Deceptive Caffeine Shows Limited Impact on Short-Term Neuromuscular Performance

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript addresses a relevant question: whether the deceptive ingestion of “caffeine” (a placebo accompanied by expectancy-inducing information) can modulate neuromuscular performance in upper- and lower-limb power and endurance tests. The topic is timely, especially given the growing body of research on expectancy, placebo effects, and ergogenic aids.

The methodology is generally clear and appropriate. However, I missed a specific assessment of expectancy, and the authors could be more explicit about this point in the limitations section. Another issue is the decision not to use any supplementation during the control condition; I would appreciate a clearer explanation and discussion of this choice.

Additionally, I would like to suggest three articles for the authors to read and consider including in the discussion, as they are highly relevant to the manuscript’s aims and findings. The list is provided below.

- Azevedo PH, Oliveira MG, Tanaka K, Pereira PE, Esteves G, Tenan MS. Perceived exertion and performance modulation: effects of caffeine ingestion and subject expectation. J Sports Med Phys Fitness. 2021 Sep;61(9):1185-1192. doi: 10.23736/S0022-4707.21.11659-7. Epub 2021 Jan 20. PMID: 33472353.
- Pereira, P.E., Motoyama, Y., Esteves, G.J. et al. Caffeine supplementation delays the fatigue through central nervous system modulation. Sport Sci Health 12, 239–245 (2016). https://doi.org/10.1007/s11332-016-0281-1
- Campelo D, Koch AJ, Machado M. Caffeine, lactic acid, or nothing: What effect does expectation have on men's performance and perceived exertion during an upper body muscular endurance task? Int J Health Sci (Qassim). 2023 Nov-Dec;17(6):39-42. PMID: 37929237; PMCID: PMC10624800.

Author Response

Dear Reviewers,

We would like to thank the Editor and the reviewers for the time and effort devoted to the evaluation of our manuscript and for their constructive and valuable comments. We believe that their suggestions have significantly contributed to improving the quality, clarity, and scientific rigor of the article.

Following the reviewers’ recommendations, we have carefully revised the manuscript. Below, we provide a detailed, point-by-point response to all the issues raised, indicating how each comment has been addressed. In addition, all changes made to the manuscript have been highlighted in red to facilitate the review of the revised version.

We sincerely appreciate the reviewers’ insightful feedback and helpful suggestions, which have been of great value in strengthening this work.

Thank you again for your consideration and assistance. We look forward to your response.

 

REVIEWER 1

The manuscript addresses a relevant question: whether the deceptive ingestion of “caffeine” (a placebo accompanied by expectancy-inducing information) can modulate neuromuscular performance in upper- and lower-limb power and endurance tests. The topic is timely, especially given the growing body of research on expectancy, placebo effects, and ergogenic aids. The methodology is generally clear and appropriate. However, I missed a specific assessment of expectancy, and the authors could be more explicit about this point in the limitations section.

Thank you for this valuable suggestion. Indeed, we did not specifically assess participants’ expectancy regarding the effects of the substance. We have revised the limitations section to explicitly acknowledge this point. It now reads as follows:

“Lastly, individual differences in caffeine-related beliefs, habitual caffeine intake, and susceptibility to placebo effects were not controlled. Participants’ expectancy regarding the effects of the substance was not specifically assessed. Although participants were informed about the potential ergogenic effects of caffeine ingestion on performance in tests similar to those performed in this study, their individual beliefs or expectations about these effects were not formally measured, potentially contributing to the inter-individual variability observed among participants.”

 

Another issue is the decision not to use any supplementation during the control condition; I would appreciate a clearer explanation and discussion of this choice.

Thank you for raising this point. Indeed, no condition involving actual caffeine ingestion was included, as comparing expectancy effects with the pharmacological effects of caffeine was not among the objectives of this study. The present work is part of the first author’s doctoral thesis (Fernando Valero), which consistently focuses on placebo effects associated with caffeine, without caffeine ingestion. Therefore, within this line of research, the inclusion of a caffeine supplementation condition was deliberately not contemplated. Nevertheless, we have included this as a limitation of this study “Second, the placebo manipulation was based solely on deceptive information rather than on comparisons with different actual caffeine doses, which prevents distinguishing the relative contributions of pharmacological and expectancy effects.”

