Influence of the windlass mechanism on arch-spring mechanics during dynamic foot arch deformation

Direct visualization and measurement of the plantar aponeurosis behavior in foot arch deformation via the windlass mechanism

The plantar aponeurosis (PA) is an elastic longitudinal band that contributes to the generation of a propulsive force in the push-off phase during walking and running through the windlass mechanism. However, the dynamic behavior of the PA remains unclear owing to the lack of direct measurement of the strain it generates. Therefore, this study aimed to visualize and quantify the PA behavior during two distinct foot postures: (i) neutral posture and (ii) windlass posture with midtarsal joint plantarflexion and metatarsophalangeal joint dorsiflexion, using computed tomography scans. Six healthy adult males participated in the experiment, and three-dimensional reconstruction of the PA was conducted to calculate its path length, width, thickness, and cross-sectional area. This study successfully visualized and quantified the morphological changes in the PA induced by the windlass mechanism, providing a precise reference for biomechanical modeling. This study also highlighted the interindividual variability in the PA morphology and stretching patterns. Although the windlass posture was not identical to that observed in the push-off phase during walking, the observed PA behavior provides valuable insights into its mechanics and potential implications for foot disorders.

Effects of Neuromuscular Electrical Stimulation with Gastrocnemius Strengthening on Foot Morphology in Stroke Patients: A Randomized Controlled Trial

This study aimed to investigate the effects of neuromuscular electrical stimulation (NMES) with gastrocnemius (GCM) strength exercise on foot morphology in patients with stroke. Herein, 31 patients with chronic stroke meeting the study criteria were enrolled and divided into two groups; 16 patients were randomized to the gastrocnemius neuromuscular electrical stimulation (GCMNMES) group, and 15 patients to the conventional neuromuscular electrical stimulation (CNMES) group. The GCMNMES group conducted GCM-strengthening exercise with NMES. CNMES group conducted NMES at paretic tibialis anterior muscle with ankle dorsiflexion movement. These patients underwent therapeutic interventions lasting 30 min/session, five times a week for 4 weeks. To analyze changes in foot morphology, 3D foot scanning was used, while a foot-pressure measurement device was used to evaluate foot pressure and weight-bearing area. In an intra-group comparison of 3D-foot-scanning results, the experimental group showed significant changes in longitudinal arch angle (p < 0.05), medial longitudinal arch angle (MLAA) (p < 0.01), transverse arch angle (TAA) (p < 0.01), rearfoot angle (RA) (p < 0.05), foot length (FL) (p < 0.05), foot width (FW) (p < 0.05), and arch height index (AHI) (p < 0.01) of the paretic side and in TAA (p < 0.05) and AHI (p < 0.05) of the non-paretic side. The CNMES group showed significant changes in TAA (p < 0.05) and FW (p < 0.05) of the paretic side and TAA (p < 0.05) and AHI (p < 0.05) of the non-paretic side. An inter-group comparison showed significant differences in MLAA (p < 0.05) and RA (p < 0.05) of the paretic side. In an intra-group comparison of foot pressure assessment, the experimental group showed significant differences in footprint area (FPA) (p < 0.05) of the paretic side and FPA symmetry (p < 0.05). The CNMES group showed a significant difference in only FPA symmetry (p < 0.05). An inter-group comparison showed no significant difference between the two groups (p < 0.05). Thus, NMES with GCM-strengthening exercises yielded positive effects on foot morphology in patients with stroke.

Technical note: A volumetric method for measuring the longitudinal arch of human tracks and feet

Fossil footprints (i.e., tracks) were believed to document arch anatomical evolution, although our recent work has shown that track arches record foot kinematics instead. Analyses of track arches can thereby inform the evolution of human locomotion, although quantifying this 3-D aspect of track morphology is difficult. Here, we present a volumetric method for measuring the arches of 3-D models of human tracks and feet, using both Autodesk Maya and Blender software. The method involves generation of a 3-D object that represents the space beneath the longitudinal arch, and measurement of that arch object's geometry and spatial orientation. We provide relevant tools and guidance for users to apply this technique to their own data. We present three case studies to demonstrate potential applications. These include, (1) measuring the arches of static and dynamic human feet, (2) comparing the arches of human tracks with the arches of the feet that made them, and (3) direct comparisons of human track and foot arch morphology throughout simulated track formation. The volumetric measurement tool proved robust for measuring 3-D models of human tracks and feet, in static and dynamic contexts. This tool enables researchers to quantitatively compare arches of fossil hominin tracks, in order to derive biomechanical interpretations from them, and/or offers a different approach for quantifying foot morphology in living humans.

Capitalizing on skin in orthotics design: the effects of texture on plantar intrinsic foot muscles during locomotion

Foot orthoses (FO) are a commonly prescribed intervention to alter foot function during walking although their effects have been primarily studied in the extrinsic muscles of the foot. Furthermore, enhancing sensory feedback under the foot sole has been recently shown to alter extrinsic muscle activity during gait; however, the effects of FOs with enhanced sensory feedback on plantar intrinsic foot muscles (PIFMs) remain unknown. Thus, the purpose of this study was to investigate the effect of FOs with and without sensory facilitation on PIFM activity during locomotion. Forty healthy adults completed a series of gait trials in non-textured and textured FOs when walking over hard and soft flooring. Outcome measures included bilateral joint kinematics and electromyography (EMG) of four PIFMs. Results of this study highlight the distinct onset and cessations of each PIFM throughout the stance phase of gait. PIFMs remained active during mid-stance when wearing FOs and textured FOs facilitated muscle activity across the stance phase of gait. Increasing cutaneous input from foot sole skin, via the addition of texture under the foot sole, appears to alter motor-neuron pool excitation of PIFMs. Future academics are encouraged to increase our understanding on which pathologies, diseases, and/or medical conditions would best benefit from textured FOs.

Human foot form and function: variable and versatile, yet sufficiently related to predict function from form

The human foot is a complex structure that plays an important role in our capacity for upright locomotion. Comparisons of our feet with those of our closest extinct and extant relatives have linked shape features (e.g. the longitudinal and transverse arches, heel size and toe length) to specific mechanical functions. However, foot shape varies widely across the human population, so it remains unclear if and how specific shape variants are related to locomotor mechanics. Here we constructed a statistical shape-function model (SFM) from 100 healthy participants to directly explore the relationship between the shape and function of our feet. We also examined if we could predict the joint motion and moments occurring within a person's foot during locomotion based purely on shape features. The SFM revealed that the longitudinal and transverse arches, relative foot proportions and toe shape along with their associated joint mechanics were most variable. However, each of these only accounted for small proportions of the overall variation in shape, deformation and joint mechanics, most likely owing to the high structural complexity of the foot. Nevertheless, a leave-one-out analysis showed that the SFM can accurately predict joint mechanics of a novel foot, based on its shape and deformation.

Lower-limb dominance does not explain subject-specific foot kinematic asymmetries observed during walking and running

Studies of human locomotion have observed asymmetries in lower-limb kinematics, especially at the more distal joints. However, it is unclear whether these asymmetries are related to functional differences between the dominant and non-dominant limb. This study aimed to determine the effect of lower-limb dominance on foot kinematics during human locomotion. Range of motion for the metatarsophalangeal joint (MPJ) and medial longitudinal arch (MLA), as well as time duration of windlass mechanism engagement, were recorded from healthy young adults (N = 12) across a range of treadmill walking and running speeds. On the group level, there were no differences in MPJ or MLA range of motion, or windlass engagement timing, between the dominant and non-dominant limb (p > 0.05). While not explained by limb dominance, between-limb differences in MPJ and MLA ranges of motion were observed for individual participants on the order of ∼2-6°, which could be clinically relevant or impact interpretation of research data.

