The role of the extrinsic thoracic limb muscles in equine locomotion

A Descriptive Study on the Carcass, Muscle, and Offal Yields of the Plains Zebra (Equus quagga) Harvested in Two Seasons

This study presents descriptive data on the meat and offal production of Plains zebras harvested in the winter (n = 8) and summer (n = 12) seasons, at different respective locations in the Western Cape Province of South Africa. The cold dressing percentages were numerically higher for the winter (58.0 ± 0.60%) than for the summer-harvested animals (56.60 ± 0.70%). Heavier internal offal yields were reported for the winter-harvested group (70.76 ± 21.8 kg) compared to the summer-harvested animals (66.13 ± 3.78 kg). As harvest season had no influence, pooled data of the percentage contribution of each muscle to cold carcass weight indicated that the Longissimus et lumborum (3.5 ± 0.18%), semimembranosus (1.6 ± 0.04%), biceps femoris (2.7 ± 0.05%) and semitendinosus (0.9 ± 0.02%) muscles differed significantly in their respective contributions to cold carcass weight. No significant differences were recorded between the contribution of the infraspinatus (0.6 ± 0.02%), supraspinatus (0.4 ± 0.03%) and psoas major (0.6 ± 0.02%) muscles. Carcass and muscle yields, as well as low-cost protein offal yields from this study indicate that the Plains zebra has the potential to be used and distributed as an alternative protein source.

Legs as linkages: an alternative paradigm for the role of tendons and isometric muscles in facilitating economical gait

Considerable attention has been given to the spring-like behaviour of stretching and recoiling tendons, and how this can reduce the work demanded from muscle for a given loss-return cycling of mechanical energy during high-speed locomotion. However, even completely isometric muscle-tendon units have the potential to act as tension struts, forming links in linkages that avoid the demand for mechanical work-cycling in the first place. Here, forelimb and hindlimb structures and geometries of quadrupeds are considered in terms of linkages that avoid mechanical work at the level of both the whole limb and the individual muscles. The scapula, isometric serratus muscles and forelimb can be viewed as a modified Roberts' straight-line mechanism that supports an approximately horizontal path of the body with vertically orientated forces, resulting in low work demand at the level of both limb and muscle. Modelled isometric triceps brachii inserting to the olecranon form part of a series of four-bar linkages (forelimb) and isometric biceps femoris cranial, rectus femoris and tensor fascia latae form part of a series of six-bar linkages (hindlimb), in both cases potentially resulting in straight-line horizontal motion, generating appropriate moments about shoulder and hip to maintain vertical ground reaction forces and again low mechanical work demand from the limb. Analysing part of the complexity of animal limb structure as linkages that avoid work at the level of both the whole limb and the supporting muscles suggests a new paradigm with which to appreciate the role of isometric muscle-tendon units and multiple muscle origins.

On the importance of integrating comparative anatomy and One Health perspectives in anatomy education

As a result of many factors, including climate change, unrestricted population growth, widespread deforestation and intensive agriculture, a new pattern of diseases in humans is emerging. With increasing encroachment by human societies into wild domains, the interfaces between human and animal ecosystems are gradually eroding. Such changes have led to zoonoses, vector‐borne diseases, infectious diseases and, most importantly, the emergence of antimicrobial‐resistant microbial strains as challenges for human health. Now would seem to be an opportune time to revisit old concepts of health and redefine some of these in the light of emerging challenges. The One Health concept addresses some of the demands of modern medical education by providing a holistic approach to explaining diseases that result from a complex set of interactions between humans, environment and animals, rather than just an amalgamation of isolated signs and symptoms. An added advantage is that the scope of One Health concepts has now expanded to include genetic diseases due to advancements in omics technology. Inspired by such ideas, a symposium was organised as part of the 19^th International Federation of Associations of Anatomists (IFAA) Congress (August 2019) to investigate the scope of One Health concepts and comparative anatomy in contemporary medical education. Speakers with expertise in both human and veterinary anatomy participated in the symposium and provided examples where these two disciplines, which have so far evolved largely independent of each other, can collaborate for mutual benefit. Finally, the speakers identified some key concepts of One Health that should be prioritised and discussed the diverse opportunities available to integrate these priorities into a broader perspective that would attempt to explain and manage diseases within the scopes of human and veterinary medicine.

