Compliance, actuation, and work characteristics of the goat foreleg and hindleg during level, uphill, and downhill running

Relation between soft tissue energy dissipation and leg stiffness in running at different step frequencies

This study aims to investigate the relationship between soft tissue energy dissipation and leg stiffness during running. Eight recreational healthy male runners (age: 22.2 ± 1.0 years; height: 1.84 ± 0.03 m; mass: 73.7 ± 5.7 kg) were asked to run at different speeds and step frequencies. Their soft tissue energy dissipation was estimated by the difference between the total mechanical work of the body, measured as the work done to move the body centre of mass relative to the surroundings plus the work to move the limbs relative to the body centre of mass, and lower-limb joint work. A mass-spring model with an actuator was used to analyse the force-length curve of the bouncing mechanism of running. In this way, the stiffness and damping coefficient were assessed at each speed and step frequency. Pearson's correlations were used to describe the relationship between the deviation from the spring-mass model and soft tissue energy fluctuations. The soft tissue dissipation was found to be significantly influenced by step frequency, with both positive and negative work phases decreasing when step frequency increases. Moreover, deviation from a spring-mass model was positively associated with the amount of soft tissue dissipation (r > 0.6). The findings emphasize the substantial role of soft tissues in dissipating or returning energy during running, behaving in a damped-elastic manner. Also, we introduce a novel approach for evaluating the elastic rebound of the body during running. The insights gained may have broad implications for assessing running mechanics, with potential applications in various contexts.

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.

The Limb Kinetics of Goat Walking on the Slope with Different Angles

The study aimed to assess the gait adjustment techniques of limbs on different slopes and investigate the relationship between forelimb and hindlimb kinetics and the center of mass (COM) during the uphill movement of a specific Boer goat using a pressure-sensitive walkway (PSW). During the uphill and downhill movements at a comfortable walking speed, we measured the ground reaction force (GRF) of the forelimbs and hindlimbs on the slope, the change in the included angle of the propulsive force direction of the forelimbs and hindlimbs, and the impulse relationship between GRF and propulsive force. According to the study, since the forelimbs of the goat were nearer the COM, they were primarily adjusted during the movement on the slope. By lowering the initial included angle of the propulsive force and the angle variation range, the forelimbs and hindlimbs could walk steadily. The forelimbs and hindlimbs exhibited completely different adjustment strategies during uphill and downhill movements. In particular, the forelimbs performed braking and the hindlimbs performed driving. In addition, we discovered that the goat altered its adjustment strategy when climbing the steep slope. All findings of this study indicate the need to understand the gait adjustment mode of the Boer goat during movement on the slope to thoroughly comprehend the driving strategy of quadrupeds with the ability to walk on specialized terrains.

Structural and pathological changes in the enthesis are influenced by the muscle contraction type during exercise

Mechanical stress is involved in the onset of sports-related enthesopathy. Although the amount of exercise undertaken is a recognized problem during disease onset, changes in muscle contraction type are also involved in the increase in mechanical stress during exercise. This study aimed to clarify the effects of increased mechanical stress associated with muscle contraction type and amount of exercise on enthesis. Twenty mice underwent treadmill exercise, and the muscle contraction type and overall load during exercise were adjusted by varying the angle and speed conditions. Histological analysis was used to the cross-sectional area of the muscle; area of the enthesis fibrocartilage (FC), and expression of inflammation-, degeneration-, and calcification-related factors in the FC area. In addition, the volume and structure of the bone and FC area were examined using microcomputer imaging. Molecular biological analysis was conducted to compare relative expression levels of inflammation and cytokine-related factors in tendons. The Overuse group, which increased the amount of exercise, showed no significant differences in parameters compared to the sedentary mice (Control group). The mice subjected to slow-speed downhill running (Misuse group) showed pathological changes compared to the Control and Overuse groups, despite the small amount of exercise. Thus, the enthesis FC area may be altered by local mechanical stress that would be increased by eccentric muscle contraction rather than by mechanical stress that increases with the overall amount of exercise. Clinical Significance: The muscle contraction type might be more involved in the onset of sports-related enthesopathy rather than the amount of exercise.

Competing Models of Work in Quadrupedal Walking: Center of Mass Work is Insufficient to Explain Stereotypical Gait