Chasing footprints in time - reframing our understanding of human foot function in the context of current evidence and emerging insights

In this narrative review we evaluate foundational biomechanical theories of human foot function in light of new data acquired with technology that was not available to early researchers. The formulation and perpetuation of early theories about foot function largely involved scientists who were medically trained with an interest in palaeoanthropology, driven by a desire to understand human foot pathologies. Early observations of people with flat feet and foot pain were analogized to those of our primate ancestors, with the concept of flat feet being a primitive trait, which was a driving influence in early foot biomechanics research. We describe the early emergence of the mobile adaptor-rigid lever theory, which was central to most biomechanical theories of human foot function. Many of these theories attempt to explain how a presumed stiffening behaviour of the foot enables forward propulsion. Interestingly, none of the subsequent theories have been able to explain how the foot stiffens for propulsion. Within this review we highlight the key omission that the mobile adaptor-rigid lever paradigm was never experimentally tested. We show based on current evidence that foot (quasi-)stiffness does not actually increase prior to, nor during propulsion. Based on current evidence, it is clear that the mechanical function of the foot is highly versatile. This function is adaptively controlled by the central nervous system to allow the foot to meet the wide variety of demands necessary for human locomotion. Importantly, it seems that substantial joint mobility is essential for this function. We suggest refraining from using simple, mechanical analogies to explain holistic foot function. We urge the scientific community to abandon the long-held mobile adaptor-rigid lever paradigm, and instead to acknowledge the versatile and non-linear mechanical behaviour of a foot that is adapted to meet constantly varying locomotory demands.

Mechanics of the human foot during walking on different slopes

When humans walk on slopes, the ankle, knee, and hip joints modulate their mechanical work to accommodate the mechanical demands. Yet, it is unclear if the foot modulates its work output during uphill and downhill walking. Therefore, we quantified the mechanical work performed by the foot and its subsections of twelve adults walked on five randomized slopes (-10°, -5°, 0°, +5°, +10°). We estimated the work of distal-to-hindfoot and distal-to-forefoot structures using unified deformable segment analysis and the work of the midtarsal, ankle, knee, and hip joints using a six-degree-of-freedom model. Further, using a geometric model, we estimated the length of the plantar structures crossing the longitudinal arch while accounting for the first metatarsophalangeal wrapping length. We hypothesized that compared to level walking, downhill walking would increase negative and net-negative work magnitude, particularly at the early stance phase, and uphill walking would increase the positive work, particularly at the mid-to-late stance phase. We found that downhill walking increased the magnitude of the foot's negative and net-negative work, especially during early stance, highlighting its capacity to absorb impacts when locomotion demands excessive energy dissipation. Notably, the foot maintained its net dissipative behavior between slopes; however, the ankle, knee, and hip shifted from net energy dissipation to net energy generation when changing from downhill to uphill. Such results indicate that humans rely more on joints proximal to the foot to modulate the body's total mechanical energy. Uphill walking increased midtarsal's positive and distal-to-forefoot negative work in near-equal amounts. That coincided with the prolonged lengthening and delayed shortening of the plantar structures, resembling a spring-like function that possibly assists the energetic demands of locomotion during mid-to-late stance. These results broaden our understanding of the foot's mechanical function relative to the leg's joints and could inspire the design of wearable assistive devices that improve walking capacity.

Age, Gender, Body Mass Index, and Foot Loading During Gait

Background

The aim was to analyze changes in normal functional parameters of gait analysis by aging, sex, and body mass index (BMI).

Methods

A cross-sectional study with a consecutive sample of asymptomatic subjects was performed between 2014 and 2020. Primary outcomes were time and force parameters (contact time and center of force [CoF] time), in the heel, midfoot, and metatarsal areas, measured using an in-office force platform.

Results

A total of 156 subjects (312 feet) were included, including 67% of women with a mean age of 47 years. The mean of total contact time was similar in males and females (P = .695) and across BMI (P = .413). Contact time did not show differences by region (P = .648 heel, P = .286 midfoot, and P = .690 metatarsal). CoF time in the heel and metatarsal areas did not change between males and females (P = .288 and P = .879, respectively); meanwhile, it was different in midfoot (P = .002). Maximum force showed a reduction between sexes in the heel (P = .039) but did not in the midfoot and metatarsal areas. By age, differences were detected in the heel and metatarsal areas in females (P = .002 and P = .001) and the metatarsal area in males (P = .001). According to the age groups, total contact time increased in females (P = .001) but not in males (P = .018), and no differences were detected between foot areas. In females, CoF time did not change either foot areas or age groups. In males, CoF time values increased in the midfoot area in the older group (P = .001).

Conclusion

Time variables did not change by foot region, independent of age, sex, and BMI. Heel maximum force decreased in females, probably linked to adaptive phenomena by aging. The midfoot remains stable, and acts as an undamaged "bridge." These parameters could be interpreted as normal in asymptomatic subjects.

Level of Evidence

Level III, diagnostic and prognostic.

Comparison of intrinsic foot muscle morphology and isometric strength among runners with different strike patterns

This study aimed to compare the intrinsic foot muscle (IFM) morphology and isometric strength among runners with habitual rearfoot strike (RFS) and non-rearfoot strike (NRFS) patterns. A total of 70 recreational male runners were included in this study (32 RFS and 38 NRFS), an ultrasound device and hand-held dynamometry were used to measure IFM morphology and isometric strength. Results indicated that the RFS runners had significantly thicker tibialis anterior (P = 0.01, ES = 0.64, 95% CI [0.01-0.07]) in IFMs morphology and higher Toe2345 flexion strength in IFMs strength (P = 0.04, ES = 0.50, 95% CI [0.01-0.27]) than NRFS runners, the cross-sectional area of flexor digitorum brevis was positively correlated with T2345 flexion strength (r = 0.33, p = 0.04), T12345 (r = 0.37, p = 0.02) and Doming (r = 0.36, p = 0.03) for runners with NRFS. IFMs morphology and isometric strength were associated with foot strike pattern, preliminary findings provide new perspectives for NRFS runners through the simple measurement of IFMs morphological characteristics predicting IFMs strength, future studies could adopt IFMs training to compensate the muscle strength defects and prevent foot-related injuries.

Three-Dimensional Analysis of the Windlass Mechanism Using Weightbearing Computed Tomography in Healthy Volunteers

BACKGROUND

The windlass mechanism (WM) increases the longitudinal arch of the foot via tension of the plantar aponeurosis during dorsiflexion of the metatarsophalangeal (MTP) joint. The purpose of this study was to perform a 3-dimensional evaluation of the displacement of each joint and the height of the navicular during dorsiflexion of the first MTP joint by using weightbearing computed tomography (CT).

METHODS

Participants were 6 men and 8 women with 23 healthy feet. CT of the foot with a load equivalent to the participant's body weight was performed. The first MTP joint was in the neutral position and dorsiflexed 30 degrees. Between the conditions, we measured the (1) rotation of each bone, (2) rotation of the distal bone with respect to the proximal bone at each joint, and (3) height of the navicular.

RESULTS

With respect to the tibia, the calcaneus was at 0.8 ± 0.7 degrees dorsiflexion and 1.4 ± 0.9 degrees inversion, while the talus was at 2.0 ± 1.2 degrees dorsiflexion and 0.1 ± 0.8 degrees eversion. The navicular was at 1.3 ± 1.2 degrees dorsiflexion and 3.2 ± 2.1 degrees inversion, whereas the medial cuneiform was at 0.3 ± 0.6 degrees plantarflexion and 1.3 ± 1.1 degrees inversion. At the talonavicular joint, the navicular was at 0.7 ± 1.3 degrees plantarflexion, whereas at the cuneonavicular joint, the medial cuneiform bone was at 1.4 ± 1.4 degrees plantarflexion. The height of the navicular increased by 1.1 ± 0.6 mm.

