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Biomechanical wear testing of running shoes

Authors:
Jens Heidenfelder at W. L. Gore & Associates
Jens Heidenfelder
Thorsten Sterzing at NIKE Sports (China) Co Ltd
Thorsten Sterzing
  • NIKE Sports (China) Co Ltd
Thomas L. Milani
Thomas L. Milani
Thomas L. Milani
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Abstract

Introduction During running a deterioration of footwear occurs when shoes are exposed to many repetitive impacts. However, only little information exists about the rate of the deterioration over increasing mileage. A 45% loss of initial shock absorption was found by simulating 800 km of running during mechanical testing (Cook et al., 1985). However, the authors reported that this mechanical test revealed differences up to 25% in shock absorption for machine-simulated running compared to in vivo loaded shoes. Shoes worn over a relatively short distance of 220 km showed reduced shock attenuation by 9% and increased rearfoot motion of 18% (Hennig & Milani, 1995). Kong et al. (2008) reported an increase of stance time of 2% for worn (320 km) compared to new running shoes. No research was found about in vivo testing of running shoes during lifetime of these shoes. Furthermore, no information was found whether deterioration in running shoe properties occurs linearly or progressively with respect to mileage of wear. Therefore, the purpose of this study was to evaluate systematically biomechanical variables at four stages of the shoe lifecycle. A second research aspect was to examine whether different running shoes show different wear effects over mileage and time.
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Biomechanical wear testing of running shoes
Jens Heidenfelder, Thorsten Sterzing, Thomas L. Milani
Department of Human Locomotion – Chemnitz University of Technology, Chemnitz, Germany
Introduction
During running a deterioration of footwear occurs when shoes are exposed to many repetitive
impacts. However, only little information exists about the rate of the deterioration over increasing
mileage. A 45% loss of initial shock absorption was found by simulating 800 km of running during
mechanical testing (Cook et al., 1985). However, the authors reported that this mechanical test revealed
differences up to 25% in shock absorption for machine-simulated running compared to in vivo loaded
shoes. Shoes worn over a relatively short distance of 220 km showed reduced shock attenuation by 9%
and increased rearfoot motion of 18% (Hennig & Milani, 1995). Kong et al. (2008) reported an increase
of stance time of 2% for worn (320 km) compared to new running shoes.
No research was found about in vivo testing of running shoes during lifetime of these shoes.
Furthermore, no information was found whether deterioration in running shoe properties occurs linearly
or progressively with respect to mileage of wear. Therefore, the purpose of this study was to evaluate
systematically biomechanical variables at four stages of the shoe lifecycle. A second research aspect was
to examine whether different running shoes show different wear effects over mileage and time.
Methods
A subject pool of 24 injury-free recreational runners was involved in this study (age: 27.8 ± 3.8
years, height: 176.9 ± 4.5 cm, weight: 72.8 ± 5.8 kg). All runners were rearfoot strikers. Six
commercially available running shoes of different brands within the middle price segment (100-125 €)
were included in the study. Ten runners of the subject pool performed the wear runs with a length of
approximately 10 km. To achieve identical wear, each subject had to run in all shoe conditions along the
same self selected individual course. Shoes were systematically switched between subjects.
The experimental laboratory design included four stages of biomechanical measurements after a
running distance of 0 km, 100 km, 300 km, and 600 km to investigate the changes in running shoe
properties. At least 19 subjects of the pool had to run (3.5±0.1 m/s) in all shoe conditions for laboratory
testing at each stage. The experimental setup consisted of a force platform (KISTLER 9287BA;
60x90cm) that was integrated into a 13-m indoor running surface. Parameters of vertical ground reaction
force like maximum force rising rate (FRR), peak impact force (PVF1) and its corresponding time
(TPVF1) were calculated. A light weight electrogoniometer (Megatron MP10 1kΩ) was fixed to the
shoe heel counter to analyze kinematic rearfoot parameters in the sagittal plane like maximum pronation
velocity (MPV) and the range of total pronation movement (TPR). A miniature accelerometer (Analog
Devices ADXL78 ± 35g) was attached to the medial aspect of the tibia to calculate peak tibial
acceleration (PTA).
