Shoe Stiffness Research Articles

Biomechanical Investigation of Lower Limbs during Slope Transformation Running with Different Longitudinal Bending Stiffness Shoes.

During city running or marathon races, shifts in level ground and up-and-down slopes are regularly encountered, resulting in changes in lower limb biomechanics. The longitudinal bending stiffness of the running shoe affects the running performance. This research aimed to investigate the biomechanical changes in the lower limbs when transitioning from level ground to an uphill slope under different longitudinal bending stiffness (LBS) levels in running shoes. Fifteen male amateur runners were recruited and tested while wearing three different LBS running shoes. The participants were asked to pass the force platform with their right foot at a speed of 3.3 m/s ± 0.2. Kinematics data and GRFs were collected synchronously. Each participant completed and recorded ten successful experiments per pair of shoes. The range of motion in the sagittal of the knee joint was reduced with the increase in the longitudinal bending stiffness. Positive work was increased in the sagittal plane of the ankle joint and reduced in the keen joint. The negative work of the knee joint increased in the sagittal plane. The positive work of the metatarsophalangeal joint in the sagittal plane increased. Transitioning from running on a level surface to running uphill, while wearing running shoes with high LBS, could lead to improved efficiency in lower limb function. However, the higher LBS of running shoes increases the energy absorption of the knee joint, potentially increasing the risk of knee injuries. Thus, amateurs should choose running shoes with optimal stiffness when running.

Relationship Between Advanced Footwear Technology Longitudinal Bending Stiffness and Energy Cost of Running.

Shoe longitudinal bending stiffness (LBS) is often considered to influence running economy (RE) and thus, running performance. However, previous results are mixed and LBS levels have not been studied in advanced footwear technology (AFT). The purpose of this study was to evaluate the effects of increased LBS from curved carbon fiber plates embedded within an AFT midsole compared to a traditional running shoe on RE and spatiotemporal parameters. Twenty-one male trained runners completed three times 4 min at 13 km/h with two experimental shoe models with a curved carbon fiber plate embedded in an AFT midsole with different LBS values (Stiff: 35.5 N/mm and Stiffest: 43.1 N/mm), and a Control condition (no carbon fiber plate: 20.1 N/mm). We measured energy cost of running (W/kg) and spatiotemporal parameters in one visit. RE improved for the Stiff shoe condition (15.71 ± 0.95 W/kg; p < 0.001; n2 = 0.374) compared to the Control condition (16.13 ± 1.08 W/kg; 2.56%) and Stiffest condition (16.03 ± 1.19 W/kg; 1.98%). However, we found no significant differences between the Stiffest and Control conditions. Moreover, there were no spatiotemporal differences between shoe conditions. Changes in LBS in AFT influences RE suggesting that moderately stiff shoes have the most effective LBS to improve RE in AFT compared to very stiff shoes and traditional, flexible shoe conditions while running at 13 km/h.

Effect of increased shoe longitudinal bending stiffness on ankle and foot biomechanics in jump-cut movements of low and high degrees

Lateral ankle sprains are the most common injuries in indoor and court sports, with ankle inversion being a primary injury driver. Stabilising the ankle during multidirectional changes is crucial for injury prevention. Conversely, increased shoe stiffness has been hypothesised to influence the magnitude of ankle inversion and may raise the risk for ankle injuries. Therefore, the purpose of this study was to investigate the influence of shoe longitudinal bending stiffness on ankle biomechanics during indoor and court sport-specific cutting movements. Biomechanical data from 19 participants were collected using a motion capture system and force plate. A jump-cut protocol with two different cutting directions after landing was performed in indoor shoes with and without carbon plate inserts of varying stiffness. Ankle kinematics and kinetics were analysed with statistical parametric mapping and repeated measures analysis of variance. A significant increase in ankle inversion during the 180° cut and a reduction in forefoot inversion (foot torsion) for stiffer footwear conditions during both the 45° and 180° cut were observed. While dorsiflexion moments differed during the last 10% of ground contact, ankle inversion moments did not significantly diverge between shoe conditions. Furthermore, a noteworthy correlation between footwear longitudinal bending stiffness and torsional stiffness was identified. In conclusion, increased bending stiffness significantly affected ankle and foot kinematics. The ankle compensated for restricted mobility and higher demands during high-degree jump-cuts, while foot torsion played a more prominent role in low-degree cuts. The heightened ankle inversion during high-degree cuts may induce an elevated risk for lateral ankle sprains. Further longitudinal studies are necessary to comprehensively understand injury incidence and the role of shoe stiffness in injury prevention.