CONCLUSION

We 3-dimensionally confirmed the dynamics of WM and found that the calcaneus, navicular, and medial cuneiform moved in all 3 planes. The results suggest that the cuneonavicular joint has the greatest movement among the joints. We believe that these findings will help to elucidate the pathogenesis of WM-related diseases and lead to advances in treatments for pathologies involving the longitudinal arch.

LEVEL OF EVIDENCE

Level IV, case series.

Does human foot anthropometry relate to plantar flexor fascicle mechanics and metabolic energy cost across various walking speeds?

Foot structures define the leverage in which the ankle muscles push off against the ground during locomotion. While prior studies have indicated that inter-individual variation in anthropometry (e.g. heel and hallux lengths) can directly affect force production of ankle plantar flexor muscles, its effect on the metabolic energy cost of locomotion has been inconclusive. Here, we tested the hypotheses that shorter heels and longer halluces are associated with slower plantar flexor (soleus) shortening velocity and greater ankle plantar flexion moment, indicating enhanced force potential as a result of the force-velocity relationship. We also hypothesized that such anthropometry profiles would reduce the metabolic energy cost of walking at faster walking speeds. Healthy young adults (N=15) walked at three speeds (1.25, 1.75 and 2.00 m s-1), and we collected in vivo muscle mechanics (via ultrasound), activation (via electromyography) and whole-body metabolic energy cost of transport (via indirect calorimetry). Contrary to our hypotheses, shorter heels and longer halluces were not associated with slower soleus shortening velocity or greater plantar flexion moment. Additionally, longer heels were associated with reduced metabolic cost of transport, but only at the fastest speed (2.00 m s-1, R2=0.305, P=0.033). We also found that individuals with longer heels required less increase in plantar flexor (soleus and gastrocnemius) muscle activation to walk at faster speeds, potentially explaining the reduced metabolic cost.

Foot shape is related to load-induced shape deformations, but neither are good predictors of plantar soft tissue stiffness

Modern human feet are considered unique among primates in their capacity to transmit propulsive forces and re-use elastic energy. Considered central to both these capabilities are their arched configuration and the plantar aponeurosis (PA). However, recent evidence has shown that their interactions are not as simple as proposed by the theoretical and mechanical models that established their significance. Using three-dimensional foot scans and statistical shape and deformation modelling, we show that the shape of the longitudinal and transverse arches varies widely among the healthy adult population, and that the former is subject to load-induced arch flattening, whereas the latter is not. However, longitudinal arch shape and flattening are only one of the various foot shape-deformation relationships. PA stiffness was also found to vary widely. Yet only a small amount of this variability (approx. 10-18%) was explained by variations in foot shape, deformation and their combination. These findings add to the mounting evidence showing that foot mechanics are complex and cannot be accurately represented by simple models. Especially the interactions between longitudinal arch and PA appear to be far less constrained than originally proposed, most likely due to the many degrees of freedom provided by the structural complexity of our feet.

An investigation into the hammer toe effects on the lower extremity mechanics and plantar fascia tension: A case for a vicious cycle and progressive damage

Hammer toes are one of the common deformities of the forefoot that can lead to compensatory changes during walking in individuals with this condition. Predicting the adverse effects of tissue damage on the performance of other limbs is very important in the prevention of progressive damage. Finite element (FE) and musculoskeletal modeling can be helpful by allowing such effects to be studied in a way where the internal stresses in the tissue could be investigated. Hence, this study aims to investigate the effects of the hammer toe deformity on the lower extremity, especially on the plantar fascia functions. To compare the joint reactions of the hammer toe foot (HTF) and healthy foot (HF), two musculoskeletal models (MSM) of the feet of a healthy individual and that of a participant with hammer toe foot were developed based on gait analysis. A previously validated 3D finite element model which was constructed using Magnetic Resonance Imaging (MRI) of the diabetic participant with the hammer toe deformity was processed at five different events during the stance phase of gait. It was found that the hammer toe deformity makes dorsiflexion of the toes and the windlass mechanism less effective during walking. Specifically, the FE analysis results showed that plantar fascia (PF) in HTF compared to HF played a less dominant role in load bearing with both medial and lateral parts of PF loaded. Also, the results indicated that the stored elastic energy in PF was less in HTF than the HF, which can indicate a higher metabolic cost during walking. Internal stress distribution shows that the majority of ground reaction forces are transmitted through the lateral metatarsals in hammer toe foot, and the probability of fifth metatarsal fracture and also progressive deformity was subsequently increased. The MSM results showed that the joint reaction forces and moments in the hammer toe foot have deviated from normal, where the metatarsophalangeal joint reactions in the hammer toe were less than the values in the healthy foot. This can indicate a vicious cycle of foot deformity, leading to changes in body weight force transmission line, and deviation of joint reactions and plantar fascia function from normal. These in turn lead to increased internal stress concentration, which in turn lead to further foot deformities. This vicious cycle cause progressive damage and can lead to an increase in the risk of ulceration in the diabetic foot.

Parámetros biomecánicos de la función del pie medidos en el consultorio del especialista en Ortopedia y Traumatología

Introducción: Los estudios dinámicos de la función del pie habitualmente se realizan en laboratorios de marcha de gran complejidad. El objetivo de este estudio fue analizar parámetros funcionales utilizando una plataforma de fuerza en una serie de pacientes asintomáticos evaluados en consultorios externos. Materiales y Métodos: Estudio de corte transversal que incluyó una serie consecutiva de pacientes asintomáticos voluntarios a quienes se les realizó una medición con una plataforma de fuerza (TekScan MatScan®, Boston, MA, EE.UU.) entre 2014 y 2020, en la Ciudad Autónoma de Buenos Aires, Argentina. Resultados: Se incluyeron 316 registros de 158 pacientes con mediciones bilaterales. La mayoría eran mujeres (66,5%) y el promedio de la edad era de 47 años (DE 16.1). Se evaluaron 14 variables, correspondientes a parámetros de fuerza, trayectoria y tiempo de contacto de la fuerza. El tiempo de contacto total fue de 0,79 segundos (DE 0,09), el CoF time según la región del pie fue del 20% en el talón, 26% en el mediopié y 46% en el antepié. El CPEI (center of pressure excursion index) fue del 16,55% (DE 7,14). Conclusiones: Se comunican los parámetros funcionales del pie en pacientes asintomáticos. Se midieronel tiempo de contacto del pie en el suelo, la fuerza (en talón, mediopié y antepié) y la trayectoria de la fuerza con una plataforma de fuerza. No se utilizaron radiaciones ionizantes. Estos hallazgos podrían ser utilizados como valores de referencia para detectar marchas patológicas. Nivel de Evidencia: II  

Changes of the in vivo kinematics of the human medial longitudinal foot arch, first metatarsophalangeal joint, and the length of plantar fascia in different running patterns

