Mechanics of locomotion of dogs (Canis familiaris) and sheep (Ovis aries)

Records have been made of the forces exerted on the ground by dogs and a sheep, in walking, trotting, cantering and slow galloping. Film has been taken simultaneously. The difference between walking and trotting was much less marked for the sheep than for the dogs.
Step length and stride length increase as speed increases. They are expressed as functions of the Froude number.
The vertical component of the force exerted by a foot on the ground shows two main maxima in walking, except in the case of the fore feet of sheep. In this case and in other gaits there is only one main maximum. The vertical movements of the fore and hind quarters which occurred in examples of each gait have been calculated from the force records.
The force exerted by a foot on the ground changes direction in the course of a step so as to remain more or less in line with a point fixed relative to the animal, but dorsal to its back.
The force records show impact disturbances in the first 003 sec of contact of each foot with the ground.
The point of application of the force on the sole of a foot tends to move posteriorly as the force increases.
The results are discussed in relation to a theoretical account of the mechanics of locomotion on legs.     

Asymmetric interlimb role-sharing in mechanical power during human sideways locomotion

Sideways movement at a wide variety of speeds is required in daily life and sports. The purpose of this study was to identify the characteristics of asymmetry in power output between lower limbs during sideways gait patterns. Seven healthy men performed steady-state sideways locomotion at various speeds. The mechanical external power of each limb was calculated and decomposed to the lateral and vertical components by the center of mass velocity and ground reaction force. We acquired data from 126 steps of sideways walking at 0.44–1.21 m/s, and from 41 steps of sideways galloping at 1.04–3.00 m/s. The results showed asymmetric power production between the limbs during sideways locomotion. During sideways walking, the trailing limb predominantly produced positive external power and the leading limb produced predominantly negative external power, and these amplitudes increased with step speed. In contrast, during sideways galloping, negative and subsequent positive power production was observed in both limbs. These differences in asymmetric interlimb role-sharing were mainly due to the vertical component. During sideways galloping, the trailing limb absorbs vertical power produced by the leading limb due to the longer flight time. This characteristic of vertical power production in the trailing limb may explain the presence of a double-support phase, which is not observed during forward running, even at high speeds. Our results will help to elucidate the asymmetric movements of the limbs in lateral directions at various speeds.     

Walk-, run- and gallop-like gait patterns in human sideways locomotion

The purpose of this study is to examine the characteristics of gait patterns in human preferred sideways locomotion at increasing speeds. Fifteen healthy young males were asked to step sideways on a treadmill at various speeds of 1.3–6.1 km/h. The times of foot contact and take-off were analyzed. Three gait patterns were observed. At slow speeds, all of the subjects performed a walk-like pattern. When the treadmill speed exceeded approximately 3.5 km/h, the subjects preferred gait patterns with a flight phase. Most of the subjects performed an asymmetric gait pattern that was similar to a forward gallop, whereas only two out of fifteen subjects performed a run-like gait pattern. Because the left and right legs are positioned along the movement direction, it might be more efficient to divide roles between the leading and trailing limbs at high speeds: the leading limb functions to produces breaking and vertical force, and the trailing limb mainly absorbs the impact of foot contact and generates propulsive forces.     

Laterality in the gallop gait of horses

Bilateral asymmetry in gallop stride limb contact patterns of four Quarter Horse fillies was documented by high-speed cinematography. Horses were filmed with rider by two cameras simultaneously while galloping along a straightaway. Even though signaled for each gallop lead an equivalent number of times, horses frequently switched leads, selecting the left lead nearly twice as often as the right. Velocities and stride lengths were greater for the left lead than the right, but stride frequencies did not differ between leads. Velocity effects were partitioned out in limb contact data analysis to enable the determination of persistent gallop stride asymmetries. The contact duration for the trailing (right) fore limb on the left lead exceeded the contact duration for the trailing (left) fore limb on the right lead. Selecting the right fore limb as the trailing fore limb may have allowed horses to use it to withstand the greater stresses and caused them to preferentially gallop with the left fore limb leading. Laterality may have an important influence on equine gallop motion patterns and thereby influence athletic performance.     

Elastic properties of the feet of deer (Cervidae)

Dynamic tests have been performed on the feet of deer, and on tendons removed from the feet, to determine their elastic properties. The results have been used to calculate the strain energy stored in each foot while it is on the ground in a fast galloping stride. This is compared with an estimate of the work done by the leg, and the energy-saving rle of tendon elasticity is assessed.     

