Energetic and kinematic consequences of weighting the distal limb

Trabecular bone morphology in big cats reflects the complex diversity of limb use but not home range size or daily travel distance

A relationship exists between mechanical loading and bone morphology. Although studies show a relationship between trabecular bone morphology and locomotor strategy in mammals, none of them have studied trabecular bone morphology in felid species occupying disparate and overlapping habitats. We investigate trabecular bone volume fraction (BVF) in the femoral and humeral heads, and distal tibia of four felid species (mountain lions, jaguars, cheetahs, and leopards) to identify whether there is a relationship between BVF and locomotor behavior. This study's goals are to identify whether felid species with high daily travel distance or large home range size have greater BVF compared with those with small daily travel distance or home range size, and whether BVF is correlated among the three elements of the fore and hindlimb studied. We quantified BVF in micro- and peripheral computed tomography images and found no significant differences across species in the femoral and humeral head (p > 0.05). However, in the distal tibia, results showed that leopards, mountain lions, and cheetahs have significantly greater (p < 0.05) BVF than jaguars. Despite differences in home range size and daily travel distance, the proximal elements did not reflect differences in BVF; however, the distal-most element did, suggesting decreased loading among jaguars. These findings suggest that the observed pattern of trabecular bone morphology is potentially due to the diversity in locomotor strategy of the forelimb. Additionally, these results imply that neither home range size nor daily travel distance are clear indicators of activity levels. A cautious approach is warranted in studying how loading influences trabecular morphology.

The effect of horseshoes and surfaces on horse and jockey centre of mass displacements at gallop

Horseshoes influence how horses' hooves interact with different ground surfaces, during the impact, loading and push-off phases of a stride cycle. Consequently, they impact on the biomechanics of horses' proximal limb segments and upper body. By implication, different shoe and surface combinations could drive changes in the magnitude and stability of movement patterns in horse-jockey dyads. This study aimed to quantify centre of mass (COM) displacements in horse-jockey dyads galloping on turf and artificial tracks in four shoeing conditions: 1) aluminium; 2) barefoot; 3) GluShu; and 4) steel. Thirteen retired racehorses and two jockeys at the British Racing School were recruited for this intervention study. Tri-axial acceleration data were collected close to the COM for the horse (girth) and jockey (kidney-belt), using iPhones (Apple Inc.) equipped with an iOS app (SensorLog, sample rate = 50 Hz). Shoe-surface combinations were tested in a randomized order and horse-jockey pairings remained constant. Tri-axial acceleration data from gallop runs were filtered using bandpass Butterworth filters with cut-off frequencies of 15 Hz and 1 Hz, then integrated for displacement using Matlab. Peak displacement was assessed in both directions (positive 'maxima', negative 'minima') along the cranio-caudal (CC, positive = forwards), medio-lateral (ML, positive = right) and dorso-ventral (DV, positive = up) axes for all strides with frequency ≥2 Hz (mean = 2.06 Hz). Linear mixed-models determined whether surfaces, shoes or shoe-surface interactions (fixed factors) significantly affected the displacement patterns observed, with day, run and horse-jockey pairs included as random factors; significance was set at p<0.05. Data indicated that surface-type significantly affected peak COM displacements in all directions for the horse (p<0.0005) and for all directions (p≤0.008) but forwards in the jockey. The largest differences were observed in the DV-axis, with an additional 5.7 mm and 2.5 mm of downwards displacement for the horse and jockey, respectively, on the artificial surface. Shoeing condition significantly affected all displacement parameters except ML-axis minima for the horse (p≤0.007), and all displacement parameters for the jockey (p<0.0005). Absolute differences were again largest vertically, with notable similarities amongst displacements from barefoot and aluminium trials compared to GluShu and steel. Shoe-surface interactions affected all but CC-axis minima for the jockey (p≤0.002), but only the ML-axis minima and maxima and DV-axis maxima for the horse (p≤0.008). The results support the idea that hoof-surface interface interventions can significantly affect horse and jockey upper-body displacements. Greater sink of hooves on impact, combined with increased push-off during the propulsive phase, could explain the higher vertical displacements on the artificial track. Variations in distal limb mass associated with shoe-type may drive compensatory COM displacements to minimize the energetic cost of movement. The artificial surface and steel shoes provoked the least CC-axis movement of the jockey, so may promote greatest stability. However, differences between horse and jockey mean displacements indicated DV-axis and CC-axis offsets with compensatory increases and decreases, suggesting the dyad might operate within displacement limits to maintain stability. Further work is needed to relate COM displacements to hoof kinematics and to determine whether there is an optimum configuration of COM displacement to optimise performance and minimise injury.

