Eccentric Quasi-Isometric Exercise Produces Greater Impulse with Less Pain than Isokinetic Heavy–Slow Resistance Exercise in Ankle Plantar Flexors: Quasi-Randomized Controlled Trial

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

The presented paper compares the EQI and the IHSR protocols in terms of their effects, and shows results that imply the EQI might be superior to IHSR for the ankle plantar flexors.

The paper is interesting and easy to follow but some corrections are warranted before it is ready for publication:

1. The references are not formatted properly (missing DOI for all papers and using et al. instead of listing all authors when there are less than 10).

2. In the introduction section, the overall concepts of muscle contractions are well explained but related work could be discussed in more detail. I understand there is a single study that compares EQI with other forms of contraction, but some other studies that compare different forms of contraction for ankle flexors (or other muscles) would be welcome. Their descriptions do not have to be long, but they could be beneficial for the reader so that the methods from literature that compare different types of contractions could be better understood (what comparison criteria is used, what size of subject groups, experimental conditions, etc.)

3. When describing statistical tests, it is mentioned that Mann Whitney and the t-test are used. These tests are used in a similar way, one just requires stricter conditions (in this case that would be normality). When reporting the results of the statistics, it is not mentioned which one was used and whether the normality test was met or not. This just needs some clarification, either in the method or the resutls.

4. Figure 4. is quite blurry, please provide a vector image (svg format) or a raster with suitable resolution.

Author Response

[for conveniance, we attached full response document as well]

The presented paper compares the EQI and the IHSR protocols in terms of their effects, and shows results that imply the EQI might be superior to IHSR for the ankle plantar flexors. The paper is interesting and easy to follow but some corrections are warranted before it is ready for publication.

RESPONSE: We thank the reviewer for the positive general assessment of the study’s quality and clarity. We have carefully addressed all specific comments provided below to improve the rigor, precision, and presentation of the manuscript.

 

1. The references are not formatted properly (missing DOI for all papers and using et al. instead of listing all authors when there are less than 10).

RESPONSE: Thank you for noticing this. We have thoroughly revised the reference list to ensure compliance with MDPI formatting guidelines. All available DOIs have been added, and all author names (up to ten) are now listed in full, replacing et al. where applicable.

 

2. In the introduction section, the overall concepts of muscle contractions are well explained but related work could be discussed in more detail. I understand there is a single study that compares EQI with other forms of contraction, but some other studies that compare different forms of contraction for ankle flexors (or other muscles) would be welcome. Their descriptions do not have to be long, but they could be beneficial for the reader so that the methods from literature that compare different types of contractions could be better understood (what comparison criteria is used, what size of subject groups, experimental conditions, etc.)

RESPONSE: We appreciate this helpful suggestion. To strengthen the contextual background, we have expanded the Introduction by adding brief summaries of studies comparing different contraction types (isometric, concentric, eccentric) in other muscle groups, as well as research on ankle plantar flexors. This provides readers with a clearer overview of existing methodological approaches and comparison criteria.

“Beyond the limited number of studies directly examining EQI, several investigations have compared distinct contraction modes in other muscle groups. For example, Royer et al. [16] compared isometric, concentric, and eccentric contractions of the knee ex-tensors matched for torque–time integral, demonstrating contraction-specific fatigue and neuromuscular responses. Similarly, Chapman et al. [17] observed greater muscle damage and soreness after fast-velocity eccentric contractions compared to slower ones. For the ankle plantar flexors, Ferri et al. [18] and Wiesinger et al. [19] examined strength and tendon adaptations following different loading regimes, highlighting the sensitivity of these muscles to contraction type and strain magnitude. These findings emphasize that contraction mode, load intensity, and velocity critically influence both mechanical output and subsequent adaptations. These factors that guided the present comparison between EQI and IHSR protocols.”

 

3. When describing statistical tests, it is mentioned that Mann Whitney and the t-test are used. These tests are used in a similar way, one just requires stricter conditions (in this case that would be normality). When reporting the results of the statistics, it is not mentioned which one was used and whether the normality test was met or not. This just needs some clarification, either in the method or the resutls.

RESPONSE: We thank the reviewer for noting this. To clarify, we expanded the text:

“We used an independent samples t-test to check the differences between the groups for body height, body mass, age, baseline MVIC, total torque impulse and time under tension. Effort levels and comfort scores were compared with Mann-Whitney test.”