Measured and estimated ground reaction forces for multi-segment foot models

Accurate measurement of ground reaction forces under discrete areas of the foot is important in the development of more advanced foot models, which can improve our understanding of foot and ankle function. To overcome current equipment limitations, a few investigators have proposed combining a pressure mat with a single force platform and using a proportionality assumption to estimate subarea shear forces and free moments. In this study, two adjacent force platforms were used to evaluate the accuracy of the proportionality assumption on a three segment foot model during normal gait. Seventeen right feet were tested using a targeted walking approach, isolating two separate joints: transverse tarsal and metatarsophalangeal. Root mean square (RMS) errors in shear forces up to 6% body weight (BW) were found using the proportionality assumption, with the highest errors (peak absolute errors up to 12% BW) occurring between the forefoot and toes in terminal stance. The hallux exerted a small braking force in opposition to the propulsive force of the forefoot, which was unaccounted for by the proportionality assumption. While the assumption may be suitable for specific applications (e.g. gait analysis models), it is important to understand that some information on foot function can be lost. The results help highlight possible limitations of the assumption. Measured ensemble average subarea shear forces during normal gait are also presented for the first time.     

A study of the viability of obtaining a generic animation of the foot while walking for the virtual testing of footwear using dorsal pressures

Establishing the appropriate pressure exerted by the shoe upper over the foot surface is fundamental for the design of specific footwear, although measuring the dorsal pressures can also provide important additional information. In previous works, a virtual simulator to perform studies of comfort and functionality in CAD footwear design was presented. This paper describes the procedure carried out to obtain the foot animations used in this simulator. The virtual feet used in the simulator are feet without a standard form scanned in a static way. Their movements are rebuilt from the register of movements of several foot anatomical points during a complete step. The dorsal pressures exerted by some shoe uppers on these anatomical points were measured for several subjects and used to establish the viability of the use of these animations in a virtual simulator for footwear.     

Force platform for rats measures fore and hind forces concurrently

Animal models are commonly used to test the efficacy of impact loading regimens on bone strength. We designed an inexpensive force platform to concurrently measure the separate peak vertical impact forces produced by the fore and hindfeet of immature F-344 rats when dropped onto the platform. The force platform consisted of three load cells placed in a triangular pattern under a flat plate. Rats were dropped from heights of 30, 45 and 60 cm onto the platform so that they landed on all four feet concurrently. The peak vertical impact forces produced by the feet of the rats were measured using a sampling frequency of 100 kHz. The location of each foot at landing relative to the load cells, and the force received by each load cell were combined in a series of static equations to solve for the vertical impact forces produced by the fore and hindfeet. The forces produced by feet when rats stood on the single platform were similarly determined. The forces exerted separately by the fore and hindfeet of young rats when landing on the plate as a ratio to standing forces were then calculated. Rats when standing bore more weight on their hindfeet but landed with more weight on their forefeet, which provides rationale for the greater response to landing forces of bones in the forelimbs than those in the hindlimbs. This system provided a useful method to simultaneously measure peak vertical impact forces in fore and hindfeet in rats.     

The gaits of chelonians: walking techniques for very low speeds

The gaits of three species of chelonians have been studied by filming and by recording the forces the feet exert on the ground. Chelonians could keep their bodies in equilibrium if they walked so as to have at least three feet on the ground at all times, and if the feet moved in appropriate sequence. However, they generally use a gait in which there are at times only two feet on the ground, and they do not maintain equilibrium, but pitch and roll through angular ranges of around 10°. Maintenance of equilibrium would require the feet to exert abruptly changing forces, which they are probably not capable of doing because of the slowness of chelonian muscle. Records of the forces exerted by the feet do not show abrupt changes. It is shown by mathematical modelling that if only slow changes of force are possible, the gaits and force patterns which chelonians use are close to the optimum which minimizes pitching and rolling. Gaits only a little different would be impracticable at low speeds because of excessive pitching and/or rolling. Slow muscle may be more efficient than fast muscle, and can maintain tension more economically.     

