A Comparison Between the Use of an Infrared Contact Mat and an IMU During Kinematic Analysis of Horizontal Jumps

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript compares measurement systems used for kinematic analysis in horizontal jumps. While it is well organized, some methodological details and discussions on the broader context require improvement to enhance the manuscript's overall impact.

Abstract:

The last sentence (Lines 25-26) should emphasize how the findings could influence practitioners' selection of measurement tools in sports training and research.

Introduction:

The introduction section is well-structured; however, there are a few points that need attention.

Lines 47-50: Optojump or OptoGate? Did authors make a mistake with OptoGate? If not, the sentence is confusing, because OptoJump and OptoGate are different systems?

Lines 56-59: Is reference correct? Authors noted that van den Tillaar et al. [14] 56 found that a laser gun combined with IMUs attached to each foot (Musclelab, Ergotest  Technology AS, Langesund, Norway) automatically detected accurate step-by-step kinematics comparable to force plates during high-speed sprinting. According to the reference title, the main goal of this paper is to compare the Optojump and Musclelab systems.

Lines 59-60: Insert the reference

A lead-in paragraph that outlines the problem for the paper is required.

Line 74: I didn’t find any validity in this paper.

Methods:

According to the participants, several factors should be clarified. Why did the authors choose to focus on female players? Why specifically that age group? Why did they select football players? All of these factors can affect the results obtained.

Procedures need to be explained more thoroughly. While the authors provided a reference, an explanation of the jumps is still requested. What are running shoes? Are they meant for sprinting or regular use? Why did the authors choose a 20 m jump (reference)? If the authors want to assess reliability, two trials are not sufficient.

The authors discusses algorithms for sprinting but lacks details on their adaptation for jumps.

Lines 128-129: Could the authors clarify how to assess the validity using the recommended tests and statistical methods?

The authors used both one-way ANOVA and 2x8 ANOVA in their analysis. What was the reason for incorporating both methods?

Results:

I couldn't understand a specific point in Figure 1. Also, does the Figure represent velocities from an IMU or from an IR-based system? Because, there is only one line for each jump type.

Discussion:

Line 234-235: In the Participants section, the authors noted that the participants are experienced football players, but they later state that the participants have moderate experience. Please clarify and explain this discrepancy.

The discussion interprets the results, highlighting key factors that contribute to systematic biases, including algorithm design, sampling rates, and landing mechanics. There is a need for better connections to previous investigations and more in-depth explanations of the obtained results.

Author Response

We want to thank the reviewers for their comments to the manuscript. We have tried to answer to all the comments of the reviewers and changes are colored red in the manuscript. We think that the manuscript now is suitable for publication.

 

Reviewer 1

This manuscript compares measurement systems used for kinematic analysis in horizontal jumps. While it is well organized, some methodological details and discussions on the broader context require improvement to enhance the manuscript's overall impact.

Abstract:

The last sentence (Lines 25-26) should emphasize how the findings could influence practitioners' selection of measurement tools in sports training and research.

We have changed it slightly so that it clarifies practical relevance for coaches and researchers.

Introduction:

The introduction section is well-structured; however, there are a few points that need attention.

Lines 47-50: Optojump or OptoGate? Did authors make a mistake with OptoGate? If not, the sentence is confusing, because OptoJump and OptoGate are different systems?

These are two different systems. Optojump is used in sports to measure contact time, flight time, stride frequency and stride length during sprints and jumps, while Optogait is developed for gait analysis and rehabilitation, where it assesses gait patterns, asymmetries and balance.

Lines 56-59: Is reference correct? Authors noted that van den Tillaar et al. [14] 56 found that a laser gun combined with IMUs attached to each foot (Musclelab, Ergotest  Technology AS, Langesund, Norway) automatically detected accurate step-by-step kinematics comparable to force plates during high-speed sprinting. According to the reference title, the main goal of this paper is to compare the Optojump and Musclelab systems.

You are right. This was an incorrect reference on our part. The correct reference should be [15], and we have corrected it.

Lines 59-60: Insert the reference

The reference is listed early in the sentence (van den Tillaar et al. [14])

A lead-in paragraph that outlines the problem for the paper is required.

The "conclusion" is based on the above references.

