Midsole Material Research Articles

Effect of ethylene vinyl acetate foam-graphene composite material on the mechanical properties of sports footwear

Ethylene vinyl acetate (EVA) foam is widely used as midsole material in athletic footwear due to its lightweight and cushioning properties. However, EVA foam suffers from low mechanical strength, abrasion resistance, and fatigue resistance. Reinforcing EVA foam with graphene nanoplatelets is a promising approach to improving its mechanical performance for footwear applications. This study investigated the effect of 0.1–1 wt% graphene nanoplatelets on the properties of EVA foam composites relevant to midsole performance. The results showed that 0.1–0.2 wt% graphene provided optimal reinforcement, exhibiting 33–40% higher impact energy absorption, 50–60% lower compressive stiffness, 30% higher flexural stiffness, and up to 40% lower abrasion volume loss. Under simulated use conditions, the composites demonstrated higher energy return and fatigue resistance. The graphene nanoplatelets acted as effective reinforcements within the EVA foam by improving stress transfer, inhibiting crack propagation, and shielding the foam surface. The findings indicate that reinforcing EVA foam with small amounts of graphene nanoplatelets can develop midsole materials with enhanced mechanical performance for athletic footwear.

Effects of individually optimized rocker midsoles and self-adjusting insoles on plantar pressure in persons with diabetes mellitus and loss of protective sensation

IntroductionRocker shoes and insoles reduce peak pressure (PP) in persons with diabetes (DM) and loss of protective sensation (LOPS). However, they are handmade, leading to inconsistent effectiveness. If foot structure changes over time, high PP-locations also change. To address this, individualized algorithm based 3D-printed rockers and self-adjusting pressure-reducing insoles are applied. MethodsPP across seven foot regions was analyzed in 21 persons with DM and LOPS. Regions with PP < 200 kPa were considered not at risk (RnoR); regions with PP ≥ 200 kPa at risk (RaR). The aim was to offload RaR, while remaining PP < 200 kPa in RnoR. ResultsIndividualized rockers and self-adjusting insoles combined successfully reduce PP < 200 kPa (on average 24 % - 48 %) in all feet with toes, central and lateral forefoot identified as RaR. Same intervention reduces PP in 68 % of the feet with medial forefoot identified as RaR. With the heel as RaR, no intervention reduces PP successfully in all feet. ConclusionsIndividualized 3D-printed rockers combined with self-adjusting insoles reduce PP (< 200 kPa) in toes, central and lateral forefoot, but not in heels. Alternative insoles with medial arch support, heel cup and compliant midsole materials might enhance success rate across entire foot.

Boosting Energy Return Using 3D Printed Midsoles Designed With Compliant Constant Force Mechanisms

Abstract The enhancement of midsole compressive energy return is associated with improved running economy. Traditional midsole materials such as ethylene vinyl acetate (EVA), thermoplastic polyurethane (TPU), and polyether block amide (PEBA) foams typically exhibit hardening force–displacement characteristics. On the other hand, a midsole with softening properties, which can be achieved through compliant constant force mechanisms (CFMs), can provide significant benefits in terms of energy storage and return. This study presents the development of such a midsole, incorporating 3D printed TPU CFM designs derived through structural optimization. The mechanical properties under cyclic loading were evaluated and compared with those of commercially available running shoes with state-of-the-art PEBA foam midsoles, specifically the Nike ZoomX Vaporfly Next% 2 (NVP). Our custom midsole demonstrated promising mechanical performance. At similar deformation levels, the new design increased energy storage by 58.1% and energy return by 47.0%, while reducing the peak compressive force by 24.3%. As per our understanding, this is the first study to prove that the inclusion of CFMs in the structural design of 3D printed midsoles can significantly enhance energy return.

Influence of different midsole foam in advanced footwear technology use on running economy and biomechanics in trained runners.