4. Figure 4. is quite blurry, please provide a vector image (svg format) or a raster with suitable resolution.

RESPONSE: We appreciate the reviewer’s attention to figure quality. However, the manuscript currently includes three figures only (Figures 1–3). It is possible that this comment refers to one of these figures, likely Figure 3, which includes two panels and may have appeared unclear? In any case, we uploaded better quality images. We will also upload even higher resolution figures into submission system, for the convenience of the production team.

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents an interesting and timely study comparing eccentric quasi-isometric (EQI) contractions with isokinetic heavy-slow resistance (IHSR) exercise in ankle plantar flexors. The work is original, well-structured, and addresses a relevant question for both sports science and rehabilitation. The findings — notably greater impulse and lower pain following EQI — are promising and may have meaningful clinical implications. However, several aspects require clarification and refinement before publication:

1)The authors should state the study design explicitly (“quasi-randomized controlled trial”) and briefly mention key limitations.

2)The authors should use consistent abbreviations and terms (e.g., “IHSR” vs. “HSR”) throughout the text.

3)The authors should improve figure legends to enhance clarity (e.g., define all symbols and abbreviations) while adding numbers at risk or participant counts where relevant.

4)The authors should shorten some sections to focus on the most important findings and avoid overinterpretation.

5)The suggestion for use in Achilles tendinopathy is compelling but speculative. The authors should phrase it more cautiously and highlight the need for dedicated clinical studies.

6)As this is a short-term, quasi-randomized trial, conclusions should avoid implying causality. The authors should revise statements to emphasize associations rather than effects.

7)The young, healthy, and physically active sample limits applicability to clinical or older populations. The authors should highlight this limitation more explicitly and temper claims about clinical translation.

8)The lack of allocation concealment and participant blinding introduces bias risk. This should be acknowledged clearly in the Methods and Limitations.

9)The protocols may not be fully load-matched despite preliminary testing. The authors should clarify how equivalence was determined and discuss how this might affect comparisons.

10)Pain outcomes are based on subjective self-report. The authors should acknowledge this limitation and discuss potential bias, especially given variability in training history.

Author Response

[we also attached full response document for your conveniance]

This manuscript presents an interesting and timely study comparing eccentric quasi-isometric (EQI) contractions with isokinetic heavy-slow resistance (IHSR) exercise in ankle plantar flexors. The work is original, well-structured, and addresses a relevant question for both sports science and rehabilitation. The findings — notably greater impulse and lower pain following EQI — are promising and may have meaningful clinical implications. However, several aspects require clarification and refinement before publication.

RESPONSE: We thank the reviewer for the positive assessment of the manuscript’s originality, structure, and clinical relevance. We have carefully addressed all the specific comments provided below, clarifying methodological details, refining the discussion, and ensuring that all statistical and interpretative aspects are transparently reported.

 

1)The authors should state the study design explicitly (“quasi-randomized controlled trial”) and briefly mention key limitations.

RESPONSE: Thank you for raising this issue, we added explicit study desing in study title and abstract, as well as methods.

In addition, we expanded the limitations:

“Finally, the quasi-randomized allocation procedure may have introduced some degree of selection bias, as group assignment was not entirely random. Although stratification by sex helped to balance participant characteristics, residual confounding effects can-not be fully excluded.”

2)The authors should use consistent abbreviations and terms (e.g., “IHSR” vs. “HSR”) throughout the text.

RESPONSE: We appreciate this observation. We have carefully reviewed the entire manuscript to ensure consistent use of abbreviations and terminology. All instances of “HSR” referring to the isokinetic heavy-slow resistance protocol have been replaced with “IHSR,” in accordance with the abbreviation defined in the Methods section.

3) The authors should improve figure legends to enhance clarity (e.g., define all symbols and abbreviations) while adding numbers at risk or participant counts where relevant.

RESPONSE: Thank you for this helpful suggestion. We have revised all figure legends to ensure that every symbol and abbreviation is clearly defined. Participant numbers (n = 16 per group) were also added where relevant to facilitate interpretation.

4)The authors should shorten some sections to focus on the most important findings and avoid overinterpretation.