That said, we agree that this is a relevant and interesting line of investigation, and we have addressed the comparison between expectancy/placebo effects and actual caffeine ingestion in other studies outside the scope of this thesis (e.g., Del Coso et al. 2025). However, in this Doctoral Thesis, we only compared expectancy with control conditions.

Coso, J., Lara, B., Gallo-Salazar, C., Areces, F., Aguilar-Navarro, M., Giráldez-Costas, V., Gutiérrez-Hellín, J., Valero, F., & Salinero, J. J. (2026). Exploring the potential synergistic pharmacological and psychological effects of caffeine on exercise performance: a placebo-balanced study. Biology of sport, 43, 95-105. https://doi.org/10.5114/biolsport.2026.153332  

 

 

Additionally, I would like to suggest three articles for the authors to read and consider including in the discussion, as they are highly relevant to the manuscript’s aims and findings. The list is provided below.

 

- Azevedo PH, Oliveira MG, Tanaka K, Pereira PE, Esteves G, Tenan MS. Perceived exertion and performance modulation: effects of caffeine ingestion and subject expectation. J Sports Med Phys Fitness. 2021 Sep;61(9):1185-1192. doi: 10.23736/S0022-4707.21.11659-7. Epub 2021 Jan 20. PMID: 33472353.

- Pereira, P.E., Motoyama, Y., Esteves, G.J. et al. Caffeine supplementation delays the fatigue through central nervous system modulation. Sport Sci Health 12, 239–245 (2016). https://doi.org/10.1007/s11332-016-0281-1

- Campelo D, Koch AJ, Machado M. Caffeine, lactic acid, or nothing: What effect does expectation have on men's performance and perceived exertion during an upper body muscular endurance task? Int J Health Sci (Qassim). 2023 Nov-Dec;17(6):39-42. PMID: 37929237; PMCID: PMC10624800.

Thank you very much for these valuable suggestions and for sharing these relevant articles. We appreciate your recommendation. We have carefully reviewed the proposed references and have included two of the three suggested references in the new version of the manuscript (Azevedo et al., and Campelo et al.), as they show a closer conceptual and methodological alignment with the aims and findings of our study. We believe their inclusion strengthens the theoretical context and interpretation of our results.

Thank you again for your constructive input, which has helped to improve the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the authors’ efforts in conducting this study. However, I have several concerns that should be addressed before the manuscript can be considered for publication:

1. Participant characteristics
   Typically, recruited participants should be comparable across groups, yet the variation in this study appears quite large—particularly with regard to the 17 male participants. Such imbalance may complicate group allocation and interpretation. The sample is described as 100 physically active young adults (17 men and 8 women; age: 22.3 ± 1.5 years; height: 170.3 ± 9.2 cm; weight: 68.0 ± 11.5 kg), but this description seems inconsistent. Please clarify the sample characteristics and recruitment process, and consider citing relevant literature such as DOI: 10.3390/nu17040681.

2. Potential contamination from daily oral liquid intake
   The oral liquid used in the intervention appears to be a common beverage in Spain. How did the authors ensure that participants did not consume similar oral liquids during their daily routines, which may confound the intervention effects? Clarification on contamination control procedures is needed.

3. Verification of experimental implementation
   The manuscript would benefit from additional visual documentation (e.g., photos or figures) to demonstrate that the experiment was conducted as described. This would greatly improve transparency and credibility.

4. Limited performance indicators
   Assessing only CMJ and 1RM as outcome measures seems insufficient for an SCI-level experimental study. Additional physiological or performance indicators should be included to strengthen the scientific rigor of the findings.

5. Absence of a pure caffeine intake group (3 mg/kg)
   It is unclear why the study did not include a group receiving 3 mg/kg of caffeine alone. Given the design, this omission raises questions about the completeness of the experimental comparison. Please justify the absence of this control condition.

6. Timing of caffeine intake
   The study does not discuss whether caffeine ingestion occurred in the morning or evening, which can substantially influence metabolic and performance responses. Please clarify whether intake timing was controlled.