The walking gaits of cursorial quadrupedal mammals tend to be highly stereotyped as a four-beat pattern with interspersed periods of double and triple stance, often with double-hump ground reaction force profiles. This pattern has long been associated with high energetic economy, due to low apparent work. However, there are differing ways of approximating the work performed during walking and, consequently, different interpretations of the primary mechanism leading to high economy. A focus on Net Center of Mass (COM) Work led to the claim that quadrupedal walking is efficient because it effectively trades potential and kinetic energy of the COM. Individual Limbs COM Work instead focuses on the ability of the limbs to manage the trajectory of the COM to limit energetic losses to the ground (“collisions”). By focusing on the COM, both these metrics effectively dismiss the importance of rotation of the elongate quadrupedal body. Limb Extension Work considers work required to extend and contract each limb like a strut, and accounts for the work of body pitching. We tested the prescriptive ability of these approximations of work by optimizing them within a quadrupedal model with two approximations of the body as a point-mass or a rigid distributed mass. Perfect potential-kinetic energy exchange of the COM was possible when optimizing Net COM Work, resulting in highly compliant gaits with duty factors close to one, far different than observed mammalian gaits. Optimizing Individual Limbs COM Work resulted in alternating periods of single limb stance. Only the distributed mass model, with Limb Extension Work as the cost, resulted in a solution similar to the stereotypical mammalian gait. These results suggest that maintaining a near-constant limb length, with distributed contacts, are more important mechanisms of economy than either transduction of potential-kinetic energy or COM collision mitigation for quadrupedal walking.

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.

Leg Joint Mechanics When Hopping at Different Frequencies

Although the dynamics of center of mass can be accounted for by a spring-mass model during hopping, less is known about how each leg joint (ie, hip, knee, and ankle) contributes to center of mass dynamics. This work investigated the function of individual leg joints when hopping unilaterally and vertically at 4 frequencies (ie, 1.6, 2.0, 2.4, and 2.8 Hz). The hypotheses are (1) all leg joints maintain the function as torsional springs and increase their stiffness when hopping faster and (2) leg joints are controlled to maintain the mechanical load in the joints or vertical peak accelerations at different body locations when hopping at different frequencies. Results showed that all leg joints behaved as torsional springs during low-frequency hopping (ie, 1.6 Hz). As hopping frequency increased, leg joints changed their functions differently; that is, the hip and knee shifted to strut, and the ankle remained as spring. When hopping fast, the body's total mechanical energy decreased, and the ankle increased the amount of energy storage and return from 50% to 62%. Leg joints did not maintain a constant load at the joints or vertical peak accelerations at different body locations when hopping at different frequencies.

Shorter heels are linked with greater elastic energy storage in the Achilles tendon

Previous research suggests that the moment arm of the m. triceps surae tendon (i.e., Achilles tendon), is positively correlated with the energetic cost of running. This relationship is derived from a model which predicts that shorter ankle moment arms place larger loads on the Achilles tendon, which should result in a greater amount of elastic energy storage and return. However, previous research has not empirically tested this assumed relationship. We test this hypothesis using an inverse dynamics approach in human subjects (n = 24) at speeds ranging from walking to sprinting. The spring function of the Achilles tendon was evaluated using specific net work, a metric of mechanical energy production versus absorption at a limb joint. We also combined kinematic and morphological data to directly estimate tendon stress and elastic energy storage. We find that moment arm length significantly determines the spring-like behavior of the Achilles tendon, as well as estimates of mass-specific tendon stress and elastic energy storage at running and sprinting speeds. Our results provide support for the relationship between short Achilles tendon moment arms and increased elastic energy storage, providing an empirical mechanical rationale for previous studies demonstrating a relationship between calcaneal length and running economy. We also demonstrate that speed and kinematics moderate tendon performance, suggesting a complex relationship between lower limb geometry and foot strike pattern.

A little damping goes a long way: a simulation study of how damping influences task-level stability in running

It is currently unclear if damping plays a functional role in legged locomotion, and simple models often do not include damping terms. We present a new model with a damping term that is isolated from other parameters: that is, the damping term can be adjusted without retuning other model parameters for nominal motion. We systematically compare how increased damping affects stability in the face of unexpected ground-height perturbations. Unlike most studies, we focus on task-level stability: instead of observing whether trajectories converge towards a nominal limit-cycle, we quantify the ability to avoid falls using a recently developed mathematical measure. This measure allows trajectories to be compared quantitatively instead of only being separated into a binary classification of 'stable' or 'unstable'. Our simulation study shows that increased damping contributes significantly to task-level stability; however, this benefit quickly plateaus after only a small amount of damping. These results suggest that the low intrinsic damping values observed experimentally may have stability benefits and are not simply minimized for energetic reasons. All Python code and data needed to generate our results are available open source.

Mechanics of walking and running up and downhill: A joint-level perspective to guide design of lower-limb exoskeletons