RESPONSE: We agree with the reviewer that the discussion could be made more concise and focused on the core findings. Accordingly, we have streamlined several parts of the Discussion to reduce redundancy and remove less essential content. In particular, the previous paragraph describing a potential Smith machine application was deleted, as it was not part of the experimental protocol and could have been misinterpreted as a practical recommendation.

5)The suggestion for use in Achilles tendinopathy is compelling but speculative. The authors should phrase it more cautiously and highlight the need for dedicated clinical studies.

RESPONSE: We appreciate this important comment. We have revised the text in the Practical application subsection to present the potential use of EQI in Achilles tendinopathy more cautiously. The revised paragraph now explicitly acknowledges that these implications are speculative and emphasizes the need for future clinical trials to verify effectiveness and safety in patient populations:

“While the current findings suggest that EQI may represent an efficient and well-tolerated loading strategy, its potential application in individuals with Achilles tendinopathy remains speculative. Further research is required to verify whether similar benefits would be observed in symptomatic populations. Therefore, future clinical studies should directly compare EQI with established rehabilitation protocols (e.g., eccentric or heavy-slow resistance training) to determine its safety, feasibility, and long-term efficacy in tendon pathology management. The practical value of the study can be identified mainly in the context of improved exercise or exercise-therapeutic interventions for ankle plantar flexors, potentially serving as an alternative approach for treating Achilles tendon pathologies, such as Achilles tendinopathy. Based on previous evidence, adaptations of injured tendons can occur with different contraction modes, provided that a minimum threshold of mechanical stress on the tendon and joint is reached [31,32], In light of the present findings, which showed that the EQI protocol produced a greater total torque impulse with less pain than the IHSR proto-col, it is reasonable to speculate that EQI training might hold potential for use in patients with Achilles tendinopathy. However, this assumption remains hypothetical, and future clinical studies are required to confirm whether such benefits translate to symptomatic populations. While EQI contractions can theoretically be performed without specialized equipment, such applications require further validation to ensure comparable loading conditions and safety before being implemented in training or rehabilitation practice.”

6) As this is a short-term, quasi-randomized trial, conclusions should avoid implying causality. The authors should revise statements to emphasize associations rather than effects.

RESPONSE: We appreciate the reviewer’s concern. However, while we acknowledge that the quasi-randomized design introduces some methodological limitations (e.g., potential selection bias), the present study remains an experimental intervention trial, not an observational one. The design allows for inferences about short-term cause–effect relationships between the applied exercise protocols and measured outcomes, albeit within the constraints of limited randomization and duration. We have therefore maintained causal terminology where appropriate but have clarified in the Limitations section that these causal interpretations should be considered within the framework of a quasi-experimental design.

“Finally, the quasi-randomized allocation procedure may have introduced some degree of selection bias, as group assignment was not entirely random. Although stratification by sex helped to balance participant characteristics, residual confounding effects can-not be fully excluded. Although the quasi-randomized design allows for inference of short-term cause–effect relationships between the applied interventions and measured outcomes, the absence of full randomization warrants cautious interpretation. Thus, while the study supports preliminary causal conclusions, further fully randomized and longer-term trials are needed to strengthen causal inference.”

7) The young, healthy, and physically active sample limits applicability to clinical or older populations. The authors should highlight this limitation more explicitly and temper claims about clinical translation.

RESPONSE: We agree with the reviewer’s observation. Although this limitation was briefly mentioned, we have now made it more explicit in the Limitations section and have softened the language in the Practical application paragraph to ensure that our conclusions are not overstated with respect to clinical populations.

“The study sample consisted of young, healthy, and regularly active participants, which restricts the generalizability of the findings. The observed responses may differ in older adults or clinical populations, where neuromuscular characteristics, pain perception, and recovery capacity could substantially vary. Consequently, any clinical implications should be interpreted with caution until validated by dedicated trials.”

 

 

8)The lack of allocation concealment and participant blinding introduces bias risk. This should be acknowledged clearly in the Methods and Limitations.

RESPONSE: We agree that the lack of blinding may have introduced potential performance and measurement bias, particularly for subjective outcomes such as pain and exertion ratings. To address this, we have added a corresponding note in the Limitations section discussing this potential source of bias and its possible impact on the findings.