Accurately obtaining the in vivo motion of the medial longitudinal arch (MLA), first metatarsophalangeal joint (MTPJ), and plantar fascia (PF) is essential for analyzing the biomechanics of these structures in different running strike patterns. Most previous studies on the biomechanics of the MLA, first MTPJ, and PF have been based on traditional skin-marker-based motion capture, which cannot acquire the natural foot motion. Therefore, this study aimed to 1) describe the movement of the MLA, first MTPJ, and PF during running by using the high-speed dual fluoroscopic imaging system (DFIS) and 2) explore changes of the in vivo kinematics of the MLA and first MTPJ, and the length of the PF during the stance phase of running with different foot strike patterns. Fifteen healthy male runners all of whom ran with a regular rearfoot strike (RFS) pattern were required to run with forefoot strike (FFS) and RFS patterns. Computed tomography scans were taken from each participant's right foot for the construction of 3D models (the calcaneus, first metatarsal, and first proximal phalanges) and local coordinate systems. A high-speed DFIS (100 Hz) and 3D force platform (2,000 Hz) were used to acquire X-ray images of the foot bones and ground reaction force data during the stance phase of running (3 m/s ± 5%) simultaneously. Then, 3D-2D registration was used to obtain the in vivo kinematic data of the MLA and first MTPJ and the length of the PF. When compared with RFS, in FFS, 1) the range of motion (ROM) of the medial/lateral (5.84 ± 5.61 mm vs. 0.75 ± 3.38 mm, p = 0.002), anterior/posterior (14.64 ± 4.33 mm vs. 11.18 ± 3.56 mm, p = 0.010), plantarflexion/dorsiflexion (7.13 ± 3.22° vs. 1.63 ± 3.29°, p < 0.001), and adduction/abduction (-3.89 ± 3.85° vs. -0.64 ± 4.39°, p = 0.034) motions of the MLA were increased significantly; 2) the ROM of the anterior/posterior (7.81 ± 2.84 mm vs. 6.24 ± 3.43 mm, p = 0.003), superior/inferior (2.11 ± 2.06 mm vs. -0.57 ± 1.65 mm, p = 0.001), and extension/flexion (-9.68 ± 9.16° vs. -5.72 ± 7.33°, p = 0.018) motions of the first MTPJ were increased significantly; 3) the maximum strain (0.093 ± 0.023 vs. 0.075 ± 0.020, p < 0.001) and the maximum power (4.36 ± 1.51 W/kg vs. 3.06 ± 1.39 W/kg, p < 0.001) of the PF were increased significantly. Running with FFS may increase deformation, energy storage, and release of the MLA and PF, as well as the push-off effect of the MTPJ. Meanwhile, the maximum extension angle of the first MTPJ and MLA deformation increased in FFS, which showed that the PF experienced more stretch and potentially indicated that FFS enhanced the PF mechanical responses.

The Effect of Arch Stiffness on the Foot-Ankle Temporal Kinematics during Gait Termination: A Statistical Nonparametric Mapping Study

This study compares foot-ankle temporal kinematics characteristics during planned and unplanned gait termination (PGT and UGT) in subjects with different arch stiffnesses (ASs) based on the statistical nonparametric mapping (SnPM) method. By measuring three-dimensional arch morphological parameters under different loading conditions, 28 healthy male subjects were classified and participated in gait termination (GT) tests to collect metatarsophalangeal (MTP) and ankle-joint kinematics data. The two-way repeated-measures ANOVA using SnPM was employed to assess the impacts of AS on foot-ankle kinematics during PGT and UGT. Our results show that joint angles (MTP and ankle joints) were altered owing to AS and GT factors. The flexible arches hahadve periods of significantly greater MTP and ankle joint angles than those of stiff arches during the stance phase of GT, whereas subjects exhibited significantly smaller ankle and MTP joint angles during UGT. These results add additional insights into the morphological arch biomechanical function, and the comprehensive compensatory adjustment of lower-limb joints during gait stopping caused by unplanned stimulation.

Examining the Relationship between Pes Planus Degree, Balance and Jump Performances in Athletes

The foot absorbs shocks with its arches, muscles, ligaments and joints, and bodyweight transmission and it pushes the body forward during all movement patterns. Pes planus is more important in sports activities that include balance and sports performance, such as walking, running, jumping, or transferring weight to a single lower limb. This study, conducted with this information in mind, aims to examine the effects of pes planus deformity on balance and vertical jump performance. Fifty athletes were included in the study. The presence of pes planus was evaluated according to the Feiss line. Balance measurements were performed with a Balance System SD Biodex. Vertical jump performance was recorded using an Omegawave jumping mat. The relationship between the pes planus grades of the participants and their balance and jump performances was analyzed using the Spearman correlation method. Vertical jump and Limit of stability (LOS) was significantly correlated with pes planus.

Foot arch rigidity in walking: In vivo evidence for the contribution of metatarsophalangeal joint dorsiflexion

Human foot rigidity is thought to provide a more effective lever with which to push against the ground. Tension of the plantar aponeurosis (PA) with increased metatarsophalangeal (MTP) joint dorsiflexion (i.e., the windlass mechanism) has been credited with providing some of this rigidity. However, there is growing debate on whether MTP joint dorsiflexion indeed increases arch rigidity. Further, the arch can be made more rigid independent of additional MTP joint dorsiflexion (e.g., when walking with added mass). The purpose of the present study was therefore to compare the influence of increased MTP joint dorsiflexion with the influence of added mass on the quasi-stiffness of the midtarsal joint in walking. Participants walked with a rounded wedge under their toes to increase MTP joint dorsiflexion in the toe-wedge condition, and wore a weighted vest with 15% of their body mass in the added mass condition. Plantar aponeurosis behavior, foot joint energetics, and midtarsal joint quasi-stiffness were compared between conditions to analyze the mechanisms and effects of arch rigidity differences. Midtarsal joint quasi-stiffness was increased in the toe-wedge and added mass conditions compared with the control condition (both p < 0.001). In the toe-wedge condition, the time-series profiles of MTP joint dorsiflexion and PA strain and force were increased throughout mid-stance (p < 0.001). When walking with added mass, the time-series profile of force in the PA did not increase compared with the control condition although quasi-stiffness did, supporting previous evidence that the rigidity of the foot can be actively modulated. Finally, more mechanical power was absorbed (p = 0.006) and negative work was performed (p < 0.001) by structures distal to the rearfoot in the toe-wedge condition, a condition which displayed increased midtarsal joint quasi-stiffness. This indicates that a more rigid foot may not necessarily transfer power to the ground more efficiently.

Immunopathogenesis, early Detection, current therapies and prevention of plantar Fasciitis: A concise review

Plantar fasciitis or the inflammation of the fascial lining on the plantar aspect of the foot continues to be the leading cause of heel pain for many Americans. Common causes can range from anatomical deformities such as pes planus or flat foot, biomechanical etiology such as excessive pronation of the subtalar joint, or chronic diseases such as obesity and diabetes mellitus. The pathophysiology of plantar fasciitis can be either inflammatory due to vasodilation and immune system activation or non-inflammatory involving fibroblastic hypertrophy. Worsening pain of the inferior and medial heel after periods of prolonged rest and late in the day after hours of ambulation and weight-bearing activities is the most common symptom of plantar fasciitis. Common treatments for plantar fasciitis include plantar fascia stretching, physical therapy, orthotics, corticosteroid injections, and even surgery. Despite these treatment strategies, fasciitis remains a clinical problem and better treatment modalities are warranted. Late diagnosis is a common issue for prolonged and equivocal treatment and early diagnostic measures might be beneficial. In this concise review, we discussed the etiology, immunopathogenesis, current treatments of plantar fasciitis and potentially preventative measures prior to the onset of chronic treatment resistant condition.

Effects of Barefoot and Shod on the In Vivo Kinematics of Medial Longitudinal Arch During Running Based on a High-Speed Dual Fluoroscopic Imaging System

Shoes affect the biomechanical properties of the medial longitudinal arch (MLA) and further influence the foot’s overall function. Most previous studies on the MLA were based on traditional skin-marker motion capture, and the observation of real foot motion inside the shoes is difficult. Thus, the effect of shoe parameters on the natural MLA movement during running remains in question. Therefore, this study aimed to investigate the differences in the MLA’s kinematics between shod and barefoot running by using a high-speed dual fluoroscopic imaging system (DFIS). Fifteen healthy habitual rearfoot runners were recruited. All participants ran at a speed of 3 m/s ± 5% along with an elevated runway in barefoot and shod conditions. High-speed DFIS was used to acquire the radiographic images of MLA movements in the whole stance phase, and the kinematics of the MLA were calculated. Paired sample t-tests were used to compare the kinematic characteristics of the MLA during the stance phase between shod and barefoot conditions. Compared with barefoot, shoe-wearing showed significant changes (p < 0.05) as follows: 1) the first metatarsal moved with less lateral direction at 80%, less anterior translation at 20%, and less superiority at 10–70% of the stance phase; 2) the first metatarsal moved with less inversion amounting to 20–60%, less dorsiflexion at 0–10% of the stance phase; 3) the inversion/eversion range of motion (ROM) of the first metatarsal relative to calcaneus was reduced; 4) the MLA angles at 0–70% of the stance phase were reduced; 5) the maximum MLA angle and MLA angle ROM were reduced in the shod condition. Based on high-speed DFIS, the above results indicated that shoe-wearing limited the movement of MLA, especially reducing the MLA angles, suggesting that shoes restricted the compression and recoil of the MLA, which further affected the spring-like function of the MLA.