Line 74: I didn’t find any validity in this paper.

The main point was to compare the measurements from both systems and determine whether they are comparable or not. They seem to be very comparable in sprinting, but in the context of jumps, we don’t know yet. That is all we have attempted to investigate in this study. It is not comparing validity against a gold standard.

Methods:

According to the participants, several factors should be clarified. Why did the authors choose to focus on female players? Why specifically that age group? Why did they select football players? All of these factors can affect the results obtained.

This was done because they were part of a training intervention study where we wanted to investigate  the effects of different types of training. That's why we used these players. Soccer players need good plyometrics and we wanted to find out which system was best for testing horizontal jumps, IMU or IR mat. We don’t think that it will influence the effects much as we were only interested the measuring details between the two systems.

Procedures need to be explained more thoroughly. While the authors provided a reference, an explanation of the jumps is still requested. What are running shoes? Are they meant for sprinting or regular use? Why did the authors choose a 20 m jump (reference)? If the authors want to assess reliability, two trials are not sufficient.

These are regular running shoes, not spike or soccer shoes. They use these shoes in this part of the season (preseason) as part of their plyometrics. During plyometrics on this surface (where they regularly did their plyometrics upon) it is normal to use running shoes.

This distance was selected to ensure that all phases of the jump sequence—acceleration and maximum velocity—were captured. They were tested during the preseason preparation period, when they engage in extensive physical training, wearing their regular running shoes for plyometric exercises. All trials were performed indoors on a tartan running track. Each trial began from a standing position, with a self-selected stance (one foot in front of the other). The jump exercises were performed in the following order: bounding for speed, followed by single-leg jumps for speed on the right and left leg. Each participant completed a total of six trials: two for bounding and two for each leg in the single leg jump condition. Recovery time between attempts was 2–3 minutes.

The main research question was to compare the measurements between the two systems. To compare these results with each other we think it was sufficient to have 19 athletes performing 2 attempts each in each exercise in which every time 8 steps were analyzed. This is for each exercise 302 results, which we think is enough to compare the two systems with each other. We hope the reviewer agrees about this.

The authors discusses algorithms for sprinting but lacks details on their adaptation for jumps.

As we had written in the text we used the sprint algorithm. Since it was an automated algorithm, we were interested to see if this algorithm was also suitable for jumping.

Lines 128-129: Could the authors clarify how to assess the validity using the recommended tests and statistical methods?

The system we used was already tested very valid for sprints. We were just interested to investigate if this algorithm also was suitable to compare when performing horizontal jumps and thereby see how accurate they are to each other.

The authors used both one-way ANOVA and 2x8 ANOVA in their analysis. What was the reason for incorporating both methods?

We used a 2x8 ANOVA to compare the findings between the two systems over both steps and systems or between the two types of jumps (figure 1). We used A One-way Anova with repeated measures was performed on DIFFERENCE in contact time between the two systems at touch down and take off for the eight steps. Since on this the difference value only steps is the independent variable and therefore a oneway ANOVA with repeated measures is used.

Results:

I couldn't understand a specific point in Figure 1. Also, does the Figure represent velocities from an IMU or from an IR-based system? Because, there is only one line for each jump type.

The point with this figure was to show the velocity development between the two different types of jumps as velocity development could have an evt. influence between the two measurement systems. The velocity was measured with laser and the same laser measurement for both systems.

Discussion:

Line 234-235: In the Participants section, the authors noted that the participants are experienced football players, but they later state that the participants have moderate experience. Please clarify and explain this discrepancy.

We have changed it to moderately experienced throughout the text. However, they have trained 6 weeks prior to this test. So they were experienced with these exercises. This is also mentioned in the text now.

The discussion interprets the results, highlighting key factors that contribute to systematic biases, including algorithm design, sampling rates, and landing mechanics. There is a need for better connections to previous investigations and more in-depth explanations of the obtained results.

We are very open for comparing the findings with earlier studies on jumping. However, to the best of our knowledge we could not find any previous studies that have evaluated horizontal jumps with these two systems. That is also why we have compared the findings to studies on sprinting between systems as the algorithm of the IMUs was used for sprinting and not known if this was similar accurate for horizontal jumps.