Author Response

Dear Editor and Reviewers,

We would like to thank the Editor and the reviewers for the time and effort devoted to the evaluation of our manuscript and for their constructive and valuable comments. We believe that their suggestions have significantly contributed to improving the quality, clarity, and scientific rigor of the article.

Following the reviewers’ recommendations, we have carefully revised the manuscript. Below, we provide a detailed, point-by-point response to all the issues raised, indicating how each comment has been addressed. In addition, all changes made to the manuscript have been highlighted in red to facilitate the review of the revised version.

We sincerely appreciate the reviewers’ insightful feedback and helpful suggestions, which have been of great value in strengthening this work.

Thank you again for your consideration and assistance. We look forward to your response.

 

REVIEWER 2

Thank you for the authors’ efforts in conducting this study. However, I have several concerns that should be addressed before the manuscript can be considered for publication:

 

Participant characteristics. Typically, recruited participants should be comparable across groups, yet the variation in this study appears quite large—particularly with regard to the 17 male participants. Such imbalance may complicate group allocation and interpretation.

We thank the reviewer for this comment. In the present study, participants were not allocated or analyzed according to sex, and therefore the difference in the number of male and female participants is not relevant for group allocation or for the interpretation of the results. All analyses were conducted considering the sample as a whole, in accordance with the study design and objectives.

 

The sample is described as 100 physically active young adults (17 men and 8 women; age: 22.3 ± 1.5 years; height: 170.3 ± 9.2 cm; weight: 68.0 ± 11.5 kg), but this description seems inconsistent. Please clarify the sample characteristics and recruitment process, and consider citing relevant literature such as DOI: 10.3390/nu17040681.

Regarding the sample description, we think that there is no inconsistency in the reported figures. At no point is a total sample size of 100 participants indicated in the manuscript. The sample consisted of 25 physically active young adults (17 men and 8 women), as clearly stated in the Methods section. The reference to “100” appears to be a misunderstanding, likely due to an error in text extraction or copying (e.g., from an automated tool), as this number could correspond to the line number in the manuscript where the sample description is reported, not to the sample size itself.

 

Potential contamination from daily oral liquid intake. The oral liquid used in the intervention appears to be a common beverage in Spain. How did the authors ensure that participants did not consume similar oral liquids during their daily routines, which may confound the intervention effects? Clarification on contamination control procedures is needed.

We thank the reviewer for this comment; however, it appears to be based on a misunderstanding of the intervention procedures. In the present study, no oral liquid or beverage was administered. The only ingestion involved a single opaque capsule containing 100 mg of cornflour (labelled as caffeine), administered 60 minutes before testing in the placebo condition, while no ingestion was performed in the control condition.

To minimize any potential contamination effects, participants were explicitly instructed to avoid intense exercise, caffeine, or energy drinks for 24 hours before each experimental session, and to replicate their nutritional and rest habits across testing days. Therefore, habitual consumption of beverages such as coffee could not have confounded the intervention effects, as liquid intake was neither manipulated nor differed between conditions.

 

Verification of experimental implementation. The manuscript would benefit from additional visual documentation (e.g., photos or figures) to demonstrate that the experiment was conducted as described. This would greatly improve transparency and credibility.

Thank you for this suggestion. We have included a new figure to provide a clearer visual representation of the experimental protocol and procedures, facilitating their understanding by the reader.

 

Limited performance indicators. Assessing only CMJ and 1RM as outcome measures seems insufficient for an SCI-level experimental study. Additional physiological or performance indicators should be included to strengthen the scientific rigor of the findings.

We acknowledge that the inclusion of additional physiological variables, such as heart rate or muscle oxygen saturation, could have provided further complementary information. However, the selected performance-based outcomes were defined a priori as the primary variables of interest for addressing the study aims and were considered sufficient to capture the relevant responses within the scope of this investigation.

However, the study assessed multiple performance outcomes beyond CMJ and 1RM, including 15-second repeated jumps, bench press throws at 25%, 50%, and 75% 1RM (mean propulsive velocity), bench press to failure at 75% 1RM, and post-session side effect questionnaires. All tests were performed using validated and reliable measurement systems, providing a comprehensive evaluation of both explosive and fatigue-related performance.