The Evolution of a Single Toe in Horses: Causes, Consequences, and the Way Forward

Horses are a classic example of macroevolution in three major traits-large body size, tall-crowned teeth (hypsodonty), and a single toe (monodactyly)-but how and why monodactyly evolved is still poorly understood. Existing hypotheses usually connect digit reduction in horses to the spread and eventual dominance of open-habitat grasslands, which took over from forests during the Cenozoic; digit reduction has been argued to be an adaptation for speed, locomotor economy, stability, and/or increased body size. In this review, we assess the evidence for these (not necessarily mutually exclusive) hypotheses from a variety of related fields, including paleoecology, phylogenetic comparative methods, and biomechanics. Convergent evolution of digit reduction, including in litopterns and artiodactyls, is also considered. We find it unlikely that a single evolutionary driver was responsible for the evolution of monodactyly, because changes in body size, foot posture, habitat, and substrate are frequently found to influence one another (and to connect to broader potential drivers, such as changing climate). We conclude with suggestions for future research to help untangle the complex dynamics of this remarkable morphological change in extinct horses. A path forward should combine regional paleoecology studies, quantitative biomechanical work, and make use of convergence and modern analogs to estimate the relative contributions of potential evolutionary drivers for digit reduction.

Comparative forelimb myology and muscular architecture of a juvenile Malayan tapir (Tapirus indicus)

The absence of preserved soft tissues in the fossil record is frequently a hindrance for palaeontologists wishing to investigate morphological shifts in key skeletal systems, such as the limbs. Understanding the soft tissue composition of modern species can aid in understanding changes in musculoskeletal features through evolution, including those pertaining to locomotion. Establishing anatomical differences in soft tissues utilising an extant phylogenetic bracket can, in turn, assist in interpreting morphological changes in hard tissues and modelling musculoskeletal movements during evolutionary transitions (e.g. digit reduction in perissodactyls). Perissodactyls (horses, rhinoceroses, tapirs and their relatives) are known to have originated with a four-toed (tetradactyl) forelimb condition. Equids proceeded to reduce all but their central digit, resulting in monodactyly, whereas tapirs retained the ancestral tetradactyl state. The modern Malayan tapir (Tapirus indicus) has been shown to exhibit fully functional tetradactyly in its forelimb, more so than any other tapir, and represents an ideal case-study for muscular arrangement and architectural comparison with the highly derived monodactyl Equus. Here, we present the first quantification of muscular architecture of a tetradactyl perissodactyl (T. indicus), and compare it to measurements from modern monodactyl caballine horse (Equus ferus caballus). Each muscle of the tapir forelimb was dissected out from a cadaver and measured for architectural properties: muscle-tendon unit (MTU) length, MTU mass, muscle mass, pennation angle, and resting fibre length. Comparative parameters [physiological cross-sectional area (PCSA), muscle volume, and % muscle mass] were then calculated from the raw measurements. In the shoulder region, the infraspinatus of T. indicus exhibits dual origination sites on either side of the deflected scapular spine. Within ungulates, this condition has only been previously reported in suids. Differences in relative contribution to limb muscle mass between T. indicus and Equus highlight forelimb muscles that affect mobility in the lateral and medial digits (e.g. extensor digitorum lateralis). These muscles were likely reduced in equids during their evolutionary transition from tetradactyl forest-dwellers to monodactyl, open-habitat specialists. Patterns of PCSA across the forelimb were similar between T. indicus and Equus, with the notable exceptions of the biceps brachii and flexor carpi ulnaris, which were much larger in Equus. The differences observed in PCSA between the tapir and horse forelimb muscles highlight muscles that are essential for maintaining stability in the monodactyl limb while moving at high speeds. This quantitative dataset of muscle architecture in a functionally tetradactyl perissodactyl is a pivotal first step towards reconstructing the locomotor capabilities of extinct, four-toed ancestors of modern perissodactyls, and providing further insights into the equid locomotor transition.