“Additionally, since neither participants nor the personnel conducting the interventions and assessments were blinded to group allocation, a potential performance and measurement bias cannot be fully excluded. This limitation may have particularly influenced subjective outcomes such as perceived pain and exertion, as participants might have been consciously or subconsciously affected by expectations related to the type of exercise performed.”

 

9)The protocols may not be fully load-matched despite preliminary testing. The authors should clarify how equivalence was determined and discuss how this might affect comparisons.

RESPONSE: We thank the reviewer for raising this important point. We agree that load matching between contraction modes is one of the shortcomings of this study. As described in the Methods section, our intention was to achieve approximate load matching based on pilot torque–time integral data. Nevertheless, it appears that our pilot data was insufficient to achieved good matching, and the EQI group achieved a higher total impulse despite a much shorter contraction duration and markedly lower perceived exertion. While this is a methodological shortcoming, but as evidence of greater efficiency of EQI is even stronger – as it elicits less pain/MVC reduction while providing greater total torque integral.

 

To address this concern, we (1) clarified in the Methods section that the matching was approximate rather than exact, (2) emphasized in the Discussion that the higher impulse reflects superior efficiency rather than unequal loading, and (3) noted that future studies could normalize impulse to contraction count or duration to further refine between-mode comparisons.

 

“The two protocols were designed to achieve approximate load matching. In the pilot phase (n = 5), within-subject comparisons were used to determine the number of repetitions producing comparable torque–time integrals between EQI and isokinetic heavy-slow resistance (IHSR) contractions performed at 30°/s. Each pilot participant completed one EQI contraction and a series of IHSR contractions (random order, 10 min break in between) until the cumulative torque–time integral of the ISHR matched that of the EQI contraction. This procedure indicated that approximately 30 IHSR repetitions were needed to match one EQI contraction, and this finding informed the de-sign of the main parallel-group study. However, since the experimental trial compared independent groups of different participants, between-subject variability in strength and contraction characteristics was expected to contribute to imperfect matching of total impulse. Therefore, the comparison should be interpreted in the context of matched loading intent rather than exact mechanical equivalence.”

Discussion:

“Although our study aimed for approximate load matching based on pilot data, the EQI group ultimately achieved a greater total impulse while reporting lower exertion and pain. Rather than contradicting the study rationale, this finding strengthens the interpretation that EQI represents a more mechanically efficient contraction mode, capable of producing higher overall work with less pain and lower MVIC reduction after-wards. Speculatively, this may reflect the controlled transition between isometric and eccentric phases allows sustained torque generation without excessive muscle damage. Nevertheless, it should be acknowledged that the protocols were not perfectly load-matched, and future work should consider normalization metrics such as impulse per contraction or impulse per second to enhance comparability.”

 

10) Pain outcomes are based on subjective self-report. The authors should acknowledge this limitation and discuss potential bias, especially given variability in training history.

RESPONSE: We agree with the reviewer. While this limitation was already briefly noted, we have expanded the relevant section to explicitly address the potential bias associated with subjective pain assessment and variability in participants’ training backgrounds.

“Pain outcomes were based on subjective self-report and may have been influenced by individual pain tolerance or prior training experience. Although standardized instructions were used, variability in pain perception between participants cannot be fully excluded.”

Reviewer 3 Report

Comments and Suggestions for Authors

Recently, there has been growing interest in optimising exercise protocols in sports training and rehabilitation, with particular attention to eccentric quasi-isometric (EQI) contractions, which involve maintaining joint position until isometric failure and then resisting the subsequent eccentric phase. Evidence directly comparing EQI with other contraction modes remains scarce.

AUTHORS examined the short-term effects of EQI versus isokinetic heavy-slow resistance (IHSR) exercise on ankle plantar flexors, focusing on pain, range of motion (RoM), and strength performance.

Thirty-two physically active participants were allocated to EQI (n = 16) or IHSR (n = 16) groups and as-sessed at baseline, immediately post-exercise, and 24 and 48 hours later. Both groups performed three exercise sets with 3-min breaks.

THEIR protocols were designed to ap-proximate matched loading, based on preliminary testing. Nevertheless, the EQI group achieved significantly greater total impulse (p = 0.028), shorter time under tension (p = 0.001), and lower effort scores (p < 0.001). Group × time analysis revealed less decline in maximal voluntary isometric contraction torque (p = 0.002; η² = 0.16), as well as lower general (p < 0.001; η² = 0.32) and activity-related pain (p < 0.001; η² = 0.32) in the EQI group, with no significant differences in dorsiflexion RoM (p = 0.893).