 

Absence of a pure caffeine intake group (3 mg/kg). It is unclear why the study did not include a group receiving 3 mg/kg of caffeine alone. Given the design, this omission raises questions about the completeness of the experimental comparison. Please justify the absence of this control condition.

Thank you for raising this point. Indeed, no condition involving actual caffeine ingestion was included, as comparing expectancy effects with the pharmacological effects of caffeine was not among the objectives of this study. The present work is part of the first author’s doctoral thesis (Fernando Valero), which consistently focuses on placebo effects associated with caffeine, without caffeine ingestion. Therefore, within this line of research, the inclusion of a caffeine supplementation condition was deliberately not contemplated. Nevertheless, we have included this as a limitation of this study “Second, the placebo manipulation was based solely on deceptive information rather than on comparisons with different actual caffeine doses, which prevents distinguishing the relative contributions of pharmacological and expectancy effects.”

That said, we agree that this is a relevant and interesting line of investigation, and we have addressed the comparison between expectancy/placebo effects and actual caffeine ingestion in other studies outside the scope of this thesis (e.g., Del Coso et al. 2025). However, in this Doctoral Thesis, we only compared expectancy with control conditions.

Coso, J., Lara, B., Gallo-Salazar, C., Areces, F., Aguilar-Navarro, M., Giráldez-Costas, V., Gutiérrez-Hellín, J., Valero, F., & Salinero, J. J. (2026). Exploring the potential synergistic pharmacological and psychological effects of caffeine on exercise performance: a placebo-balanced study. Biology of sport, 43, 95-105. https://doi.org/10.5114/biolsport.2026.153332  

 

Timing of caffeine intake. The study does not discuss whether caffeine ingestion occurred in the morning or evening, which can substantially influence metabolic and performance responses. Please clarify whether intake timing was controlled.

We thank the reviewer for the comment. As correctly noted in your previous comment, no caffeine was ingested in this study; the intervention involved only a single placebo capsule. In addition, as described in the Methods, the placebo was administered in the morning, and for greater clarity, we will specify in the revised version that each participant took it at the same time across sessions to control for potential circadian influences on performance. Now it reads: “All tests were conducted over two sessions, both held in the morning, scheduled at the same time of day to minimize potential circadian influences”.

 

Reviewer 3 Report

Comments and Suggestions for Authors

Why did the authors not use exercise tasks for which the literature has shown that there is a consistent ergogenic effect of caffeine. Strong justification needs to be provided for the battery of tests/tasks that was selected.

Did the study have written participant information what the study was all about. More detail needs to be provided.

What was the rationale for using exercise tasksI suggest to use doi: 10.1249/01.mss.0000233805.56315.a9.

I suggest to clarify when there is reference to review articles when not referring to primary sources. However, the authors should use more primary sources as it seems ~75% of references are reviews.

The introduction is very general and lacks justification of the novelty of the study. Please revise the introduction and provide stronger justification and rationale.

L92. Please clarify what was counterbalanced.

L97. What parameter and values from the literature were selected for the power analysis for sample size.

L99. If the sample size was calculated to be 24, then adding one more for dropouts (more than one) does not make sense. Please revise.

I suggest to change “22.3 ± 1.5 years; height: 170.3 ± 9.2 cm; weight: 68.0 ± 11.5 kg” to “22 ± 2 years; height: 170 ± 9 cm; weight: 68 ± 12 kg”.

L102. I suggest clarify 0.98 ± 0.26 1RM·body mass-1.”

References numbers in the text need to be provided in square brackets.

L110. Please revise “body weight was measured to the nearest 0.1cm with a portable stadiometer (Seca Ltd., Germany”.

L120. For women within 72 hr hormonal changes can be substantial. This seems to be very incorrect.

L127. There is no mention of CMJ at the end of the introduction.

L132. Was it reliable in your hands?

L135. The description of the repeated jump test lacks detail. Where hands on hips for example.

L164. The smallest worthwhile change is calculated but the introduction lacks information on responders/non-responders. In addition, I suggest to provide a reference for the smallest worthwhile change.

