Terrestrial organisms adept at locomotion employ strut-like legs for economical and robust movement across the substrate. Although it is relatively easy to observe and analyze details of the solutions these organic systems have arrived at, it is not as easy to identify the problems these movement strategies have solved. As such, it is useful to investigate fundamental challenges that effective legged locomotion overcomes in order to understand why the mechanisms employed by biological systems provide viable solutions to these challenges.
View Article and Find Full Text PDFMetabolic rate appears to increase with the rate of force application for running. Leg function during ground contact is similar in hopping and running, so one might expect that this relationship would hold for hopping as well. Surprisingly, metabolic rate appeared to decrease with increasing force rate for hopping.
View Article and Find Full Text PDFBackground. Although the trot is described as a diagonal gait, contacts of the diagonal pairs of hooves are not usually perfectly synchronized. Although subtle, the timing dissociation between contacts of each diagonal pair could have consequences on gait dynamics and provide insight into the functional strategies employed.
View Article and Find Full Text PDFThe maximum hop height attainable for a given hop frequency falls well below the theoretical limit dictated by gravity, h = g/8f(2). However, maximum hop height is proportional to 1/f(2), suggesting that ground reaction force and, hence, force production capabilities of the leg muscles limit human hopping performance. Curiously, during one-legged hopping, subjects were able to produce substantially more than 50% the ground reaction force produced during two-legged maximum height hopping-66% on average and as much as 90% the total force produced during two-legged hopping.
View Article and Find Full Text PDFThe way we walk determines the energetic investment needed. Humans spontaneously alter their walking style to exploit energetic opportunities. New research demonstrates the sensitivity and timing of this optimization and opens the door to discovering the underlying mechanisms.
View Article and Find Full Text PDFThe digital flexors of horses must produce high force to support the body weight during running, and a need for these muscles to generate power is likely limited during locomotion over level ground. Measurements of power output from horse muscle fibers close to physiological temperatures, and when cyclic strain is imposed, will help to better understand the in vivo performance of the muscles as power absorbers and generators. Skinned fibers from the deep (DDF) and superficial (SDF) digital flexors, and the soleus (SOL) underwent sinusoidal oscillations in length over a range of frequencies (0.
View Article and Find Full Text PDFTo evaluate how fundamental gait parameters used in walking (stride length, frequency, speed) are selected by cats we compared stride characteristics selected when walking on a solid surface to those selected when they were constrained to specific stride lengths using a pedestal walkway. Humans spontaneously select substantially different stride length-stride frequency-speed relationships in walking when each of these parameters is constrained, as in walking to a metronome beat (frequency constrained), evenly spaced floor markers (stride length constrained) or on a treadmill (speed constrained). In humans such adjustments largely provide energetic economy under the prescribed walking conditions.
View Article and Find Full Text PDFMany studies have examined how legged mammals move, defining 'what' happens in locomotion. However, few ask 'why' those motions occur as they do. The energetic and functional constraints acting on an animal require that locomotion should be metabolically 'cost effective' and this in large part determines the strategies available to accomplish the task.
View Article and Find Full Text PDFThis study compares human walking and running, and places them within the context of other mammalian gaits. We use a collision-based approach to analyse the fundamental dynamics of the centre of mass (CoM) according to three angles derived from the instantaneous force and velocity vectors. These dimensionless angles permit comparisons across gait, species and size.
View Article and Find Full Text PDFWe analyzed gait and function of the supporting limb in participants of a marathon race at three stages: prerace, midrace (18 km), and near the end of the race (36 km). We confirmed that the most successful runners were able to maintain running speed for the duration of the race with little change in speed or gait. Speed slowed progressively during the race for those with slower race times, but stride frequency-stride length relationships remained normal for the speed they ran.
View Article and Find Full Text PDFConstrained optimization of metabolic cost/distance travelled largely predicts the gait parameters selected by humans during walking and running. This study evaluates whether this is also the case for human hopping. Hop frequency (f), height (h) and metabolic energy expenditure were measured in partly constrained (f, h or hop speed, s ≡ fh, specified), fully constrained (both f and h specified) and unconstrained conditions (neither f nor h specified) for 4 min trials.
View Article and Find Full Text PDFAs one of the most energetically demanding daily activities, locomotion has attracted substantial investigative attention. Although legged locomotion has been well described, it is currently not well understood. Looking at energy accounting might be a good pathway with which to solve this problem.
View Article and Find Full Text PDFThe analysis of terrestrial locomotion over the past half century has focused largely on strategies of mechanical energy recovery used during walking and running. In contrast, we describe the underlying mechanics of legged locomotion as a collision-like interaction that redirects the centre of mass (CoM). We introduce the collision angle, determined by the angle between the CoM force and velocity vectors, and show by computing the collision fraction, a ratio of actual to potential collision, that the quadrupedal walk and gallop employ collision-reduction strategies while the trot permits greater collisions.