The Impact of Running Experience and Shoe Longitudinal Bending Stiffness on Lower Extremity Biomechanics

Purpose The impacts of shoe stiffness on running biomechanics are well-documented, while the specific effects on the performance of biomechanically distinct groups such as novice runners and experienced runners are still largely unexplored. The study aimed to evaluate the biomechanical effects of different shoe longitudinal bending stiffness (adjusted by inserting carbon plate) on the lower limb during running in novice runners and experienced runners. Methods Twelve experienced runners and ten novice runners ran at a speed of 4.47 m/s while randomly wearing shoes with either low stiffness (5.9 Nm/rad) or high stiffness (8.6 Nm/rad). An Opensim musculoskeletal model was adopted for estimating lower limb joint angles, joint angular velocities, joint moment, joint work, peak joint reaction forces during running stance phase. Results Results showed that novice runners displayed greater lower limb joint mobility and less joint moment, while experienced runners exhibited less joint mobility but greater joint moment, and higher peak joint reaction forces were observed at the knee and ankle joints. Furthermore, increased shoe longitudinal bending stiffness resulted in higher peak joint reaction forces at the metatarsophalangeal joint for novice runners while lower for experienced runners. Conclusions Novice runners may face an increased risk of metatarsal pain or stress fractures when dealing with higher shoe stiffness. This nuanced understanding of joint dynamics underscores the need for tailored training and footwear recommendations to mitigate injury risks specific to different levels of running experience.

Effects of Shoe Midfoot Bending Stiffness on Multi-Segment Foot Kinematics and Ground Reaction Force during Heel-Toe Running.

We investigated how midfoot stiffness of running shoes influences foot segment kinematics and ground reaction force (GRF) during heel-toe running. Nineteen male rearfoot strike runners performed overground heel-toe running at 3.3 m/s when wearing shoes with different midfoot bending stiffnesses (low, medium, and high) in a randomized order. A synchronized motion capture system (200 Hz) and force plate (1000 Hz) were used to collect the foot-marker trajectories and GRF data. Foot kinematics, including rearfoot-lab, midfoot-rearfoot, forefoot-rearfoot, and forefoot-midfoot interactions, and kinetics, including GRF characteristics, were analyzed. Our results indicated that high midfoot stiffness shoes reduced the forefoot-rearfoot range of motion (mean ± SD; high stiffness, 7.8 ± 2.0°, low stiffness, 8.7 ± 2.1°; p < 0.05) and forefoot-midfoot range of motion (mean ± SD; high stiffness, 4.2 ± 1.1°, medium stiffness, 4.6 ± 0.9°; p < 0.05) in the frontal plane. No differences were found in the GRF characteristics among the shoe conditions. These findings suggest that an increase in midsole stiffness only in the midfoot region can reduce intersegmental foot medial-lateral movements during the stance phase of running. This may further decrease the tension of the foot muscles and tendons during prolonged exercises.

Novel testing system to determine shoe mechanical properties.

Shoes play an important role in ankle foot orthosis (AFO) function and alignment. Despite this, shoe mechanical testing systems are rarely colocated with gait analysis systems, limiting their availability and use during AFO-related studies. The purpose of this study was to evaluate a novel mechanical testing system used to measure shoe heel stiffness and change in height with loading using equipment available in most gait analysis laboratories. The novel testing system will allow for shoe assessment during AFO studies at little additional cost. Shoes were tested to determine initial stiffness, terminal stiffness, and total stiffness, and whether these measures changed with repeated compressions (early vs. late). The novel testing system consists of a baseplate for counterweights, uprights that support a low-friction hinge, and a lever arm with a heel-shaped indenter to apply force to the shoe. Minimal detectable change values were calculated using the standard error of measurement. Intraclass correlation coefficients were calculated in SPSS using a (2, k) model. No significant differences in mean values, or interactions, were observed between rounds of testing and early and late compressions (P > .05). Intraclass correlation coefficient values were greater than 0.98, and minimal detectable change values were less than 20% of the average for each measure. The novel mechanical testing system, combined with pre-existing gait analysis equipment, can be used to reliably assess shoe stiffness and change in height.