AUTHORS highlighted that EQI produced a higher torque impulse while inducing less fatigue and post-exercise pain than IHSR, suggesting it may be a more efficient loading strategy for the ankle plantar flexors.

The study has merits and contributes to the scientific literature.

I have the following comments for the authors.

1) The abstract could be improved. I suggest minimizing the data/formulas and better explaining the true contribution.

2) The intro could be improved by better detailing the contribution of each study. The first opening sentence, “Over the last decade, there has been a growing interest in optimizing exercise protocols in the scientific literature, with research focusing on exercise intensity 1–3, volume 4, 5,

and the type of muscle contraction 2, 6–9.” condenses 9 citations.

3) Use “[]” to cite references according to the MDPI standard.

4) The methods are perfect, but perhaps a flowchart illustrating the design could be further helpful.

5) In the results, I suggest including a piece of text introducing the excellent thematic analysis organized into sections. In some figures, data labels could improve the readability of the work.

Author Response

[we attached full response document for your conveniance as well]

Recently, there has been growing interest in optimising exercise protocols in sports training and rehabilitation, with particular attention to eccentric quasi-isometric (EQI) contractions, which involve maintaining joint position until isometric failure and then resisting the subsequent eccentric phase. Evidence directly comparing EQI with other contraction modes remains scarce. AUTHORS examined the short-term effects of EQI versus isokinetic heavy-slow resistance (IHSR) exercise on ankle plantar flexors, focusing on pain, range of motion (RoM), and strength performance. Thirty-two physically active participants were allocated to EQI (n = 16) or IHSR (n = 16) groups and assessed at baseline, immediately post-exercise, and 24 and 48 hours later. Both groups performed three exercise sets with 3-min breaks. THEIR protocols were designed to ap-proximate matched loading, based on preliminary testing. Nevertheless, the EQI group achieved significantly greater total impulse (p = 0.028), shorter time under tension (p = 0.001), and lower effort scores (p < 0.001). Group × time analysis revealed less decline in maximal voluntary isometric contraction torque (p = 0.002; η² = 0.16), as well as lower general (p < 0.001; η² = 0.32) and activity-related pain (p < 0.001; η² = 0.32) in the EQI group, with no significant differences in dorsiflexion RoM (p = 0.893). AUTHORS highlighted that EQI produced a higher torque impulse while inducing less fatigue and post-exercise pain than IHSR, suggesting it may be a more efficient loading strategy for the ankle plantar flexors.

The study has merits and contributes to the scientific literature.

RESPONSE: We thank the reviewer for the positive assessment and constructive feedback.

I have the following comments for the authors.

 

• The abstract could be improved. I suggest minimizing the data/formulas and better explaining the true contribution.

RESPONSE: We appreciate the reviewer’s feedback. Given that other reviewers valued the clarity and completeness of the reported results, we retained the existing data presentation but expanded the concluding part of the abstract to better highlight the broader contribution and practical relevance of the findings.

 

“The results contribute to the understanding of contraction-specific efficiency and may inform the design of future training and rehabilitation protocols targeting the ankle plantar flexors.”

 

2) The intro could be improved by better detailing the contribution of each study. The first opening sentence, “Over the last decade, there has been a growing interest in optimizing exercise protocols in the scientific literature, with research focusing on exercise intensity 1–3, volume 4, 5, and the type of muscle contraction 2, 6–9.” condenses 9 citations.

RESPONSE: We appreciate the reviewer’s suggestion. However, other reviewers advised the opposite — to reduce the excessive length and citation density of the introduction to improve readability. To balance both perspectives, we have retained the concise structure of the opening sentence but added short explanatory phrases to clarify the thematic contribution of each research area without overextending the paragraph.

 

3) Use “[]” to cite references according to the MDPI standard.

RESPONSE: All reference citations throughout the manuscript were reformatted from parentheses “( )” to square brackets “[ ]” in accordance with MDPI style guidelines.

 

4) The methods are perfect, but perhaps a flowchart illustrating the design could be further helpful.