Analysis of the human and ape foot during bipedal standing with implications for the evolution of the foot

The ratio of the power arm (the distance from the heel to the talocrural joint) to the load arm (that from the talocrural joint to the distal head of the metatarsals), or RPL, differs markedly between the human and ape foot. The arches are relatively higher in the human foot in comparison with those in apes. This study evaluates the effect of these two differences on biomechanical effectiveness during bipedal standing, estimating the forces acting across the talocrural and tarsometatarsal joints, and attempts to identify which type of foot is optimal for bipedal standing. A simple model of the foot musculoskeletal system was built to represent the geometric and force relationships in the foot during bipedal standing, and measurements for a variety of human and ape feet applied. The results show that: (1) an RPL of around 40% (as is the case in the human foot) minimizes required muscle force at the talocrural joint; (2) the presence of an high arch in the human foot reduces forces in the plantar musculature and aponeurosis; and (3) the human foot has a lower total of force in joints and muscles than do the ape feet. These results indicate that the proportions of the human foot, and the height of the medial arch are indeed better optimized for bipedal standing than those of apes, further suggesting that their current state is to some extent the product of positive selection for enhanced bipedal standing during the evolution of the foot.     

Postural control in healthy young adults using a double seesaw device

Postural control on single and double seesaws was investigated in young healthy adults required to stand as still as possible on two side-by-side seesaws favoring pitch motion and lying on two separate force platforms. The device offers the possibility to get associated or dissociated seesaws and, if dissociated, to induce asymmetric patterns for the centers-of-pressure (CP) under both left and right feet by using different radii for the two seesaws. Substituting a parallelepiped volume to one seesaw offering a firm contact to one foot is also possible. The results indicated that dissociating the two seesaws led to increased resultant CP (CP_Res) and vertically projected center-of-gravity movements (CG_v) only along the mediolateral axis, whereas a slight decreasing tendency characterized these movements along the antero-posterior axis. When standing on two independent seesaws with different radii, significantly larger CP displacements were seen along the antero-posterior axis under the foot lying on the more stable support, i.e., the seesaw with the longer radius or the parallelepiped volume. In these two asymmetrical conditions, the CP_Res output results from a compensatory mechanism, i.e. larger movements under one foot to compensate for the decreased movements occurring under the opposite foot. This postural control strategy is aimed at allowing sufficient CP_Res displacements in order to appropriately secure balance. Because of the complex sensorimotor coordination induced, involving differentially in certain cases both legs, the double seesaw device can be viewed as a possible tool for challenging postural control by inducing asymmetrical patterns between left and right feet CP movements.     

Method of healing diabetic forefoot ulcers.

Six diabetic patients with neuropathic ulceration of the sole of the foot (seven feet, eight ulcers) were treated by the application of a below knee walking plaster with a rubber rocker. All the ulcers healed with this treatment, greatly reducing the usual period of hospital inpatient stay. After healing, study of the forces acting on the sole of the foot showed that these ulcers occur at the site of maximal horizontal shear force and confirmed that they occur at the site of maximal vertical force. This treatment is highly effective for neuropathic ulcers of the sole not affecting bone or complicated by deep sepsis. There may be a high rate of recurrence, however, reflecting inadequacy of methods of protecting damaged neuropathic feet.     

Drag-Based ‘Hovering’ in Ducks: The Hydrodynamics and Energetic Cost of Bottom Feeding

Diving ducks use their webbed feet to provide the propulsive force that moves them underwater. To hold position near the bottom while feeding, ducks paddle constantly to resist the buoyant force of the body. Using video sequences from two orthogonal cameras we reconstructed the 3-dimensional motion of the feet through water and estimated the forces involved with a quasi-steady blade-element model. We found that during station holding, near the bottom, ducks use drag based propulsion with the webbed area of the foot moving perpendicular to the trajectory of the foot. The body was pitched at 76±3.47° below the horizon and the propulsive force was directed 26±1.9° ventral to the body so that 98% of the propulsive force in the sagittal plane of the duck worked to oppose buoyancy. The mechanical work done by moving both feet through a paddling cycle was 1.1±0.2 J which was equivalent to an energy expenditure of 3.7±0.5 W to hold position while feeding at 1.5 m depth. We conclude that in shallow water the high energetic cost of feeding in ducks is due to the need to paddle constantly against buoyancy even after reaching the bottom. The mechanical energy spent on holding position near the bottom, while feeding, is approximately 2 fold higher than previous estimates that were made for similar bottom depths but based on the presumed motion of the body instead of motion of the feet.     