Shoe Bending Stiffness Influence on Lower Extremity Energetics in Consecutive Jump Take-Off.

Objective This study examined the influence of shoe bending stiffness on lower extremity energetics in the take-off phase of consecutive jump. Methods Fifteen basketball and volleyball players wearing control shoes and stiff shoes performed consecutive jumps. Joint angle, angular velocity, moments, power, jump height, take-off velocity, take-off time, and peak vertical ground reaction force data were simultaneously captured by motion capture system and force platform. Paired t-tests were performed on data for the two shoe conditions that fit the normal distribution assumptions, otherwise Wilcoxon signed-rank tests. Results There are significant differences (P < 0.05) in take-off velocity and take-off time between stiff and control shoe conditions; the stiff shoes had faster take-off velocity and shorter take-off time than control shoes. There was no significant difference between two conditions in jump height (P = 0.512) and peak vertical ground reaction force (P = 0.589). The stiff shoes had significantly lower MTP dorsiflexion angle and greater joint work than the control shoes (P < 0.05). The MTP range of motion and maximum angular velocity in stiff shoe condition were significantly lower than those in control shoe condition (P < 0.01). However, there are no significant differences between two conditions in kinetics and kinematics of the ankle, knee, and hip joint. Conclusions The findings suggest that wearing stiff shoes can reduce the effect of participation of the MTP joint at work and optimize the energy structure of lower-limb movement during consecutive jumps.

Variable Stiffness Shoes for Knee Osteoarthritis: An Evaluation of 3-Dimensional Gait Mechanics and Medial Joint Contact Forces.

The study aim was to quantify the impact of a commercially available variable stiffness shoe (VSS) on 3-dimensional ankle, knee, and hip mechanics and estimated knee contact forces compared with a control shoe. Fourteen participants (10females) with knee osteoarthritis completed gait analysis after providing informed consent. Shoe conditions tested were control shoe (New Balance MW411v2) and VSS (Abeo SMART3400). An OpenSim musculoskeletal model with static optimization was used to estimate knee contact forces. There were no differences in joint kinematics or in the knee adduction or flexion moments (P = .06; P = .2). There were increases in the knee internal and external rotation (P = .02; P = .03) and hip adduction and internal rotation moments for VSS versus control (P = .03; P = .02). The estimated contact forces were not different between shoes (total P = .3, medial P = .1, and lateral P = .8), but contact force changes were correlated with changes in the knee adduction moment (medial r2 = .61; P < .007). High variability in knee flexion moment changes and increases in the internal rotation moment combined with small decreases in the knee adduction moment did not lead to decreases in estimated contact forces. These results suggest that evaluation of VSS using only the knee adduction moment may not adequately capture its impact on osteoarthritis.

Layer Jamming for Variable Stiffness Shoes

In this work we presented the application of the layer jamming technology as variable stiffness mechanism for tech approach shoes. This scenario leads to the development of a novel kind of layer jamming system, with significant stiffness variation, yet minimized shape-locking effect. The system performances have been evaluated through subsequent experimental tests. This also allowed to better understand the behavior of shoes with different features. The results led to the identification of solutions with satisfactory performances with respect to target values and with the potential to be extended also to shoes with different requirements. The generality of the final considerations drawn for the examined application could lead to a novel way to exploit the layer jamming technology in different scenarios.

Lower impact forces but greater burden for the musculoskeletal system in running shoes with greater cushioning stiffness