Infrared Thermography Correlates with Lactate Concentration in Blood during Race Training in Horses

In horse racing the most acceptable way to objectively evaluate adaptation to increased exertion is to measure lactate blood concentration. However, this may be stressful for the horse, therefore, a simple, noninvasive procedure to monitor race progress is desirable. Forty Thoroughbreds attended race training, with blood samples collected at rest, immediately after, and 30 min after exercise. The lactate concentration was determined 60 s after blood collection using an Accusport®. Thermal imaging of the neck and trunk areas was performed following international veterinary standards from a distance of approximately 2 m from the horse using the same protocol as the blood sampling. The Spearman rank correlation coefficients (ρ) between the changes in the blood lactate concentration and surface temperature measures were found for the regions of interest. The highest positive correlation coefficients were found in the musculus trapezius pars thoracica region for the maximal temperature (T Max; ρ = 0.83; p < 0.0001), the minimal temperature (T Min; ρ = 0.83; p < 0.0001), and the average temperature (T Aver; ρ = 0.85; p < 0.0001) 30 min after the exercise. The results showed that infrared thermography may supplement blood measurements to evaluate adaptation to increased workload during race training, however, more research and references values are needed.

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.

Ground reaction forces of overground galloping in ridden Thoroughbred racehorses

The horse has evolved to gallop economically at high speed. Limb force increases with speed but direct measures of limb ground reaction forces (GRFs) at gallop are sparse. This study reports GRFs for multiple limbs, using force plates, across seven Thoroughbred racehorses during ridden galloping. The results show peak vertical GRF values of 13.6 N kg^-1 (non-lead hindlimb), 12.3 N kg^-1 (lead hindlimb), 14.0 N kg^-1 (non-lead forelimb) and 13.6 N kg^-1 (lead forelimb) at 11.4 m s^-1 and recorded values are consistent with those predicted from duty factor. The distribution of body weight between the forelimbs and hindlimbs is approximated to 50:50, and is variable with speed, unlike the 60:40 commonly stated for cursorial quadrupeds in the literature. An even distribution of load on all limbs may help minimise accumulation of fatigue and assist in injury avoidance. Cranio-caudal force data concur with the observation that horses apply a net accelerative impulse with the hindlimbs and a net decelerative impulse with the forelimbs. Capturing GRFs enhances our knowledge on the mechanics of galloping in fast-moving species and provides insight into injury risk and factors limiting athletic performance.

Structural characteristics and predicted functional capacities of epaxial muscles in chondrodystrophic and non-chondrodystrophic dogs with and without suspected intervertebral disc herniation- a preliminary study

Epaxial muscle atrophy is related to spinal diseases in dogs. However, the influence of intervertebral disc herniation (IVDH) on the functional capacity of epaxial muscles has not been investigated. We aimed to estimate force and power-generating capacity of epaxial muscles in chondrodystrophic Dachshunds and non-chondrodystrophic Border terriers bred for similar purposes. Further we aimed to compare these features in Dachshunds with and without IVDH. Cadavers of Dachshunds (n = 16) and Border terriers (n = 7) were investigated with MRI. In the absence of clinical information, MRI findings were used to categorize the Dachshunds into affected (n = 8) and non-affected (n = 8). Epaxial muscle mass, muscle belly length, fascicle length, architectural index and physiological cross-sectional area (PCSA) were obtained through dissections, pain and exercise history through questionnaires. Difference between groups and effect of covariates were assessed with ANCOVA models. Dachshunds had greater muscle mass in M. splenius, M. longissimus capitis and M. iliocostalis thoracis (all P < .05). Dachshunds had higher PCSA in M. semispinalis complexus (P = .004) and M. iliocostalis lumborum (P = .016) than Border terriers, which had longer muscle fascicles in these muscles (P = .004 and P = .002, respectively). Affected Dachshunds had longer muscle fascicles than non-affected Dachshunds in M. longissimus thoracis et lumborum (P = .004) and M. longissimus cervicis (P = .011). Body weight had a significant impact on all muscle variables, but pain and exercise had none. Dachshund epaxial muscles have greater potential for force production than those of the Border terrier. This may imply that Dachshunds, due to predisposition to IVDH, require more spinal stability provided by the epaxial muscles.

Biomechanics of predator-prey arms race in lion, zebra, cheetah and impala

The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator-prey pairs, lion-zebra and cheetah-impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator-prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate.

