An Exploratory Study on Whether the Interference Effect Occurs When High-Intensity Strength Training Is Performed Prior to High-Intensity Interval Aerobic Training

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript titled, “Does the interference effect occur when high-intensity strength training is performed prior to high-intensity interval aerobic training,” by Gabriel O. Bernedo et al, is an exploratory pilot study that evaluates if concurrent training (CT), which combines high-intensity strength training with high-intensity interval training (HIIT), can have an interfering effect or contribute to synergistic benefits in strength and endurance.

The study is to determine whether completing strength training before HIIT in a four-week program improves both strength and aerobic capacity. The study concludes that, while concurrent training can result in simultaneous improvements in strength and endurance, the exercise prescription should be customized to individual fitness levels to prevent restrictions in adaptive responses.

However, there are a few constraints that should be considered:

 

1.      Could the limited sample size of only ten people result in findings that are not representative of larger or more diverse groups, potentially leading to Type I and Type II errors?

2.      Does the lack of a control group make it difficult to determine whether improvements in strength and endurance are due to the current training or prior experience?

3.      Does the homogeneity of the participants limit the applicability of the results to other groups, such as elite athletes, older adults, or individuals with varying fitness levels?

4.      Was the lack of significant improvements in VO2max for aerobically trained individuals with a higher baseline aerobic capacity (>40 ml/kg/min) due to insufficient HIIT stimulus? Could this mean that the HIIT protocol may not have provided enough intensity or volume to induce further aerobic adaptations in these individuals, and that highly customized HIIT programs may be required for those with higher levels of aerobic fitness?

5.      Intersession recovery is not discussed: Performance outcomes may have been impacted by inadequate recovery in between training sessions.

6.      Nutritional considerations were not considered: Participants were instructed to stick to their present diet and avoid supplements, but there was no active monitoring or management of their nutritional intake, which may have had an impact on their performance.

Decision : The paper may be accepted with minor revision because it focuses on experimental or proof-of-concept research. Adding a more thorough explanation of the study's limitations, recommending topics for more investigation (such as longer-duration studies or the inclusion of a control group), and clarifying the conclusions to more explicitly reflect the limitations (e.g., acknowledging the non-significant aerobic gains and sample size constraints).

 

 

 

Author Response

The manuscript titled, “Does the interference effect occur when high-intensity strength training is performed prior to high-intensity interval aerobic training,” by Gabriel O. Bernedo et al, is an exploratory pilot study that evaluates if concurrent training (CT), which combines high-intensity strength training with high-intensity interval training (HIIT), can have an interfering effect or contribute to synergistic benefits in strength and endurance. 

 

The study is to determine whether completing strength training before HIIT in a four-week program improves both strength and aerobic capacity. The study concludes that, while concurrent training can result in simultaneous improvements in strength and endurance, the exercise prescription should be customized to individual fitness levels to prevent restrictions in adaptive responses.

 

However, there are a few constraints that should be considered:

 

1. Could the limited sample size of only ten people result in findings that are not representative of larger or more diverse groups, potentially leading to Type I and Type II errors?

 

We agree with the reviewer’s query which we sought to account for in the original submission by; A) indicating in the title that this was an exploratory study; B) recognising the limited sample size in the choice of p value to avoid Type II errors with false negative (Ln 231-237); and C) by recognising this in the discussion section of the manuscript, please see Ln 337-340.

 

2. Does the lack of a control group make it difficult to determine whether improvements in strength and endurance are due to the current training or prior experience?

 

While we agree with the reviewer that a full 5-way RCT design (control, strength/aerobic, aerobic/strength, strength only, and aerobic only) would be the most appropriate study design. The practicalities of implementing such a design make it extremely difficult to achieve. Hence, we sought to provide a proof-of-concept exploratory research, reporting systematic evidence to support the notion when strength adaptations are prioritised by completing the strength training session first before a HIIT style aerobic training session there is a limited if any interference effect shown. No specific change has been made.

 

3. Does the homogeneity of the participants limit the applicability of the results to other groups, such as elite athletes, older adults, or individuals with varying fitness levels?