Mean values of 5 valid trials were used for statistical analysis. A repeated measures ANOVA
with Post-Hoc tests according to Fisher’s LSD (p<0.05) was used to analyze differences in each variable
of interest. The within-group factors were mileage and shoe conditions.
Results
A continuous change of impact parameters was found within four stages of biomechanical
testing (Tab.1). After 600 km PTA was increased by 15%, whereas TPVF1 was decreased by 4%. This
systematic trend to higher load could be observed for all six shoe conditions. FRR was increased as well
by 6% at stage four but showed no continuous change across the four stages. The slightly unsystematic
-5
0
5
10
15
0 300 600[km]
[%] S1 S2 S3
S4 S5 S6
100
behavior of FRR is also caused by differences between shoes. While one shoe showed no alteration of
FRR during 600 km, another shoe showed an increase of 14%.
For kinematic rearfoot parameters most changes occurred already at the second stage of
biomechanical testing. After 100 km MPV was increased by 12% and TPR by 7%. Between 100 km and
600 km MPV remained nearly unchanged in five of six shoes while TPR decreased in all shoe
conditions.
Between shoes, differences up to 25% were found within MPV and MPA. For impact parameters
differences between shoes ranged from 5% to 14% after 600 km of running.
Discussion
Increased FRR and PTA as well as decreased TPVF1 indicate reduced shock attenuation for all
shoe conditions after 600 km of running. It could be shown that shock attenuation declined
continuously. Assuming that shock attenuation is mainly influenced by the properties of midsole
materials, a continuous deterioration of midsole material was observed.
In contrast, progression of TPR indicates that pronation control of running shoes does not alter
continuously. The fact that all running shoes showed the same trend indicates that the investigated
changes are systematically. Differences between shoes up to 25% indicate that changes of MPV and
MPA are shoe specific.
Conclusions
It is concluded that deterioration in shoe properties occurs during 600 km of running. Cushioning
properties decreased consistently, whereas pronation control of tested shoes decreased mainly during the
first 100 km of running. In further studies the change of pronation behavior during the first 100 km
should be investigated with higher resolution. Thus, it might be possible to give evidence how many
kilometers new running shoes must be worn before performing meaningful biomechanical testing. Big
differences between shoes showed that for developing running shoes the constancy of shoe properties
during shoe lifetime needs to be improved.
Acknowledgements
This research was supported by Puma Inc., Germany.
References
Cook S.D., et al., 1985. Shock absorption characteristics of running shoes. Am j sp med, 4:248–253.
Hennig E.M., T.L. Milani, 1995. Biomechanical profiles of new against used running shoes.
Proceedings American Society of Biomechanics, 43–44.
Kong P.W., et al., 2008. Running in New and Worn Shoes – a comparison of three types of cushioning
footwear. Brit j sp med, online since October 9th.
TPVF1
[ms]**
FRR
[BW/s]*
PTA
[g]*
MPV
[°/s]**
MPA
[°]
TPR
[°]**
0 km 35.4 81.4 5.9 468 5.6 12.8
100 km 35.0 86.7 6.2 522 5.8 13.7
300 km 34.7 88.1 - 531 5.6 13.3
600 km 33.9 86.1 6.8 514 5.4 12.9
Tab. 1: Alteration of biomechanical parameters, mean of six
running shoes for in vivo running
*p<.05 **p<.01 (PTA data not available for 300 km) Fig. 1: Change (%) of TPR for six running shoes
at four stages during 600 km wear test
... And usually, the direction of the changes goes towards an increased shoe stiffness, reduced midsole thickness and decreased energy absorption (Lippa et al., 2017a). Although the literature is sparse on this topic, such modifications are believed to affect running patterns (Heidenfelder et al., 2009) and increase ground impacts (Chambon et al., 2014b;Morio et al., 2009). For instance, the shoe impairment after either a mechanical (Morio et al., 2009) or an ecological ageing protocol (Heidenfelder et al., 2009) has been associated with an increase in ground impact measured through tibial accelerations. ...