Head and pelvic vertical displacement in dogs with induced swinging limb lameness: an experimental study

Background

Swinging limb lameness is defined as a motion disturbance ascribed to a limb in swing phase. Little is known about its biomechanics in dogs, particularly about the body motions that accompany it, such as vertical head and pelvic motion asymmetry. The aim of this study was to describe the changes in vertical head and pelvic motion asymmetry in dogs with induced swinging limb motion disturbance, mimicking a swinging limb lameness. Fore- and hind-limb lameness was induced in ten sound dogs by placing a weight (200 g) proximal to the carpus or tarsus, respectively. Marker-based motion capture by eight infrared light emitting video cameras recorded the dogs when trotting on a treadmill. Body symmetry parameters were calculated, including differences between the two highest positions of the head (HDmax) and pelvis (PDmax) and between the two lowest positions of the head (HDmin) and pelvis (PDmin), with a value of zero indicating perfect symmetry.

Results

Induction of swinging forelimb lameness showed significant changes in HDmax (median and range: sound 1.3 mm [− 4.7 to 3.1], in the left side − 28.5 mm [− 61.2 to − 17.9] and in the right side 20.1 mm [− 4.4 to 47.5]) and, induction of swinging hind limb lameness showed significant changes in PDmax (sound 2.7 mm [− 7.4 to 7.2], in the left side − 10.9 mm [− 22.4 to 0.5] and in the right side 8.6 mm [− 3 to 30]), as well as an increased hip movement asymmetry (sound 1.6 mm [− 8.6 to 19.9], in the left side − 18.1 mm [− 36.7 to 5.4] and in the right side 15 mm [− 20.7 to 32.1]) (P < 0.05).

Conclusions

Induced swinging fore- and hind limb lameness resulted in significant increased asymmetry of the maximal vertical displacement movement of the head and pelvis, due to decreased lifting of the head in forelimb lameness and of the pelvis in hind limb lameness. The results suggest that asymmetry of the maximal vertical displacement of the head and pelvis (i.e. lifting) is a key lameness sign to evaluate during examination of swinging limb lameness.

Lateral movements of a massive tail influence gecko locomotion: an integrative study comparing tail restriction and autotomy

Tails are an intricate component of the locomotor system for many vertebrates. Leopard geckos (Eublepharis macularius) possess a large tail that is laterally undulated during steady locomotion. However, the tail is readily shed via autotomy, resulting in the loss of tail function, loss in body mass, and a cranial shift in the center of mass. To elucidate the function of tail undulations, we investigated changes in limb kinematics after manipulating the tail artificially by restricting tail undulations and naturally by removing the tail via autotomy. Restricting tail undulations resulted in kinematic adjustments similar to those that occur following tail autotomy, characterized by more flexed hind limb joints. These data suggest that effects of autotomy on locomotion may be linked to the loss of tail movements rather than the loss of mass or a shift in center of mass. We also provide empirical support for the link between lateral tail undulations and step length through the rotation of the pelvic girdle and retraction of the femur. Restriction and autotomy of the tail limits pelvic rotation, which reduces femur retraction and decreases step length. Our findings demonstrate a functional role for tail undulations in geckos, which likely applies to other terrestrial vertebrates.

Segmental morphometrics of the olive baboon (Papio anubis): a longitudinal study from birth to adulthood

The linear dimensions and inertial characteristics of the body are important in locomotion and they change considerably during the ontogeny of animals, including humans. This longitudinal and ontogenetic study has produced the largest dataset to date of segmental morphometrics in a Catarrhini species, the olive baboon. The objectives of the study were to quantify the changes in body linear and inertial dimensions and to explore their (theoretical) mechanical significance for locomotion. We took full-body measurements of captive individuals at regular intervals. Altogether, 14 females and 16 males were followed over a 7-year period, i.e. from infancy to adulthood. Our results show that individual patterns of growth are very consistent and follow the general growth pattern previously described in olive baboons. Furthermore, we obtained similar growth curve structures for segment lengths and masses, although the respective time scales were slightly different. The most significant changes in body morphometrics occurred during the first 2 years of life and concerned the distal parts of the body. Females and males were similar in size and shape at birth. The rate and duration of growth produced substantial size-related differences throughout ontogeny, while body shapes remained very similar between the sexes. We also observed significant age-related variations in limb composition, with a proximal shift of the centre of mass within the limbs, mainly due to changes in mass distribution and in the length of distal segments. Finally, we observed what we hypothesize to be 'early biomechanical optimization' of the limbs for quadrupedal walking. This is due to a high degree of convergence between the limbs' natural pendular periods in infants, which may facilitate the onset of quadrupedal walking. Furthermore, the mechanical significance of the morphological changes observed in growing baboons may be related to changing functional demands with the onset of autonomous (quadrupedal) locomotion. From a wider perspective, these data provide unique insights into questions surrounding both the processes of locomotor development in primates and how these processes might evolve.