ABSTRACT In a recent randomised trial investigating running shoe cushioning, injury risk was greater in recreational runners who trained in the shoe version with greater cushioning stiffness (Stiff) compared to those using the Soft version. However, vertical impact peak force (VIPF) was lower in the Stiff version. To investigate further the mechanisms involved in the protective effect of greater cushioning, the present study used an intra-subject design and analysed the differences in running kinematics and kinetics between the Stiff and Soft shoe versions on a subsample of 41 runners from the previous trial. Data were recorded in the two shoe conditions using an instrumented treadmill at 10 km.h−1. VIPF was confirmed to be lower in the Stiff version compared to the Soft version (1.39 ± 0.25 vs. 1.50 ± 0.25 BW, respectively; p = 0.009, d = 0.42), but not difference was observed in vertical loading rate (p = 0.255 and 0.897 for vertical average and instantaneous loading rate, respectively). Ankle eversion maximal velocity was not different (p = 0.099), but the Stiff version induced greater ankle negative work (−0.55 ± 0.09 vs. −0.52 ± 0.10 J.kg−1; p = 0.009, d = 0.32), maximal ankle negative power (−7.21 ± 1.90 vs. −6.96 ± 1.92 W.kg−1; p = 0.037, d = 0.13) and maximal hip extension moment (1.25 ± 0.32 vs.1.18 ± 0.30 N.m.kg−1; p = 0.009, d = 0.22). Our results suggest that the Stiff shoe version is related to increased mechanical burden for the musculoskeletal system, especially around the ankle joint. Trial registration: ClinicalTrials.gov identifier: NCT03115437.

The long-term effects of wearing moderate minimalist shoes on a child’s foot strength, muscle structure and balance: A randomised controlled trial

BackgroundFrom retrospective research, it is believed that children who predominantly spend their time shod have poorer foot strength and performance than those who are predominantly barefoot. Children’s foot motion has been shown to be adversely affected by standard school shoes; however, the long-term effect of moderate minimalist shoes on foot strength, muscle structure and balance in children is unknown. Research questionDoes wearing moderate minimalist shoes, compared to stiff shoes, benefit a child’s foot strength, muscle structure and performance over time? MethodsSeventy healthy children (9–12 yr) were randomly assigned to wear standard (control), or minimalist shoes (experimental) at school, for nine months. Cross-sectional areas (CSA) of Abductor Hallucis (AH) and Flexor Digitorum Brevis (FDB) muscles, and toe flexor strength (TFS) of hallux and lesser toes separately, were primary outcome measures. Single leg balance (SLB), Y-balance test (YBT) and standing long jump (SLJ) were secondary outcome measures. Pre- and post-intervention measurements were analysed for between group differences with ANCOVA. ResultsMinimalist shoes resulted in moderate but statistically non-significant increases in muscle CSA (AH η2p =.04, FDB η2p =.05) and TFS (hallux η2p =.05, lesser toes η2p =.04). Significant moderate to large improvements in YBT in the experimental group were found in the postero-medial (P = .04, η2p =.07) and postero-lateral (P = .01, η2p =.10) directions. YBT (anterior, postero-medial and postero-lateral) was correlated with hallux TFS (R =.29,.27 and.33 respectively), lesser toes TFS (R =.28,.35 and.38 respectively) and SLJ (R =.30,.39 and.57 respectively). CSA of FDB was correlated with SLJ (R =.34) and SLB (R =.42). SignificanceWearing moderate minimalist shoes long-term improves balance in children. TFS is correlated with better balance and SLJ. Moderate minimalist school shoes are recommended for children.

Effects Of Shoe Midfoot Bending Stiffness On Inner-foot Joints Rom During Heel-toe Running

Shoe manufacturers focus on footwear design which might affect the function of the footwear as well as foot motion and joint loading to improve running performance and prevent running injury. The longitudinal bending stiffness is considered to be a key feature in running shoe development. However, the majority of the longitudinal bending stiffness studies focus on the forefoot region, little investigation is carried out for midfoot bending stiffness. It is expected that changes in shoe midfoot bending stiffness would alter the foot motion. PURPOSE: The purpose of this study was to examine whether midfoot bending stiffness affects inner-foot joints ROM on frontal plane, thus providing scienticfic priciples for midfoot structure design of running footwear to enhance foot stability during heel-toe running. METHODS: The midfoot bending stiffness of experimental running shoe conditions were 0.069 Nm/°, 0.091 Nm/° and 0.163 Nm/°. Nineteen male runners with a rearfoot strike pattern, and running at least 10 Km/week, were recruited for this study. Kinematic and ground reaction force data were collected at 3.3 m/s using motion capture system (Vicon T20&T40, 200 Hz) and force platform (AMTI OR6-GT, 1000 Hz) during heel-toe running. A custom-made sock technology and a multi-segmental foot model were used to find the internal movements of foot segment in the shoe. RESULTS: Forefoot to midfoot interaction indicated the frontal plane ROM (p = 0.020, η2 = 0.196) was significantly greater in both the low stiffness (4.7 ± 1.3°) and medium stiffness (4.6 ± 0.9°) shoes compared to the high stiffness shoe (4.2 ± 1.1°) during running stance phase. A significant main effect was seen for the frontal plane ROM (p = 0.005, η2 = 0.258) on the forefoot to rearfoot discrete joint. The amplitude was greater in low stiffness (8.7 ± 2.1°) and medium stiffness (8.4 ± 2.0°) shoes relative to high stiffness shoe (7.8 ± 2.0°) during running stance phase. No difference was found for midfoot to rearfoot frontal plane ROM. CONCLUSIONS: The increased stiffness shoe had a splinting effect on the midfoot and rearfoot by reducing ROM in frontal plane to increase the stability of foot segments movement during running stance phase.