Reviewer 2 Report

Comments and Suggestions for Authors

First of all, I would like to thank you for invited to read the document.

The authors have done an excellent job. Each of the comments shared are intended to improve the study.

The comments can be found in the PDF document.

Also, some of the comments on some of the points that need to be reworded in the paper are shared below:

 

Title

A Comparison of Using an Infrared Contact Mat with IMU on Kinematic Analysis in Horizontal Jumps

Introduction

It is suggested to be able to review the literature on studies that have used IMU in team sports in order to have a broader view of its usefulness and reference values.

Material and Methods

Participants

It is suggested that the inclusion and exclusion criteria of the selected participants be reviewed and added. Also, indicate the type of sampling used.

Another important question would be to indicate how they defined the level of sports experience, by years, competitive level, etc. 

All the players evaluated played in the same role or playing position. This is because if goalkeepers were included, they may be more familiar with horizontal jumps than outfield players. Please clarify these issues to give more methodological soundness to the study.

It is suggested to add a table with the main characteristics of the evaluated sample.

 

At a methodological level, how did they control that only 19 players were significant to carry out the study. Please argue.

Procedure

It would be important to point out the difficulties that may be suggested by the fact that female soccer players have used running shoes. 

Another question would be why the present investigation was not conducted with runners who are perhaps more familiar with running shoes.

 

It is also suggested to describe more precisely each of the tests analyzed.

 

Statistics. Change. 2.6 Statistical analysis

Discussion

It is suggested that a subsection on limitations and a subsection on future perspectives be added.

Thus, we can focus on extending the discussion with several studies that have used force platforms and IMUs to assess jumps, mainly in team sports such as soccer. 

 

The discussion is really short and shallow to contrast the findings of the present research with the available scientific evidence. It is suggested that a more in-depth review could be conducted to broaden the topic of discussion.

 

Line 207-215

A review of the literature is suggested to support these ideas and to provide a more rigorous basis for the study presented.

 

Conclusions

What methodological difficulty may arise in the present study because the athletes do not use the boots that they commonly use in the game?

 

Finally, I thank the authors for the excellent work and encourage you to review the comments shared.

Comments for author File: Comments.pdf

Author Response

We want to thank the reviewers for their comments to the manuscript. We have tried to answer to all the comments of the reviewers and changes are colored red in the manuscript. We think that the manuscript now is suitable for publication.

 

Reviewer 2

First of all, I would like to thank you for invited to read the document.

The authors have done an excellent job. Each of the comments shared are intended to improve the study.

The comments can be found in the PDF document.

Also, some of the comments on some of the points that need to be reworded in the paper are shared below:

 

Title

A Comparison of Using an Infrared Contact Mat with IMU on Kinematic Analysis in Horizontal Jumps

Introduction

It is suggested to be able to review the literature on studies that have used IMU in team sports in order to have a broader view of its usefulness and reference values.

It is difficult to review literature on this issue as to the best of our knowledge no studies have been done on this equipment on jumps. Therefore is the study also very interesting as the systems can both be used to evaluate horizontal jumps.

Material and Methods

Participants

It is suggested that the inclusion and exclusion criteria of the selected participants be reviewed and added. Also, indicate the type of sampling used.

Another important question would be to indicate how they defined the level of sports experience, by years, competitive level, etc. 

All the players evaluated played in the same role or playing position. This is because if goalkeepers were included, they may be more familiar with horizontal jumps than outfield players. Please clarify these issues to give more methodological soundness to the study.

It is suggested to add a table with the main characteristics of the evaluated sample.

The main reason for the study was to compare two different systems, so soccer experience level is not that important here. Furthermore The participants were a part of a larger training study where this equipment was used to assess their performance. They were familiar with the exercises, having practiced them for six weeks prior to the tests. For the present research question, information about competition levels and a table of main characteristics of the sample is not of interest as we compare two measuring systems with each other, not the performance of the subjects themselves. We hope that the reviewer agrees with our opinion.

We have updated the text.

At a methodological level, how did they control that only 19 players were significant to carry out the study. Please argue.

We used one soccer team and these were the available players who completed the study. The team did not consist of more players. Based upon earlier studies on sprinting with two different systems the number of subjects was enough in our opinion as also shown by the significant differences in results with large effect sizes.