Ethylene and vinyl acetate (EVA) and polyether block amide (PEBA) are recently the most widely used materials for advanced footwear technology (AFT) that has been shown to improve running economy (RE). This study investigated the effects of these midsole materials on RE and biomechanics, in both fresh and worn state (after 450 km). Twenty-two male trained runners participated in this study. Subjects ran four 4-min trials at 13 km‧h-1 with both fresh EVA and PEBA AFT and with the same models with 450 km of wear using a randomized crossover experimental design. We measured energy cost of running (W/kg), spatiotemporal, and neuromuscular parameters. There were significant differences in RE between conditions (p = 0.01; n2 = 0.17). There was a significant increase in energy cost in the worn PEBA condition compared with new (15.21 ± 1.01 and 14.87 ± 0.99 W/kg; p < 0.05; ES = 0.54), without differences between worn EVA (15.13 ± 1.14 W/kg; p > 0.05), and new EVA (15.15 ± 1.13 w/kg; ES = 0.02). The increase in energy cost between new and worn was significantly higher for the PEBA shoes (0.32 ± 0.38 W/kg) but without significant increase for the EVA shoes (0.06 ± 0.58 W/kg) (p < 0.01; ES = 0.51) with changes in step frequency and step length. The new PEBA shoes had lower energy cost than the new EVA shoes (p < 0.05; ES = 0.27) with significant differences between conditions in contact time. There is a clear RE advantage of incorporating PEBA versus EVA in an AFT when the models are new. However, after 450 km of use, the PEBA and EVA shoes had similar RE.

Influence of spiked shoes with soft and bouncy midsole material on sprint performance

Influence of spiked shoes with soft and bouncy midsole material on sprint performance

Product Development of Futsal Shoes Using the QFD Method (Survey of Futsal Shoe Consumers in The Tangerang District Area)

Futsal shoe products are one of the products needed to support when playing futsal because they are useful for protecting all parts of the foot when playing futsal from hitting the ball or opposing players. This study aims to identify technical characteristics according to customer needs and desires and design product design concepts for futsal shoes. This research uses the Quality Function Deployment (QFD) method, as a result, to identify technical characteristics and customer needs and design product design concepts using tools in the form of Rhinoceros applications. The data collection technique is in the form of distributing questionnaires to 100 respondents with the target respondents being male or female, members of the futsal community, employment status (students, students, and workers), domiciled in the Tangerang Regency area. The results of identifying technical characteristics are futsal shoes with PU synthetic upper material, phylon midsole material, rubber outsole material, Ethyl Vinyl Acetate (EVA) insole material, vamp width dimensions of 9.6 cm, and features without shoelaces. The result of identifying technical characteristics that are following customer needs and desires from using the house of quality matrix format, where the priority level is the width dimension of 9.6 cm with a weight importance value of 180

Design feature combinations effects of running shoe on plantar pressure during heel landing: A finite element analysis with Taguchi optimization approach.

Large and repeated impacts on the heel during running are among the primary reasons behind runners’ injuries. Reducing plantar pressure can be conducive to reducing running injury and improving running performance and is primarily achieved by modifying the design parameters of running shoes. This study examines the effect of design parameters of running shoes (i.e., heel-cup, insole material, midsole material, and insole thickness) on landing peak plantar pressure and determines the combination of different parameters that optimize cushion effects by employing the Taguchi method. We developed the foot–shoe finite element (FE) model through reverse engineering. Model assembly with different design parameters was generated in accordance with the Taguchi method orthogonal table. The effectiveness of the model was verified using the static standing model in Ansys. The significance and contribution of different design parameters, and the optimal design to reduce plantar pressure during landing, were determined using the Taguchi method. In the descending order of percentage contribution was a conforming heel-cup (53.18%), insole material (25.89%), midsole material (7.81%), and insole thickness (2.69%). The more conforming heel-cup (p < 0.001) and softer insole (p = 0.001) reduced the heel pressure during landing impact. The optimal design of running shoe in this study was achieved with a latex insole, a 6 mm insole thickness, an Asker C-45 hardness midsole, and a 100% conforming heel-cup. The conforming heel-cup and the insole material significantly affected the peak plantar pressure during heel landing. The implementation of a custom conforming heel-cup is imperative for relieving high plantar pressure for long-distance heel-strike runners.

The Influence of Footwear Longitudinal Bending Stiffness on Running Economy and Biomechanics in Older Runners