Musculoskeletal networks reveal topological disparity in mammalian neck evolution

BACKGROUND

The increase in locomotor and metabolic performance during mammalian evolution was accompanied by the limitation of the number of cervical vertebrae to only seven. In turn, nuchal muscles underwent a reorganization while forelimb muscles expanded into the neck region. As variation in the cervical spine is low, the variation in the arrangement of the neck muscles and their attachment sites (i.e., the variability of the neck's musculoskeletal organization) is thus proposed to be an important source of neck disparity across mammals. Anatomical network analysis provides a novel framework to study the organization of the anatomical arrangement, or connectivity pattern, of the bones and muscles that constitute the mammalian neck in an evolutionary context.

RESULTS

Neck organization in mammals is characterized by a combination of conserved and highly variable network properties. We uncovered a conserved regionalization of the musculoskeletal organization of the neck into upper, mid and lower cervical modules. In contrast, there is a varying degree of complexity or specialization and of the integration of the pectoral elements. The musculoskeletal organization of the monotreme neck is distinctively different from that of therian mammals.

CONCLUSIONS

Our findings reveal that the limited number of vertebrae in the mammalian neck does not result in a low musculoskeletal disparity when examined in an evolutionary context. However, this disparity evolved late in mammalian history in parallel with the radiation of certain lineages (e.g., cetartiodactyls, xenarthrans). Disparity is further facilitated by the enhanced incorporation of forelimb muscles into the neck and their variability in attachment sites.

Submaximal exercise training improves mitochondrial efficiency in the gluteus medius but not in the triceps brachii of young equine athletes

We tested the hypothesis that, similar to humans and rodents, exercise training would enhance mitochondrial (Mt) biogenesis and function in skeletal muscle of young horses. Twenty-four Quarter Horse yearlings were randomly assigned to either submaximal exercise training or no forced exercise (untrained). Biopsies were collected from the gluteus medius and triceps brachii before and after 9 wk of treatment. Citrate synthase activity was lower (P < 0.0001) and cytochrome c oxidase activity per Mt unit was higher (P < 0.0001) in gluteus compared to triceps, but neither changed over the trial period. From wk 0 to 9, intrinsic Mt respiration (P_CI, P_CI+II; P = 0.008) and electron transport capacity (E_CI+II; P = 0.01) increased, and LEAK-related flux control factor (FCF_L; P = 0.02) decreased in both muscles. After 9 wk of training, gluteus muscle exhibited higher (P < 0.05) intrinsic P_CI, P_CI+II, E_CI+II, and FCF_CI and FCF_CI+II, and lower FCF_L (P = 0.0002). Mitochondrial content did not change from wk 0 to 9, and also not in response to submaximal exercise training. Improvements in Mt function were most directly related to ongoing growth of horses independent of muscle group, and training further enhanced Mt function in the gluteus medius.

A three-dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology

Forelimb morphology is an indicator for terrestrial locomotor ecology. The limb morphology of the enigmatic tapir (Perissodactyla: Tapirus) has often been compared to that of basal perissodactyls, despite the lack of quantitative studies comparing forelimb variation in modern tapirs. Here, we present a quantitative assessment of tapir upper forelimb osteology using three-dimensional geometric morphometrics to test whether the four modern tapir species are monomorphic in their forelimb skeleton. The shape of the upper forelimb bones across four species (T. indicus; T. bairdii; T. terrestris; T. pinchaque) was investigated. Bones were laser scanned to capture surface morphology and 3D landmark analysis was used to quantify shape. Discriminant function analyses were performed to reveal features which could be used for interspecific discrimination. Overall our results show that the appendicular skeleton contains notable interspecific differences. We demonstrate that upper forelimb bones can be used to discriminate between species (>91% accuracy), with the scapula proving the most diagnostic bone (100% accuracy). Features that most successfully discriminate between the four species include the placement of the cranial angle of the scapula, depth of the humeral condyle, and the caudal deflection of the olecranon. Previous studies comparing the limbs of T. indicus and T. terrestris are corroborated by our quantitative findings. Moreover, the mountain tapir T. pinchaque consistently exhibited the greatest divergence in morphology from the other three species. Despite previous studies describing tapirs as functionally mediportal in their locomotor style, we find osteological evidence suggesting a spectrum of locomotor adaptations in the tapirs. We conclude that modern tapir forelimbs are neither monomorphic nor are tapirs as conserved in their locomotor habits as previously described. J. Morphol. 277:1469-1485, 2016. © 2016 Wiley Periodicals, Inc.