L174. I suggest to provide the mean and SD for the positive, negative and no responders. I suggest to do that for all parameters, e.g. L198.

L183. Jumps were recorded with whole numbers so I suggest to express without decimal places.

For the repeated jump test, the p-values show no differences between conditions.

L232. “Although jump height in the CMJ test increased by 1.6%, this improvement was not statistically significant.” So there was no increase. The 1.6% is likely within the variation of the measurement. Please revise.

There is inconsistency in the referencing format.

Author Response

Dear Editor and Reviewers,

We would like to thank the Editor and the reviewers for the time and effort devoted to the evaluation of our manuscript and for their constructive and valuable comments. We believe that their suggestions have significantly contributed to improving the quality, clarity, and scientific rigor of the article.

Following the reviewers’ recommendations, we have carefully revised the manuscript. Below, we provide a detailed, point-by-point response to all the issues raised, indicating how each comment has been addressed. In addition, all changes made to the manuscript have been highlighted in red to facilitate the review of the revised version.

We sincerely appreciate the reviewers’ insightful feedback and helpful suggestions, which have been of great value in strengthening this work.

Thank you again for your consideration and assistance. We look forward to your response.

 

REVIEWER 3

Why did the authors not use exercise tasks for which the literature has shown that there is a consistent ergogenic effect of caffeine. Strong justification needs to be provided for the battery of tests/tasks that was selected.

We thank the reviewer for this comment. As already stated in the Introduction, there is strong and consistent evidence that acute caffeine intake (3–6 mg·kg⁻¹) enhances maximal strength, power output, and muscular endurance, as supported by numerous experimental studies and systematic reviews. Accordingly, the selected test battery (countermovement jump, repeated jumps, and bench press at different relative loads and to failure) was intentionally chosen because ergogenic effects of caffeine have been consistently demonstrated in these neuromuscular tasks, including in several of our previous studies [1-6], supporting their suitability. In addition, prior to testing, participants were informed about the well-documented positive effects of caffeine on these exercise tasks, in line with the existing literature.

1              Del Coso J, Salinero JJ, González-Millán C, Abián-Vicén J, Pérez-González B. Dose response effects of a caffeine-containing energy drink on muscle performance: a repeated measures design. Journal of the International Society of Sports Nutrition. 2012;9(1):21-.

2. Giraldez-Costas V, Aguilar-Navarro M, Gonzalez-Garcia J, Del Coso J, Salinero JJ. Acute caffeine supplementation enhances several aspects of shot put performance in trained athletes. Journal of the International Society of Sports Nutrition. 2022;19(1):366-80.
3. Lara B, Gonzalez-Millán C, Salinero JJ, Abian-Vicen J, Areces F, Barbero-Alvarez JC, et al. Caffeine-containing energy drink improves physical performance in female soccer players. Amino Acids. 2014;46(5):1385-92.
4. Del Coso J, Pérez-López A, Abian-Vicen J, Salinero JJ, Lara B, Valadés D. Enhancing physical performance in male volleyball players with a caffeine-containing energy drink. International Journal of Sports Physiology and Performance. 2014;9(6):1013-8.
5. Pérez-López A, Salinero JJ, Abian-Vicen J, Valadés D, Lara B, Hernandez C, et al. Caffeinated energy drinks improve volleyball performance in elite female players. Medicine and Science in Sports and Exercise. 2015;47(4):850-6.
6. Giráldez-Costas V, González-García J, Lara B, Coso JD, Wilk M, Salinero JJ. Caffeine Increases Muscle Performance during a Bench Press Training Session. Journal of Human Kinetics. 2020;74(1):185-93.

 

We have modified the introduction section to further clarify this point, although using other references to minimize self-cites. Now it reads: “Specifically, in tests such as the bench press [19–22], repetitions to failure [21, 23], the countermovement jump (CMJ) [24–26], or repeated jumps [25], multiple studies have demonstrated that caffeine improves performance.”

 

Did the study have written participant information what the study was all about. More detail needs to be provided.