Morphology and motion: hindlimb proportions and swing phase kinematics in terrestrially locomoting charadriiform birds

Differing limb proportions in terms of length and mass, as well as differences in mass being concentrated proximally or distally, influence the limb's moment of inertia (MOI), which represents its resistance to being swung. Limb morphology—including limb segment proportions—thus likely has direct relevance for the metabolic cost of swinging the limb during locomotion. However, it remains largely unexplored how differences in limb proportions influence limb kinematics during swing phase. To test whether differences in limb proportions are associated with differences in swing phase kinematics, we collected hindlimb kinematic data from three species of charadriiform birds differing widely in their hindlimb proportions: lapwings, oystercatchers, and avocets. Using these three species, we tested for differences in maximum joint flexion, maximum joint extension, and range of motion (RoM), in addition to differences in maximum segment angular velocity and excursion. We found that the taxa with greater limb MOI—oystercatchers and avocets—flex their limbs more than lapwings. However, we found no consistent differences in joint extension and RoM among species. Likewise, we found no consistent differences in limb segment angular velocity and excursion, indicating that differences in limb inertia in these three avian species do not necessarily underlie the rate or extent of limb segment movements. The observed increased limb flexion among these taxa with distally heavy limbs resulted in reduced MOI of the limb when compared to a neutral pose. A trade-off between exerting force to actively flex the limb and potential savings by a reduction of MOI is skewed towards reducing the limb's MOI due to MOI being in part a function of the radius of gyration squared. Increased limb flexion likely is a means to lower the cost of swinging the limbs.

Effects of barefoot trimming on hoof morphology

OBJECTIVE

To monitor changes in hoof morphology in response to barefoot trimming.

METHODS

Seven horses were trimmed every 6 weeks according to barefoot trimming principles, which involved levelling the hoof to live sole, lowering the heels, bevelling the toe and rounding the peripheral wall, while leaving the sole, frog and bars intact. A 4-month period was allowed to lower the heels sufficiently to achieve a hoof shape representative of the barefoot trim. This was regarded as the starting point for morphological adaptations in response to maintenance of the trim. Hoof morphology was measured from lateral, dorsal and solar view photographs and lateromedial radiographs taken at 0, 4 and 16 months. Changes from 0 to 4 months represented differences between a natural hoof shape and the trim, while changes from 4 to 16 months represented adaptive effects during hoof growth.

RESULTS

Establishment of the barefoot trim involved significant shortening of the toe, heel and medial and lateral walls, with increases in angulation at the toe, medial and lateral walls, but not at the heel. Maintenance of the trim resulted in a palmar/plantar migration of the heels, with increases in support length, heel angle and solar angle of the distal phalanx (P3).

CONCLUSIONS

Bevelling the toe and engaging the frog and bars in the weight-bearing function of the foot resulted in elevation of the heel angle and solar angle of P3. These changes may be beneficial in treating under-run heels and negative solar plane angulation of P3.