... Although the literature is sparse on this topic, such modifications are believed to affect running patterns (Heidenfelder et al., 2009) and increase ground impacts (Chambon et al., 2014b;Morio et al., 2009). For instance, the shoe impairment after either a mechanical (Morio et al., 2009) or an ecological ageing protocol (Heidenfelder et al., 2009) has been associated with an increase in ground impact measured through tibial accelerations. To the best of our knowledge, no studies have investigated the interaction between changes in mechanical properties of footwear and changes in running mechanics due to fatigue in competitive conditions. ...
... However, since the mileage of the personal shoes could not be controlled before our study, this assumption requires further investigation. Previous studies have also reported similar and continuous deterioration of the midsole materials after relatively low (i.e. 100 km) shoe-loading in laboratory (Heidenfelder et al., 2009) or human-based (Wang et al., 2010) ageing protocols. An average significant increase of 9% of ST final and reduction 4% of E LOSS were found after the TR race. ...
View
... And usually, the direction of the changes goes towards an increased shoe stiffness, reduced midsole thickness and decreased energy absorption (Lippa et al., 2017a). Although the literature is sparse on this topic, such modifications are believed to affect running patterns (Heidenfelder et al., 2009) and increase ground impacts (Chambon et al., 2014b;Morio et al., 2009). For instance, the shoe impairment after either a mechanical (Morio et al., 2009) or an ecological ageing protocol (Heidenfelder et al., 2009) has been associated with an increase in ground impact measured through tibial accelerations. ...
... Although the literature is sparse on this topic, such modifications are believed to affect running patterns (Heidenfelder et al., 2009) and increase ground impacts (Chambon et al., 2014b;Morio et al., 2009). For instance, the shoe impairment after either a mechanical (Morio et al., 2009) or an ecological ageing protocol (Heidenfelder et al., 2009) has been associated with an increase in ground impact measured through tibial accelerations. To the best of our knowledge, no studies have investigated the interaction between changes in mechanical properties of footwear and changes in running mechanics due to fatigue in competitive conditions. ...
... However, since the mileage of the personal shoes could not be controlled before our study, this assumption requires further investigation. Previous studies have also reported similar and continuous deterioration of the midsole materials after relatively low (i.e. 100 km) shoe-loading in laboratory (Heidenfelder et al., 2009) or human-based (Wang et al., 2010) ageing protocols. An average significant increase of 9% of ST final and reduction 4% of E LOSS were found after the TR race. ...
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The aim of this study was to investigate if acute impairments of the footwear midsole materials could interact with the modifications of the running patterns after a fatiguing trail running race. We hypothesized that introducing a control pair of shoes after the race, would modify running mechanics by partially correcting the alterations generated by the deteriorated properties of the shoes worn during the race. Eighteen participants ran on a treadmill at 10km/h pre- and post-race in three conditions varying the step frequency (free or fixed) or the footwear (control or personal shoes). Spatiotemporal parameters, tibial accelerations across the running conditions and shoe mechanical properties were measured. Significant changes in shoe characteristics (i.e. reduced thickness and increased stiffness) were measured after the race in the personal footwear. At free step frequency, significant changes in contact (+1.3 ± 3.5%) and flight (-19.4 ± 23.7%) times, step frequency (+2.9 ± 2.9%) and peak-to-peak amplitude acceleration at the tibia level (-3.6 ± 18%) were found. The peak-to-peak amplitude of the mediolateral axis showed a significant shoe x time interaction meaning that the control footwear could have had an impact in the running pattern. However, contrary to our hypothesis, no interaction effects were found between the changes in footwear and the changes in spatiotemporal parameters. In conclusion, impairments of shoes characteristics affect impact but not running mechanics.
View
... Midsole cushioning technology has the potential to greatly alter reaction forces during running (Maropoulos et al., 2017), while other factors associated to shoe construction (e.g., shoe drop and midsole density) can affect the lever arm about the subtalar joint axes, which has been determined to affect running related injuries (Stacoff et al., 1988) and running in inappropriate footwear has indeed been associated to injury (Komi et al., 1987;Wilk et al., 2000). Heidenfelder et al. (2009) argued that the shock attenuating capacity of technical footwear deteriorates consistently during the first 600 km of running, whereas pronation patterns adapt to such changes early on. Since footwear stiffness is widely accepted to affect running biomechanics (Hardin et al., 2004), it stands to reason that worn-down midsoles will do so as well, thus directly influencing injury prevalence among runners. ...