Forelimb and hindlimb forces in walking and galloping primates

One trait that distinguishes the walking gaits of most primates from those of most mammalian nonprimates is the distribution of weight between the forelimbs and hindlimbs. Nonprimate mammals generally experience higher vertical peak substrate reaction forces on the forelimb than on the hindlimb. Primates, in contrast, generally experience higher vertical peak substrate reaction forces on the hindlimb than on the forelimb. It is currently unclear whether this unusual pattern of force distribution characterizes other primate gaits as well. The available kinetic data for galloping primates are limited and present an ambiguous picture about peak-force distribution among the limbs. The present study investigates whether the pattern of forelimb-to-hindlimb force distribution seen during walking in primates is also displayed during galloping. Six species of primates were video-recorded during walking and galloping across a runway or horizontal pole instrumented with a force-plate. The results show that while the force differences between forelimb and hindlimb are not significantly different from zero during galloping, the pattern of force distribution is generally the same during walking and galloping for most primate species. These patterns and statistical results are similar to data collected during walking on the ground. The pattern of limb differentiation exhibited by primates during walking and galloping stands in contrast to the pattern seen in most nonprimate mammals, in which forelimb forces are significantly higher. The data reported here and by Demes et al. ([1994] J. Hum. Evol. 26:353-374) suggest that a relative reduction of forelimb vertical peak forces is part of an overall difference in locomotor mechanics between most primates and most nonprimate mammals during both walking and galloping.     

Multiscale mechanisms of cell migration during development: theory and experiment

Long-distance cell migration is an important feature of embryonic development, adult morphogenesis and cancer, yet the mechanisms that drive subpopulations of cells to distinct targets are poorly understood. Here, we use the embryonic neural crest (NC) in tandem with theoretical studies to evaluate model mechanisms of long-distance cell migration. We find that a simple chemotaxis model is insufficient to explain our experimental data. Instead, model simulations predict that NC cell migration requires leading cells to respond to long-range guidance signals and trailing cells to short-range cues in order to maintain a directed, multicellular stream. Experiments confirm differences in leading versus trailing NC cell subpopulations, manifested in unique cell orientation and gene expression patterns that respond to non-linear tissue growth of the migratory domain. Ablation experiments that delete the trailing NC cell subpopulation reveal that leading NC cells distribute all along the migratory pathway and develop a leading/trailing cellular orientation and gene expression profile that is predicted by model simulations. Transplantation experiments and model predictions that move trailing NC cells to the migratory front, or vice versa, reveal that cells adopt a gene expression profile and cell behaviors corresponding to the new position within the migratory stream. These results offer a mechanistic model in which leading cells create and respond to a cell-induced chemotactic gradient and transmit guidance information to trailing cells that use short-range signals to move in a directional manner.     

Assessing pedometer accuracy while walking, skipping, galloping, sliding, and hopping

The purpose of this study was to determine the accuracy of the pedometer when walking, skipping, galloping, sliding, and hopping. One hundred-two college students were fitted with a pedometer (Walk4Life LS-7010) at mid-thigh on the right and left of the hip. Participants then performed the randomly assigned movements for the length (26 m) of a hardwood court playing surface, during which time the investigator tallied the steps with a hand counter. Each step with the lead foot elicited a tally on the counter. Participants were instructed to perform the movement at a brisk pace, to jump-stop at the end of the court, and to remain still until after the pedometer reading was recorded. Repeated measure ANOVAs using the Bonferroni technique were used to compare differences between pedometer counts and hand counts. Significant differences were evident between the hand tally counts and readings from the right and left pedometers during all five locomotor movements (P < .01). Mean error was lowest between the hand tally and the average of the right and left pedometers while walking (-1.35 +/- 1.60) and hopping (-2.94 +/- 2.33), and increased while sliding (-6.42 +/- 4.78), galloping (-8.22 +/- 4.63), and skipping (-8.30 +/- 4.45). Results indicate the pedometer may not consistently register the vertical force produced by the trail foot contact, the lead foot contact, or a combination of the two while skipping, galloping, and sliding. Though the pedometer is a valid instrument when estimating physical activity levels, caution is urged when interpreting movements other than walking.     

Tribological Behavior of Gampsocleis Gratiosa Foot Pad Against Vertical Flat Surfaces

Some tribological behavior between mature Gampsocleis gratiosa foot pads and vertical flats of different materials were studied in this work. stereomicroscope （SMS） and scanning electron microscope （SEM） were used to measure the morphology of the Gampsocleis gratiosa foot pads. An atomic force microscope （AFM） was used to measure the morphologies of the surfaces of glass and a wall doped with calcium carbonate material. The attaching behavior of Gampsocleis gratiosa feet on the two vertical surfaces was observed. The attaching force （perpendicular to the vertical surface） and the static frictional force （along the direction of gravitation） of Gampsocleis gratiosa foot pads on a vertical glass were measured. It was shown that the average attaching force is 50.59 mN and the static frictional force is 259.10 mN. The physical models of the attaching interface between Gampsocleis gratiosa foot pads and the two vertical surfaces were proposed. It was observed that the foot pads are smooth in macroscale; however, the pad surface is composed by approximate hexagonal units with sizes of 3 μm to 7 μm in microscale; the adjacent units are separated by nanoscale grooves. The Observations showed that the Gampsocleis gratiosa can not climb the vertical calcium carbonate wall; in contrast, they can easily climb the vertical glass surface. Based on the features of the geometrical morphologies of the foot pads and the glass surface, we speculate that the attaching force and strong static frictional force are attributed to the interinlays between the deformable Gampsocleis gratiosa foot pads and the nanoscale sharp tips of the glass surface.     