Effect of sports shoe mileage on running mechanics and lower limb muscular activities in male individuals with and without genu varus

The aim of the present study was to evaluate the long-term effects of shoes wearing on lower limb kinetics and electromyography activity of selected muscles of genu varus males compared with healthy age-matched controls during running. Equipment and methods Fifteen healthy males (age: 23.20 ± 1.78 years) and 14 males with genu varus (age: 21.57 ± 2.34 years) were eligible for inclusion in this study. Participants received new shoes before the baseline test and were measured with the same shoes (used shoes) after six months in the post-test. Ground reaction forces and muscle activities were recorded in both pre-test and post-test during running. Irrespective of the groups, pair-wise comparisons revealed that peak medial ground reaction force (p = 0.002; d = 0.316) values were higher at post-test. Furthermore, peak negative free moment (p = 0.008; d = 0.235) and peak positive free moment (p < 0.002; d = 0.298) were higher and lower respectively at the post-test. For electromyography activity at the loading phase, the tibialis anterior and vastus medialis muscle activities were higher in the post-test, while the vastus medialis, vastus lateralis, and rectus femoris muscles activities were higher at the mid-stance phase. The gluteus medius muscle activity was reduced at the push-off phase in the post-test. Shoe mileage appears to have an impact on ground reaction force and selected muscle activities in healthy male individuals with and without genu varus. Together with the observed findings on shoe stiffness, it seems appropriate to change running shoes after a great wearing time of approximately six months with walking and to run mileage about 17 km/week. Le but de la présente étude était d’évaluer les effets à long terme du port de chaussures sur la cinétique des membres inférieurs et l’activité électromyographique de certains muscles de genu varus mâles par rapport à des témoins sains en fonction de l’âge pendant la course. Quinze hommes en bonne santé (âge: 23,20 ± 1,78 ans) et 14 hommes atteints de genu varus (âge: 21,57 ± 2,34 ans) étaient éligibles à l’inclusion dans cette étude. Les participants ont reçu de nouvelles chaussures avant le test de base et ont été mesurés avec les mêmes chaussures (chaussures usagées) après six mois dans le post-test. Les forces de réaction au sol et les activités musculaires ont été enregistrées à la fois avant et après les tests pendant la course. Indépendamment des groupes, des comparaisons par paires ont révélé que les valeurs maximales de la force de réaction au sol médiane (p = 0,002; d = 0,316) étaient plus élevées au post-test. De plus, le moment libre négatif maximal (p = 0,008; d = 0,235) et le moment libre positif maximal (p <0,002; d = 0,298) étaient respectivement plus élevés et plus faibles au post-test. Pour l’activité d’électromyographie à la phase de chargement, les activités musculaires du tibial antérieur et du vaste médial étaient plus élevées dans le post-test, tandis que les activités des muscles du vaste médial, du vaste latéral et du rectus fémoral étaient plus élevées à la phase intermédiaire. L’activité musculaire du fessier moyen a été réduite lors de la phase de poussée dans le post-test. Le kilométrage des chaussures semble avoir un impact sur la force de réaction au sol et certaines activités musculaires chez les individus masculins en bonne santé avec et sans genu varus. Parallèlement aux résultats observés sur la rigidité des chaussures, il semble approprié de changer de chaussures de course après une grande durée de port d’environ six mois avec un kilométrage à pied et à pied d’environ 17 km/semaine.

