Elsevier

Gait & Posture

Volume 56, July 2017, Pages 123-128
Gait & Posture

Full length article
The influence of shoe aging on children running biomechanics

https://doi.org/10.1016/j.gaitpost.2017.05.011Get rights and content

Highlights

  • 14 children performed a running task with new shoes and used shoes.

  • GRF loading rate increased by 23% in used shoes compared to new shoes.

  • Peak ankle and knee power absorptions decreased by 11% and 12% in used shoes.

Abstract

Athletic children are prone to overuse injuries, especially at the heel and knee. Since footwear is an extrinsic factor of lower limb injury risk, the aim of this study was to assess the influence of shoe aging on children running biomechanics. Fourteen children active in sports participated in a laboratory biomechanical evaluation. A new pair of shoes was provided to each participant at an inclusion visit. Four months later, the participants performed a running task and their kinematics and kinetics were assessed both with their used shoes and with a new pair of shoes identical to the first. Furthermore, mechanical cushioning properties of shoes were evaluated before and after in-vivo aging. After 4 months of use, the sole stiffness increased by 16% and the energy loss capacity decreased by 18% (p < 0.001). No ankle or knee kinematic adjustment was found at foot strike in used shoes but changes were observed later during stance. Running with used shoes produced a higher loading rate of the vertical ground reaction force (+23%, p = 0.016), suggesting higher compressive forces under the heel and placing children at risk to experience impact-related injuries. Nevertheless, the decreased peak ankle and knee power absorption in used shoes (−11%, p = 0.010 and −12%, p = 0.029, respectively) suggests a lower ankle and knee joints loading during the absorption phase that may be beneficial regarding stretch-related injuries.

Introduction

Worldwide, millions of children and adolescents are involved in organized sports. The physiological repetitive loadings during sports practice may be beneficial, especially to stimulate bone growth [1]. However, high training volumes, particularly for elite athletes, place children at risk of overuse injuries [2]. The growing bones of the young athlete cannot handle as much stress as the mature bones of adults [3]. The enthesis, where tendon meets bone, is a notably vulnerable zone for children because of the immature skeleton and the constant remodeling process of bones during growth [4]. The most common sites for overuse injuries are the insertion of the Achilles tendon onto the calcaneus (Sever’s disease) and the insertion of the patellar tendon onto the tibial tubercle (Osgood-Schlatter disease). These pathologies are caused by the combination of repetitive impact that creates compressive forces and the excessive traction of the tendons that produces tensile forces on the apophysis [5].

Several extrinsic factors were suggested to affect overuse injury rates [6]. Among them, footwear was reported to have a major impact on children’s running biomechanics [7], [8]. Wearing suitable shoes seems particularly important since footwear is the first interface between the body structures and the ground, damping the reaction force and thereby attenuating the shock wave when the foot hits the ground. However, although the cushioning in new shoes may be sufficient to protect the wearer, the repeated impact in the course of regular use causes fatigue damage to the midsole and eventually reduces the mechanical capacity to dissipate energy [9], [10], [11]. A 15% decrease in the energy loss capacity of the midsole due to shoe aging is enough to affect lower limb muscular activities and to induce increased tibial acceleration peak and rate in a step-down laboratory task from a staircase [12]. Furthermore, finite-element analyses showed that fatigued ethylene vinyl acetate (EVA) in used shoes increased peak plantar pressure and heel pad stress when running [9], [13]. These studies suggest that as shoes age, their capacity to protect body structures decreases, with the heel particularly becoming vulnerable to ground impact, which then potentially increases the risk of overuse injury.

Adults running with worn shoes were shown to be able to adapt their running patterns to maintain constant external loads, notably by increasing the running stance time [14]. However, children’s proprioception is less developed than that of adults, which might explain why they barely − or do not at all − perceive the signs of injury [3]. The consequence may be a lack of kinematic adjustment at foot strike to compensate shoe degradation. Therefore, the purpose of this study was to examine the consequences of shoe aging on the running biomechanics of children. It was hypothesized that running with used shoes, which midsole would become stiffer with aging, results in an increased loading rate of the vertical ground reaction force. This increase in the early phase of support could be explained by the fact that shoe cushioning degradation may not be compensated by lower limb kinematic adjustments at foot strike (ankle and knee flexions) in children. It was also expected that running with used shoes would induce ankle and knee joints kinematic and kinetic changes later during stance. Specifically, increased peak ankle and knee power absorptions due to decreased ability of used shoes to dissipate energy were hypothesized.

Section snippets

Study design

Fourteen young males (age = 10.7 ± 0.4 years old, height = 1.46 ± 0.05 m, body mass = 35.0 ± 4.2 kg) were recruited from local sport associations to participate in this study. Inclusion criteria were weekly sports practice (≥ 3 h/week), age from 9 to 12 years, and shoe size  EU39. Parents were informed of the experimental procedures that complied with the Declaration of Helsinki, and gave written consent for their child’s participation in this study, which was approved by the local ethics committee.

The

Shoes characteristics

After 4 months of use, the mean thickness under the heel decreased by 19% (−4.9 mm), the stiffness increased by 16%, and the energy loss and energy returned capacity of shoes were reduced by 18% and 10%, respectively (p < 0.001) (Fig. 3).

Biomechanics

No effect of shoe aging was detected for either the participants’ speed or the stance time, allowing to compare the biomechanical variables of interest and to use SPM.

The vGRF time to peak was shorter (−10%, p = 0.047, d = 0.49) and the loading rate was steeper (+23%, p

Discussion

This study was the first to examine the influence of shoe aging on children’s running kinetics and kinematics. The main findings were that running with used shoes increased the vGRF loading rate and induced no ankle and knee joints kinematic adjustments at foot strike but some changes later during stance.

Conclusion

This study showed that children running with used shoes exhibited a higher loading rate of the vertical GRF compared to running with new shoes. That may be explained by the shoe cushioning degradation and the absence of kinematic adjustment at foot strike to compensate for it, whether at the level of the ankle or knee. Given the suggested relationship between high loading rate and running-related injuries, practicing sport activities with used shoes might place children at risk to experience

Conflict of interest statement

The authors declare no conflict of interest. The tested shoes were non-commercial, with an original design based on authors’ specifications.

Acknowledgements

The authors would like to thank ®Decathlon for providing the shoes and Christophe Gillet for his support during the experimentations. Special thanks to the reviewers for their valuable suggestions and to Nicolas Delattre and Cédric Morio for their assistance.

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