View Article and Find Full Text PDFBMC Musculoskelet Disord
October 2010
Background: As a relatively non-regenerative tissue, articular cartilage has been targeted for cryopreservation as a method of mitigating a lack of donor tissue availability for transplant surgeries. In addition, subzero storage of articular cartilage has long been used in biomedical studies using various storage temperatures. The current investigation studies the potential for freeze-thaw to affect the mechanical properties of articular cartilage through direct comparison of various subzero storage temperatures.
View Article and Find Full Text PDFMammals use two distinct gallops referred to as the transverse (where landing and take-off are contralateral) and rotary (where landing and take-off are ipsilateral). These two gallops are used by a variety of mammals, but the transverse gallop is epitomized by the horse and the rotary gallop by the cheetah. In this paper, we argue that the fundamental difference between these gaits is determined by which set of limbs, fore or hind, initiates the transition of the centre of mass from a downward-forward to upward-forward trajectory that occurs between the main ballistic (non-contact) portions of the stride when the animal makes contact with the ground.
View Article and Find Full Text PDFThe effect of step length on minimum required coefficient of friction (microR) during a walking step was isolated from other features that influence the mechanics of foot contact (such as speed). Ground reaction force (GRF) from defined step lengths at consistent forward speed was used to calculate (microR), required coefficent of friction. Some individuals walked in a manner that generated a (microR) that was 50% larger than others, in spite of being restricted to the same speed, step length and step frequency.
View Article and Find Full Text PDFThe distal forelimb of the horse has a complex array of ligaments that play a critical role in determining function of the digit and are often associated with the initiation of foot pathologies. The collateral ligaments of the distal sesamoid bone (CLDS) play an important role in digit stabilization near the end of foot contact and there is also limited evidence to suggest that the CLDS stabilize the proximal interphalangeal joint (PIPJ) during weight bearing. By virtue of their anatomical attachments where the ligaments pass dorsal to the axis of rotation of the PIPJ, it is reasonable to assume that the CLDS prevent flexion of the PIPJ during weight bearing or midstance in a moving horse.
View Article and Find Full Text PDFWalking humans spontaneously select different speed, frequency and step length combinations, depending on which of these three parameters is specified. This behavior can be explained by constrained optimization of cost of transport (metabolic cost/distance) where cost of transport is seen as the main component of an underlying objective function that is minimized within the limitations of specified constraints. It is then of interest to ask whether or not such results are specific to walking only, or indicate a more general feature of locomotion control.
View Article and Find Full Text PDFTerrestrial legged locomotion requires repeated support forces to redirect the body's vertical velocity component from down to up. We assume that the redirection is accomplished by impulsive leg forces that cause small-angle glancing collisions of a point-mass model of the animal. We estimate the energetic costs of these collisions by assuming a metabolic cost proportional to positive muscle work involved in generating the impulses.
View Article and Find Full Text PDFIn the evolution of flight bats appear to have suffered a trade-off; they have become poor crawlers relative to terrestrial mammals. Capable walking does occur in a few disparate taxa, including the vampire bats, but the vast majority of bats are able only to shuffle awkwardly along the ground, and the morphological bases of differences in crawling ability are not currently understood. One widely cited hypothesis suggests that the femora of most bats are too weak to withstand the compressive forces that occur during terrestrial locomotion, and that the vampire bats can walk because they possess more robust hindlimb skeletons.
View Article and Find Full Text PDFAs walking speed increases, consistent relationships emerge between the three determinant parameters of walking, speed, step frequency and step length. However, when step length or step frequency are predetermined rather than speed, different relationships are spontaneously selected. This result is expected if walking parameters are selected to optimize to an underlying objective function, known as the constrained optimization hypothesis.
View Article and Find Full Text PDFThis review is designed to evaluate and interpret studies relevant to the locomotory mode known as brachiation, particularly as performed by the Hylobatid apes: the gibbon and siamang species. The older literature and its conclusions are evaluated against recent work performed by the author and other research groups working on brachiation models, either computer simulations or physical robots. The gibbon displays two types of brachiation: continuous contact, analogous to walking, and ricochetal, analogous to running.
View Article and Find Full Text PDFThe energetics of locomotion depend largely on speed, gait and body size. Gait selection for a given speed appears partly, but perhaps not wholly, related to metabolic cost. One cost normally omitted from considerations of locomotion efficiency is the metabolic cost of the transition between gaits.
View Article and Find Full Text PDFObjective: To determine whether dorsal loading of the pelvis and type of chemical restraint affected the dorsolateral subluxation (DLS) score of dog hips. STYDY DESIGN: In vivo testing of diagnostic method.
Animals: Labrador retrievers, Greyhounds, and crosses between both breeds (n = 119 dogs).