... Since footwear stiffness is widely accepted to affect running biomechanics (Hardin et al., 2004), it stands to reason that worn-down midsoles will do so as well, thus directly influencing injury prevalence among runners. A crossevaluation of experimental and in vivo studies (Heidenfelder et al., 2009;Kong et al., 2014), would sustain the notion that running biomechanics are affected at higher mileages (more worn-down shoes), whereas cushioning properties tend to fade at a significantly higher rate, thus restricting the effectiveness of technical footwear systems to a shorter life span. ...
Running-Related Injury From an Engineering, Medical and Sport Science Perspective
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Etiologic factors associated to running injuries are reviewed, with an emphasis on the transient shock waves experienced during foot strike. In these terms, impact mechanics are analyzed from both, a biomechanical and medical standpoint and evaluated with respect injury etiology, precursors and morbidity. The complex interaction of runner specific characteristics on the employed footwear system are examined, providing insight into footwear selection that could act as a preventive measure against non-acute trauma incidence. In conclusion, and despite the vast literature on running-related injury-risks, only few records could be identified to consider the effect of shoe cushioning and anthropometric data on injury prevalence. Based on this literature, we would stress the importance of such considerations in future studies aspiring to provide insight into running related injury etiology and prevention.
View
... Regarding the shoe, cushioning properties mostly depend on the stiffness (ST) of the midsole (Shorten, 2000). For example, high midsole ST has been shown to increase tibial acceleration peak and rate during running (Heidenfelder, Sterzing, & Milani, 2009). A similar increase of tibial acceleration peak with increase of the impact surface ST has been highlighted by in a human pendulum task. ...
... Besides being realistic regarding the mechanical loading applied, the aging protocol designed for the present study has the advantage of being highly reproducible. Indeed, as opposed to previous studies in which shoe aging was performed by human participants in real conditions (Brueckner, Heidenfelder, Odenwald, & Milani, 2011; Heidenfelder et al., 2009), the aging protocol was implemented on a mechanical machine, thus avoiding the questions of long-term biomechanical adaptation and homogeneity in shoe's aging levels. Our results are consistent with the previous ones in which shoes were fatigued by human participants with decreased damping capacity (Cook, Kester, Brunet, & Haddad, 1985) and increased ST of the shoes with aging (Schwanitz, Möser, & Odenwald, 2010). ...
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Abstract This study investigates the effect of running shoes' aging on mechanical and biomechanical parameters as a function of midsole materials (viscous, intermediate, elastic) and ground inclination. To this aim, heel area of the shoe (under calcaneal tuberosity) was first mechanically aged at realistic frequency and impact magnitudes based on a 660 km training plan. Stiffness (ST) and viscosity were then measured on both aged and matching new shoes, and repercussions on biomechanical variables (joint kinematics, muscular pre-activation, vertical ground reaction force and tibial acceleration) were assessed during a leg-extended stepping-down task designed to mimic the characteristics of running impacts. Shoes' aging led to increased ST (means: from 127 to 154 N ∙ mm(-1)) and decreased energy dissipation (viscosity) (means: from 2.19 to 1.88 J). The effects induced by mechanical changes on body kinematics were very small. However, they led with the elastic shoe to increased vastus lateralis pre-activation, tibial acceleration peak (means: from 4.5 g to 5.2 g) and rate. Among the three shoes tested, the shoe with intermediate midsole foam provided the best compromise between viscosity and elasticity. The optimum balance remains to be found for the design of shoes regarding at once cushioning, durability and injury prevention.
View
... On the other hand, depending on the shape and materials of running shoe models, natural abrasion may result in a rounding of the lateral heel to a small extent during extended wear. However, long-term use (i.e., shoe age or mileage) may decrease the functions of impact attenuation and stability because of the degradation of shoe material compared with new shoes with an originally curved heel shape [46,47]. ...