Energetic benefits and adaptations in mammalian limbs: Scale effects and selective pressures

Differences in limb size and shape are fundamental to mammalian morphological diversity; however, their relevance to locomotor costs has long been subject to debate. In particular, it remains unknown if scale effects in whole limb morphology could partially underlie decreasing mass-specific locomotor costs with increasing limb length. Whole fore- and hindlimb inertial properties reflecting limb size and shape-moment of inertia (MOI), mass, mass distribution, and natural frequency-were regressed against limb length for 44 species of quadrupedal mammals. Limb mass, MOI, and center of mass position are negatively allometric, having a strong potential for lowering mass-specific locomotor costs in large terrestrial mammals. Negative allometry of limb MOI results in a 40% reduction in MOI relative to isometry's prediction for our largest sampled taxa. However, fitting regression residuals to adaptive diversification models reveals that codiversification of limb mass, limb length, and body mass likely results from selection for differing locomotor modes of running, climbing, digging, and swimming. The observed allometric scaling does not result from selection for energetically beneficial whole limb morphology with increasing size. Instead, our data suggest that it is a consequence of differing morphological adaptations and body size distributions among quadrupedal mammals, highlighting the role of differing limb functions in mammalian evolution.

The foot-surface interaction and its impact on musculoskeletal adaptation and injury risk in the horse

The equine limb has evolved for efficient locomotion and high-speed performance, with adaptations of bone, tendon and muscle. However, the system lacks the ability seen in some species to dynamically adapt to different circumstances. The mechanical interaction of the limb and the ground is influenced by internal and external factors including fore-hind mass distribution, lead limb, moving on a curve, shoeing and surface properties. It is unclear which of the components of limb loading have the largest effect on injury and performance but peak load, impact and vibration all play a role. Factors related to the foot-ground interface that limit performance are poorly understood. Peak performance varies vastly between disciplines but at high speeds such as racing and polo, force and grip are key limits to performance.

Anatomical and biomechanical traits of broiler chickens across ontogeny. Part II. Body segment inertial properties and muscle architecture of the pelvic limb

In broiler chickens, genetic success for desired production traits is often shadowed by welfare concerns related to musculoskeletal health. Whilst these concerns are clear, a viable solution is still elusive. Part of the solution lies in knowing how anatomical changes in afflicted body systems that occur across ontogeny influence standing and moving. Here, to demonstrate these changes we quantify the segment inertial properties of the whole body, trunk (legs removed) and the right pelvic limb segments of five broilers at three different age groups across development. We also consider how muscle architecture (mass, fascicle length and other properties related to mechanics) changes for selected muscles of the pelvic limb. All broilers used had no observed lameness, but we document the limb pathologies identified post mortem, since these two factors do not always correlate, as shown here. The most common leg disorders, including bacterial chondronecrosis with osteomyelitis and rotational and angular deformities of the lower limb, were observed in chickens at all developmental stages. Whole limb morphology is not uniform relative to body size, with broilers obtaining large thighs and feet between four and six weeks of age. This implies that the energetic cost of swinging the limbs is markedly increased across this growth period, perhaps contributing to reduced activity levels. Hindlimb bone length does not change during this period, which may be advantageous for increased stability despite the increased energetic costs. Increased pectoral muscle growth appears to move the centre of mass cranio-dorsally in the last two weeks of growth. This has direct consequences for locomotion (potentially greater limb muscle stresses during standing and moving). Our study is the first to measure these changes in the musculoskeletal system across growth in chickens, and reveals how artificially selected changes of the morphology of the pectoral apparatus may cause deficits in locomotion.

How animals move: comparative lessons on animal locomotion

Comparative physiology often provides unique insights in animal structure and function. It is specifically through this lens that we discuss the fundamental properties of skeletal muscle and animal locomotion, incorporating variation in body size and evolved difference among species. For example, muscle frequencies in vivo are highly constrained by body size, which apparently tunes muscle use to maximize recovery of elastic recoil potential energy. Secondary to this constraint, there is an expected linking of skeletal muscle structural and functional properties. Muscle is relatively simple structurally, but by changing proportions of the few muscle components, a diverse range of functional outputs is possible. Thus, there is a consistent and predictable relation between muscle function and myocyte composition that illuminates animal locomotion. When animals move, the mechanical properties of muscle diverge from the static textbook force-velocity relations described by A. V. Hill, as recovery of elastic potential energy together with force and power enhancement with activation during stretch combine to modulate performance. These relations are best understood through the tool of work loops. Also, when animals move, locomotion is often conveniently categorized energetically. Burst locomotion is typified by high-power outputs and short durations while sustained, cyclic, locomotion engages a smaller fraction of the muscle tissue, yielding lower force and power. However, closer examination reveals that rather than a dichotomy, energetics of locomotion is a continuum. There is a remarkably predictable relationship between duration of activity and peak sustainable performance.