 

Yes as with all research outcomes, the research outcomes are only directly applicable to the investigation cohort. We have been careful to not overextend the applicability of our results. We believe that the structure and content of our discussion suitably positions our findings relative to our investigation cohort. We did seek to indicate to the reader where appropriate, where we felt the outcomes could be best applied, please see Ln 319-324.

 

4. Was the lack of significant improvements in VO2max for aerobically trained individuals with a higher baseline aerobic capacity (>40 ml/kg/min) due to insufficient HIIT stimulus? Could this mean that the HIIT protocol may not have provided enough intensity or volume to induce further aerobic adaptations in these individuals, and that highly customized HIIT programs may be required for those with higher levels of aerobic fitness?

 

Yes, we agree with the reviewer’s interpretation of the VO2 outcome. We had originally provided a brief discussion on this topic and due to the exploratory nature of the investigation we feel it is inappropriate to expand further. To expand our discussion on this lack of adaptive response would result in a discussion of a possible type I or II error that may not be present if the sample was larger; please see Ln 304-324

 

5. Intersession recovery is not discussed: Performance outcomes may have been impacted by inadequate recovery in between training sessions. 

 

This is an interesting aspect raised by the reviewer and not one that we had considered because intersession recovery is rarely if ever discussed in prior concurrent training interference literature. While we did not control or intervene in the intersession recovery, we have briefly added in statements highlighting this issue to readers, please see Ln 366-371

 

6. Nutritional considerations were not considered: Participants were instructed to stick to their present diet and avoid supplements, but there was no active monitoring or management of their nutritional intake, which may have had an impact on their performance. 

 

The reviewer is correct that we did not monitor participant nutritional intake beyond asking participants to maintain their current diets and not start taking any additional supplementations. In our opinion the nutritional considerations for this study fall into the category of intersession recovery, and as such we have made specific reference to this, please see Ln 362-365

 

Decision : The paper may be accepted with minor revision because it focuses on experimental or proof-of-concept research. Adding a more thorough explanation of the study's limitations, recommending topics for more investigation (such as longer-duration studies or the inclusion of a control group), and clarifying the conclusions to more explicitly reflect the limitations (e.g., acknowledging the non-significant aerobic gains and sample size constraints). 

Reviewer 2 Report

Comments and Suggestions for Authors

Study Design and Sample Size: The manuscript employs a single cohort, within-subject observational study design with a small sample size (n=10 after withdrawals). While appropriate for a pilot study, the limited sample size and lack of a control group reduce the generalizability and reliability of the findings.

Lack of Control Group: The absence of a control group in the study limits the ability to attribute observed changes specifically to the intervention rather than other external factors.

Data Analysis and Significance: The manuscript uses a significance level of p<0.1, which is less stringent than the commonly used p<0.05. This may increase the likelihood of Type I errors (false positives), especially in a small sample size study. A justification for this choice is needed.

Study Duration: The four-week duration of the intervention may be too short to observe significant adaptations in both strength and aerobic capacity, particularly in trained individuals. The authors should discuss the potential limitations of the study duration on the observed outcomes.

Intervention Protocol: The manuscript does not clearly define the rationale behind the specific combination and ordering of resistance training (RT) and high-intensity interval training (HIIT). Clarifying the reasoning for these choices would strengthen the argument for the proposed training regimen.

Participant Characteristics: The study's generalizability is limited by the homogeneous participant group (young, physically active, non-elite individuals). Expanding the participant pool to include diverse age ranges and fitness levels would provide a broader understanding of the intervention's effects.

Outcome Measures and Testing Procedures: The manuscript details several outcome measures (e.g., 3RM tests, V̇O2max) but lacks clarity on the reliability and validity of these tests within the context of the study. Discussing the choice of measures and their relevance to the research question would improve the manuscript.

Statistical Methods: While Pearson correlations are provided to assess relationships between variables, additional statistical analyses (e.g., regression analysis) could offer deeper insights into the factors influencing the observed outcomes.