All participants took part in this study voluntarily after providing written informed consent. Prior to participation, they were fully informed about the experimental procedures, including the battery of exercise tests to be performed, as well as the potential ergogenic effects of caffeine, in order to enhance their understanding of the intervention and ensure an adequate level of expectancy and susceptibility. This information was provided verbally, and its credibility was further reinforced by the scientific background and previous research experience of the corresponding author (JJS) in the use of caffeine as an ergogenic aid, who was present during all experimental sessions. The use of deception was necessary to achieve the objectives of the study. Upon completion of the study, participants were fully debriefed and informed that they had in fact ingested a placebo. For clarity, we have incorporated this additional information in the revised version of the manuscript.

Now it reads: At that moment, information about the ergogenic effects of caffeine was provided to reinforce participants’ expectancy. Specifically, participants were informed about previous studies reporting performance improvements in jumping tasks and in bench press exercises performed at different loads. This information was conveyed by one of the authors (JJS), who has extensive research experience in caffeine and sports performance and was known to the participants, thereby further reinforcing their expectancy regarding the potential ergogenic effects of caffeine.

Additionally, at the end of the procedure, we have included the following statement in the revised manuscript: Once data collection was completed, all participants were debriefed regarding the true aim of the study and the use of a placebo.

 

What was the rationale for using exercise tasksI suggest to use doi: 10.1249/01.mss.0000233805.56315.a9.

Given the objectives of the present study, we employed experimental tasks that have been widely used and validated in the scientific literature on strength and power performance. Specifically, to assess placebo-induced changes in muscular power output, we selected ballistic bench press tests performed at 25%, 50%, and 75% of one-repetition maximum (1RM), as well as the countermovement jump. In addition, to assess performance under conditions of muscular fatigue, participants completed a 15-s repeated jump test and a bench press exercise performed to failure at 75% of one-repetition maximum (1RM). All these tests have been previously used in caffeine-related studies, as indicated in the first commentary.

I suggest to clarify when there is reference to review articles when not referring to primary sources. However, the authors should use more primary sources as it seems ~75% of references are reviews.

We thank the reviewer for this valuable suggestion. We have carefully revised the manuscript to clearly identify when review articles are cited. In the initial part of the introduction, we have specifically included systematic reviews to summarize the accumulated evidence and provide a comprehensive overview of the field. In addition, we have increased the number of primary research articles cited throughout the manuscript. As a result, the proportion of primary sources has increased.

The introduction is very general and lacks justification of the novelty of the study. Please revise the introduction and provide stronger justification and rationale.

We thank the reviewer for this comment. Specifically, the novelty of the present study is supported by several aspects already outlined in the Introduction:

1. Previous studies examining placebo caffeine effects on jumping and resistance exercises have reported contradictory findings, with some showing improvements and others reporting null effects. Importantly, these studies have focused almost exclusively on moderate-to-high loads (≥50% 1RM), leaving lower loads unexplored.
2. To our knowledge, no previous study has examined the placebo effect of deceptive caffeine ingestion on ballistic bench press performance at low loads (e.g., 25% 1RM), despite the relevance of this loading range for power-oriented movements.

Taken together, these points define a clear gap in the literature and provide a strong rationale for the present investigation. For clarity, we have slightly refined the wording of the Introduction to further emphasize these novel aspects and guide the reader more explicitly toward the study objectives.

Now it reads:

Nevertheless, in explosive exercises such as jumps, other studies have found that although ingesting a placebo or caffeine may enhance CMJ performance compared with a control condition, the effects of caffeine versus control appear greater than those of placebo versus control. Moreover, some studies did not find significant effects on jump performance when deceptive caffeine was administered [28, 29]. Thus, the results are somewhat contradictory, highlighting the need for further research in this area. Similarly, in other power-strength tests, such as ballistic bench press at different loads, contradictory results have been found [30, 31]. Both Costa et al. [30] and Ortiz et al. [31] found improvement in propulsive mean velocity at 50% of 1RM, but not at higher loads (60 to 90% 1RM). Notably, none of these studies included loads below 50% 1RM, leaving this range unexplored.

 

L92. Please clarify what was counterbalanced.

The order of the experimental conditions (placebo and control) was counterbalanced across participants, such that approximately half of the participants (i.e. 13 vs 12) completed the placebo condition first and the control condition second, while the remaining participants completed the conditions in the opposite order, in order to minimize potential order and learning effects, despite the inclusion of a prior familiarization session with all testing procedures.