RESPONSE: We appreciate the reviewer’s positive comment on the Methods section and the thoughtful suggestion. Given the study’s straightforward parallel-group design with clearly described procedures and time points, we believe that an additional flowchart would not substantially enhance clarity. Therefore, we have chosen to retain the concise text-based description, which already provides a clear overview of the experimental design.

 

5) In the results, I suggest including a piece of text introducing the excellent thematic analysis organized into sections. In some figures, data labels could improve the readability of the work.

RESPONSE: We thank the reviewer for this thoughtful comment and for the positive feedback on the organization of the Results section. To further improve readability and flow, we added a brief introductory paragraph at the beginning of the Results section to guide the reader through its structure. Additionally, data labels were added to relevant figures to enhance visual clarity and facilitate interpretation.

“The results are presented in thematic sections covering (1) baseline comparisons between groups, (2) mechanical outcomes derived from torque–time analysis, and (3) changes in performance, pain, and range of motion across time points. Descriptive statistics are followed by inferential analyses to provide a comprehensive overview of group differences and temporal effects.”

Reviewer 4 Report

Comments and Suggestions for Authors

This study compared the short-term effects of centrifugal quasi-isometric contraction versus isokinetic slow-speed heavy-load training on the ankle plantar flexors. The results support the EQI protocol's advantages in generating greater impulse, lower fatigue, and reduced pain. However, the manuscript exhibits substantial shortcomings in validating core hypotheses, the logic of protocol matching, the depth of discussion, and the clarity of practical translation. Major revisions are required to strengthen the argumentation and enhance the reliability of conclusions.

1. The introduction states that IHSR was chosen due to its superiority over simple eccentric training, but it fails to directly cite key literature supporting IHSR's superiority over traditional eccentric training in ankle/Achilles tendon applications. This makes the rationale for selecting this control group appear weak.
2. The study aimed to achieve “approximate load matching,” yet results revealed significantly higher total impulse in the EQI group. This directly challenges the premise of ‘matching’ and undermines the core conclusion that “EQI is superior under equivalent loads.” The authors must re-examine and explicitly clarify the comparative basis of this study—whether it was load matching or comparing efficacy under a given protocol.
3. Given the substantial differences in repetition count (3 vs. 90) and total duration between the two sets of protocols, a direct comparison of total impulse may be unfair. It is recommended to supplement the analysis with metrics such as average impulse per contraction or impulse per unit time to provide a more balanced comparative perspective.
4. The article's recommendation to use the Smith machine for EQI training is overly general and lacks critical details (such as how to set the starting position and how to ensure a safe transition to the eccentric phase). It is not highly actionable and may mislead readers.
5. The manuscript explicitly states that allocation was not blinded for participants and personnel. This may introduce performance bias and measurement bias. The potential impact of this on outcomes—particularly subjective pain and exertion ratings—should be discussed in the limitations section.
6. The discussion fails to sufficiently explore the significant finding that the MVIC of the IHSR group remained markedly below baseline levels even after 48 hours. The physiological mechanisms and clinical implications should be examined in greater detail, particularly in relation to DOMS and potential micro-muscle damage.

Author Response

[we also attached full response document for your conveniance]

This study compared the short-term effects of centrifugal quasi-isometric contraction versus isokinetic slow-speed heavy-load training on the ankle plantar flexors. The results support the EQI protocol's advantages in generating greater impulse, lower fatigue, and reduced pain. However, the manuscript exhibits substantial shortcomings in validating core hypotheses, the logic of protocol matching, the depth of discussion, and the clarity of practical translation. Major revisions are required to strengthen the argumentation and enhance the reliability of conclusions.

RESPONSE: We thank the reviewer for this overall assessment and constructive feedback. In the revised version, we have addressed all major concerns by: (1) clarifying the rationale and logic of the protocol matching in the Methods section, including the pilot testing procedure used to approximate equivalent loading; (2) expanding the Discussion to provide deeper interpretation of key findings—particularly regarding MVIC reduction, DOMS mechanisms, and potential applications; and (3) refining the Practical application subsection to present a clearer and more balanced translation of the results, avoiding overgeneralization. We believe these revisions substantially improve the coherence and validity of our conclusions.

The introduction states that IHSR was chosen due to its superiority over simple eccentric training, but it fails to directly cite key literature supporting IHSR's superiority over traditional eccentric training in ankle/Achilles tendon applications. This makes the rationale for selecting this control group appear weak.