Lower-limb wearable robotic devices can improve clinical gait and reduce energetic demand in healthy populations. To help enable real-world use, we sought to examine how assistance should be applied in variable gait conditions and suggest an approach derived from knowledge of human locomotion mechanics to establish a 'roadmap' for wearable robot design. We characterized the changes in joint mechanics during walking and running across a range of incline/decline grades and then provide an analysis that informs the development of lower-limb exoskeletons capable of operating across a range of mechanical demands. We hypothesized that the distribution of limb-joint positive mechanical power would shift to the hip for incline walking and running and that the distribution of limb-joint negative mechanical power would shift to the knee for decline walking and running. Eight subjects (6M,2F) completed five walking (1.25 m s-1) trials at -8.53°, -5.71°, 0°, 5.71°, and 8.53° grade and five running (2.25 m s-1) trials at -5.71°, -2.86°, 0°, 2.86°, and 5.71° grade on a treadmill. We calculated time-varying joint moment and power output for the ankle, knee, and hip. For each gait, we examined how individual limb-joints contributed to total limb positive, negative and net power across grades. For both walking and running, changes in grade caused a redistribution of joint mechanical power generation and absorption. From level to incline walking, the ankle's contribution to limb positive power decreased from 44% on the level to 28% at 8.53° uphill grade (p < 0.0001) while the hip's contribution increased from 27% to 52% (p < 0.0001). In running, regardless of the surface gradient, the ankle was consistently the dominant source of lower-limb positive mechanical power (47-55%). In the context of our results, we outline three distinct use-modes that could be emphasized in future lower-limb exoskeleton designs 1) Energy injection: adding positive work into the gait cycle, 2) Energy extraction: removing negative work from the gait cycle, and 3) Energy transfer: extracting energy in one gait phase and then injecting it in another phase (i.e., regenerative braking).

The Passive Contact Stability of Blue Sheep Hoof Based on Structure, Mechanical Properties, and Surface Morphology

As the only component that contacts the ground and rock, the hooves of blue sheep may play a crucial role in their excellent climbing abilities. In this study, we used a combination of techniques, including scanning electron microscopy, infrared spectroscopy and nanoindentation, to characterize the surface morphology, structure, material composition, and mechanical properties of blue sheep hoof and investigate the potential contributions of these properties to the establishment of passive contact stability. Straight and curled microscopic lamellar morphology were found on the hoof surfaces. The cross section of the hoof revealed four layers, and each layer had a unique structure. Finite element analysis was employed to verify that the surface morphology and microstructure effectively contributed to the slip resistance and impact cushioning, respectively. Analyses of the energy and infrared spectra showed that the organic and inorganic substances in different regions of the hoof had similar components but different contents of those components. The hoof was mainly composed of keratin. From the outside to the inside, gradients in both the modulus and hardness were observed. These factors help the hoof alleviate high impact strengths and increase contact stability. These findings further our understanding of the unique mechanism of blue sheep hoof and may help in the development of novel biomimetic materials and mechanical components with enhanced friction and contact stability properties.

Goats decrease hindlimb stiffness when walking over compliant surfaces

Leg stiffness, commonly estimated as the 'compression' of a defined leg element in response to a load, has long been used to characterize terrestrial locomotion. This study investigated how goats adjust the stiffness of their hindlimbs to accommodate surfaces of different stiffness. Goats provide a compelling animal model for studying leg stiffness modulation, because they skillfully ambulate over a range of substrates that vary in compliance. To investigate the adjustments that goats make when walking over such substrates, ground reaction forces and three-dimensional trajectories of hindlimb markers were recorded as goats walked on rigid, rubber and foam surfaces. Net joint moments, power and work at the hip, knee, ankle and metatarsophalangeal joints were estimated throughout stance via inverse dynamics. Hindlimb stiffness was estimated from plots of total leg force versus total leg length, and individual joint stiffness was estimated from plots of joint moment versus joint angle. Our results support the hypothesis that goats modulate hindlimb stiffness in response to surface stiffness; specifically, hindlimb stiffness decreased on the more compliant surfaces (P<0.002). Estimates of joint stiffness identified hip and ankle muscles as the primary drivers of these adjustments. When humans run on compliant surfaces, they generally increase leg stiffness to preserve their center-of-mass mechanics. We did not estimate center-of-mass mechanics in this study; nevertheless, our estimates of hindlimb stiffness suggest that goats exhibit a different behavior. This study offers new insight into mechanisms that allow quadrupeds to modulate their gait mechanics when walking on surfaces of variable compliance.

Vertical leaping mechanics of the Lesser Egyptian Jerboa reveal specialization for maneuverability rather than elastic energy storage

BACKGROUND

Numerous historical descriptions of the Lesser Egyptian jerboa, Jaculus jaculus, a small bipedal mammal with elongate hindlimbs, make special note of their extraordinary leaping ability. We observed jerboa locomotion in a laboratory setting and performed inverse dynamics analysis to understand how this small rodent generates such impressive leaps. We combined kinematic data from video, kinetic data from a force platform, and morphometric data from dissections to calculate the relative contributions of each hindlimb muscle and tendon to the total movement.

RESULTS

Jerboas leapt in excess of 10 times their hip height. At the maximum recorded leap height (not the maximum observed leap height), peak moments for metatarso-phalangeal, ankle, knee, and hip joints were 13.1, 58.4, 65.1, and 66.9 Nmm, respectively. Muscles acting at the ankle joint contributed the most work (mean 231.6 mJ / kg Body Mass) to produce the energy of vertical leaping, while muscles acting at the metatarso-phalangeal joint produced the most stress (peak 317.1 kPa). The plantaris, digital flexors, and gastrocnemius tendons encountered peak stresses of 25.6, 19.1, and 6.0 MPa, respectively, transmitting the forces of their corresponding muscles (peak force 3.3, 2.0, and 3.8 N, respectively). Notably, we found that the mean elastic energy recovered in the primary tendons of both hindlimbs comprised on average only 4.4% of the energy of the associated leap.