ABSTRACTPurpose: This study assessed the effects of footwear longitudinal bending stiffness on running economy and biomechanics of rearfoot striking older runners. Methods: Nine runners over 60 years of age completed two running bouts at their preferred running pace in each of three footwear conditions: low (4.4 ± 1.8 N·m-1), moderate (5.7 ± 1.7 N·m-1), and high (6.4 ± 1.6 N·m-1) bending stiffness. Testing order was randomized and a mirror protocol was used (i.e., A,B,C,C,B,A). Expired gases, lower limb kinematics, and ground reaction forces were collected simultaneously and lower limb joint kinetics, running economy (i.e., VO2), leg stiffness, and spatio-temporal variables were calculated. Results: Running economy was not different among stiffness conditions (p = 0.60, p = 0.53 [mass adjusted]). Greater footwear stiffness reduced step length (p = 0.046) and increased peak vertical ground reaction force (p = 0.019) but did not change peak ankle plantarflexor torque (p = 0.65), peak positive ankle power (p = 0.48), ankle positive work (p = 0.86), propulsive force (p = 0.081), and leg stiffness (p = 0.46). Moderate footwear stiffness yielded greater peak negative knee power compared to low (p = 0.04) and high (p = 0.03) stiffness. Conclusions: These novel findings demonstrate that increasing footwear longitudinal bending stiffness using flat carbon fiber inserts does not improve running economy and generally does not alter lower limb joint mechanics of rearfoot strike runners over 60 years. Future studies should investigate how other footwear characteristics (e.g., midsole material, plate location, and sole curvature) influence economy and biomechanics in this population.

Running pattern changes after a 38-km trail running race: does shoe fatigue play a role?

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 10 km·h−1 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 × 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.

A Re-examination of the Measurement of Foot Strike Mechanics During Running: The Immediate Effect of Footwear Midsole Thickness.

PurposeMidsole cushioning thickness (MT) is a key component of running footwear that may influence the stiffness setting of the joints, performance enhancement, and injury prevention. Most studies that have investigated the influence of manipulating shoe midsole characteristics on foot strike patterns and vertical force loading rates have not considered the dynamic conditions of initial landing and the associated initial lower limb joint stiffness. In this study, we examined the effect of running in shoes with large changes in MT on both the posture and dynamics associated with foot strike.Methods12 injury-free runners with habitual rearfoot strike patterns ran at 4.5 m/s along a 40-m runway in shoe conditions with MT of 30, 42, and 54 mm, respectively. Ground reaction force and the right leg kinematic data were collected. One-way repeated measures ANOVA was conducted to statistically analyze the effect of MT on key variables linked to foot strike.ResultsIncreased midsole thickness resulted in a slightly flatter foot strike posture (p < 0.05), a decreased shank retraction velocity (p < 0.05), and an increase in forward horizontal foot velocity (p < 0.05), all at initial ground contact. Vertical force loading rates were reduced with increasing MT (p < 0.05), but this was associated with large increases in the initial ankle and knee joint stiffness (p < 0.05).ConclusionAdjustments in the initial conditions of contact with the ground during running were seen in both the posture and dynamics of the lower limbs. To help to mitigate the impact severity from foot-ground collision with the thinnest shoe condition, there was an increased shank retraction velocity and decreased forward velocity of the foot at landing. These active impact-moderating adaptations likely served to reduce the changes in impact severity expected due to midsole material properties alone and should be considered in relation to altering the risk of running-related injuries.

Effects of midsole cushioning stiffness on Achilles tendon stretch during running

Footwear midsole material can have a direct influence on running performance. However, the exact mechanism of improved performance remains unknown. The purpose of this study was to determine if Achilles tendon energetics could potentially play a role in the performance improvements, by testing if changes in footwear midsole stiffness elicit changes in Achilles tendon stretch. Fourteen runners ran in two footwear conditions while kinematic, kinetic, metabolic and ultrasound data were recorded. There was a moderate positive correlation between the difference in stretch and the difference in performance, which was statistically significant (r(12) = 0.563, p = 0.036). Twelve participants had greater stretch and better performance in the same footwear condition. Based on stretch estimates, the difference between conditions in energy returned from the Achilles tendon was 3.9% of the mechanical energy required per step. Energy return of this magnitude would be relevant and could cause the improved performance observed. These results suggest that increasing energy returned from the Achilles could be a valid mechanism for improving running performance due to changes in footwear. These findings lead the way for future research to further understand internal mechanisms behind improved running performance.

Effects of footwear cushioning on leg and longitudinal arch stiffness during running

During running, humans increase leg stiffness on more compliant surfaces through an in-series spring relationship to maintain constant support mechanics. Following this notion, the compliant midsole material of standard footwear may cause individuals to increase leg stiffness while running, especially in footwear with very thick midsoles. Recently, researchers have also proposed that footwear stiffness can affect the stiffness of the foot’s longitudinal arch (LA) via a similar mechanism. To test these ideas, we used 3D motion capture to record 20 participants running on a forceplate-instrumented treadmill while barefoot, and while wearing three types of sandals composed of materials ranging an order of magnitude in Young’s modulus: ethylene vinyl acetate (EVA), and two varieties of polyurethane rubber (R30 and R60). We calculated leg stiffness using standard methods, and measured LA stiffness based on medial midfoot kinematics. While there was an overall significant effect of footwear on leg stiffness (P = 0.047), post-hoc tests revealed no significant differences among individual pairs of conditions, and there was no effect of footwear on LA stiffness. However, participants exhibited significantly greater LA compression when barefoot than when running in EVA (P = 0.004) or R30 (P = 0.036) sandals. These results indicate that standard footwear midsole materials are too stiff to appreciably affect leg stiffness during running, meaning that increasing midsole thickness is unlikely to cause individuals to alter their leg stiffness. However, use of footwear does cause individuals to restrict LA compression when compared to running barefoot, and further research is needed to understand why.