RESPONSE: We thank the reviewer for this valuable observation. We have strengthened the rationale for selecting the IHSR protocol by adding direct citations from studies demonstrating its comparable or superior effects to traditional eccentric loading in the management of Achilles tendon conditions. This addition provides a clearer justification for using IHSR as the comparison condition.

 

“The IHSR protocol was selected as the comparison condition because heavy-slow resistance training has been shown to produce similar or sometimes even superior clinical and structural improvements compared with traditional eccentric exercise in patients with mid-portion Achilles tendinopathy [20–22]. ISHR allows for greater control of movement velocity and consistent loading throughout the entire range of motion, making it a suitable and widely accepted benchmark for high-load tendon rehabilitation.”

The study aimed to achieve “approximate load matching,” yet results revealed significantly higher total impulse in the EQI group. This directly challenges the premise of ‘matching’ and undermines the core conclusion that “EQI is superior under equivalent loads.” The authors must re-examine and explicitly clarify the comparative basis of this study—whether it was load matching or comparing efficacy under a given protocol. Given the substantial differences in repetition count (3 vs. 90) and total duration between the two sets of protocols, a direct comparison of total impulse may be unfair. It is recommended to supplement the analysis with metrics such as average impulse per contraction or impulse per unit time to provide a more balanced comparative perspective.

RESPONSE: We thank the reviewer for raising this important point. We agree that perfect load matching between contraction modes is methodologically challenging due to their inherently different temporal and mechanical characteristics. As described in the Methods section, our intention was to achieve approximate load matching based on pilot torque–time integral data. Nevertheless, it appears that our pilot data was insufficient to achieved good matching, and the EQI group achieved a higher total impulse despite a much shorter contraction duration and markedly lower perceived exertion. While this is a methodological shortcoming, but as evidence of greater efficiency of EQI is even stronger – as it elicits less pain/MVC reduction while providing greater total torque integral.

 

To address this concern, we (1) clarified in the Methods section that the matching was approximate rather than exact, (2) emphasized in the Discussion that the higher impulse reflects superior efficiency rather than unequal loading, and (3) noted that future studies could normalize impulse to contraction count or duration to further refine between-mode comparisons.

 

“The two protocols were designed to achieve approximate load matching. In the pilot phase (n = 5), within-subject comparisons were used to determine the number of repetitions producing comparable torque–time integrals between EQI and isokinetic heavy-slow resistance (IHSR) contractions performed at 30°/s. Each pilot participant completed one EQI contraction and a series of IHSR contractions (random order, 10 min break in between) until the cumulative torque–time integral of the ISHR matched that of the EQI contraction. This procedure indicated that approximately 30 IHSR repetitions were needed to match one EQI contraction, and this finding informed the de-sign of the main parallel-group study. However, since the experimental trial compared independent groups of different participants, between-subject variability in strength and contraction characteristics was expected to contribute to imperfect matching of total impulse. Therefore, the comparison should be interpreted in the context of matched loading intent rather than exact mechanical equivalence.”

Discussion:

“Although our study aimed for approximate load matching based on pilot data, the EQI group ultimately achieved a greater total impulse while reporting lower exertion and pain. Rather than contradicting the study rationale, this finding strengthens the interpretation that EQI represents a more mechanically efficient contraction mode, capable of producing higher overall work with less pain and lower MVIC reduction after-wards. Speculatively, this may reflect the controlled transition between isometric and eccentric phases allows sustained torque generation without excessive muscle damage. Nevertheless, it should be acknowledged that the protocols were not perfectly load-matched, and future work should consider normalization metrics such as impulse per contraction or impulse per second to enhance comparability.”

 

The article's recommendation to use the Smith machine for EQI training is overly general and lacks critical details (such as how to set the starting position and how to ensure a safe transition to the eccentric phase). It is not highly actionable and may mislead readers.

RESPONSE: Thank you for this important clarification. We agree that, since the Smith machine setup was not part of our experimental procedures, providing detailed exercise instructions could be misleading or interpreted as a validated application of our findings. We have therefore removed this speculative paragraph from the manuscript and adjusted the text to state more generally that EQI exercises can potentially be performed without specialized equipment, while emphasizing the need for further validation before practical implementation.