Interpretation of Results: The manuscript suggests that concurrent training (CT) improves strength and aerobic capacity in non-elite individuals, but this conclusion is not strongly supported due to the lack of synergistic enhancement observed in all outcome measures. The authors should provide a more nuanced discussion of these findings.

Future Research Directions: The manuscript does not adequately address future research needs, such as the need for longer-duration studies, larger and more diverse samples, or studies with varying training protocols. Including these would help guide future work in this area.

Author Response

Study Design and Sample Size: The manuscript employs a single cohort, within-subject observational study design with a small sample size (n=10 after withdrawals). While appropriate for a pilot study, the limited sample size and lack of a control group reduce the generalizability and reliability of the findings.

 

Lack of Control Group: The absence of a control group in the study limits the ability to attribute observed changes specifically to the intervention rather than other external factors.

 

While we agree with the reviewer that a full 5-way RCT design (control, strength/aerobic, aerobic/strength, strength only, and aerobic only) would be the most appropriate study design. The practicalities of implementing such a design make it extremely difficult to achieve. Hence, we sought to provide a proof-of-concept exploratory research, giving some systematic evidence to support the notion when strength adaptations are prioritised by completing the strength training session first before a HIIT style aerobic training session there is a limited if any interference effect shown. We have reinforced the fact that we did not include a control group as a final statement in the conclusion, please see Ln 378-380.

 

Data Analysis and Significance: The manuscript uses a significance level of p<0.1, which is less stringent than the commonly used p<0.05. This may increase the likelihood of Type I errors (false positives), especially in a small sample size study. A justification for this choice is needed.

 

We thank the reviewer for the comment and recognising that we have chosen to use an unconventional p value for accepting statistical significance. As detailed in the original submission, this choice was in recognition of the limited sample size and seeking to avoid Type II false negative errors. In our opinion, with pilot studies, this is the better approach because the investigators are recognising that future work should be conducted with larger samples with a more stringent p value for accepting statistical significance. But in pilot work research you wish to avoid missing potentially relevant and important findings that might go overlooked due to a conventional choice of statistical significance acceptance when using a smaller than ideal sample. Please see Ln 231-237

 

Study Duration: The four-week duration of the intervention may be too short to observe significant adaptations in both strength and aerobic capacity, particularly in trained individuals. The authors should discuss the potential limitations of the study duration on the observed outcomes.

 

Thank you for the comment we have sought to improve the justification for the study duration, please see Ln 337-340

 

Intervention Protocol: The manuscript does not clearly define the rationale behind the specific combination and ordering of resistance training (RT) and high-intensity interval training (HIIT). Clarifying the reasoning for these choices would strengthen the argument for the proposed training regimen.

 

We disagree that the rationale was not included, as the original manuscript clearly stated that exercise choice was based on previous CT literature (Marshall et al 2018; Marshall et al 2021). Furthermore, the order of exercises was not standardised to provide each participant with an element of choice which has been reported to positively influence adaptive response (Avelar et al 2019). No further change has been made.

 

Participant Characteristics: The study's generalizability is limited by the homogeneous participant group (young, physically active, non-elite individuals). Expanding the participant pool to include diverse age ranges and fitness levels would provide a broader understanding of the intervention's effects.

 

While we agree that expanding the participant pool would lead to an increase in generalisability, this argument could be made for any human research sample. We have also very openly recognised the limitations of a small sample exploratory study and sort to highlight which populations might benefit from this CT protocol.

 

Outcome Measures and Testing Procedures: The manuscript details several outcome measures (e.g., 3RM tests, V̇O2max) but lacks clarity on the reliability and validity of these tests within the context of the study. Discussing the choice of measures and their relevance to the research question would improve the manuscript.

 

We are confused by the reviewer’s request to justify a direct measure of strength (repetition maximum and the IMTP) and endurance capacity (expired oxygen consumption), considering the research question posed which was a comparison of strength or endurance capacity adaptation. While we agree that providing an indication of the tests reliability in this cohort would have been marginally beneficial, unfortunately we are unable to provide this information. However, the validity of the tests for the measures and interpretations made has been very well documented in the literature and we disagree that restating these facts is necessary.