To provide greater clarity, we have added the following information to the Procedures section:  “One session involved the ingestion of a placebo substance (100 mg of cornflour), administered in an opaque capsule 60 minutes before testing (placebo), while the other session involved no ingestion (control). The order of the experimental conditions was counterbalanced, with 12 participants completing the placebo session first and 13 participants completing the control session first.”

 

L97. What parameter and values from the literature were selected for the power analysis for sample size.

We thank the reviewer for this comment. The sample size was determined based on an a priori power analysis for a paired-samples t-test, assuming a moderate effect size (d = 0.6), a two-tailed α = 0.05, and a desired statistical power of 0.80. The selection of this effect size was informed by the heterogeneity of findings in previous literature, where reported effects range from values below 0.6 to larger magnitudes. In this context, our most recent study using the same deception protocol in running-based performance tests (Valero et al. 2024) reported an effect size of d = 0.69. Taken together, and considering the exploratory nature of the present study, we considered the assumption of a moderate effect size (consistent with the classification proposed by Hopkins, d = 0.6) to be a reasonable and methodologically sound choice.

Valero, F., González-Mohíno, F., & Salinero, J. J. (2024). Belief That Caffeine Ingestion Improves Performance in a 6-Minute Time Trial Test without Affecting Pacing Strategy. Nutrients, 16(2), 327. https://doi.org/10.3390/nu16020327

 

L99. If the sample size was calculated to be 24, then adding one more for dropouts (more than one) does not make sense. Please revise.

We thank the reviewer for this comment. The original sample size calculation indicated that 24 participants would be sufficient to achieve the desired statistical power. An additional participant was included as a precaution against potential dropouts; however, all participants completed the study except for one, who did not complete the 15-s repeated jump test (as already indicated in the Methods section: “15-Second Repeated Jump Test. Participants were required to perform all jumps at maximum height for 15 seconds. Participants were instructed to ‘jump as fast and as high as you can in 15 seconds.’ Only one attempt was performed. Arms were placed on the hips during all jumps, as in the CMJ. The jump height for each jump was recorded using the same optical measurement system. One participant reported knee pain during the repeated jumps test and stopped it, so their data were excluded from the analysis for this test”). As this participant was able to complete all other tests, we decided not to exclude them from the study, so the remaining variables included data from all 25 participants. Consequently, 24 participants were used for the 15-s repeated jump test.

I suggest to change “22.3 ± 1.5 years; height: 170.3 ± 9.2 cm; weight: 68.0 ± 11.5 kg” to “22 ± 2 years; height: 170 ± 9 cm; weight: 68 ± 12 kg”.

We have modified it.

L102. I suggest clarify 0.98 ± 0.26 1RM·body mass-1.”

This means that participants practically lifted their own body weight. However, to improve clarity, we have now reported the mean and standard deviation of the absolute 1RM values, instead of expressing them relative to body mass as in the previous version. Now it reads: “They were physically active young participants (17 men and 8 women; age: 22 ± 2 years; height: 170 ± 9 cm; weight: 68 ± 12 kg; 1RM: 68 ± 12 kg)”

References numbers in the text need to be provided in square brackets.

The reviewer is right. We have modified it.

L110. Please revise “body weight was measured to the nearest 0.1cm with a portable stadiometer (Seca Ltd., Germany”.

Sorry for the mistake. We have modified it.

L120. For women within 72 hr hormonal changes can be substantial. This seems to be very incorrect.

We thank the reviewer for this comment. All sessions were scheduled to occur after the bleeding phase of the menstrual cycle, in an attempt to minimize (not eliminate) hormonal fluctuations. However, we agree that substantial hormonal changes can still occur within a 72-hour interval. Extending the period to a full month would have introduced other confounding factors, such as changes in fitness status, while reducing the interval could have affected performance due to insufficient recovery and fatigue. This is a challenge that is always present in sports science research, but we specifically chose not to exclude female participants in order to avoid this potential source of bias. We considered this scheduling to be the most appropriate compromise to limit potential hormonal influences. Moreover, although some studies report no significant differences in performance in these types of efforts across menstrual cycle phases (Romero Moraleda et al. 2019), we acknowledge that large individual differences can exist.

