. Another suggestion is to convert the graph into a line graph, which provides readers with a more adequate temporal view of the data. Please follow these guidelines for the remaining figures.

R2_Q28_Response: We thank the reviewer for their feedback. The legends have been removed in all figures and only symbols used to indicate the differences. Line graphs have also now been used throughout to provide a more adequate temporal view of the data.

Please see updated figures throughout the amended manuscript.

R2_Q29: Regarding Table 3, I suggest moving all results that did not reach statistical significance to the text and presenting the significant results as figures.

R2_Q29_Response:

Thank you. The relevant figures have been converted to line graphs, and the presentation of statistical significance has been simplified as requested.

Please see Figures 4-7 on pages 18-21.

R2_Q30: The discussion does not clearly address the absence of a control group (no LIPA intervention). Part of the improvement in the 30STS may reflect a learning/familiarization effect with the test itself, since the same test was repeated at all assessment time points. Please discuss this possibility and justify why the improvements can be attributed to the intervention.

R2_Q30_Response: Thank you. The Discussion (STUDY LIMITATIONS) now explicitly acknowledges that, without a non-intervention control group, temporal and repeated-testing effects cannot be excluded. Although familiarisation was undertaken before baseline assessment, we have tempered the causal interpretation and now describe the improvements as intervention-associated rather than definitively attributable to LIPA.

 

Please see page 22 lines 801-805 in the revised manuscript.

Please see page 25 lines 958-963 in the revised manuscript.

R2_Q31: The statement that adaptations in repetition duration "may precede" the increase in the total number of repetitions is based on a comparison that was not statistically significant after correction (p = 0.076). Please temper this interpretation in the discussion, making explicit that this is a trend and not a confirmed finding, and avoid building conclusions on it.

R2_Q31_Response: Thank you the Abstract, Discussion and Conclusions have been revised to identify the observed time-course pattern explicitly as a statistical trend and to clarify that it does not confirm that changes in repetition duration preceded improvements in total repetitions.

Please see page 2 lines 47-50

Please see page 22 lines 789-793

R2_Q32: The divergent response of the ultrasound-based sarcopenia index between groups (a decrease with intermittent LIPA and an increase with continuous LIPA) is described, but the discussion does not offer plausible physiological explanations for this opposite behavior. Please discuss possible mechanisms and acknowledge that, given the sample size, this result may be spurious.

R2_Q32_Response: Thank you. The Discussion now presents repeated knee-extensor loading during intermittent LIPA as a plausible explanation for the divergent USI response, while acknowledging that the proposed mechanism remains speculative and that the small subsample means a chance finding cannot be excluded.

.

Please see page 23 lines 873-883 in the revised manuscript.

R2_Q33: The exploratory correlation (rs = 0.82) was calculated in a small subsample (n = 12) and in only one group, apparently without correction for multiple correlations. Please report how many correlations were tested, discuss these findings with greater caution, and avoid the physiological overinterpretation of a single association.

R2_Q33_Response: Thank you. Twelve exploratory correlations were tested, with a Bonferroni-adjusted significance threshold of p < 0.0042. One association within the intermittent-LIPA subgroup remained significant after correction (rₛ = 0.82, p = 0.001, n = 12). The complete set of exploratory correlations is reported transparently in Supplementary Table S1. The Discussion identifies the group-specific finding as hypothesis-generating, avoids causal interpretation and notes that confirmation in a larger sample is required.

 

Please see pages 1-2 lines 41-45 in the revised manuscript

Please see page 21 lines 770-779 in the revised manuscript

Please see page 24 lines 898-901 in the revised manuscript.

 

R2_Q34: Please discuss the clinical meaning of the observed changes. How many additional repetitions in the 30STS are considered clinically relevant for older adults? Without this reference, it is difficult for readers to judge whether the improvement after 8 weeks matters in practice.

R2_Q34_Response: We thank the reviewer for their feedback. The clinical meaning of observed changes in 30STS was present in the original manuscript:

‘Our results demonstrate that displacing SB with LIPA in older women improved 30STS performance by approximately 2–3 repetitions over eight weeks. This exceeds the minimal detectable change of 1 repetition determined in older adults [115], and comparable to the minimal clinically important difference of 2 repetitions observed in clinical populations [116]. This suggests that such a change is both statistically significant and potentially clinically relevant.’

Please see page 22 lines 798-803 in the revised manuscript.

Furthermore, we also believe that the text in the subsequent paragraph does help readers further judge whether the observed improvement is relevant to practice:

‘The current results also provide novel insights concerning the time course of change in 30STS performance. Although improvement from baseline to week 4 approached significance, statistically significant improvements were evident at week 8, suggesting that functional adaptation may begin earlier but becomes more consistently detectable following eight weeks of SB displacement with LIPA. A recent systematic review identified a large effect size on STS performance following 12-16 weeks of progressive resistance exercise in older adults [122]. Chair based exercise (i.e. remaining seated and more stable), which may be suitable for frail or deconditioned older adults [123], produces a mean improvement of ~2.3 reps over 14–15 weeks [124]. Although, comparisons between different studies and populations require caution, the present home-based LIPA intervention produced a similar magnitude of improvement over eight weeks and required little equipment or direct supervision. Older adults exhibit poor lifelong adherence to MVPA [44,45], and report lack of equipment/ knowledge [48-50], travel infrastructure [52] and supervision [51], as barriers. LIPA may therefore provide a more accessible home-based approach to improving physical function, particularly for older adults unable or unwilling to undertake structured MVPA [47].’

Please see page 22 lines 813-828 in the revised manuscript.

 

R2_Q35: The discussion should address the generalizability of the findings: the sample included only older women, within a narrow age range, and with a specific LIPA dose. Please make explicit to which populations the results can and cannot be extended.

R2_Q35_Response: Thank you. The Strengths and Limitations section now specifies the population and intervention conditions to which the findings most directly apply and identifies the populations and activity prescriptions to which they should not be assumed to generalise.

 

Please see page 25 lines 972-977 in the revised manuscript.

R2_Q36: 36: Please rewrite this section so that it directly answers the objectives presented at the end of the introduction. Avoid statements that go beyond the data (for example, the recommendation that LIPA "can be prescribed flexibly" should be conditional on the limitations discussed) and briefly acknowledge the main limitations (absence of a control group, small sample, women only).

R2_Q36_Response: Thank you. The Conclusion has been revised to address the study objectives directly by summarising the overall STS response, the time-course findings and the ultrasound-derived outcomes. Interpretations have been tempered to reflect the small women-only sample, absence of a non-intervention control group and exploratory nature of the physiological associations. The practical implication of intermittent LIPA is now presented conditionally.

 

Please see pages 25&26 lines 979-990 in the revised manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors,

Thank you for providing the revised version of the manuscript. Upon critical review of the adjusted material, I have noted significant improvement in the text. Therefore, I recommend that the work be accepted for publication.