The manuscript explicitly states that allocation was not blinded for participants and personnel. This may introduce performance bias and measurement bias. The potential impact of this on outcomes—particularly subjective pain and exertion ratings—should be discussed in the limitations section.

RESPONSE: We agree that the lack of blinding may have introduced potential performance and measurement bias, particularly for subjective outcomes such as pain and exertion ratings. To address this, we have added a corresponding note in the Limitations section discussing this potential source of bias and its possible impact on the findings.

“Additionally, since neither participants nor the personnel conducting the interventions and assessments were blinded to group allocation, a potential performance and measurement bias cannot be fully excluded. This limitation may have particularly influenced subjective outcomes such as perceived pain and exertion, as participants might have been consciously or subconsciously affected by expectations related to the type of exercise performed.”

The discussion fails to sufficiently explore the significant finding that the MVIC of the IHSR group remained markedly below baseline levels even after 48 hours. The physiological mechanisms and clinical implications should be examined in greater detail, particularly in relation to DOMS and potential micro-muscle damage.

RESPONSE: We appreciate this insightful comment. We have expanded the Discussion to further elaborate on possible physiological explanations for the sustained MVIC reduction in the IHSR group. The revised text now discusses the role of exercise-induced muscle damage, inflammatory responses, and delayed recovery associated with high-volume eccentric loading.

“The persistent reduction in MVIC observed in the IHSR group even after 48 hours may reflect delayed recovery associated with greater muscle damage and prolonged excitation–contraction coupling impairment [27]. High-repetition eccentric actions per-formed under slow velocity and wide range of motion are known to induce micro-structural disruptions within muscle fibres [28], accompanied by inflammatory pro-cesses and swelling that can persist for several days [29,30]. These mechanisms likely contributed to the sustained strength deficit observed in the IHSR group. In contrast, the EQI protocol, despite higher mechanical impulse, may have induced less fibre disruption due to the more gradual force development and reduced muscle lengthening velocity. From a practical standpoint, this suggests that EQI loading might facilitate faster recovery and lower cumulative fatigue.”

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear authors,

Thank you for a thorough review of the paper, all relevant issues were addressed and the paper is now ready to be accepted for publication.

Author Response

Thank you again for your feedback.

Reviewer 4 Report

Comments and Suggestions for Authors

Thank the authors for their efforts in improving the quality of their papers. The quality of the article has already improved a bit with the revisions. Lines: 46-51: “Meanwhile, an isokinetic contraction is defined as a transition between…”, Range of motion is of paramount importance in joint function. To provide more effective evidence, the authors may consider referring to the following updated relevant studies: New insights optimize landing strategies to reduce lower limb injury risk (https://doi.org/10.34133/cbsystems.0126). Could the authors provide more and relevant results, including more detailed data, in addition to suggesting that the results be presented in the form of figures to improve the readability of the results.

Author Response

We sincerely thank the reviewer for suggesting an additional reference. After carefully reviewing the cited article (Xu et al., 2024, Cyborg and Bionic Systems), we concluded that it is not directly relevant to the present study. That paper focuses on landing biomechanics and anterior cruciate ligament injury mechanisms during dynamic, high-impact single-leg landings, employing musculoskeletal modeling of the knee and ankle.

In contrast, our study investigates controlled resistance exercise modes (eccentric quasi-isometric and isokinetic heavy-slow contractions) of the ankle plantar flexors under laboratory-based dynamometer conditions, with no jumping, landing, or impact components. While both areas relate to lower-limb function, the neuromechanical context, aims, and loading characteristics differ fundamentally. Therefore, citing this reference would not meaningfully strengthen the rationale or interpretation of our findings.

We have, however, ensured that the introduction sufficiently emphasizes the relevance of range of motion control and mechanical loading characteristics in tendon and muscle adaptation, supported by existing evidence already cited (e.g., [15, 19, 20]).

 

Regarding the results presentation, our dataset already provides detailed quantitative summaries in Tables 1 and 2, as well as Figures 2 and 3, which illustrate the primary outcomes (pain, torque, and RoM) with corresponding statistical annotations. Given the relatively small sample size and the focused scope of the study, we believe the current figures sufficiently balance clarity and conciseness. Nonetheless, we have refined the figure legends for better readability and included additional descriptive text to guide interpretation of key results.