Procedure

It would be important to point out the difficulties that may be suggested by the fact that female soccer players have used running shoes. 

They were tested during the preseason preparation period, when they engage in extensive physical training, wearing their regular running shoes for plyometric exercises.

I have updated the text.

Another question would be why the present investigation was not conducted with runners who are perhaps more familiar with running shoes.

We wanted to test soccer players who do plyometric training. During such training, they do not wear soccer shoes. As this was a part of a training intervention of soccer players.

It is also suggested to describe more precisely each of the tests analyzed.

We believe we have provided sufficient information for the reader, allowing us to be brief and concise. The exact analyses have already been conducted in previous studies. The algorithm in the Muscle Lab system has been used in prior research, and we have applied the same algorithm, as it is already integrated into the system. We have now included that the automatic measurements were performed by the Musclelab systems that the readers now know where the analysis were based upon. This is added to the text now: These parameters were automatically calculated by the Musclelab system for both meas-uring tools (Ergotest Technology AS, Langesund, Norway) and were both earlier validated as very accurate in sprint step-by-step comparisons [14, 15].

Statistics. Change. 2.6 Statistical analysis

I have updated the text.

Discussion

It is suggested that a subsection on limitations and a subsection on future perspectives be added.

We have added a sub-section limitations and future studies to the discussion.

Thus, we can focus on extending the discussion with several studies that have used force platforms and IMUs to assess jumps, mainly in team sports such as soccer. The discussion is really short and shallow to contrast the findings of the present research with the available scientific evidence. It is suggested that a more in-depth review could be conducted to broaden the topic of discussion.

To our knowledge, no other studies have examined jumping using these system. The primary goal is to compare these two systems, as such tests have not been conducted before, making it difficult to compare them to studies that do not exist. We have compared them to sprint studies and observed differences. We aim to be brief and concise so we keep the reader interested.

Line 207-215

A review of the literature is suggested to support these ideas and to provide a more rigorous basis for the study presented.

I have added a reference that confirms this.

Conclusions

What methodological difficulty may arise in the present study because the athletes do not use the boots that they commonly use in the game?

That was not the main reason for our study. The main reason for the study was to compare the two systems with each other when it comes to plyometric training. Plyometric training is not done in soccer shoes, but with running shoes on.

 

Finally, I thank the authors for the excellent work and encourage you to review the comments shared.

Reviewer 3 Report

Comments and Suggestions for Authors

Introduction

The introduction is quite technical. While this is fine, more background should be provided for readers not familiar with the research topic. The research aim could be expanded, stating more clearly what is known, what the gaps in the field are, and how this specific study aims to fill in these gaps of knowledge. Research hypotheses should be formulated. Moreover, the introduction is rich in self-citations. Also, studies of authors outside of the group of RVDT should be properly acknowledged, cited, and discussed. 

Methods

Start with descriptive statistics, which is now at the end of the section. How was data normality distribution tested? State more clearly what is the 2X8 ANOVA you used. Is it a fully factorial ANOVA, in which both main and interaction effects were tested? To my understanding, is it not a repeated measure ANOVA with covariates/factors?

Was an a prior sample size and power analysis conducted? 

Results

Results are fine, maybe they could be enriched by at least one table. 

Discussion

The discussion reads very short and contains formulas and equations that appear to be in the wrong place (maybe they should be moved earlier to the method section). It reads quite superficial, without clear insights and broader contexts/implications. Also, it does not compare the findings with prior work.

Please add a separate section titled strength and limitations. 

Add a future direction section.  

Author Response

We want to thank the reviewers for their comments to the manuscript. We have tried to answer to all the comments of the reviewers and changes are colored red in the manuscript. We think that the manuscript now is suitable for publication.

Introduction

The introduction is quite technical. While this is fine, more background should be provided for readers not familiar with the research topic. The research aim could be expanded, stating more clearly what is known, what the gaps in the field are, and how this specific study aims to fill in these gaps of knowledge. Research hypotheses should be formulated. Moreover, the introduction is rich in self-citations. Also, studies of authors outside of the group of RVDT should be properly acknowledged, cited, and discussed.