Contributions of Intrinsic and Extrinsic Foot Muscles during Functional Standing Postures

Purpose. Maintaining balance during static standing postures requires the coordination of many neuromuscular mechanisms. The role of the intrinsic and extrinsic foot muscles in this paradigm has yet to be clearly defined. The purpose of this study was to explore foot muscle activation during static phases on common weight-bearing tasks of varying loads and balance demands. Methods. Twenty healthy young adults performed 6 standing postures (single-limb and double-limb stand, squat, and heel raise) with one foot on a force plate. Muscle activity was recorded from the abductor hallucis, flexor hallucis longus and brevis, and tibialis posterior using intramuscular electrodes; surface electrodes were used to record activity from the peroneus longus and tibialis anterior. Two-way repeated measures ANOVA (2 loading conditions × 3 postures) were run to compare muscle activation and center of pressure velocity. Results. Intrinsic foot muscle activity increased as loading and postural demand increased; however, the specific effects varied for each of the extrinsic foot muscles. Conclusions. These results suggest that the intrinsic foot muscles play an important role in maintaining static balance. Strengthening intrinsic and extrinsic foot muscles may help increase stability in people who have weak toe flexors or who suffer from a variety of foot pathologies.

Effect of intrinsic foot muscles training on foot function and dynamic postural balance: A systematic review and meta-analysis

This systematic review aimed to analyse the effects of intrinsic foot muscle (IFM) training on foot function and dynamic postural balance. Keywords related to IFM training were used to search four databases (PubMed, CINAHL, SPORTDiscus and Web of Science databases.) for relevant studies published between January 2011 and February 2021. The methodological quality of the intervention studies was assessed independently by two reviewers by using the modified Downs and Black quality index. Publication bias was also assessed on the basis of funnel plots. This study was registered in PROSPERO (CRD42021232984). Sixteen studies met the inclusion criteria (10 with high quality and 6 with moderate quality). Numerous biomechanical variables were evaluated after IFM training intervention. These variables included IFM characteristics, medial longitudinal arch morphology and dynamic postural balance. This systematic review demonstrated that IFM training can exert positive biomechanical effects on the medial longitudinal arch, improve dynamic postural balance and act as an important training method for sports enthusiasts. Future studies should optimise standardised IFM training methods in accordance with the demands of different sports.

Determination of relationship between foot arch, hindfoot, and hallux motion using Oxford foot model: Comparison between walking and running

BACKGROUND

The foot arch plays an important role in propulsion and shock absorption during walking and running; however, the relationship among the foot arch, metatarsal locking theory, and nature of the windlass mechanism (WM) remain unclear.

RESEARCH QUESTION

What are the differences in the kinematic relationship between the foot arch, hindfoot, and hallux during walking and running?

METHODS

Relative angles within the foot were measured in 18 healthy men using the Oxford foot model (OFM). Data for barefoot walking at a comfortable speed and rearfoot running at 2.0 m/s were collected. Angles of the forefoot relative to the hindfoot (OFM-arch), hallux relative to the forefoot (Hallux) on the sagittal plane, and hindfoot relative to the shank (Hindfoot) on three anatomical planes were obtained. The medial longitudinal arch (MLA) angle was calculated to verify that OFM-arch can substitute the MLA angle. Each parameter was subjected to cross-correlation analysis and Wilcoxon signed-rank tests to examine the relationship with OFM-arch and compare them during walking and running.

RESULT

OFM-arch was similar to the conventional MLA projection angle in both trials (gait: 0.79, running: 0.96 p < 0.01). Synchronization of the OFM-arch and Hallux angles was higher in running than in walking (gait: -0.09, running: -0.75 p < 0.01). Hindfoot supination was unrelated to OFM-arch. Hindfoot angle on the transverse plane exhibited a moderate relationship with OFM-arch, indicating different correlations in walking and running (gait: 0.63, running: -0.68 p < 0.01).

SIGNIFICANCE

The elevation of the foot arch due to hallux dorsiflexion differed during walking and running; hence, other factors besides WM (such as intrinsic muscles) may affect the foot arch elevation during running. The hindfoot in the frontal plane does not contribute to arch raising and foot stability during running; it features different relationships with OFM-arch during walking and running.

Design of 3D printable prosthetic foot to implement nonlinear stiffness behavior of human toe joint based on finite element analysis

Toe joint is known as one of the critical factors in designing a prosthetic foot due to its nonlinear stiffness characteristic. This stiffness characteristic provides a general feeling of springiness in the toe-off and it also affects the ankle kinetics. In this study, the toe part of the prosthetic foot was designed to improve walking performance. The toe joint was implemented as a single part suitable for 3D printing. The various shape factors such as curved shape, bending space, auxetic structure, and bending zone were applied to mimic human foot characteristics. The finite element analysis (FEA) was conducted to simulate terminal stance (from heel-off to toe-off) using the designed prosthetic foot. To find the structure with characteristics similar to the human foot, the optimization was performed based on the toe joint geometries. As a result, the optimized foot showed good agreement with human foot behavior in the toe torque-angle curve. Finally, the simulation conditions were validated by comparing with human walking data and it was confirmed that the designed prosthetic foot structure can implement the human foot function.

Daily activity in minimal footwear increases foot strength

The human foot is uniquely adapted to bipedal locomotion and has a deformable arch of variable stiffness. Intrinsic foot muscles regulate arch deformation, making them important for foot function. In this study we explore the hypothesis that normal daily activity in minimal footwear, which provides little or no support, increases foot muscle strength. Western adults wore minimal footwear for a six-month period (the “intervention” group). Foot strength, i.e., maximum isometric plantarflexion strength at the metatarsophalangeal joints, and foot biometrics were measured before and after the intervention. An additional group was investigated to add further insight on the long-term effects of footwear, consisting of Western adults with an average 2.5 years of experience in minimal footwear (the “experienced” group). This study shows that foot strength increases by, on average, 57.4% (p < 0.001) after six months of daily activity in minimal footwear. The experienced group had similar foot strength as the post intervention group, suggesting that six months of regular minimal footwear use is sufficient to gain full strength, which may aid healthy balance and gait.

Alligators employ intermetatarsal reconfiguration to modulate plantigrade ground contact

Feet must mediate substrate interactions across an animal's entire range of limb poses used in life. Metatarsals, the ‘bones of the sole’, are the dominant pedal skeletal elements for most tetrapods. In plantigrade species that walk on the entirety of their sole, such as living crocodylians, intermetatarsal mobility offers the potential for a continuum of reconfiguration within the foot itself. Alligator hindlimbs are capable of postural extremes from a belly sprawl to a high walk to sharp turns – how does the foot morphology dynamically accommodate these diverse demands? We implemented a hybrid combination of marker-based and markerless X-ray reconstruction of moving morphology (XROMM) to measure 3D metatarsal kinematics in three juvenile American alligators (Alligator mississippiensis) across their locomotor and maneuvering repertoire on a motorized treadmill and flat-surfaced arena. We found that alligators adaptively conformed their metatarsals to the ground, maintaining plantigrade contact throughout a spectrum of limb placements with non-planar feet. Deformation of the metatarsus as a whole occurred through variable abduction (twofold range of spread) and differential metatarsal pitching (45 deg arc of skew). Internally, metatarsals also underwent up to 65 deg of long-axis rotation. Such reorientation, which correlated with skew, was constrained by the overlapping arrangement of the obliquely expanded metatarsal bases. Such a proximally overlapping metatarsal morphology is shared by fossil archosaurs and archosaur relatives. In these extinct taxa, we suggest that intermetatarsal mobility likely played a significant role in maintaining ground contact across plantigrade postural extremes.