Effect of outdoor footwear bending stiffness on metatarsophalangeal joint kinematics, kinetics, and energy balance during level and uphill walking

In outdoor footwear, sole properties must guarantee grip with the ground and support the forefoot without altering the kinematics of the metatarsophalangeal joints (MPJ). The present study aimed to implement an objective measure of shoe bending stiffness and investigate the effect of shoes with different bending stiffness on MPJ kinematics, kinetics, and energy balance during walking. The bending stiffness of four shoes was calculated using a customized flexometer. Then, the influence of each footwear on MPJ biomechanics during level and uphill walking was investigated with a motion capture system and a force plate on 10 healthy subjects. Results showed that MPJ peak dorsiflexion angle, stiffness, and energy balance were affected both by shoe bending stiffness ( p&lt;0.001) and walking slope ( p&lt;0.001). The findings of the study, which quantify the influence of shoe stiffness on MPJ biomechanics, will be helpful in the design of outdoor footwear.

Increasing the midsole bending stiffness of shoes alters gastrocnemius medialis muscle function during running

In recent years, increasing the midsole bending stiffness (MBS) of running shoes by embedding carbon fibre plates in the midsole resulted in many world records set during long-distance running competitions. Although several theories were introduced to unravel the mechanisms behind these performance benefits, no definitive explanation was provided so far. This study aimed to investigate how the function of the gastrocnemius medialis (GM) muscle and Achilles tendon is altered when running in shoes with increased MBS. Here, we provide the first direct evidence that the amount and velocity of GM muscle fascicle shortening is reduced when running with increased MBS. Compared to control, running in the stiffest condition at 90% of speed at lactate threshold resulted in less muscle fascicle shortening (p = 0.006, d = 0.87), slower average shortening velocity (p = 0.002, d = 0.93) and greater estimated Achilles tendon energy return (p ≤ 0.001, d = 0.96), without a significant change in GM fascicle work (p = 0.335, d = 0.40) or GM energy cost (p = 0.569, d = 0.30). The findings of this study suggest that running in stiff shoes allows the ankle plantarflexor muscle–tendon unit to continue to operate on a more favourable position of the muscle’s force–length–velocity relationship by lowering muscle shortening velocity and increasing tendon energy return.

Does running speed affect the response of joint level mechanics in non-rearfoot strike runners to footwear of varying longitudinal bending stiffness?

BackgroundModifying the longitudinal bending stiffness (LBS) of footwear has become a popular method to improve sport performance. It has been demonstrated to influence running economy by altering lower extremity joint level mechanics. Previous studies have only examined within-participant effects at one running speed. Research questionDo joint level mechanics differ in response to varying footwear LBS at a range of running speeds? MethodsThis study utilized a cross-sectional repeated measure study design using a convenience sample. Ten well trained non-rearfoot strike male distance runners ran at 3.89, 4.70, and 5.56 m/s (14, 17, 20 km/hr) in footwear of three different LBS levels. Mechanics and energetics of the metatarsophalangeal joint (MTPJ), ankle, knee, and hip joints during stance phase were assessed using an 8-camera optical motion capture system (fs = 200 Hz), a force instrumented treadmill (fs = 1000 Hz) and standard inverse dynamics theory. ResultsRange of motion and negative work decreased and angular stiffness increased for the MTPJ with increasing LBS at all speeds (p < .001). Peak MTPJ moment did not change at any speed in response to increased LBS. Negative work at the ankle decreased in the stiff shoe at 17 km/hr (p = .036). Peak ankle plantar flexion velocity decreased with increasing LBS at all speeds (p < .05). SignificanceWhile changes in MTPJ mechanics were consistent across speeds, decreased negative ankle work was only observed at 17 km/hr in the stiff shoe, suggesting that perhaps tuned footwear LBS may need to focus primarily on metabolically beneficial changes in ankle plantar flexor mechanical behavior to improve performance in distance runners. Tuning footwear stiffness may also be beneficial to clinical populations, as clinicians seek to optimize their patients’ locomotion economy.