CONCLUSIONS

The limited use of tendon elastic energy storage in the jerboa parallels the morphologically similar heteromyid kangaroo rat, Dipodomys spectabilis. When compared to larger saltatory kangaroos and wallabies that sustain hopping over longer periods of time, these small saltatory rodents store and recover less elastic strain energy in their tendons. The large contribution of muscle work, rather than elastic strain energy, to the vertical leap suggests that the fitness benefit of rapid acceleration for predator avoidance dominated over the need to enhance locomotor economy in the evolutionary history of jerboas.

Investigation of feet functions of large ruminants with a decoupled model of equivalent mechanism

Cloven hooves of ruminants adapt to diverse terrain, provide propulsive force and support the whole body during movement in natural environments. To reveal how the feet ensure terrain adaptability by choosing the proper configurations and terrain conditions, we model the feet of ruminants as an equivalent mechanism with flexion-extension and lateral movement decoupled. The upper part of the equivalent mechanism can flex and extend, while the lower part performs the lateral movement. Combination of the two parts can adapt to longitudinal slope (anterior-posterior) and transverse slope (medial-lateral), respectively. When one of two digits closes laterally, the workspace of the other decreases. The distal interdigital ligament between two digits limits their motion by elastic force and stores energy during movement. Differences in elastic energy variation of the ligament on different transverse slopes are characterized based on the configurations of two digits and the elastic energy between them. If the upper one of two symmetric digits is fixed, the foot landing on the grade surface (2°) shows greater capacity for absorbing energy; otherwise, level ground is the best choice for ruminants. As for the asymmetric digits, longer lateral digits enhance the optimal adaptive lateral angle. The asymmetry predisposes the feet to damage on the hard ground, which indicates soft ground is more suitable.

Summary: This study shows that level and soft grounds are best for symmetric and asymmetric digits, respectively, as revealed by kinematic analysis using a decoupled equivalent mechanism of the foot of ruminants.

Grizzly bear (Ursus arctos horribilis) locomotion: forelimb joint mechanics across speed in the sagittal and frontal planes

The majority of terrestrial locomotion studies have focused on parasagittal motion and paid less attention to forces or movement in the frontal plane. Our previous research has shown that grizzly bears produce higher medial ground reaction forces (lateral pushing from the animal) than would be expected for an upright mammal, suggesting frontal plane movement may be an important aspect of their locomotion. To examine this, we conducted an inverse dynamics analysis in the sagittal and frontal planes, using ground reaction forces and position data from three high-speed cameras of four adult female grizzly bears. Over the speed range collected, the bears used walks, running walks and canters. The scapulohumeral joint, wrist and the limb overall absorb energy (average total net work of the forelimb joints, -0.97 W kg^-1). The scapulohumeral joint, elbow and total net work of the forelimb joints have negative relationships with speed, resulting in more energy absorbed by the forelimb at higher speeds (running walks and canters). The net joint moment and power curves maintain similar patterns across speed as in previously studied species, suggesting grizzly bears maintain similar joint dynamics to other mammalian quadrupeds. There is no significant relationship with net work and speed at any joint in the frontal plane. The total net work of the forelimb joints in the frontal plane was not significantly different from zero, suggesting that, despite the high medial ground reaction forces, the forelimb acts as a strut in that plane.

A model for differential leg joint function during human running

Locomotion requires coordination of leg joints to maintain stability and to maneuver. We studied leg joint function during constant-average-velocity running and the sagittal-plane maneuvers of step ascent and descent. We tested two hypotheses: (1) that leg joints perform distinct functions during locomotion; and (2) that humans select functional parameters to maximize intrinsic dynamic stability. We recorded whole-body kinematics and forces when participants stepped up or down a single vertical step, and found that leg joints show functional differences during both constant-average-velocity locomotion and maneuvers. The hip, knee and ankle function as a motor, damper, and spring, respectively. We therefore constructed a simplified computational model of a human leg with a motor, damper, and spring in series (MDS). The intrinsic dynamics of the model resulted in sustained locomotion on level ground within narrow parameter ranges. However, using parameters experimentally derived from humans, the model showed only short-term stability. Humans may not optimize intrinsic dynamic stability alone, but may instead choose mechanical and behavioral parameters appropriate for both constant-average-velocity locomotion and maneuvers. Understanding joint-level mechanical function during unsteady locomotion helps to understand how differential joint function contributes to whole-body performance, and could lead to improvements in rehabilitation, prosthetic and robotic design.