Effect of the Shoe Sole on the Vibration Transmitted from the Supporting Surface to the Feet

Vibration transmitted through the foot can lead to vibration white feet, resulting in blanching of the toes and the disruption of blood circulation. Controlled studies identifying industrial boot characteristics effective at attenuating vibration exposure are lacking. This work focused on the evaluation of vibration transmissibility of boot midsole materials and insoles across the range 10–200 Hz at different foot locations. Questionnaires were used to evaluate the comfort of each material. The materials were less effective at attenuating vibration transmitted to the toe region of the foot than the heel. Between 10 and 20 Hz, all midsole materials reduced the average vibration transmitted to the foot. The average transmissibility at the toes above 100 Hz was larger than 1, evidencing that none of the tested material protects the worker from vibration-related risks. There was a poor correlation between the vibration transmissibility and the subjective evaluation of comfort. Future research is needed to identify materials effective for protecting both the toe and the heel regions of the foot. Specific standards for shoe testing are required as well.

Individual response to multi-density midsoles to minimise biomechanical injury risk factors of Achilles tendinopathy in distance running

Modifications of midsole geometry and material properties are essential footwear design features to prevent overuse injuries (OIs) in distance running. With an injury frequency of 10.9%, Achilles t...

Effects of midsole cushioning stiffness on Achilles tendon stretch during running

Footwear midsole material can have a direct influence on running performance. However, the exact mechanism of improved performance remains unknown. When running, elastic energy is thought to be sto...

Effects from loaded walking with polyurethane and styrene-butadiene rubber midsole military boots on kinematics and external forces: A statistical parametric mapping analysis

This study compared ground reaction forces (GRF) and lower limb two-dimensional (2D) kinematic waveforms, with and without load carriage, in military personnel walking in two different types of boots. Data were measured in 24-soldiers walking on a 10-m walkway under four randomized crossover trials: wearing two military boots (styrene-butadiene rubber midsole – SBR – 63 Shore A; and polyurethane midsole – PU – 48 Shore A); with and without a 15-kg backpack. GRF traditional parameters were evaluated by two-way ANOVAs. GRF and kinematic waveforms were assessed using a statistical parametric mapping (SPM) method (two-way ANOVA). No interaction effects were observed between footwear and load. GRF at the beginning of stance was lower while wearing the SBR boot condition compared to the PU boot condition. Load carriage increased trunk, hip, and knee flexion. The analyzed military boots did not affect movement patterns during loaded walking and the military boot with SBR midsole material reduced impact to a greater extent. The study demonstrated that the design and materials (e.g., midsole material and thickness) used in boot manufacturing can influence military boot performance.

A method to quantify stiffness across the entire surface of a shoe‘s midsole

Quantifying the midsole material characteristics of athletic footwear is a standard task in footwear research and development. Current material testing protocols primarily focus on the determination of cushioning properties of the heel region or the quantification of the midsole properties as one assembly. However, midsoles possess different spatial material properties that have not been quantified from previous methodologies. Therefore, new material testing methods are required to quantify the local material response of athletic footwear. We developed a cyclical force-controlled material testing protocol for the determination of non-homogeneously distributed material stiffness with a high spatial resolution. In five prototype shoes varying in their stiffness distribution, we found that the material properties can be reliably measured across the midsole. Furthermore, we observed a characteristic non-linear material response regardless of the midsole location. We found that the material stiffness increased with an increase of the applied force and that this effect is further intensified by higher testing cycles. Additionally, the obtained midsole stiffness depends on the geometry of the midsole. We explored different approaches to reduce the measurement time of the testing protocol and found that the number of measurements can be reduced by 70% using 2 D-interpolation procedures. Determining the spatial material properties of midsoles needs to be considered to understand foot-shoe interactions. Furthermore, this measurement protocol can be used for quality control within the footwear and can be adapted for considering the effects of different running styles or speeds on ground force application characteristics.