Histochemistry profile of the biceps brachii muscle fibres of capuchin monkeys (Cebus apella, Linnaeus, 1758)

A general analysis of the behaviour of "Cebus" shows that when this primate moves position to feed or perform another activity, it presents different ways of locomotion. This information shows that the brachial biceps muscle of this animal is frequently used in their locomotion activities, but it should also be remembered that this muscle is also used for other development activities like hiding, searching for objects, searching out in the woods, and digging in the soil. Considering the above, it was decided to research the histoenzimologic characteristics of the brachial biceps muscle to observe whether it is better adpted to postural or phasic function. To that end, samples were taken from the superficial and deep regions, the inserts proximal (medial and lateral) and distal brachial biceps six capuchin monkeys male and adult, which were subjected to the reactions of m-ATPase, NADH-Tr. Based on the results of these reactions fibres were classified as in Fast Twitch Glycolitic (FG), Fast Twitch Oxidative Glycolitic (FOG) and Slow Twitc (SO). In general, the results, considering the muscle as a whole, show a trend of frequency FOG> FG> SO. The data on the frequency were studied on three superficial regions FOG=FG>SO; the deep regions of the inserts proximal FOG=FG=SO and inserting the distal FOG>FG=SO. In conclusion, the biceps brachii of the capuchin monkey is well adapted for both postural and phasic activities.

Girth pressure measurements reveal high peak pressures that can be avoided using an alternative girth design that also results in increased limb protraction and flexion in the swing phase

Girths are frequently blamed for veterinary and performance problems, but research into girth/horse interaction is sparse. The study objectives were (1) to determine location of peak pressure under a range of girths, and (2) to compare horse gait between the horse's standard girth and a girth designed to avoid detected peak pressure locations. In the first part of the study, and following validation procedures, a calibrated pressure mat placed under the girth of 10 horses was used to determine the location of peak pressures. A girth was designed to avoid peak pressure locations (Girth F). In the second part, 20 elite horses/riders with no lameness or performance problem were ridden in Girth F and their standard girth (Girth S) in a double blind crossover design. Pressure mat data were acquired from under the girths. High speed video was captured and forelimb and hindlimb protraction, maximal carpal and tarsal flexion during flight were determined in trot. In standard girths, peak pressures were located over the musculature behind the elbow. Pressure mat results revealed that the maximum forces with Girth S were 22% (left) and 14% (right) greater than Girth F, and peak pressures were 76% (left) and 98% (right) greater (P<0.01 for all). On gait evaluation, Girth F was associated with 6-11% greater forelimb protraction, 10-20% greater hindlimb protraction, 4% greater carpal flexion, and 3% greater tarsal flexion than Girth S (P<0.01 for all). Peak pressures were located where horses tend to develop pressure sores. Girth F reduced peak pressures under the girth, and improved limb protraction and carpal/ tarsal flexion, which may reflect improved posture and comfort.

Forelimb muscle activity during equine locomotion

Few quantitative data exist to describe the activity of the distal muscles of the equine forelimb during locomotion, and there is an incomplete understanding of the functional roles of the majority of the forelimb muscles. Based on morphology alone it would appear that the larger proximal muscles perform the majority of work in the forelimb, whereas the smaller distal muscles fulfil supplementary roles such as stabilizing the joints and positioning the limb for impact with the ground. We measured the timing and amplitude of the electromyographic activity of the intrinsic muscles of the forelimb in relation to the phase of gait (stance versus swing) and the torque demand placed on each joint during walking, trotting and cantering. We found that all forelimb muscles, except the extensor carpi radialis (ECR), were activated just prior to hoof-strike and deactivated during stance. Only the ECR was activated during swing. The amplitudes of muscle activation typically increased as gait speed increased. However, the amplitudes of muscle activation were not proportional to the net joint torques, indicating that passive structures may also contribute significantly to torque generation. Our results suggest that the smaller distal muscles help to stabilize the forelimb in early stance, in preparation for the passive structures (tendons and ligaments) to be stretched. The distal forelimb muscles remain active throughout stance only during canter, when the net torques acting about the distal forelimb joints are highest. The larger proximal muscles activate in a complex coordination to position and stabilize the shoulder and elbow joints during ground contact.