Adaptive and Energy Efficient Walking in a Hexapod Robot Under Neuromechanical Control and Sensorimotor Learning

The control of multilegged animal walking is a neuromechanical process, and to achieve this in an adaptive and energy efficient way is a difficult and challenging problem. This is due to the fact that this process needs in real time: 1) to coordinate very many degrees of freedom of jointed legs; 2) to generate the proper leg stiffness (i.e., compliance); and 3) to determine joint angles that give rise to particular positions at the endpoints of the legs. To tackle this problem for a robotic application, here we present a neuromechanical controller coupled with sensorimotor learning. The controller consists of a modular neural network for coordinating 18 joints and several virtual agonist-antagonist muscle mechanisms (VAAMs) for variable compliant joint motions. In addition, sensorimotor learning, including forward models and dual-rate learning processes, is introduced for predicting foot force feedback and for online tuning the VAAMs' stiffness parameters. The control and learning mechanisms enable the hexapod robot advanced mobility sensor driven-walking device (AMOS) to achieve variable compliant walking that accommodates different gaits and surfaces. As a consequence, AMOS can perform more energy efficient walking, compared to other small legged robots. In addition, this paper also shows that the tight combination of neural control with tunable muscle-like functions, guided by sensory feedback and coupled with sensorimotor learning, is a way forward to better understand and solve adaptive coordination problems in multilegged locomotion.

Controlling legs for locomotion-insights from robotics and neurobiology

Walking is the most common terrestrial form of locomotion in animals. Its great versatility and flexibility has led to many attempts at building walking machines with similar capabilities. The control of walking is an active research area both in neurobiology and robotics, with a large and growing body of work. This paper gives an overview of the current knowledge on the control of legged locomotion in animals and machines and attempts to give walking control researchers from biology and robotics an overview of the current knowledge in both fields. We try to summarize the knowledge on the neurobiological basis of walking control in animals, emphasizing common principles seen in different species. In a section on walking robots, we review common approaches to walking controller design with a slight emphasis on biped walking control. We show where parallels between robotic and neurobiological walking controllers exist and how robotics and biology may benefit from each other. Finally, we discuss where research in the two fields diverges and suggest ways to bridge these gaps.

Tail loss and narrow surfaces decrease locomotor stability in the arboreal green anole lizard (Anolis carolinensis)

Tails play an important role for dynamic stabilization during falling and jumping in lizards. Yet, tail autotomy (the voluntary loss of an appendage) is a common mechanism used for predator evasion among these animals. How tail autotomy impacts locomotor performance and stability remains poorly understood. The goal of this study was to determine how tail loss affects running kinematics and performance in the arboreal green anole lizard, Anolis carolinensis (Voigt, 1832). Lizards were run along four surface widths (9.5 mm, 15.9 mm, 19.0 mm, and flat), before and following 75% tail autotomy. Results indicate that when perturbed with changes in surface breadth and tail condition, surface breadth tends to have greater impacts on locomotor performance than does tail loss. Furthermore, while tail loss does have a destabilizing effect during regular running in these lizards, its function during steady locomotion is minimal. Instead, the tail likely plays a more active role during dynamic maneuvers that require dramatic changes in whole body orientation or center of mass trajectories.

Terrain Adaptability Mechanism of Large Ruminants' Feet on the Kinematics View

Ruminants live in various parts of land. Similar cloven hooves assist ruminants in adapting to different ground environment during locomotion. This paper analyzes the general terrain adaptability of the feet of ruminants using kinematics of the equivalent mechanism model based on screw theory. Cloven hooves could adjust attitude by changing relative positions between two digits in swing phase. This function helps to choose better landing orientation. "Grasping" or "holding" a rock or other object on the ground passively provides extra adhesion force in stance phase. Ruminants could adjust the position of the metacarpophalangeal joint or metatarsophalangeal joint (MTP or MCP) with no relative motion between the tip of feet and the ground, which ensures the adhesion and dexterity in stance phase. These functions are derived from an example from chamois' feet and several assumptions, which are believed to demonstrate the foundation of adaptation of ruminants and ensure a stable and continuous movement.

Scaling of the spring in the leg during bouncing gaits of mammals

Trotting, bipedal running, and especially hopping have long been considered the principal bouncing gaits of legged animals. We use the radial-leg spring constant [Formula: see text] to quantify the stiffness of the physical leg during bouncing gaits. The radial-leg is modeled as an extensible strut between the hip and the ground and [Formula: see text] is determined from the force and deflection of this strut in each instance of stance. A Hookean spring is modeled in-series with a linear actuator and the stiffness of this spring [Formula: see text] is determined by minimizing the work of the actuator while reproducing the measured force-deflection dynamics of an individual leg during trotting or running, and of the paired legs during hopping. Prior studies have estimated leg stiffness using [Formula: see text], a metric that imagines a virtual-leg connected to the center of mass. While [Formula: see text] has been applied extensively in human and comparative biomechanics, we show that [Formula: see text] more accurately models the spring in the leg when actuation is allowed, as is the case in biological and robotic systems. Our allometric analysis of [Formula: see text] in the kangaroo rat, tammar wallaby, dog, goat, and human during hopping, trotting, or running show that [Formula: see text] scales as body mass to the two-third power, which is consistent with the predictions of dynamic similarity and with the scaling of [Formula: see text]. Hence, two-third scaling of locomotor spring constants among mammals is supported by both the radial-leg and virtual-leg models, yet the scaling of [Formula: see text] emerges from work-minimization in the radial-leg model instead of being a defacto result of the ratio of force to length used to compute [Formula: see text]. Another key distinction between the virtual-leg and radial-leg is that [Formula: see text] is substantially greater than [Formula: see text], as indicated by a 30-37% greater scaling coefficient for [Formula: see text]. We also show that the legs of goats are on average twice as stiff as those of dogs of the same mass and that goats increase the stiffness of their legs, in part, by more nearly aligning their distal limb-joints with the ground reaction force vector. This study is the first allometric analysis of leg spring constants in two decades. By means of an independent model, our findings reinforce the two-third scaling of spring constants with body mass, while showing that springs in-series with actuators are stiffer than those predicted by energy-conservative models of the leg.

