Rearfoot, Midfoot, and Forefoot Motion in Naturally Forefoot and Rearfoot Strike Runners during Treadmill Running

Round 1

Reviewer 1 Report

The manuscript aims to evaluate the effects of the striking pattern on foot kinematics in runners.

Minor comments:

• lines 62-63 - it is not necessary to say in the introduction section the statistical tests used to analyze data.
• Are the different striking patterns associated with some lower limb injuries in runners?
• Have the participants had some lower limb injuries in the past (not in the past 2 months)?
• How can the present findings ”expand the comprehension of the relationship between foot function and running-related injuries”?

Author Response

Reviewer 01

 

We thank the reviewer for the comments and for your commitment in reviewing this manuscript. Below, we respond to your relevant questions and suggestions. If we have not yet been clear enough in our answers and points in this response letter, as well as throughout the manuscript, we would like to have an additional opportunity to better addressing your further questions or comments. First, we bring back your comments (in bold) and, subsequently, we provide our response. In the paper, the revised text is underlined for this reviewer to follow what we have adjusted in this new version.

 

1. lines 62-63 - it is not necessary to say in the introduction section the statistical tests used to analyze data.

Response:  we agree with the reviewer and have removed this specific sentence from the Introduction.

 

2. Are the different striking patterns associated with some lower limb injuries in runners?

Response:  Indeed. There are differences in injury type between FFS and RFS. We have now reported this information, as in the paragraph here below, and we have also introduced a sentence in the Introduction to point out this association.

 

“In particular, FFS has been found to be associated with the attenuation of the lower limbs loads, which helps to reduce the incidence of running-related injuries [4,5]. However, RFS mitigates part of the Achilles tendon loading rate the foot is accountable for, especially in early stance [3].”

 

“The present results may contribute to further expand our comprehension of the relationships between foot function and running-related injuries, as there are differences in type of injuries reported in FFS and RFS. For example, posterior lower leg injuries are reported for FFS and repetitive stress injuries are reported in RFS [3-5]. Moreover, differences have also been reported in running economy strategies, with FFS being more efficient, therefore resulting in an increased performance compared to RFS during acute transitioning from one pattern to another [36].”

 

3. Have the participants had some lower limb injuries in the past (not in the past 2 months)?

Response:  Prior to the previous two months of baseline assessment, 24 participants have experienced some lower limb injury. From? these, 15 (30.6%) were rear foot strikers and 9 (36%) were forefoot strikers. This data was self-reported, gathered during eligibility assessment and lack confirmation through medical exams.

 

4. How can the present findings ”expand the comprehension of the relationship between foot function and running-related injuries”?

Response: Relevant question, thank you. We now have included at the end of the Discussion a sentence pointing out the importance of the results of our study to further comprehend the relationship between foot function and Running Related Injuries.

 

“The kinematic findings of the present study may be of interest to clinicians and other health professionals to support strategies to prevent or to rehab specific types of injury associated to FFS or RFS, such as plantar fasciitis, Achilles tendinopathy, and metatarsals stress fractures [1], through biomechanics guidance regarding the footstrike patterns.”

Reviewer 2 Report

Thank you for the opportunity to review this interesting article. 

Recommendations:

for Introduction -

The introduction should be extended to highlight the general aspects and especially the particular ones of the approached topic.

The degree of topicality and innovation of the approached topic should be highlighted compared to the previous studies.

For Conclussions -

We recommend adding specific conclusions in relation to the results found.

In the conclusions section I would recommend highlighting the degree of applicability of relevant results of the study.

Author Response

Reviewer 02

 

We thank the reviewer for the comments and for your commitment in reviewing this manuscript. Below, we respond to your relevant questions and suggestions. If we have not yet been clear enough in our answers and points in this response letter, as well as throughout the manuscript, we would like to have an additional opportunity to better addressing your further questions or comments. First, we bring back your comments (in bold) and, subsequently, we provide our response. In the paper, the revised text is underlined for this reviewer to follow what we have adjusted in this new version.

 

1. for Introduction - The introduction should be extended to highlight the general aspects and especially the particular ones of the approached topic. The degree of topicality and innovation of the approached topic should be highlighted compared to the previous studies.