Speed and incline during thoroughbred horse racing: racehorse speed supports a metabolic power constraint to incline running but not to decline running

We used a radio tracking system to examine the speed of 373 racehorses on different gradients on an undulating racecourse during 33 races, each lasting a few minutes. Horses show a speed detriment on inclines (0.68 m · s(-1) · 1% gradient(-1), r(2) = 0.97), the magnitude of which corresponds to trading off the metabolic cost (power) of height gain with the metabolic cost (power) of horizontal galloping. A similar relationship can be derived from published data for human runners. The horses, however, were also slower on the decline (-0.45 m · s(-1) · 1% gradient(-1), r(2) = 0.92). Human athletes run faster on a decline, which can be explained by the energy gained by the center of mass from height loss. This study has shown that horses go slower, which may be attributable to the anatomical simplicity of their front legs limiting weight support and stability when going downhill. These findings provide insight into limits to athletic performance in racehorses, which may be used to inform training regimens, as well as advancing knowledge from both veterinary and basic science perspectives.

Relationship between muscle forces, joint loading and utilization of elastic strain energy in equine locomotion

Storage and utilization of strain energy in the elastic tissues of the distal forelimb of the horse is thought to contribute to the excellent locomotory efficiency of the animal. However, the structures that facilitate elastic energy storage may also be exposed to dangerously high forces, especially at the fastest galloping speeds. In the present study, experimental gait data were combined with a musculoskeletal model of the distal forelimb of the horse to determine muscle and joint contact loading and muscle–tendon work during the stance phase of walking, trotting and galloping. The flexor tendons spanning the metacarpophalangeal (MCP) joint – specifically, the superficial digital flexor (SDF), interosseus muscle (IM) and deep digital flexor (DDF) – experienced the highest forces. Peak forces normalized to body mass for the SDF were 7.3±2.1, 14.0±2.5 and 16.7±1.1 N kg–1 in walking, trotting and galloping, respectively. The contact forces transmitted by the MCP joint were higher than those acting at any other joint in the distal forelimb, reaching 20.6±2.8, 40.6±5.6 and 45.9±0.9 N kg–1 in walking, trotting and galloping, respectively. The tendons of the distal forelimb (primarily SDF and IM) contributed between 69 and 90% of the total work done by the muscles and tendons, depending on the type of gait. The tendons and joints that facilitate storage of elastic strain energy in the distal forelimb also experienced the highest loads, which may explain the high frequency of injuries observed at these sites.

Functional specialization and ontogenetic scaling of limb anatomy in Alligator mississippiensis

Crocodylians exhibit a fascinating diversity of terrestrial gaits and limb motions that remain poorly described and are of great importance to understanding their natural history and evolution. Their musculoskeletal anatomy is pivotal to this diversity and yet only qualitative studies of muscle-tendon unit anatomy exist. The relative masses and internal architecture (fascicle lengths and physiological cross-sectional areas) of muscles of the pectoral and pelvic limbs of American alligators (Alligator mississippiensis Daudin 1801) were recorded for an ontogenetic series of wild specimens (n = 15, body masses from 0.5 to 60 kg). The data were analysed by reduced major axis regression to determine scaling relationships with body mass. Physiological cross-sectional areas and therefore muscle force-generating capacity were found to be greater in the extensor (anti-gravity) muscles of the pelvic limb than in the pectoral limb, reflecting how crocodylians differ from mammals in having greater loading of the hindlimbs than the forelimbs. Muscle masses and architecture were generally found to scale isometrically with body mass, suggesting an ontogenetic decrease in terrestrial athleticism. This concurs with the findings of previous studies showing ontogenetic decreases in limb bone length and the general scaling principle of a decline of strength : weight ratios with increasing size in animals. Exceptions to isometric scaling found included positive allometry in fascicle length for extensor musculature of both limbs, suggesting an ontogenetic increase in working range interpreted as increasing postural variability - in particular the major hip extensors - the interpretation of which is complicated by previous described ontogenetic increase of moment arms for these muscles.

The distal forelimb musculature in aquatic and terrestrial turtles: phylogeny or environmental constraints?