Stability Limits for Vertical Vibrations of Paraplegic Subjects while Using Passive Orthosis

Spinal cord injury (SCI) subjects use passive orthosis to assist them with the postural balance in daily life. Vertical vibrations are used to improve the postural balance of theses patients, mainly in terms of whole-body-vibrations, as in therapies. It is noteworthy to understand in what situation these patients are able to tolerate vertical vibrations while wearing orthosis. The main focus of this paper is to model vertical vibrations in the postural balance of arm free standing of the paraplegic subjects who use passive orthosis, and, mathematically understand the stability limits for these vibrations. To find the stable amplitudes and frequencies, equations of motions of the system are translated into non-homogeneous Mathieu equations, which are then analytically solved and the results are numerically plotted. In addition, the effect of shoe stiffness on the amplitude and frequency of the vibrations which violate stability are studied. The results show to be sure of the stability of the paraplegics in vertical vibrations, the shoe sole of the orthosis should have high values of stiffness, and this will guarauntee bigger ranges of stable vibrations and safer stance for the patients. Using the results, one can interpret how a paraplegic subject with passive orthosis may react to vertical perturbations, meaning, what ranges of frequencies and amplitudes of perturbations is tolerable without losing stability. This study is one of the necessities in designing new passive orthosis with more stability when exposed to perturbations.

Relationship between changes in the knee adduction moment and medial compartment contact force with variable stiffness shoes

Purpose: Despite early promising results of Variable Stiffness Shoes (VSS) on pain and function in medial compartment knee osteoarthritis (OA) patients, randomized controlled trials have not found a significant effect on structural disease progression. Significant biomechanical effects of VSS have been found with several studies showing reductions in the external knee adduction moment (KAM) for healthy, mild, moderate and severe medial compartment knee OA participants as compared to shoes with homogenous midsole stiffness.

Improving running economy through altered shoe bending stiffness across speeds

Increasing the longitudinal bending stiffness of running shoes decreases energy cost until a low point is reached, suggesting an optimal shoe stiffness. Previous research found optimal stiffness varies among individuals, however, none has determined the causes of variation both between individuals and running speeds. The primary purpose of this study was to understand how optimal shoe stiffness is affected by running speed. A secondary purpose examined the anatomical and biomechanical characteristics associated with optimal stiffness variation. Six shoe stiffness conditions were manufactured with a carbon fibre plate between the midsole and outsole of a standard running shoe. Twenty-one male runners (mass = 67.1 ± 5.0 kg, height = 178.9 cm ± 4.0 cm, age = 26.4 ± 8.4 years) completed testing at 2.98 m/s and 4.47 m/s in all shoe conditions, measuring metabolic cost, and several biomechanical and anatomical variables. Data were separated by foot strike. At the fast speed, average optimal stiffness was 19.29 ± 5.62 N/mm with a metabolic benefit of 3.02 ± 2.62%. Slow speed average optimal stiffness was 17.04 ± 6.09 N/mm with a metabolic benefit of 1.93 ± 1.82%. Only rearfoot strikers demonstrated a significant increase in optimal stiffness (p = .04) across speeds. There were no correlations between any of the measured anatomical or biomechanical variables and optimal stiffness. Optimal stiffness varied between subjects but was not correlated to any of our measured characteristics. Rearfoot striking runners may benefit from a higher stiffness shoe at faster speeds to enable optimal performance.

Long-term effects of shoe mileage on ground reaction forces and lower limb muscle activities during walking in individuals with genu varus

BackgroundShoe mileage is an important factor that may influence the risk of sustaining injuries during walking. The aims of this study were to examine the effects of shoe mileage on ground reaction forces and activity of lower limb muscles during walking in genu varus individuals compared with controls. MethodsFifteen healthy and 15 genu varus females received a new pair of running shoes. They were asked to wear these shoes over 6 months. Pre and post intervention, mechanical shoe testing was conducted and ground reaction forces and muscle activities of the right leg were recorded during walking at preferred gait speed. FindingsSignificant group-by-time interactions were found for shoe stiffness, antero-posterior and vertical impact peak. We observed higher shoe stiffness and lower impact peaks after intervention in both groups with larger effect sizes in genu varus. Significant group-by-time interactions were identified for vastus medialis (loading phase) and rectus femoris (loading and push-off). For vastus medialis, significant decreases were found from pre-to-post during the loading phase in the control group. Rectus femoris activity was higher post intervention during the loading and push-off phases in both groups with larger effect sizes in genu varus. InterpretationOur findings indicate that the observed changes in ground reaction forces are more prominent in genu varus individuals. Together with our findings on shoe stiffness, it seems appropriate to change running shoes after an intense wearing time of 6 months, particularly in genu varus individuals.