Response:  We have included two paragraphs pointing out the innovation of our approach comparing to other studies in the literature, and we have complemented this literature with new papers dealing with this sensible reviewer’s suggestion, particularly in the Introduction. Here below the three paragraphs we have now included, accordingly.

 

“The effect of striking patterns on lower limb joint kinetics and kinematics has thus far been reported, while foot joint and segment kinematics have rarely been investigated and in a limited number of foot joints and segments only [6–9]. Lower limb kinematics showed that FFS presents the foot angle at initial contact in a plantar flexed position and RFS in dorsiflexed position [21]. In addition, FFS runners contact the ground with greater knee flexion compared to RFS runners [21]. Kinematic differences have also been reported in the frontal plane, where greater rearfoot eversion is observed in FFS compared to RFS [21].”

 

“We propose another way of analyzing the foot kinematic without immediately resorting to reductionism of variables, analyzing the whole time series using a functional data analysis, instead of a collection of discrete variables within a time series. In this study, we focus on improving our understanding on the effects of the striking pattern on foot kinematics by using a validated multi-segment foot model applied on a large population of naturally RFS and FFS runners. The present results may contribute to further expand our comprehension of the relationships between foot function and running-related injuries, as there are differences in type of injuries reported in FFS and RFS. For example, posterior lower leg injuries are reported for FFS and repetitive stress injuries are reported in RFS [3-5]. Moreover, differences have also been reported in running economy strategies, with FFS being more efficient, therefore resulting in an increased performance compared to RFS during acute transitioning from one pattern to another [36]”

 

“In summary, the main limitations of the previous studies were (i) the populations analyzed, these being not naturally FFS and RFS runners; (ii) the lack of control the motor adaptations which occur as runners forcibly convert their footstrike pattern; and (iii) the small sample, the largest size being 18 runners only [9]. Thus, the aim of the present study was to overcome these limitations, investigating and comparing 3D kinematic patterns of foot joints and segments between large populations of naturally RFS and FFS recreational runners. Our hypotheses were: (i) FFS runners land with the more plantarflexed forefoot compared to RFS runners; (ii) first and second metatarsal bones of FFS runners are less inclined with respect to the ground at foot contact due to the their landing strategy; and (iii) metatarsal bones of RFS runners present an upward orientation with respect to the ground at initial contact. “

 

2. For Conclusions - We recommend adding specific conclusions in relation to the results found.

Response:  We have rewritten the whole Conclusion section according to all these reviewer’s suggestions, particularly to relate to the results found in a more specific way.

 

“FFS and RFS runners were found to be characterized by distinct foot joint rotations and bone orientations. In particular, FFS runners landed with the metatarsal bones less tilted with respect to the ground, maintained the metatarsus less adducted during stance and, after landing, maintained the ankle more in dorsiflexion, to return to plantarflexion at push-off. Additionally, FFS runners showed a more adducted calcaneus to the shank and a less inverted midfoot with respect to the calcaneus in the entire stance phase. The present results also brought more evidence on the effect of the footstrike angle on the kinematic pattern of the foot-ankle complex which can be responsible for the differences in running-related injuries, load responses and running economy strategies between FFS and RFS as largely reported in the literature.”

 

3. In the conclusions section I would recommend highlighting the degree of applicability of relevant results of the study.

Response:  Compatible with the other reviewers’ suggestion a concise Conclusion, we have included at the end of the discussion a sentence highlighting the importance of the results of our study.

 

“The kinematic findings of the present study may be of interest to clinicians and other health professionals to support strategies to prevent or to rehab specific types of injury associated to FFS or RFS, such as plantar fasciitis, Achilles tendinopathy, and metatarsals stress fractures [1], through biomechanics guidance regarding the footstrike patterns.”

 

Reviewer 3 Report

I think this is a very important paper for those researchers looking at foot Biomechanical problems. Specifically, intrinsic injuries to the foot including mid-foot and hind foot problems are common in runners. These biomechanics may help assist in evaluation and treatment 

 

Author Response

Response:  We thank you very much the reviewer for the compliments and comments. We also think that our results would benefit biomechanicists and researchers related to running rehabilitation.