Knowledge Management Systems and Disaster Management in Malaysia: An Action Research Approach

This paper examines the role of knowledge management systems (KMS) for disaster planning and response in the context of social work in Malaysia. The research is focused on the client — the Malaysian Association of Social Workers (MASW), where a web-based system to support disaster management was developed and implemented. The research objectives required the researchers' direct involvement with the MASW. Canonical Action Research (CAR) was used as the research methodology. The process and outcomes of this action research initiative is presented based on the five-stage CAR approach, consisting of (i) problem diagnosis, (ii) action planning, (iii) intervention, (iv) evaluation and (v) learning outcomes. The evaluation of the system is supported by quantitative analysis driven by survey instrumentation. Our findings suggests that successful utilisation of the system in the context of MASW's efforts and roles in disaster management in Malaysia, is contingent upon issues such as acceptance of KMS, and availability of resources to maintain the system. Other issues such as clear definition of the role of Information Technology (IT) for disaster management and willingness to share knowledge are also vital in this regard.

Locomotion in degus on terrestrial substrates varying in orientation - implications for biomechanical constraints and gait selection

To gain new insights into running gaits on sloped terrestrial substrates, metric and selected kinematic parameters of the common degu (Octodon degus) were examined. Individuals were filmed at their maximum voluntary running speed using a high-speed camera placed laterally to the terrestrial substrate varying in orientations from -30° to +30°, at 10° increments. Degus used trotting, lateral-sequence (LS) and diagonal-sequence (DS) running gaits at all substrate orientations. Trotting was observed across the whole speed range whereas DS running gaits occurred at significantly higher speeds than LS running gaits. Metric and kinematic changes on sloped substrates in degus paralleled those noted for most other mammals. However, the timing of metric and kinematic locomotor adjustments differed significantly between individual degus. In addition, most of these adjustments took place at 10° rather than 30° inclines and declines, indicating significant biomechanical demands even on slightly sloped terrestrial substrates. The results of this study suggest that DS and LS running gaits may represent an advantage in small to medium-sized mammals for counteracting some level of locomotor instability. Finally, changes in locomotor parameters of the forelimbs rather than the hindlimbs seem to play an important role in gait selection in small to medium-sized mammals.

A Work-Loop Method for Characterizing Leg Function During Sagittal Plane Movements

The work-loop method is frequently used to determine the mechanical work performed by a system, for instance, when analyzing muscles or describing the work balance at the joint level. While for these examples usually only one-dimensional movements are investigated, for two- or three-dimensional movements, such as leg function during walking and running, the work-loop has to be adapted. In this paper, we present an analytical derivation that extends the work-loop method to two-dimensional sagittal plane movements. Three effects contribute to the mechanical work of the leg: (1) forces directed along the leg axis, (2) forces acting perpendicular to the leg axis, and (3) a shift of the center of pressure (COP) during stance. These three contributors to the mechanical work performed can be interpreted as three general tasks of the leg. To demonstrate the new work-loop method, we analyzed experimental data on hopping, running and walking. The results indicate that the proposed new generalized work-loop concept is suitable for describing the overall mechanical work performed on the COM during stance with energy consistent net work balances. Depending on the type of gait, specific contributions of each work term were found that characterize leg function during locomotion.

Modulation of joint moments and work in the goat hindlimb with locomotor speed and surface grade

Goats and other quadrupeds must modulate the work output of their muscles to accommodate the changing mechanical demands associated with locomotion in their natural environments. This study examined which hindlimb joint moments goats use to generate and absorb mechanical energy on level and sloped surfaces over a range of locomotor speeds. Ground reaction forces and the three-dimensional locations of joint markers were recorded as goats walked, trotted and galloped over 0, +15 and -15 deg sloped surfaces. Net joint moments, powers and work were estimated at the goats' hip, knee, ankle and metatarsophalangeal joints throughout the stance phase via inverse dynamics calculations. Differences in locomotor speed on the level, inclined and declined surfaces were characterized and accounted for by fitting regression equations to the joint moment, power and work data plotted versus non-dimensionalized speed. During level locomotion, the net work generated by moments at each of the hindlimb joints was small (less than 0.1 J kg(-1) body mass) and did not vary substantially with gait or locomotor speed. During uphill running, by contrast, mechanical energy was generated at the hip, knee and ankle, and the net work at each of these joints increased dramatically with speed (P<0.05). The greatest increases in positive joint work occurred at the hip and ankle. During downhill running, mechanical energy was decreased in two main ways: goats generated larger knee extension moments in the first half of stance, absorbing energy as the knee flexed, and goats generated smaller ankle extension moments in the second half of stance, delivering less energy. The goats' hip extension moment in mid-stance was also diminished, contributing to the decrease in energy. These analyses offer new insight into quadrupedal locomotion, clarifying how the moments generated by hindlimb muscles modulate mechanical energy at different locomotor speeds and grades, as needed to accommodate the demands of variable terrain.

