The Integral Reactive Strength Index: An Accurate Measurement for Evaluating Drop Jump Performance in Sprinter Athletes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study aims to explore the relationship between overall IRSI and RSI and to compare the performance of 100-meter and 400-meter Olympic sprinters in terms of flight time, ground contact time, jump height, RSI, reaction ability, and IRSI. The overall framework is complete, and from an overall advantage perspective, this study is reasonable and should be published. However, I have a few suggestions:

The sample is very small for this type of study that should pay careful attention to its inference results, and this limitation should be addressed in the article.

Several points should be considered for inclusion in the study limitations:

Technique: RSI is highly dependent on technique. When athletes reduce contact time, it may affect jump height, which needs to be taken into account during measurement.

Large-Group Training: Individualized height settings are impractical in large-scale training, which may affect the specificity and applicability of test results.

Discuss the limitations, including sample limitations (Is it possible to extrapolate these findings to other fields?), and include strength points, future directions, and practical applications.

Author Response

We thank the reviewer for raising their doubts and presenting their main concerns about the study. We also express gratitude for the recommendations and suggestions that undoubtedly improved the study.

The sample is very small for this type of study, which should pay careful attention to its inference results, and this limitation should be addressed in the article.

A/ Thank you very much for your comment. Our purpose was: (I)To test the correlation of a new variable denominated integral reactive strength index (IRSI) with the RSI, and (II) to compare the flight time, ground contact time, jump height, RSI, reactive capacity, and IRSI between Olympic athletes in 100 m and 400 m events. This study only involved Olympic qualification sprinters with a high level of plyometric experience, which forced us to look for athletes inside and outside Portugal. The research did not intend to compare athletes who did not present these characteristics and did not train in explosive activities daily. The authors believe that more research like this is needed in the scientific literature. Other researchers have analyzed plyometric activity at school age [1,2] in non-Olympic athletes [3,4]; however, very few investigations present results with high-quality samples, including small ones (n=6) [5]. Despite the small sample size of the present study (n 10), our comparison results are clear for this type of population, and the magnitude of significance and effect size seem to support our findings. As indicated in the limitations section, these results could vary in other populations. But we also recognize that further research will be needed to refine the results of these comparisons in other, more diverse populations or other sports.

 

Several points should be considered for inclusion in the study limitations:

Technique: RSI is highly dependent on technique. When athletes reduce contact time, it may affect jump height, which needs to be taken into account during measurement.

A/ Thank you very much for your comment. This point was debated in our discussion. I quote.

“Similarly, during the assessment of RSI [6], the researchers pointed out that athletes were asked to maintain the GCT below 250ms. Otherwise, the repetition should be repeated. However, it was not considered that RSI is highly modifiable, and it depends a lot on the technique. Athletes who showed a decrease in contact time may compromise jump height [7,8]. This could explain the results of a study [8] with national and international sprinters that showed considerably good values for GCT but very poor values for JH and RSI performing a DJ30 (GCT= 0.170 ± 0.028; HJ= 0.340 ± 0.049; RSI= 2.06 ± 0.043). In the current study, athletes were asked to maintain the correct relationship between JH and GCT, as it was reported by others [7,9]”.

Large-Group Training: Individualized height settings are impractical in large-scale training, which may affect the specificity and applicability of test results.

A/ Thank you very much for your comment. The authors take the other view, as set out in the discussion chapter cited above: “…In the same vein, although one study [10] recommends that it is impractical when working with large groups to individualize the HF and proposes a moderate HF (30 cm), this strategy may not be useful for high-level 100m and 400m sprinters. According to this training task variable, it aims to show the maximum RSI associated with the highest HJ to seek greater specificity [9] and magnitude of the adaptations [11]. In addition, when training large groups, individualized drop heights, which require different box sizes, would considerably help distribute the groups and reduce training time due to the concentration of athletes in the same box.

 

Discuss the limitations, including sample limitations (Is it possible to extrapolate these findings to other fields?), and include strength points, future directions, and practical applications.