Reviewer 4 Report

Introduction

The state of the art in the area studied must be improved, explaining actual knowledge and the necessity of the present research

The objective must be concise, according to the introduction proposed

Include a study hypothesis

 

Methods

For better comprehension, the procedure must be in deep described and I would recommend including a figure to visually explain the procedure

Results

Try to improve figure quality for better comprehension

 

Discussion

Explain if the hypothesis is confirmed and why

Discuss results obtained and explain differences according to previous studies

Conclusion

Must be concise, responding to the study aim

 

Author Response

Reviewer 04

 

We thank the reviewer for the comments and for your commitment in reviewing this manuscript. Below, we respond to your relevant questions and suggestions. If we have not yet been clear enough in our answers and points in this response letter, as well as throughout the manuscript, we would like to have an additional opportunity to better addressing your further questions or comments. First, we bring back your comments (in bold) and, subsequently, we provide our response. In the paper, the revised text is underlined for this reviewer to follow what we have adjusted in this new version.

 

1. Introduction - The state of the art in the area studied must be improved, explaining actual knowledge and the necessity of the present research

Response:  We have included two new paragraphs pointing out the necessity of our approach/ study also by comparing this with what has been already published; we have also complemented the literature with papers addressing this reviewer’s suggestion, possibly to improve in fact the Introduction. The following two paragraphs we have included.

 

“The effect of striking patterns on lower limb joint kinetics and kinematics has thus far been reported, while foot joint and segment kinematics have rarely been investigated and in a limited number of foot joints and segments only [6–9]. Lower limb kinematics showed that FFS presents the foot angle at initial contact in a plantar flexed position and RFS in dorsiflexed position [21]. In addition, FFS runners contact the ground with greater knee flexion compared to RFS runners [21]. Kinematic differences have also been reported in the frontal plane, where greater rearfoot eversion is observed in FFS compared to RFS [21].”

 

“We propose another way of analyzing the foot kinematic without immediately resorting to reductionism of variables, analyzing the whole time series using a functional data analysis, instead of a collection of discrete variables within a time series. In this study, we focus on improving our understanding on the effects of the striking pattern on foot kinematics by using a validated multisegment foot model applied on a large population of naturally RFS and FFS runners. The present results may contribute to further expand our comprehension of the relationships between foot function and running-related injuries, as there are differences in type of injuries reported in FFS and RFS. For example, posterior lower leg injuries are reported for FFS and repetitive stress injuries are reported in RFS [3-5]. Moreover, differences have also been reported in running economy strategies, with FFS being more efficient, therefore resulting in an increased performance compared to RFS during acute transitioning from one pattern to another [36]”

 

2. The objective must be concise, according to the introduction proposed. Include a study hypothesis

Response:  We agree with the reviewer that the objective was not precise. Thus, we have rewritten the aim in the introduction to follow our rationale in the text and we have included our hypotheses, as requested. Please check bellow:

 

“In summary, the main limitations of the previous studies were (i) the populations analyzed, these being not naturally FFS and RFS runners; (ii) the lack of control the motor adaptations which occur as runners forcibly convert their footstrike pattern; and (iii) the small sample, the largest size being 18 runners only [9]. Thus, the aim of the present study was to overcome these limitations, investigating and comparing 3D kinematic patterns of foot joints and segments between large populations of naturally RFS and FFS recreational runners. Our hypotheses were: (i) FFS runners land with the more plantarflexed forefoot compared to RFS runners; (ii) first and second metatarsal bones of FFS runners are less inclined with respect to the ground at foot contact due to the their landing strategy; and (iii) metatarsal bones of RFS runners present an upward orientation with respect to the ground at initial contact.”

 

3. Methods - For better comprehension, the procedure must be in deep described and I would recommend including a figure to visually explain the procedure

Response:  The figures 1 and 2 described the kinematic procedures used to calculate multi-segment kinematics, and the overall foot angles necessary to determine the foostrike patterns. We have included another figure to better elucidate the two running strike patterns analyzed. The caption of the new Figure is below.

“Figure 2. Illustrations showing the experimental protocol, taken while subjects were running on the force-sensing tandem treadmill at their self-selected speed. Runner’s typical footstrike pattern, either forefoot (FFS, left picture) or rearfoot strike (RFS, right picture) pattern, was verified against kinematic data and slow-motion sagittal plane videos from high-speed cameras.”