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(1) Background: The purpose of this study was to investigate the effects of a rounded heel shoe (RHS) and rounded lateral heel shoe (RLHS) on impact and lower extremity stability as well as their relationships with comfort during running. (2) Methods: Twenty healthy male adults participated in the study. The data were collected using eight infrared cameras while participants were running at a speed of 2.7 m/s in three shoe conditions on an instrumented treadmill. (3) Results: The peak vertical ground reaction force (PVGRF) was statistically smaller for the RHS and RLHS compared with the normal shoes (NS) (p < 0.05). The range of motion of inversion–eversion at the ankle joint was statistically smaller for the RLHS compared with the NS and RHS (p < 0.05). Increased dorsiflexion of the ankle joint at heel contact was negatively related to the comfort of a running shoe, and increased dorsi-plantarflexion ROM was positively related to comfort. (4) Conclusions: Based on these results, a curved heel shape of a running shoe may provide a positive influence on the biomechanical function and the comfort of running shoes. Future study, including measurements of lower extremity muscle activations and long-term comfort, would be beneficial to help validate current findings and develop further applications.
View
... Presently, various foam materials derived from synthetic polymers, such as ethylene-vinyl acetate or polyurethane, are routinely employed in footwear products due to their well-known ability to absorb impact force. However, a nontrivial drawback of such foam materials is their relative lack of durability [2,[7][8][9][10][11]. Therefore, to improve the durability of shoes and retain comfort, parts of many shoes are constructed from both natural rubber (NR) and synthetic materials. ...
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Impact force remains the primary cause of foot injury and general discomfort with regard to footwear. The footwear industry traditionally relies on modified elastomers (including natural rubber) whose properties can be physically adjusted by varying the constituents in the rubber formulations. This work aims to investigate the effect of filler/plasticizer fractions on shock attenuation of natural rubber soles. The statistical response surface method (RSM) was used to optimize the loading of natural rubber, fillers (carbon black and china clay) and a plasticizer (paraffinic oil). A novel predictive equation addressing the effects of additives on the physical and mechanical properties of the shoe sole was successfully created using the RSM. Our results demonstrate how the concentrations of these components regulate final properties, such as impact force absorption and hardness, in the commercial manufacture of shoe soles. While a higher loading level of plasticizer promotes reductions in hardness and impact force, as well as energy dissipation, in these modified elastomers, these properties were improved by increasing the filler content.
View
... These distances were selected as achievable running distance derived by an average runner within 8-12 months of periodic running and that significant wear differences can be recorded at each comparison stage. There is also sufficient footwear deterioration to recognize some biomechanical changes in the runners, 21 increasing the need to quantify wear. ...
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Wear identification and projection have eluded shoe manufacturers due to the myriad of factors that affect the abrasion wear of shoes. Using a gridded three-dimensional cloud comparison in CloudCompare software, abrasion wear thickness of shoes was identified using the CIE-L-a-b colour system that is interpolated with the physical formula representation of colours. After obtaining the thickness lost, other wear factors like the material properties of the shoe sole, the runners’ personal profile and the running schedule were combined for wear projection. The methodological process from a non-destructive wear detection to wear projection allows shoe manufacturers to reduce the iterations of wear testing while maximizing the entire analysis of shoe wear. Shoe samples were kindly sponsored by ASICS Institute of Sport Science.
View
... However, these robotic systems were not able to mimic the running gaits and even not able to reach the average running speed of the human (8 km/h to 12 km/h). Further, their end effectors were limited at a maximum speed of 2 m/s compared to actual wear trials of about 3.5 m/s [3]. . The left picture is the 6-DOF industrial robot from Fanuc while the right picture shows the structure of the prosthetic foot wearing the test shoe The most applicable system for footwear testing is the STM 528 Pedatron™ developed by SATRA Technology Centre and it is recognised as the world's leading agency in footwear testing [6]. ...