We agree that it is rich in self-citations, but that is also because not many have investigated with this system these parameters. We have included more information about the other studies that have done some studies with IR mats and sprinting with their shortcoming / gap to the present study. This is  now included to the text: Previous studies have validated the accuracy of the Optojump system against force plates and high speed cameras for sprint and jump kinematics [16,17]. However, the Optojump system was in both these studies [16, 17] compared to a stationary system of a treadmill or vertical jumps. Thereby, not known how accuracy  would be with horizontal jumps.

Methods

Start with descriptive statistics, which is now at the end of the section. How was data normality distribution tested? State more clearly what is the 2X8 ANOVA you used. Is it a fully factorial ANOVA, in which both main and interaction effects were tested? To my understanding, is it not a repeated measure ANOVA with covariates/factors?

Normality was tested with the Shapiro Wilks test and we found that all data were normally distributed. We have updated the text.

We have included more details about the statistical analysis. We performed two 2 (measuring device: IMU vs. IR mat / jump type: single leg jumps and bounding) x 8 (steps) ANOVA’s with repeated measures. So two factors with interaction effect in these tests. A oneway ANOVA was performed on the differences in contact times between the two devices over 8 steps. We hope it is clear now.

Was an a prior sample size and power analysis conducted?

The sample size was based upon experiences of earlier studies in which sprint kinematics between two systems were compared. Furthermore, when significant difference were found with a p < 0.05 with large effect sizes than the sample size is high enough to avoid a type II error. So we are convinced that the sample size for the present study was high enough.

 

Results

Results are fine, maybe they could be enriched by at least one table.

What kind of table would you see? As we have shown all data in figures, in our opinion the best way to show differences between the two systems, we can not report an extra table based on the same numbers. This would be double presentation which is not normal to do in articles. We choose to be short and concise to attract the readers.

Discussion

The discussion reads very short and contains formulas and equations that appear to be in the wrong place (maybe they should be moved earlier to the method section). It reads quite superficial, without clear insights and broader contexts/implications. Also, it does not compare the findings with prior work.

The challenges with the present study was that to our knowledge now previous studies have investigated IMUs compared to a laser mat system in horizontal jumping. Therefore it is difficult to it with other studies on jumping. We have compared it with studies in sprinting as the algorithm of IMU measurements was based upon sprinting. Which also was one of the main points that it should probably be adapted for jumps. That is why the discussion is a bit superficial as we just wanted to compare two systems with each other that were never used in jumping.

 

Please add a separate section titled strength and limitations.

Add a future direction section.

As we have combined the limitations with some future studies suggestions, we have added a section called limitations and future  studies.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

After reviewing the revised manuscript, I have few comments to add:

Introduction:

Line 74: Please, delete expression validity. There is no validity exploration in this paper.

Methods:

Lines 96-98: Please provide a reference for this explanation.

Results:

Figure 1: According to the authors' response, the explanation provided in the heading of Figure 1 is incorrect. There is no exploration of the difference between the IMU and IR-mat; the only difference lies in the different jump types, and the measuring device used is a laser gun.

Author Response

Thank you for reviewing the manuscript again. We have answered to all comments of the reviewer and think that it is now suitable for publication.

Introduction:

Line 74: Please, delete expression validity. There is no validity exploration in this paper.

We have deleted this here

 

Methods:

Lines 96-98: Please provide a reference for this explanation.

We have now provided two references in this.

Results:

Figure 1: According to the authors' response, the explanation provided in the heading of Figure 1 is incorrect. There is no exploration of the difference between the IMU and IR-mat; the only difference lies in the different jump types, and the measuring device used is a laser gun.

That is true. Thank you for the observation. We have changed it now correctly in:

Mean (±SD) step velocity for bounding and single leg jumps measured with IR-mat and laser gun. † indicates a significant difference between the two types of jumps for all steps, → indicates a significant difference in velocity between this step and everything right from the arrow.

Reviewer 2 Report

Comments and Suggestions for Authors

Thank you for the opportunity to review the manuscript.

The authors have managed to respond to each of the comments made.

I can suggest the suitability of the manuscript for publication.

Author Response

Thank you for the opportunity to review the manuscript.

The authors have managed to respond to each of the comments made.

I can suggest the suitability of the manuscript for publication.

Thank you for reviewing the manuscript again.