 

Statistical Methods: While Pearson correlations are provided to assess relationships between variables, additional statistical analyses (e.g., regression analysis) could offer deeper insights into the factors influencing the observed outcomes.

 

We thank the reviewer for the suggestion to include further statistical analysis, as such we have now added in a simple linear regression to consider how post intervention VO2max has affected the strength measures. But we are mindful that the data set does not have the statistical power to more extensively explore the data set. Please see Ln 229-230; 270-272 and Table 3.

 

Interpretation of Results: The manuscript suggests that concurrent training (CT) improves strength and aerobic capacity in non-elite individuals, but this conclusion is not strongly supported due to the lack of synergistic enhancement observed in all outcome measures. The authors should provide a more nuanced discussion of these findings.

 

We appreciate the reviewers comment however the submission discusses each of the variables and the changes or not, observed. We have sought to ensure that we positioned this discussion within the context of the exploratory study recognising the limitations of the sample size and not overextending the generalisation of our interpretation. In fact, we highlighted that we did not observe changes in dynamic performance of the CMJ which could represent the lack of dynamic power exercises in the training intervention; please see Ln 342-349.

 

Future Research Directions: The manuscript does not adequately address future research needs, such as the need for longer-duration studies, larger and more diverse samples, or studies with varying training protocols. Including these would help guide future work in this area.

 

Thank you for the suggestion to expand on the limitation and future directions of concurrent training interference literature, please see Ln 337-340; 369-371.

Reviewer 3 Report

Comments and Suggestions for Authors

In the present work, the relations of concurrent training to muscular strength and aerobic capacity are studied. Nevertheless, there is several issues that require clarification.

1. The sample size of the study is rather limited. The authors need to either increase the sample size or acknowledge this limitation and discuss its implications.

2. There are also concerns regarding the statistical analysis. The decision to use a significance level of p < 0.1 is unconventional and may risk inflating the type I error rate.

3. The manuscript would be improved with a more comprehensive literature review. The authors should discuss their findings in the context of existing research more thoroughly.

4. In the conclusion section, it is recommended to include suggestions for future research, for example, the impact of increasing the duration of the intervention or using different order of training for specification of the outcomes.

Author Response

In the present work, the relations of concurrent training to muscular strength and aerobic capacity are studied. Nevertheless, there is several issues that require clarification.

1. The sample size of the study is rather limited. The authors need to either increase the sample size or acknowledge this limitation and discuss its implications.

 

We agree with the reviewer’s query which we sought to account for in the original submission by; A) indicating in the title that this was an exploratory study; B) recognising the limited sample size in the choice of p value to avoid Type II errors with false negative (Ln 231-237); and C) by recognising this in the discussion section of the manuscript, please see Ln 337-340.

 

2. There are also concerns regarding the statistical analysis. The decision to use a significance level of p < 0.1 is unconventional and may risk inflating the type I error rate.

 

We thank the reviewer for the comment and recognising that we have chosen to use an unconventional p value for accepting statistical significance. As detailed in the original submission this choice was in recognition of the limited sample size and seeking to avoid Type II false negative errors, please see Ln 231-237. In our opinion, with pilot studies, this is the better approach because the investigators are recognising that future work should be conducted with larger samples with a more stringent p value for accepting statistical significance. But in pilot work research you wish to avoid missing potentially relevant and important findings that might go overlooked due to a conventional choice of statistical significance acceptance when using a smaller than ideal sample.

 

3. The manuscript would be improved with a more comprehensive literature review. The authors should discuss their findings in the context of existing research more thoroughly.

 

While we understand the reviewer’s point of view that an introduction should summarise the existing literature and contextualise how the current investigation fits to the literature, we are confused as to what areas of the introduction need to be improved? Similarly in the discussion which topics or interpretations have we not adequately compared to the existing literature?

 

4. In the conclusion section, it is recommended to include suggestions for future research, for example, the impact of increasing the duration of the intervention or using different order of training for specification of the outcomes.

 

Thank you for the suggestion to expand on the limitation and future directions of concurrent training interference literature, please see Ln 337-340; 369-371.