Recruitment of faster motor units is associated with greater rates of fascicle strain and rapid changes in muscle force during locomotion

Animals modulate the power output needed for different locomotor tasks by changing muscle forces and fascicle strain rates. To generate the necessary forces, appropriate motor units must be recruited. Faster motor units have faster activation-deactivation rates than slower motor units, and they contract at higher strain rates; therefore, recruitment of faster motor units may be advantageous for tasks that involve rapid movements or high rates of work. This study identified motor unit recruitment patterns in the gastrocnemii muscles of goats and examined whether faster motor units are recruited when locomotor speed is increased. The study also examined whether locomotor tasks that elicit faster (or slower) motor units are associated with increased (or decreased) in vivo tendon forces, force rise and relaxation rates, fascicle strains and/or strain rates. Electromyography (EMG), sonomicrometry and muscle-tendon force data were collected from the lateral and medial gastrocnemius muscles of goats during level walking, trotting and galloping and during inclined walking and trotting. EMG signals were analyzed using wavelet and principal component analyses to quantify changes in the EMG frequency spectra across the different locomotor conditions. Fascicle strain and strain rate were calculated from the sonomicrometric data, and force rise and relaxation rates were determined from the tendon force data. The results of this study showed that faster motor units were recruited as goats increased their locomotor speeds from level walking to galloping. Slow inclined walking elicited EMG intensities similar to those of fast level galloping but different EMG frequency spectra, indicating that recruitment of the different motor unit types depended, in part, on characteristics of the task. For the locomotor tasks and muscles analyzed here, recruitment patterns were generally associated with in vivo fascicle strain rates, EMG intensity and tendon force. Together, these data provide new evidence that changes in motor unit recruitment have an underlying mechanical basis, at least for certain locomotor tasks.

Effects of grade and mass distribution on the mechanics of trotting in dogs

Quadrupedal running on grades requires balancing of pitch moments about the center of mass (COM) while supplying sufficient impulse to maintain a steady uphill or downhill velocity. Here, trotting mechanics on a 15 deg grade were characterized by the distribution of impulse between the limbs and the angle of resultant impulse at each limb. Anterior-posterior manipulation of COM position has previously been shown to influence limb mechanics during level trotting of dogs; hence, the combined effects of grade and COM manipulations were explored by adding 10% body mass at the COM, shoulder or pelvis. Whole body and individual limb ground reaction forces, as well as spatiotemporal step parameters, were measured during downhill and uphill trotting. Deviations from steady-speed locomotion were determined by the net impulse angle and accounted for in the statistical model. The limbs exerted only propulsive force during uphill trotting and, with the exception of slight hindlimb propulsion in late stance, only braking force during downhill trotting. Ratios of forelimb impulse to total impulse were computed for normal and shear components. Normal impulse ratios were more different from level values during uphill than downhill trotting, indicating that the limbs act more as levers on the incline. Differential limb function was evident in the extreme divergence of forelimb and hindlimb impulse angles, amplifying forelimb braking and hindlimb propulsive biases observed during level trotting. In both downhill and uphill trotting, added mass at the up-slope limb resulted in fore-hind distributions of normal impulse more similar to those of level trotting and more equal fore-hind distributions of shear impulse. The latter result suggests a functional trade-off in quadruped design: a COM closer to the hindlimbs would distribute downhill braking more equally, whereas a COM closer to the forelimbs would distribute uphill propulsion more equally. Because muscles exert less force when actively shortening than when lengthening, it would be advantageous for the forelimb and hindlimb muscles to share the propulsive burden more equally during uphill trotting. This functional advantage is consistent with the anterior COM position of most terrestrial quadrupeds.