 

4. Results - Try to improve figure quality for better comprehension

Response:  The figures were reformatted to improve readability and comprehension. We hope it improved the way the results are presented. Please check in the manuscript the new revised figures.

 

5. Discussion - Explain if the hypothesis is confirmed and why

Response:  We have explained now in the first paragraph of the Discussion section if the hypotheses raised (now formulated more clearly) were confirmed or not. Please check in the text bellow:

 

“The purpose of this study was to investigate and compare foot joint and segment kinematics between naturally RFS and FFS runners using an established and validated multi-segment kinematic model. In accordance with the first hypothesis, FFS runners landed with the forefoot first and showed an anticipated change in the Sha-Foo plantar/dorsiflexion in the stance phase compared to RFS runners. However, at mid-stance (15–40%), the Sha-Foo of FFS runners was more dorsiflexed, probably due to the larger external ankle dorsiflexion moment associated with this landing strategy [9].The second hypothesis was also confirmed, as the first and second metatarsal bones in FFS runners was less inclined in relation to the ground (more dorsiflexed) at initial contact. With respect to the third hypothesis, RFS runners showed the fifth metatarsal bone in a upward orientation with respect to the ground and this orientation was combined with a greater adduction of the metatarsus relative to the calcaneus (Cal-Met) at initial contact. These observations are consistent with the theoretical model of an oblique midtarsal joint where plantarflexion is associated with adduction [18–20] when running with an RFS pattern, which was not found in FFS runners.”

 

6. Discuss results obtained and explain differences according to previous studies

Response:  We have highlighted the parts in the manuscript where comparisons with the literature was possible. This has been interesting also to point out that there are only two recent studies that have used multi-segment foot kinematics to investigate and compare kinematic patterns from RFS or FFS runners; both of them are cited and discussed in the paper, also by comparing their results with those of the present study.

 

“In agreement with Bruening et al. [9], the midfoot of FFS runners was less inverted with respect to the calcaneus (i.e., Cal-Mid joint) throughout the stance phase. In RFS runners, the larger inversion may play an important role in the so-called twisted osteoligamentous plate in the foot structure [25], resulting in an increased resistance to overall foot pronation during the loading phase of running, when this plate tends to untwist, thus providing the necessary protection for the tibiotalar joint from high-impact forces during the stance phase [6,26]. This larger inversion in RFS may also contribute to the conversion of the foot into a sort of rigid lever, which is necessary for effective propulsion during running [27,28]. “

 

“The calcaneus was more adducted with respect to the shank (i.e., Sha-Cal joint) in the FFS group during the whole stance phase. Fisher et al. [29] showed that calcaneus adduction may be beneficial to the ankle joint coupling, acting as a mechanism to control excessive tibial rotation. This was reported to be associated with patellofemoral pain and iliotibial band syndrome [30], as high relative rotation between the tibia and femur may alter the patella tracking on the distal femur [31]. The present results seem to suggest a biomechanical mechanism that might explain how a transition from RFS to FFS patterns in gait retraining could reduce patellofemoral pain in runners [32,33] since FFS runners run with a more adducted calcaneus, thus improving ankle joint coupling and tibial rotation control.”

 

7. Conclusion - Must be concise, responding to the study aim

Response:  We have rewritten the whole Conclusion to follow the reviewer’s suggestions to respond to the study aim in a more direct and objective way.

 

“FFS and RFS runners were found to be characterized by distinct foot joint rotations and bone orientations. In particular, FFS runners landed with the metatarsal bones less tilted with respect to the ground, maintained the metatarsus less adducted during stance and, after landing, maintained the ankle more in dorsiflexion, to return to plantarflexion at push-off. Additionally, FFS runners showed a more adducted calcaneus to the shank and a less inverted midfoot with respect to the calcaneus in the entire stance phase. The present results also brought more evidence on the effect of the footstrike angle on the kinematic pattern of the foot-ankle complex which can be responsible for the differences in running-related injuries, load responses and running economy strategies between FFS and RFS as largely reported in the literature.”

Round 2

Reviewer 2 Report

The article was improved according with recommendations.