 

Romero-Moraleda, B., Coso, J. D., Gutiérrez-Hellín, J., Ruiz-Moreno, C., Grgic, J., & Lara, B. (2019). The Influence of the Menstrual Cycle on Muscle Strength and Power Performance. Journal of Human Kinetics, 68(1), 123-133. https://doi.org/10.2478/HUKIN-2019-0061 

 

L127. There is no mention of CMJ at the end of the introduction.

We have incorporated the abbreviation CMJ in the introduction and revised the section to include additional information on CMJ, highlighting its relevance and the evidence on the effects of placebo and caffeine on this test.

 

L132. Was it reliable in your hands?

We believe that the assessments were reliable, as they were conducted by a researcher with extensive experience in jump performance evaluation, who applied standardized procedures and consistent criteria across all participants. In addition, a familiarization session was performed prior to data collection to ensure proper understanding and execution of the tests. During the warm-up, submaximal trials were also used to reinforce correct jumping technique and address any technical issues before the maximal attempts. These procedures were implemented to enhance measurement reliability and reduce potential variability.

 

L135. The description of the repeated jump test lacks detail. Where hands on hips for example.

Thanks for the suggestion. We have incorporated the clarification similar to the CMJ.

L164. The smallest worthwhile change is calculated but the introduction lacks information on responders/non-responders. In addition, I suggest to provide a reference for the smallest worthwhile change.

Thanks for your suggestion. We have provided a reference for the SWC.

L174. I suggest to provide the mean and SD for the positive, negative and no responders. I suggest to do that for all parameters, e.g. L198.

We thank the reviewer for the suggestion. From an applied performance perspective, and to enhance clarity in the presentation and interpretation of the results, we considered it most informative to report mean ± SD values only for positive and negative responders. These groups represent athletes who experienced substantial and practically meaningful changes exceeding the smallest worthwhile change (SWC), which are directly relevant for performance interpretation and decision-making.

In contrast, non-responders are defined by trivial changes within the SWC, including both small positive and negative fluctuations. Reporting a mean value for this group would result in an average close to zero due to the cancellation of opposing responses, which may be misleading and does not provide clear or meaningful information for practitioners.

Therefore, to improve clarity and applied relevance, we focused on descriptive statistics for participants showing clear performance improvements or decrements, rather than trivial individual responses.

If the reviewer considers this approach appropriate, we have revised the manuscript accordingly. Should the reviewer prefer the inclusion of descriptive values for non-responders as well, we would be happy to add them in a subsequent revision.

 

L183. Jumps were recorded with whole numbers so I suggest to express without decimal places.

We have modified it accordingly.

 

For the repeated jump test, the p-values show no differences between conditions.

The reviewer is right. We have modified the sentence.

 

L232. “Although jump height in the CMJ test increased by 1.6%, this improvement was not statistically significant.” So there was no increase. The 1.6% is likely within the variation of the measurement. Please revise.

The reviewer is right. We have modified the sentence.

 

There is inconsistency in the referencing format.

We have corrected the references.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for your careful revision of the manuscript and for addressing all the suggestions raised in the review process. I appreciate the effort you put into improving the clarity and quality of the work. In my opinion, the changes have strengthened the manuscript and adequately addressed the reviewers’ comments.

Kind regards,

Author Response

Thank you very much for your kind words and for the time you devoted to reviewing our manuscript. We greatly appreciate your positive evaluation and are pleased to hear that the revisions have improved the clarity and quality of the work.

Thank you again for your constructive comments and support throughout the review process.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you very much for your reply. However, the timing of caffeine consumption is also important. I recommend citing the relevant reference 10.3390/nu16101421. Thank you.

Author Response

Dear Reviewer,

Thank you very much for your comment. We would like to clarify that no caffeine was ingested in any condition of our study. However, to control for potential diurnal effects, all testing in both conditions was conducted in the morning at the same time for each participant.

We hope this clarifies the study protocol and addresses your concern regarding timing.