Acute effect of engineered thermoplastic polyurethane elastomer knockoff running footwear on foot loading and comfort during heel-to-toe running

BackgroundBetter midsole materials and comfort have been incorporated into more expensive shoes and are popular with runners. Consequently, knockoff running shoes are currently widely distributed in the Chinese market and and cost only 30%–50% of the total price of genuine branded products. Research questionUncertainty exists concerning the beneficial effects of advanced shoe material application in decreasing foot loading or impact force during running. Additionally, using comfort as a criterion to identify genuine branded running shoes may exclude brand factor. MethodsFifteen healthy male volunteers were asked to perform two different tests, including running and a comfort evaluation. Each participant was asked to identify which footwear was the Adidas brand shoe based on their perception of comfort. ResultsTime to the first peak of the vertical ground reaction force occurred significantly later when subjects wore the genuine branded shoe compared to knockoff shoe 1 (p = 0.003) and knockoff shoe 2 (p = 0.015) footwea. The genuine branded shoe (p = 0.005) and knockoff shoe 1 (p = 0.029) were significantly more comfortable compared to the knockoff shoe 2. Only four subjects selected the genuine branded shoe, whereas six subjects selected both the genuine branded shoe and knockoff shoe 1. SignificanceKnockoff running footwear significantly increases impact loading compared to the genuine branded product, thereby posing greater risk of running injury.

Optimal footwear longitudinal bending stiffness to improve running economy is speed dependent

The primary footwear components of interest to improve performance are midsole material, weight, and longitudinal bending stiffness. Little is known about the effects of varied longitudinal bending stiffness across a range of running speeds. The purpose of this study was to identify changes in spatiotemporal variables, horizontal ground reaction forces, subjective comfort, and metabolic cost at different running speeds in response to varied longitudinal bending stiffness. Ten highly trained males ran at 14, 17 and 20 km/h in shoes with varying longitudinal bending stiffness (normal 5.9, stiff 10.5 and very stiff 17.0 N-m/rad). Ground reaction forces, metabolics and subjective comfort assessments were collected. There were significant changes (p < .05) in contact time, stride frequency, and stride length between shoe conditions at all three speeds. Peak propulsive force decreased with increased bending stiffness at all three speeds, but there was no change in braking or propulsive impulse. The patterns of changes in stride length and stride frequency were different between speeds. At 14 km/h, most participants elicited a minimum metabolic rate in the normal shoe. However, at 17 km/h an increased number of participants were more economical in the stiff shoe, despite it weighing an extra 50 g compared to the normal shoe. Running speed had an influence on subjective comfort, with participants tending to prefer the normal shoe at 14 km/h and the stiff shoe at 17 km/h. These results suggest that an optimal bending stiffness to reduce metabolic cost and improve comfort may be running speed dependent.

Midsole Properties Affect the Amplitude of Soft Tissue Vibrations in Heel-Toe Runners.

Soft tissue vibrations can generate discomfort and may necessitate a greater energy demand to preserve an efficient motion in running. Vibration damping is thus of interest from a comfort and performance standpoint. Our purpose was to assess whether changes in midsole material affect the properties of (a) soft tissue vibrations and (b) myoelectric activity. Two midsole conditions were compared. The control condition corresponded to a full ethylene-vinyl acetate foam midsole. The experimental condition was a bimaterial midsole with a material combination of viscous and viscoelastic materials. Twelve participants ran on an indoor track in both conditions while recording the longitudinal acceleration and the EMG activity of vastus medialis (VM) and gastrocnemius medialis (GM). Wavelet transforms were performed for EMG and acceleration signals to assess the intensity of the muscle activity at low and high frequencies (37-128 and 170-395 Hz, respectively) and to calculate the damping coefficient (D) for soft tissue vibrations. The soft tissue vibrations were also characterized by the peak of acceleration (apeak), the frequency of the power peak (fpeak), and the power of the soft tissue vibrations (PSD[8-55]). The variables apeak and PSD[8-55] decreased for VM and GM in the viscous condition. Before heel strike, low-frequency EMG activity decreased for VM, and high-frequency EMG activity tended to decrease for GM in the viscous condition. The damping D was reduced only for VM, and fpeak was unchanged. A more viscous midsole substantially reduced the amplitude of soft tissue vibrations, but not their frequency. Looking at individual results, it was noted that muscle activity was tuned in response to the acceleration input, and that the damping of soft tissue vibrations was affected by the intensity of muscle activity.