Summary: We measured 3D metatarsal kinematics in American alligators. Alligator metatarsals conform with the ground across a diversity of high walk and maneuvering postures, providing a context for interpreting the evolutionary history of metatarsals in the fossil record.

Speed-Related Energy Flow and Joint Function Change During Human Walking

During human walking, mechanical energy transfers between segments via joints. Joint mechanics of the human body are coordinated with each other to adapt to speed change. The aim of this study is to analyze the functional behaviors of major joints during walking, and how joints and segments alter walking speed during different periods (collision, rebound, preload, and push-off) of stance phase. In this study, gait experiment was performed with three different self-selected speeds. Mechanical works of joints and segments were determined with collected data. Joint function indices were calculated based on net joint work. The results show that the primary functional behaviors of joints would not change with altering walking speed, but the function indices might be changed slightly (e.g., strut functions decrease with increasing walking speed). Waist acts as strut during stance phase and contributes to keep stability during collision when walking faster. Knee of stance leg does not contribute to altering walking speed. Hip and ankle absorb more mechanical energy to buffer the strike during collision with increasing walking speed. What is more, hip and ankle generate more energy during push-off with greater motion to push distal segments forward with increasing walking speed. Ankle also produces more mechanical energy during push-off to compensate the increased heel-strike collision of contralateral leg during faster walking. Thus, human may utilize the cooperation of hip and ankle during collision and push-off to alter walking speed. These findings indicate that speed change in walking leads to fundamental changes to joint mechanics.

Foot anatomy, walking energetics, and the evolution of human bipedalism

Interspecies differences in locomotor efficiency have been extensively researched, but within-species variation in the metabolic cost of walking and its underlying causes have received much less attention. This is somewhat surprising given the importance of walking energetics to natural selection, and the fact that the mechanical efficiency of striding bipedalism in modern humans is thought to be related in some part to the unique morphology of the human foot. Previous studies of human running have linked specific anatomical traits in the foot to variations in locomotor energetics to provide insight into form-function relationships in human evolution. However, such studies are relatively rare, particularly for walking. In this study, relationships between a range of functional musculoskeletal traits in the human lower limb and the energetics of walking over compliant and noncompliant substrates are examined, with particular focus on the lower limb and foot. Twenty-nine young, healthy individuals walked across three surfaces-a noncompliant laboratory floor, and compliant 6 cm and 13 cm thick foams-at self-selected speeds while oxygen consumption was measured, from which the metabolic cost of transport was calculated. Lower limb lengths, calcaneus lengths, foot shape indices, and maximum isometric plantarflexion torques were also measured and subsequently tested for relationships with metabolic cost over these surfaces using linear regression. It was found that metabolic cost varied considerably between individuals within and across substrate types, but this variation was not statistically related to or explained by variations in musculoskeletal parameters considered to be adaptively important to efficient bipedal locomotion. This therefore provides no supportive evidence that variations in these gross anatomical parameters confer significant advantages to the efficiency of walking, and therefore suggest caution in the use of similar metrics to infer differences in walking energetics in closely related fossil species.

Intrinsic foot muscle hardness is related to dynamic postural stability after landing in healthy young men

BACKGROUND

The human foot has competent mechanisms for supporting weight and adapting movement to various surfaces; in particular, the toe flexor muscles aid in supporting the foot arches and may be important contributors to postural stability. However, the role of intrinsic foot muscle morphology and structure in the postural control system remains unclear, and the relationship between them is not well known.

RESEARCH QUESTION

Are intrinsic foot muscle morphology and toe flexor strength related to static and dynamic postural stability in healthy young men?.

METHODS

A total of 27 healthy men aged 19-27 years participated in this study. intrinsic foot muscle morphology included muscle hardness and thickness. Cross-sectional area was measured by ultrasonography at an ankle dorsiflexion angle of 0°. The hardness of the abductor hallucis (AbH), flexor hallucis brevis, and flexor digitorum brevis (FDB) muscles was measured using ultrasound real-time tissue elastography. Static postural stability during single-leg standing on a single force platform with closed eyes was assessed for the right leg. In the assessment of dynamic postural stability, the subjects jumped and landed on single-leg onto a force platform and the dynamic postural stability index (DPSI) was measured.

RESULTS

FDB muscle thickness showed a positive correlation with anteroposterior stability index (APSI) (r = 0.398, p = 0.040). AbH muscle hardness was negatively correlated with APSI (r = -0.407, p = 0.035); whereas FDB muscle hardness was positively correlated with DPSI (r = 0.534, p = 0.004), vertical stability index (r = 0.545, p = 0.003), and maximum vertical ground reaction force (r = 0.447, p = 0.020). Multiple regression with forced entry revealed that only DPSI was significantly correlated with FDB muscle hardness (p = 0.003).

SIGNIFICANCE

The results indicated that intrinsic foot muscle hardness plays an important role in dynamic postural control among healthy young men, which may enable a more rapid muscular response to changes in condition during jump landing and better performance in balance tasks.

The extensibility of the plantar fascia influences the windlass mechanism during human running

The arch of the human foot is unique among hominins as it is compliant at ground contact but sufficiently stiff to enable push-off. These behaviours are partly facilitated by the ligamentous plantar fascia whose role is central to two mechanisms. The ideal windlass mechanism assumes that the plantar fascia has a nearly constant length to directly couple toe dorsiflexion with a change in arch shape. However, the plantar fascia also stretches and then shortens throughout gait as the arch-spring stores and releases elastic energy. We aimed to understand how the extensible plantar fascia could behave as an ideal windlass when it has been shown to strain throughout gait, potentially compromising the one-to-one coupling between toe arc length and arch length. We measured foot bone motion and plantar fascia elongation using high-speed X-ray during running. We discovered that toe plantarflexion delays plantar fascia stretching at foot strike, which probably modifies the distribution of the load through other arch tissues. Through a pure windlass effect in propulsion, a quasi-isometric plantar fascia's shortening is delayed to later in stance. The plantar fascia then shortens concurrently to the windlass mechanism, likely enhancing arch recoil at push-off.

The human foot functions like a spring of adjustable stiffness during running

Like other animals, humans use their legs like springs to save energy during running. One potential contributor to leg stiffness in humans is the longitudinal arch (LA) of the foot. Studies of cadaveric feet have demonstrated that the LA can function like a spring, but it is unknown whether humans can adjust LA stiffness in coordination with more proximal joints to help control leg stiffness during running. Here, we used 3D motion capture to record 27 adult participants running on a forceplate-instrumented treadmill, and calculated LA stiffness using beam bending and midfoot kinematics models of the foot. Because changing stride frequency causes humans to adjust overall leg stiffness, we had participants run at their preferred frequency and frequencies 35% above and 20% below preferred frequency to test for similar adjustments in the LA. Regardless of which foot model we used, we found that participants increased LA quasi-stiffness significantly between low and high frequency runs, mirroring changes at the ankle, knee and leg overall. However, among foot models, we found that the model incorporating triceps surae force into bending force on the foot produced unrealistically high LA work estimates, leading us to discourage this modeling approach. Additionally, we found that there was not a consistent correlation between LA height and quasi-stiffness values among the participants, indicating that static LA height measurements are not good predictors of dynamic function. Overall, our findings support the hypothesis that humans dynamically adjust LA stiffness during running in concert with other structures of the leg.