A/ Thank you very much for your comment. We consider that the first of these aspects was previously addressed in the Introduction section.

For example, “… Is it possible to extrapolate these findings to other fields?”

Introduction

“… Similar studies [12] found differences in RSI with power athletes (jumpers, sprinters, and throwers; RSI = 2.19 ± 0.58 cm) outperforming endurance athletes (RSI = 0.84 ± 0.39)…” 

Conclusions

“… These criteria could be manifested at another level of sports training, but this study refutes these criteria for high-level athletes in 100m and 400m dash sprinters …” 

 

... and include strength points, future directions, and practical applications.

A/ Thank you very much for your comment. This was briefly included in the text:

Our work is not without limitations. The study was conducted solely with high-level competitive sprint athletes, and we acknowledge that these results may vary in other populations. Additionally, this study did not include data from female athletes; therefore, future researchers may be able to make such comparisons. Despite these limitations, we consider these comparisons of reactive strength variables with Olympic-level athletes to be a strength of our research, not only to increase the quality of the sample but also to provide practical information to top-level coaches. Future lines of research can create criteria for the IRSI and create training programs that compare IRSI-based training versus traditional RSI programs. 

 

 

Reference

1. Elnaggar, R.K. Effects of plyometric exercises on muscle-activation strategies and response-capacity to balance threats in children with hemiplegic cerebral palsy. Physiother Theory Pract 2022, 38, 1165-1173, doi:10.1080/09593985.2020.1833389.
2. Elnaggar, R.K.; Mahmoud, W.S.; Alsubaie, S.F.; Abd El-Nabie, W.A. Effectiveness of a Multi-Modal Exercise Program Incorporating Plyometric and Balance Training in Children With Hemiplegic Cerebral Palsy: A Three-Armed Randomized Clinical Trial. Phys Occup Ther Pediatr 2022, 42, 113-129, doi:10.1080/01942638.2021.1964674.
3. Watkins, C.M.; Gill, N.D.; Maunder, E.; Downes, P.; Young, J.D.; McGuigan, M.R.; Storey, A.G. The Effect of Low-Volume Preseason Plyometric Training on Force-Velocity Profiles in Semiprofessional Rugby Union Players. Journal of Strength and Conditioning Research 2021, 35, 604-615, doi:10.1519/jsc.0000000000003917.
4. Nonnato, A.; Hulton, A.T.; Brownlee, T.E.; Beato, M. The Effect of a Single Session of Plyometric Training Per Week on Fitness Parameters in Professional Female Soccer Players: A Randomized Controlled Trial. J Strength Cond Res 2022, 36, 1046-1052, doi:10.1519/jsc.0000000000003591.
5. Jensen, R.L.; Ebben, W.P. Quantifying plyometric intensity via rate of force development, knee joint, and ground reaction forces. J Strength Cond Res 2007, 21, 763-767, doi:10.1519/r-18735.1.
6. Ramirez-Campillo, R.; Moran, J.; Drury, B.; Williams, M.; Keogh, J.W.; Chaabene, H.; Granacher, U. Effects of Equal Volume But Different Plyometric Jump Training Intensities on Components of Physical Fitness in Physically Active Young Males. J Strength Cond Res 2019, doi:10.1519/JSC.0000000000003057.
7. Newton, R.U.; Dugan, E. Application of strength diagnosis. Strength Cond J 2002, 24, 50-59.
8. Healy, R.; Kenny, I.C.; Harrison, A.J. Reactive Strength Index: A Poor Indicator of Reactive Strength? Int J Sports Physiol Perform 2018, 13, 802-809, doi:10.1123/ijspp.2017-0511.
9. Ebben, W.P.; Petushek, E.J. Using the reactive strength index modified to evaluate plyometric performance. J Strength Cond Res 2010, 24, 1983-1987, doi:10.1519/JSC.0b013e3181e72466.
10. Ramirez-Campillo, R.; Alvarez, C.; Garcia-Pinillos, F.; Sanchez-Sanchez, J.; Yanci, J.; Castillo, D.; Loturco, I.; Chaabene, H.; Moran, J.; Izquierdo, M. Optimal Reactive Strength Index: Is It an Accurate Variable to Optimize Plyometric Training Effects on Measures of Physical Fitness in Young Soccer Players? J Strength Cond Res. 2018, 32, 885-893.
11. Young, W. Laboratory strength assessment of athletes. New Studies in Athletics 1995.
12. Loturco, I.; Gil, S.; Laurino, C.F.D.; Roschel, H.; Kobal, R.; Abad, C.C.C.; Nakamura, F.Y. Differences in Muscle Mechanical Properties between Elite Power and Endurance Athletes: A Comparative Study. J Strength Cond Res 2015, 29, 1723-1728, doi:Doi 10.1519/Jsc.0000000000000803.