A case study of Chinese bound feet: application of footprint analysis

Foot print patterns of the bound feet of a 90-year-old Chinese female were made to obtain insight into the ergonomic consequences of a Chinese custom that caused significant disabilities for many women throughout history. Pressure patterns were evaluated using the techniques applied to standard thumb print analsyis. A digital summary of the pressure patterns were compared to the patterns obtained from a normal subject. The outcomes indicated that the bound foot produced greater plantar tissue pressures than the non-bound foot. These observations help explain the discomfort, gait abnormalities, and disabilities exhibited by many older women with bound feet living in China today. Although foot-binding is no longer practiced, this study offers an ergonomic perspective on a custom practiced in China for centuries.     

Functional Locomotor Consequences of Uneven Forefeet for Trot Symmetry in Individual Riding Horses

Left-right symmetrical distal limb conformation can be an important prerequisite for a successful performance, and it is often hypothesized that asymmetric or uneven feet are important enhancing factors for the development of lameness. On a population level, it has been demonstrated that uneven footed horses are retiring earlier from elite level competition, but the biomechanical consequences are not yet known. The objectives of this study were to compare the functional locomotor asymmetries of horses with uneven to those with even feet.Hoof kinetics and distal limb kinematics were collected from horses (n = 34) at trot. Dorsal hoof wall angle was used to classify horses as even or uneven (<1.5 and >1.5° difference between forefeet respectively) and individual feet as flat (<50°), medium (between 50° and 55°) or upright (>55°). Functional kinetic parameters were compared between even and uneven forefeet using MANOVA followed by ANOVA. The relative influences of differences in hoof angle between the forefeet and of absolute hoof angle on functional parameters were analysed using multiple regression analysis (P<0.05).In horses with uneven feet, the side with the flatter foot showed a significantly larger maximal horizontal braking and vertical ground reaction force, a larger vertical fetlock displacement and a suppler fetlock spring. The foot with a steeper hoof angle was linearly correlated with an earlier braking-propulsion transition. The conformational differences between both forefeet were more important for loading characteristics than the individual foot conformation of each individual horse. The differences in vertical force and braking force between uneven forefeet could imply either an asymmetrical loading pattern without a pathological component or a subclinical lameness as a result of a pathological development in the steeper foot.     

Functional differentiation of trailing and leading forelimbs during locomotion on the ground and on a horizontal branch in the European red squirrel (Sciurus vulgaris, Rodentia)

Mammalian locomotion is characterized by the frequent use of in-phase gaits in which the footfalls of the left and right fore- or hindlimbs are unevenly spaced in time. Although previous studies have identified a functional differentiation between the first limb (trailing limb) and the second limb (leading limb) to touch the ground during terrestrial locomotion, the influence of a horizontal branch on limb function has never been explored. To determine the functional differences between trailing and leading forelimbs during locomotion on the ground and on a horizontal branch, X-ray motion analysis and force measurements were carried out in two European red squirrels (Sciurus vulgaris, Rodentia). The differences observed between trailing and leading forelimbs were minimal during terrestrial locomotion, where both limbs fulfill two functions and go through a shock-absorbing phase followed by a generating phase. During locomotion on a horizontal branch, European red squirrels reduce speed and all substrate reaction forces transmitted may be due to the reduction of vertical oscillation of the center of mass. Further adjustments during locomotion on a horizontal branch differ significantly between trailing and leading forelimbs and include limb flexion, lead intervals, limb protraction and vertical displacement of the scapular pivot. Consequently, trailing and leading forelimbs perform different functions. Trailing forelimbs function primarily as shock-absorbing elements, whereas leading forelimbs are characterized by a high level of stiffness. This functional differentiation indicates that European red squirrels ‘test’ the substrate for stability with the trailing forelimb, while the leading forelimb responds to or counteracts swinging or snapping branches.