Scale effects between body size and limb design in quadrupedal mammals

Recently the metabolic cost of swinging the limbs has been found to be much greater than previously thought, raising the possibility that limb rotational inertia influences the energetics of locomotion. Larger mammals have a lower mass-specific cost of transport than smaller mammals. The scaling of the mass-specific cost of transport is partly explained by decreasing stride frequency with increasing body size; however, it is unknown if limb rotational inertia also influences the mass-specific cost of transport. Limb length and inertial properties--limb mass, center of mass (COM) position, moment of inertia, radius of gyration, and natural frequency--were measured in 44 species of terrestrial mammals, spanning eight taxonomic orders. Limb length increases disproportionately with body mass via positive allometry (length ∝ body mass(0.40)); the positive allometry of limb length may help explain the scaling of the metabolic cost of transport. When scaled against body mass, forelimb inertial properties, apart from mass, scale with positive allometry. Fore- and hindlimb mass scale according to geometric similarity (limb mass ∝ body mass(1.0)), as do the remaining hindlimb inertial properties. The positive allometry of limb length is largely the result of absolute differences in limb inertial properties between mammalian subgroups. Though likely detrimental to locomotor costs in large mammals, scale effects in limb inertial properties appear to be concomitant with scale effects in sensorimotor control and locomotor ability in terrestrial mammals. Across mammals, the forelimb's potential for angular acceleration scales according to geometric similarity, whereas the hindlimb's potential for angular acceleration scales with positive allometry.

Kinematics and ground reaction force determination: a demonstration quantifying locomotor abilities of young adult, middle-aged, and geriatric rats

Behavior, in its broadest definition, can be defined as the motor manifestation of physiologic processes. As such, all behaviors manifest through the motor system. In the fields of neuroscience and orthopedics, locomotion is a commonly evaluated behavior for a variety of disease models. For example, locomotor recovery after traumatic injury to the nervous system is one of the most commonly evaluated behaviors ^1-3. Though locomotion can be evaluated using a variety of endpoint measurements (e.g. time taken to complete a locomotor task, etc), semiquantitative kinematic measures (e.g. ordinal rating scales (e.g. Basso Beattie and Bresnahan locomotor (BBB) rating scale, etc)) and surrogate measures of behaviour (e.g. muscle force, nerve conduction velocity, etc), only kinetics (force measurements) and kinematics (measurements of body segments in space) provide a detailed description of the strategy by which an animal is able to locomote ¹. Though not new, kinematic and kinetic measurements of locomoting rodents is now more readily accessible due to the availability of commercially available equipment designed for this purpose. Importantly, however, experimenters need to be very familiar with theory of biomechanical analyses and understand the benefits and limitations of these forms of analyses prior to embarking on what will become a relatively labor-intensive study. The present paper aims to describe a method for collecting kinematic and ground reaction force data using commercially available equipment. Details of equipment and apparatus set-up, pre-training of animals, inclusion and exclusion criteria of acceptable runs, and methods for collecting the data are described. We illustrate the utility of this behavioral analysis technique by describing the kinematics and kinetics of strain-matched young adult, middle-aged, and geriatric rats.

Swing phase kinematic and kinetic response to weighting the hind pasterns

REASONS FOR PERFORMING STUDY

It is considered that specific exercises to strengthen limb musculature would be helpful.

OBJECTIVE

To describe swing phase kinematic and kinetic changes in the hindlimbs of trotting horses in response to the addition of leg weights to the hind pasterns.

METHODS

Six horses were prepared by placing reflective skin markers on the hindlimbs, the withers and fore hooves. Horses were evaluated at trot for 6 trials with and without leg weights (700 g) attached around the pasterns, with the 2 conditions applied in random order. The markers were tracked to determine peak heights of the flight arc of the hind hooves and swing phase joint angulations. Inverse dynamic analysis was used to calculate positive and negative work done across each joint in the first and second halves of the swing phase. Comparisons between conditions were made using paired t tests (normally distributed data) or the Wilcoxon rank-sum test (non-normally distributed data).