 

Reviewer 2 Report

Comments and Suggestions for Authors

My suggestion for authors to do some corrections concerns the following aspects:

1. In the Discussion (lines 268-295), the text mentions differences in the size of the effect between the groups (100m vs. 400m sprinters) even though no significant differences were found in the reactive resistance variables. Even though effect sizes are valuable for understanding the magnitude of differences, their interpretation without appropriate statistical significance can be misleading. Only the effect sizes do not take into account the sample size, which, let's not forget, is n=10, an aspect that may predispose to overestimating the practical importance of findings that may be due to chance or other variables that could not be controlled.

2. Bibliographic sources:

- of the 27 - 11 of these are older than 10 years, and the vast majority are older than 5 years.

Author Response

We thank the reviewer for raising his doubts and main concerns about the study. We also express our gratitude for his suggestion and will try to give our point of view on it.

In the Discussion (lines 268-295), the text mentions differences in the size of the effect between the groups (100m vs. 400m sprinters) even though no significant differences were found in the reactive resistance variables. Even though effect sizes are valuable for understanding the magnitude of differences, their interpretation without appropriate statistical significance can be misleading. Only the effect sizes do not consider the sample size, which, let's not forget, is n=10, an aspect that may predispose to overestimating the practical importance of findings due to chance or other variables that could not be controlled.

 

A/ Thank you very much for your comment. This criterion is highly debatable. Although the p-value indicated no significant difference between the two groups, the researchers observed a trend suggesting the dominance of one group in some reactive strength variables. We used the effect size (ES) to determine the magnitude of this tendency. We agree with the reviewer regarding the limitation of using the effect size with small samples. Nevertheless, from the author's perspective, the ES could provide an insight into how large or small this tendency was [1].

In practice, the p-value presents some limitations as it cannot report trends; with careful analysis, effect sizes seem to be more useful for this kind of information. Looking for practical significance can make a big difference for coaches, as even a thousandth of a second can determine victory. For this reason, we report effect sizes even without statistical significance. In our view, we can conduct more in-depth analyses when reporting effect sizes, as shown below. I quote:

“… Analyzed separately the metrics that make up the reactive strength calculation (GCT and FT), we can observe that regarding FT, we found no significant differences between the groups. But even so, we observe that between DJ30-50, there is a trend that 100m group sprinters show trivially better FT (ES ≤ 0.50) than 400m sprinters (see table 2). These effects tend to be slightly large between DJ50-60, where moderate effects are already observed (ES = 0.72). When examining the GCT, we also observed that between DJ30 and DJ50, the 100m group tends to show an increment in this value relative to the 400m group (ES DJ30 = 0.12; DJ40 = 0.33; DJ50 = 0.46, and DJ60 = 0.68). This may explain why the 100m group improved RSI during all HF, while the 400m group decreased RSI in the DJ60…”

 

 

Reference

1. Sullivan, G.M.; Feinn, R. Using Effect Size-or Why the P Value Is Not Enough. J Grad Med Educ 2012, 4, 279-282, doi:10.4300/jgme-d-12-00156.1.