Hand and foot pressures in the aye-aye (Daubentonia madagascariensis) reveal novel biomechanical trade-offs required for walking on gracile digits

Arboreal animals with prehensile hands must balance the complex demands of bone strength, grasping and manipulation. An informative example of this problem is that of the aye-aye (Daubentonia madagascariensis), a rare lemuriform primate that is unusual in having exceptionally long, gracile fingers specialized for foraging. In addition, they are among the largest primates to engage in head-first descent on arboreal supports, a posture that should increase loads on their gracile digits. We test the hypothesis that aye-ayes will reduce pressure on their digits during locomotion by curling their fingers off the substrate. This hypothesis was tested using simultaneous videographic and pressure analysis of the hand, foot and digits for five adult aye-ayes during horizontal locomotion and during ascent and descent on a 30° instrumented runway. Aye-ayes consistently curled their fingers during locomotion on all slopes. When the digits were in contact with the substrate, pressures were negligible and significantly less than those experienced by the palm or pedal digits. In addition, aye-ayes lifted their hands vertically off the substrate instead of ‘toeing-off’ and descended head-first at significantly slower speeds than on other slopes. Pressure on the hand increased during head-first descent relative to horizontal locomotion but not as much as the pressure increased on the foot during ascent. This distribution of pressure suggests that aye-ayes shift their weight posteriorly during head-first descent to reduce loads on their gracile fingers. This research demonstrates several novel biomechanical trade-offs to deal with complex functional demands on the mammalian skeleton.

Dynamics of goat distal hind limb muscle-tendon function in response to locomotor grade

The functional roles of the lateral gastrocnemius (LG), medial gastrocnemius (MG) and superficial digital flexor (SDF) muscle-tendon units (MTUs) in domestic goats (N=6) were studied as a function of locomotor grade, testing the hypothesis that changes in distal limb muscle work would reflect changes in mechanical work requirements while goats walked or trotted on the level, 15 deg. decline and 15 deg. incline. As steep terrain-adapted animals, changes in muscle work output are expected to be particularly important for goats. In vivo muscle-tendon forces, fascicle length changes and muscle activation were recorded via tendon force buckles, sonomicrometry and electromyography to evaluate the work performance and elastic energy recovery of the three distal MTUs. These recordings confirmed that fascicle strain and force within goat distal hind limb muscles are adjusted in response to changes in mechanical work demand associated with locomotor grade. In general, muscle work was modulated most consistently by changes in fascicle strain, with increased net shortening (P<0.001) observed as goats switched from decline to level to incline locomotion. Peak muscle stresses increased as goats increased speed from a walk to a trot within each grade condition (P<0.05), and also increased significantly with grade (P<0.05 to P<0.01). Due to the increase in net fascicle shortening and muscle force, net muscle work per cycle also increased significantly (P<0.05 to P<0.005) as goats switched from decline to level to incline conditions (LG work: 20 mJ to 56 mJ to 209 mJ; MG work: -7 mJ to 34 mJ to 179 mJ; SDF work: -42 mJ to 14 mJ to 71 mJ, at a 2.5 ms(-1) trot). Although muscle work was modulated in response to changes in grade, the amount of work produced by these three distal pennate muscles was small (being <3%) in comparison with the change in mechanical energy required of the limb as a whole. Elastic energy recovery in the SDF and gastrocnemius (GA) tendons was substantial across all three grades, with the SDF tendon recovering 2.4 times more energy, on average, than the GA tendon. In parallel with the increase in muscle-tendon force, tendon energy recovery also increased as goats increased speed and changed gait, reaching the highest levels when goats trotted on an incline at 2.5 ms(-1) (GA: 173 mJ; SDF: 316 mJ). In general, tendon elastic energy exceeded net muscle work across all grade and gait conditions. These results demonstrate, for the first time in a quadruped, similar findings to those observed in ankle extensor muscles in humans, wallabies, turkeys and guinea fowl, suggesting that distal muscle-tendon architecture more generally favors a design for economic force production and tendon elastic energy recovery, with the majority of limb work during incline or decline running performed by larger proximal muscles.

Differential muscle function between muscle synergists: long and lateral heads of the triceps in jumping and landing goats (Capra hircus)

We investigate how the biarticular long head and monoarticular lateral head of the triceps brachii function in goats (Capra hircus) during jumping and landing. Elbow moment and work were measured from high-speed video and ground reaction force (GRF) recordings. Muscle activation and strain were measured via electromyography and sonomicrometry, and muscle stress was estimated from elbow moment and by partitioning stress based on its relative strain rate. Elbow joint and muscle function were compared among three types of limb usage: jump take-off (lead limb), the step prior to jump take-off (lag limb), and landing. We predicted that the strain and work patterns in the monoarticular lateral head would follow the kinematics and work of the elbow more closely than would those of the biarticular long head. In general this prediction was supported. For instance, the lateral head stretched (5 +/- 2%; mean +/- SE) in the lead and lag limbs to absorb work during elbow flexion and joint work absorption, while the long head shortened (-7 +/- 1%) to produce work. During elbow extension, both muscles shortened by similar amounts (-10 +/- 2% long; -13 +/- 4% lateral) in the lead limb to produce work. Both triceps heads functioned similarly in landing, stretching (13 +/- 3% in the long head and 19 +/- 5% in the lateral) to absorb energy. In general, the long head functioned to produce power at the shoulder and elbow, while the lateral head functioned to resist elbow flexion and absorb work, demonstrating that functional diversification can arise between mono- and biarticular muscle agonists operating at the same joint.