RESULTS

Peak height of the flight arc of the hind hooves was significantly higher with leg weights as a result of increased flexions of the stifle, tarsal and metatarsophalangeal joints. Increased positive (concentric) work was performed by the hip and tarsal musculature to protract and raise the limb in early swing, then to retract and lower the limb in late swing. Increased negative (eccentric) work was performed across the stifle and metatarsophalangeal joints to control their movements in response to increases in inertia and momentum due to the weights.

CONCLUSIONS

The addition of weight to the hind pasterns stimulates increased muscular activity across all the hindlimb joints from the hip to the metatarsophalangeal joint.

CLINICAL SIGNIFICANCE

The addition of weight to the hind pasterns may have therapeutic applications in activating and strengthening the hindlimb musculature. This is particularly relevant in the hip region, which appears more sensitive and responsive to the effect of weights than to tactile stimulation alone.

Task-dependent force sharing between muscle synergists during locomotion in turkeys

At most joints, there is a redundancy of muscle function. For any given movement, there are a wide range of possible solutions to the problem of how force is shared among muscle synergists. A better understanding of how force is shared among muscle synergists can provide insight into the mechanics and control of movement. We examined force sharing in the gastrocnemius of wild turkeys (Meleagris gallopavo), using strain gauges bonded to bony tendons. Force was measured separately in the lateral (LG) and medial (MG)heads of the gastrocnemius, to evaluate force sharing. We also used inverse dynamics to determine the total force required during swing phase. To determine whether the pattern of force sharing varied depending on the mechanical task, we used running speed (1 to 3.5 m s–1) and limb loading (30 and 60 g added tarsometatarsal mass) to vary the force required at the intertarsal joint. We found that the distribution of force between these two heads varied depending on the phase of the stride cycle. During stance, force was shared in near equal amounts between the two heads and this distribution was unaffected by changes in running speed or limb load. During swing phase, however, there was no force sharing. Force was produced only in the lateral head, and this force was not significantly different from the total force required, as calculated from inverse dynamics. Thus, the LG produced all of the force required for limb extension during swing. This change in the pattern of force sharing between stance and swing supports the theory that force sharing between muscle synergists is task-dependent.

The energetic costs of trunk and distal-limb loading during walking and running in guinea fowl Numida meleagris: I. Organismal metabolism and biomechanics

We examined the energetic cost of loading the trunk or distal portion of the leg in walking and running guinea fowl (Numida meleagris). These different loading regimes were designed to separately influence the energy use by muscles used during the stance and swing phases of the stride. Metabolic rate, estimated from oxygen consumption, was measured while birds locomoted on a motorized treadmill at speeds from 0.5 to 2.0 m s-1, either unloaded, or with a mass equivalent to 23% of their body mass carried on their backs, or with masses equal to approximately 2.5% of their body mass attached to each tarsometatarsal segment. In separate experiments, we also measured the duration of stance and swing in unloaded, trunk-loaded, or limb-loaded birds. In the unloaded and limb-loaded birds, we also calculated the mechanical energy of the tarsometatarsal segment throughout the stride. Trunk and limb loads caused similar increases in metabolic rate. During trunk loading, the net metabolic rate (gross metabolic rate-resting metabolic rate) increased by 17% above the unloaded value across all speeds. This percentage increase is less than has been found in most studies of humans and other mammals. The economical load carriage of guinea fowl is consistent with predictions based on the relative cost of the stance and swing phases of the stride in this species. However, the available comparative data and considerations of the factors that determine the cost of carrying extra mass lead us to the conclusion that the cost of load carrying is unlikely to be a reliable indicator of the distribution of energy use in stance and swing. Both loading regimes caused small changes in the swing and/or stance durations, but these changes were less than 10%. Loading the tarsometatarsal segment increased its segmental energy by 4.1 times and the segmental mechanical power averaged over the stride by 3.8 times. The increases in metabolism associated with limb loading appear to be linked to the increases in mechanical power. The delta efficiency (change in mechanical power divided by the change in metabolic power) of producing this power increased from 11% in walking to approximately 25% in running. Although tarsometatarsal loading was designed to increase the mechanical energy during swing phase, 40% of the increase in segmental energy occurred during late stance. Thus, the increased energy demand of distal limb loading in guinea fowl is predicted to cause increases in energy use by both stance- and swing-phase muscles.