Effect of the upward curvature of toe springs on walking biomechanics in humans

Although most features of modern footwear have been intensively studied, there has been almost no research on the effects of toe springs. This nearly ubiquitous upward curvature of the sole at the front of the shoe elevates the toe box dorsally above the ground and thereby holds the toes in a constantly dorsiflexed position. While it is generally recognized that toe springs facilitate the forefoot’s ability to roll forward at the end of stance, toe springs may also have some effect on natural foot function. This study investigated the effects of toe springs on foot biomechanics in a controlled experiment in which participants walked in specially-designed sandals with varying curvature in the toe region to simulate toe springs ranging from 10 to 40 degrees of curvature. Using inverse dynamics techniques, we found that toe springs alter the joint moments and work at the toes such that greater degrees of toe spring curvature resulted in lower work requirements during walking. Our results help explain why toe springs have been a pervasive feature in shoes for centuries but also suggest that toe springs may contribute to weakening of the foot muscles and possibly to increased susceptibility to common pathological conditions such as plantar fasciitis.

Posteromedial Release versus Ponseti Treatment of Congenital Idiopathic Clubfoot: A Long-Term Retrospective Follow-Up Study into Adolescence

Purpose

Although many short-term studies have shown the superiority of Ponseti treatment to surgical treatment, studies with long-term follow-up of patients into adolescence are lacking. The aim of this study was to compare the morphological, functional and radiological results of the two methods into and during adolescent age, when both soft tissue and bony procedures can be performed to correct residual deformities.

Patients and Methods

We retrospectively evaluated two groups of patients diagnosed with congenital idiopathic clubfoot and treated with either the Ponseti method (34 clubfeet) and surgery in the form of posteromedial release (31 clubfeet). All included clubfeet were clinically fully corrected after initial treatment and final plaster removal. Evaluation was performed with the International Clubfoot Study Group (ICFSG) score.

Results

The age at follow-up was 12.8±1.6 years in the Ponseti group and 13.5±1.7 years in the surgical group. Excellent or good results were obtained in 26 feet (76%) of the Ponseti group and in 14 feet (45%) in the surgical group. The Ponseti treatment was significantly superior to posteromedial release in terms of the final score (10.58±6.49 versus 17.26±8.83, p<0.001), functional score (p<0.001) and radiological score (p<0.001). Residual deformities were clinically present in both groups but were less frequent and less severe in Ponseti-treated patients. Flat-top talus was found to be present in both groups, but the Ponseti method was more protective than surgical treatment against this outcome (relative risk=0.494, p=0.002). The overall foot and ankle mobility was significantly better in the Ponseti group (p<0.001).

Conclusion

The Ponseti method was superior to surgery for treatment of clubfoot and achieved better long-term morphological, functional and radiological results. It preserves better mobility of the foot and ankle, and results in less frequent and less severe residual deformities than surgical treatment.

Foot stiffening during the push-off phase of human walking is linked to active muscle contraction, and not the windlass mechanism

The rigidity of the human foot is often described as a feature of our evolution for upright walking and is bolstered by a thick plantar aponeurosis that connects the heel to the toes. Previous descriptions of human foot function consider stretch of the plantar aponeurosis via toe extension (windlass mechanism) to stiffen the foot as it is levered against the ground for push-off during walking. In this study, we applied controlled loading to human feet in vivo, and studied foot function during the push-off phase of walking, with the aim of carefully testing how the foot is tensioned during contact with the ground. Both experimental paradigms revealed that plantar aponeurosis strain via the 'windlass mechanism' could not explain the tensioning and stiffening of the foot that is observed with increased foot-ground contact forces and push-off effort. Instead, electromyographic recordings suggested that active contractions of ankle plantar flexors provide the source of tension in the plantar aponeurosis. Furthermore, plantar intrinsic foot muscles were also contributing to the developed tension along the plantar aspect of the foot. We conclude that active muscular contraction, not the passive windlass mechanism, is the foot's primary source of rigidity for push-off against the ground during bipedal walking.

Walking with added mass magnifies salient features of human foot energetics

The human foot serves numerous functional roles during walking, including shock absorption and energy return. Here, we investigated walking with added mass to determine how the foot would alter its mechanical work production in response to a greater force demand. Twenty-one healthy young adults walked with varying levels of added body mass: 0%, +15% and +30% (relative to their body mass). We quantified mechanical work performed by the foot using a unified deformable segment analysis and a multi-segment foot model. We found that walking with added mass tended to magnify certain features of the foot's functions. Magnitudes of both positive and negative mechanical work, during stance in the foot, increased when walking with added mass. Yet, the foot preserved similar amounts of net negative work, indicating that the foot dissipates energy overall. Furthermore, walking with added mass increased the foot's negative work during early stance phase, highlighting the foot's role as a shock-absorber. During mid to late stance, the foot produced greater positive work when walking with added mass, which coincided with greater work from the structures spanning the midtarsal joint (i.e. arch). While this study captured the overall behavior of the foot when walking with varying force demands, future studies are needed to further determine the relative contribution of active muscles and elastic tissues to the foot's overall energy.

The shape of the transverse arch in high heels while standing

Introduction

High heeled shoes have long been worn in society and they are known to cause biomechanical imbalances to not only the foot, but the whole musculoskeletal system. This study aims to show the detailed changes that happen to the shape of the transverse arch of the foot in high heels, using two different inclination degrees.

Methods

68 women participated in this study. Two custom-made high heels were made with inclinations of 15 degrees and 30 degrees (cm). A weight-bearing ultrasound was used to assess the coronal view of the transverse arch in standing. ANOVA and Tuckey tests were used to compare the results between 0 degrees, 15 degrees and 30 degrees inclinations.

Results

The transverse arch height was slightly increased as the heel height increased (0DI-15DI: p = 0.5852 / 15DI-30DI: p = 0.395 / 0DI-30DI: p = 0.0593). The transverse arch length (0DI-15DI: p = 0.0486 / 15DI-30DI: p = 0.0004 / 0DI-30DI: p = 0.1105) and the area under the metatarsal heads (0DI-15DI: p = 0.0422 / 15DI-30DI: p = 0.0180 / 0DI-30DI: p = 0.9463) significantly decreased as the heel height increased.

Discussion

The main changes were viewed in the 30 degrees inclinations compared to 0 degrees inclination. When the toes are dorsiflexed in high heels, it stimulates the Windlass mechanism which in turn stiffens the plantar fascia and adducts the metatarsal heads, while the soft tissues shrink in response to loads.

Conclusion

High heels affected the shape of the transverse arch even in short term standing, and these effects increased as the height of the heel increased.

Effects of Novel Inverted Rocker Orthoses for First Metatarsophalangeal Joint on Gastrocnemius Muscle Electromyographic Activity during Running: A Cross-Sectional Pilot Study

BACKGROUND

The mobility of the first metatarsophalangeal joint (I MPTJ) has been related to the proper windlass mechanism and the triceps surae during the heel-off phase of running gait; the orthopedic treatment of the I MPTJ restriction has been made with typical Morton extension orthoses (TMEO). Nowadays it is unclear what effects TMEO or the novel inverted rocker orthoses (NIRO) have on the EMG activity of triceps surae during running.

OBJECTIVE

To compare the TMEO effects versus NIRO on EMG triceps surae on medialis and lateralis gastrocnemius activity during running.

STUDY DESIGN

A cross-sectional pilot study.

METHODS

21 healthy, recreational runners were enrolled in the present research (mean age 31.41 ± 4.33) to run on a treadmill at 9 km/h using aleatory NIRO of 6 mm, NIRO of 8 mm, TMEO of 6 mm, TMEO of 8 mm, and sports shoes only (SO), while the muscular EMG of medial and lateral gastrocnemius activity during 30 s was recorded. Statistical intraclass correlation coefficient (ICC) to test reliability was calculated and the Wilcoxon test of all five different situations were tested.