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Footwear effects on the human feet have been widely studied to prevent injuries, improve sports performance, and human health through running exercise. Due to the dynamics of human joints and passive imitative feet, current automatic footwear testing systems reported in the literature are not very realistic, are limited in the imitation of running gaits, and still use the passive prosthetic foot. In addition, many studies on humanoid walking robots, orthotic ankles, and prosthetic foot for amputees only focus on the human ankle joint and walking gaits. In this project, the design and control of a realistic robotic running foot-leg testing of shoes are introduced. The designed robotic foot possesses a higher number of degrees of freedom compared to other robotic systems in the literature and have abilities to mimic accurately biomechanical patterns of the human foot as well as to replicate the plantar pressure distribution under the foot sole in running in the sagittal plane. Because of lightweight, flexibility, and ease of power transmission, the Bowden-cable or the tendon-sheath mechanism (TSM) is used in this project for the actuation of the robotic joints. However, nonlinear friction and backlash hysteresis in such mechanisms vary with the change of cable configuration and they degrade the system performances. In this project, novel nonlinear and adaptive schemes for controlling the position of the ankle and metatarsophalangeal joints will also be presented. The control schemes consider the nonlinear and backlash hysteresis as uncertainties and are able to deal with unexpected disturbances due to the change of the cable configuration and the unknown environments. In addition, no knowledge of the model parameters is required. To validate the design systems and control approaches, simulations are also introduced. There are good agreements between the proposed approaches and simulation results.
View
... They explain the reduction of the midsole properties and foam hardness with the reduction of the cells' air content [8], which represents a controversial point of discussion regarding Verdejo et al. [6]. In order to precisely determine the changes in the foam structure during running, and therefore the aging behavior of EVA and PU, further investigations such as SEM micrographs before and after biomechanical aging are necessary [9]. ...
As far as my soles will carry me
Article
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Two institutes in Chemnitz, Germany, subjected various pure polyurethanes and ethylene vinyl acetates to cyclic impact loading in order to obtain comparable results for the shock absorbing properties of midsoles in running shoes. The samples were subjected to a hydraulic impact test (HIT). The test equipment consists of a crown-shaped die mounted at an angle of 90° to the firm footprint of the shoe to be tested. The short-term test with 100 load cycles is carried out on four running shoes for each material type. The test results show that pure PU midsole materials exhibit a wide range of properties. They are comparable with the properties of commercially available running shoes. also found in the parameters not shown. The results of the two standard EVA materials correspond to the average values. The curves of the aging processes clearly show that the mechanical resistance of PU is far higher than that of EVA.
View
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Shock absorption characteristics of running shoes
Article
  • Jul 1985
  • AM J SPORT MED
The change in shock absorption properties of running shoes was evaluated as a function of miles run. Differ ent models of running shoes encompassing a wide range in retail price were obtained and mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at the equivalent of 0, 5, 10, 25, 50, 75, 100, 125, 150, 200, 250, 300, and 500 miles of running. Shoes were also tested at similar intervals after having been worn by volunteers during normal training. An approximate 33% difference in the initial shock absorption was observed in the different shoe models. In general, the shoes retained approximately 75% of their initial shock absorption capability after 50 miles of simulated running, and approximately 67% after 100 to 150 miles. Between 250 and 500 miles the shoes retained less than 60% of their initial shock absorption capacity. No differences in shock absorption character istics were apparent based upon either shoe price or the manufacturer model. The results of shoes tested by the volunteer runners also showed a marked reduc tion in shock absorption with mileage. The loss, how ever, was not as great as in the machine-simulated running, with approximately 70% of initial shock ab sorption retained at 500 miles.
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Running in New and Worn Shoes – a comparison of three types of cushioning footwear Brit j sp med, online since October 9 th . TPVF1 [ms
  • Jan 2008
  • P W Kong
Kong P.W., et al., 2008. Running in New and Worn Shoes – a comparison of three types of cushioning footwear. Brit j sp med, online since October 9 th. TPVF1 [ms]** FRR [BW/s]* PTA [g]* MPV [°/s]** MPA [°] TPR [°]** 0 km 35.4 81.4 5.9 468 5.6 12.8 100 km 35.0 86.7 6.2 522 5.8 13.7 300 km 34.7 88.1 - 531 5.6 13.3 600 km 33.9 86.1 6.8 514 5.4 12.9
Alteration of biomechanical parameters, mean of six running shoes for in vivo running *p<.05 **p<.01 (PTA data not available for 300 km) Fig. 1: Change (%) of TPR for six running shoes at four stages during 600 km wear test
  • Tab
Tab. 1: Alteration of biomechanical parameters, mean of six running shoes for in vivo running *p<.05 **p<.01 (PTA data not available for 300 km) Fig. 1: Change (%) of TPR for six running shoes at four stages during 600 km wear test