RESULTS

The reliability of values was almost perfect. Data showed that the gastrocnemius lateralis increased its EMG activity between SO vs. NIRO-8 mm (22.27 ± 2.51 vs. 25.96 ± 4.68 mV, p < 0.05) and SO vs. TMEO-6mm (22.27 ± 2.51 vs. 24.72 ± 5.08 mV, p < 0.05). Regarding gastrocnemius medialis, values showed an EMG notable increase in activity between SO vs. NIRO-6mm (22.93 ± 2.1 vs. 26.44 ± 3.63, p < 0.001), vs. NIRO-8mm (28.89 ± 3.6, p < 0.001), and vs. TMEO-6mm (25.12 ± 3.51, p < 0.05).

CONCLUSIONS

Both TMEO and NIRO have shown an increased EMG of the lateralis and medialis gastrocnemius muscles activity during a full running cycle gait. Clinicians should take into account the present evidence when they want to treat I MTPJ restriction with orthoses, and consider the inherent triceps surae muscular cost relative to running economy.

The Effects of Increased Midsole Bending Stiffness of Sport Shoes on Muscle-Tendon Unit Shortening and Shortening Velocity: a Randomised Crossover Trial in Recreational Male Runners

BACKGROUND

Individual compliances of the foot-shoe interface have been suggested to store and release elastic strain energy via ligamentous and tendinous structures or by increased midsole bending stiffness (MBS), compression stiffness, and resilience of running shoes. It is unknown, however, how these compliances interact with each other when the MBS of a running shoe is increased. The purpose of this study was to investigate how structures of the foot-shoe interface are influenced during running by changes to the MBS of sport shoes.

METHODS

A randomised crossover trial was performed, where 13 male, recreational runners ran on an instrumented treadmill at 3.5 m·s-1 while motion capture was used to estimate foot arch, plantar muscle-tendon unit (pMTU), and shank muscle-tendon unit (sMTU) behaviour in two conditions: (1) control shoe and (2) the same shoe with carbon fibre plates inserted to increase the MBS.

RESULTS

Running in a shoe with increased MBS resulted in less deformation of the arch (mean ± SD; stiff, 7.26 ± 1.78°; control, 8.84 ± 2.87°; p ≤ 0.05), reduced pMTU shortening (stiff, 4.39 ± 1.59 mm; control, 6.46 ± 1.42 mm; p ≤ 0.01), and lower shortening velocities of the pMTU (stiff, - 0.21 ± 0.03 m·s-1; control, - 0.30 ± 0.05 m·s-1; p ≤ 0.01) and sMTU (stiff, - 0.35 ± 0.08 m·s-1; control, - 0.45 ± 0.11 m·s-1; p ≤ 0.001) compared to a control condition. The positive and net work performed at the arch and pMTU, and the net work at the sMTU were significantly lower in the stiff compared to the control condition.

CONCLUSION

The findings of this study showed that if a compliance of the foot-shoe interface is altered during running (e.g. by increasing the MBS of a shoe), the mechanics of other structures change as well. This could potentially affect long-distance running performance.

Anatomy of the Lateral Plantar Ligaments of the Transverse Metatarsal Arch

BACKGROUND

While the anatomy of the Lisfranc complex is well understood, the lateral tarsometatarsal ligamentous structures, in contrast, are less well studied. Our aim in this study was to identify an anatomical explanation as to why the second to fifth metatarsals function as a unit in homolateral and divergent midfoot injuries.

METHODS

Eleven cadaveric lower limbs, preserved in formaldehyde, were examined at the University of Liverpool Human Anatomy and Resource Centre. Each of the lower limbs was dissected to identify the plantar aspect of the transverse metatarsal arch.

RESULTS

On removal of the long plantar ligament, the peroneal longus tendon was visible, as was its insertion onto the first metatarsal base. A lateral Lisfranc ligament (which was a transverse suspensory metatarsal ligament) spanned between the bases of the second and fifth metatarsals in all specimens with an average length of 33.7 mm and width of 4.6 mm. This ligament has not previously been described. It was noted that in all specimens, the long plantar ligament blended with the lateral Lisfranc ligament. In addition to the lateral Lisfranc ligament, separate intermetatarsal ligaments were identifiable connecting each metatarsal. The long plantar ligament provided a connection through the lateral Lisfranc ligament connecting the transverse and longitudinal arches of the foot.

CONCLUSION

We found a plantar ligament that provided connection through the long plantar ligament of both the transverse and the longitudinal arches. It spanned from the second to the fifth metatarsal, which we believe may explain that in some cases, lateral instability can be overcome when the middle column is stabilized.

CLINICAL RELEVANCE

We suspect that in the majority of homolateral and divergent types of tarsometatarsal injuries that the lateral Lisfranc ligament remains intact and thus it has significant clinical ramifications.

Ankle and midtarsal joint quasi-stiffness during walking with added mass

Examination of how the ankle and midtarsal joints modulate stiffness in response to increased force demand will aid understanding of overall limb function and inform the development of bio-inspired assistive and robotic devices. The purpose of this study is to identify how ankle and midtarsal joint quasi-stiffness are affected by added body mass during over-ground walking. Healthy participants walked barefoot over-ground at 1.25 m/s wearing a weighted vest with 0%, 15% and 30% additional body mass. The effect of added mass was investigated on ankle and midtarsal joint range of motion (ROM), peak moment and quasi-stiffness. Joint quasi-stiffness was broken into two phases, dorsiflexion (DF) and plantarflexion (PF), representing approximately linear regions of their moment-angle curve. Added mass significantly increased ankle joint quasi-stiffness in DF (p < 0.001) and PF (p < 0.001), as well as midtarsal joint quasi-stiffness in DF (p < 0.006) and PF (p < 0.001). Notably, the midtarsal joint quasi-stiffness during DF was ~2.5 times higher than that of the ankle joint. The increase in midtarsal quasi-stiffness when walking with added mass could not be explained by the windlass mechanism, as the ROM of the metatarsophalangeal joints was not correlated with midtarsal joint quasi-stiffness (r = -0.142, p = 0.540). The likely source for the quasi-stiffness modulation may be from active foot muscles, however, future research is needed to confirm which anatomical structures (passive or active) contribute to the overall joint quasi-stiffness across locomotor tasks.

Number of Segments Within Musculoskeletal Foot Models Influences Ankle Kinematics and Strains of Ligaments and Muscles

Multi-segment foot models (MFMs) are becoming a common tool in musculoskeletal research on the ankle-foot complex. The purpose of this study was to compare ankle joint kinematics as well as ligament and muscle strains that result from MFM with a different number of segments during vertical hopping. Ten participants were recruited and performed double-limb vertical hops. Marker positions and ground reaction forces were collected. Two-segment (2MFM), three-segment (3MFM), and five-segment MFM (5MFM) were used to calculate ankle kinematics and the strains of the anterior talofibular and calcaneofibular ligaments and of the soleus and gastrocnemius muscles. Ranges of motion and peak strains were analyzed with Kruskal-Wallis and post hoc tests, whereas the time-series of the ankle kinematics and ligament and muscle strains were analyzed with statistical parametric mapping. There were significant main effects for MFM in the talocrural joint range of motion and peak strains of ligaments and muscles. In addition, there were significant main effects for MFM in time-series data of the talocrural joint angle as well as for ligament and muscle strains. In all cases, the post hoc analyses showed that the 2MFM consistently overestimated the range of motion and tissue strains compared to the 3MFM and 5MFM, while 3MFM and 5MFM did not differ from each other in the most variables. This study showed that the number of segments in MFM significantly affects the biomechanical estimates of joint kinematics and tissue strains during hopping. Clinical significance: MFM that combine all foot structures beyond the talus into one segment likely overestimate ankle joint biomechanics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2231-2240, 2019.