We compared the muscular anatomy of the distal front limb in terrestrial and aquatic chelonians to test whether observed differences between the two groups are associated with their divergent lifestyles and locomotor modes. Given the different use of the forelimb in the two environments (body support and propulsion on land vs. mainly propulsion in water) we expected that: (1) aquatic and terrestrial turtles would show differences in their muscular anatomy, with aquatic species having more individualized muscle bundlesto allow for the complex forearm movements observed during swimming, and (2) that terrestrial turtles would have more robust muscles to support their body weight against gravity. To address these questions, we examined the forelimb myology and associated tissues in six aquatic or semi-aquatic turtles (Phyrnops hilarii, Podocnemis unifilis, Trachemys scripta, Sacalia bealei, Cuora amboinensis and Mauremys caspica) and six terrestrial or semi-terrestrial turtles (Geochelone chilensis, Testudo graeca, Cuora galbinifrons, Glyptemys insculpta, Terrapene carolina and Rhinoclemmys pulcherrima). This paper describes the general structure of the forelimb musculature in all species, and quantifies muscle masses in those species with more than five specimens available (Ph. hilarii, Po. unifilis and Ge. chilensis). The general structure of the forelimb muscles in the strictly terrestrial species Ge. chilensis and Tes. graeca was found to be notably different from the pattern of the aquatic and semi-aquatic species examined, showing a distinct fusion of the different muscular bodies. Ter. carolina also show a distinctly terrestrial pattern, but a less extensive tendon development. R. pulcherrima and GI. insculpta were found to be morphologically intermediate; in the geoemydids the strictly terrestrial bauplan never appears. Quantitative differences in the robustness or mass of the distal forelimb muscles were also observed for the species investigated, supporting our prediction that the extensor muscles are more robust in terrestrial turtles. However, in contrast to our expectations, not only the extensor muscles of the distal forelimb (which are crucial in providing both body support and propulsion), but all muscles acting around the wrist were found to be heavier in terrestrial turtles.

High-speed gallop locomotion in the Thoroughbred racehorse. II. The effect of incline on centre of mass movement and mechanical energy fluctuation

During locomotion on an incline, mechanical work is performed to move an animal up the slope and increase the potential energy (PE) of the trunk and hence the centre of mass (CoM). Thus, at a given speed the total net mechanical work increases with the PE of the animal. In this study we investigate the mechanical energy (ME) fluctuations and the mechanical cost of transport (MCT) in six horses galloping up a range of gradients. We captured trunk movement with a six degrees-of-freedom inertial sensor mounted over the dorsal spinous process of the fourth to sixth thoracic vertebrae of the horse. Footfall timings were measured using a previously validated system of limb-mounted accelerometers. Speed was measured using a Global Positioning System (GPS) data logger. A track survey provided detailed incline information for the track. Linear (craniocaudal, mediolateral and dorsoventral) and rotational (roll, pitch and heading) kinematic parameters(displacement, velocity and acceleration) were calculated at speeds ranging from 9.0 to 12.0 m s–1 during routine training over a range of inclines. Estimates of ME fluctuations and the MCT were made. Results showed the effect of incline on trunk motion during galloping was small. Increases in linear mechanical work and MCT were primarily explained by an increase in the work required to move the animal up the slope (and increase the PE of the CoM). Within the stride the majority of the work was performed during hindlimb stance. Our results have provided new insights into how horses power uphill locomotion.

Comparative anatomy and muscle architecture of selected hind limb muscles in the Quarter Horse and Arab

The Quarter Horse (bred for acceleration) and the Arab (bred for endurance) are situated at either end of the equine athletic spectrum. Studies into the form and function of the leg muscles in human sprint and endurance runners have demonstrated that differences exist in their muscle architecture. It is not known whether similar differences exist in the horse. Six Quarter Horse and six Arab fresh hind limb cadavers were dissected to gain information on the muscle mass and architecture of the following muscles: gluteus medius; biceps femoris; semitendinosus; vastus lateralis; gastrocnemius; tibialis cranialis and extensor digitorum longus. Specifically, muscle mass, fascicle length and pennation angle were quantified and physiological cross-sectional area (PCSA) and maximum isometric force were estimated. The hind limb muscles of the Quarter Horse were of a significantly greater mass, but had similar fascicle lengths and pennation angles when compared with those of the Arab; this resulted in the Quarter Horse hind limb muscles having greater PCSAs and hence greater isometric force potential. This study suggests that Quarter Horses as a breed inherently possess large strong hind limb muscles, with the potential to accelerate their body mass more rapidly than those of the Arab.

Effects of treadmill inclination and speed on forelimb muscle activity and kinematics in the horse

The study aimed to investigate the effect of speed and incline on EMG activity in thebrachiocephalicusmuscle and the long and lateral heads of thetriceps brachiimuscle. Six horses were exercised on a treadmill at walk (1.7 m s-1), trot (4.0 m s-1) and right lead canter (7.2 m s-1) on a 0 and 8% incline. Kinematics (120 Hz) and electromyography (EMG) (2000 Hz) data were collected simultaneously from the left forelimb of each horse. Significant differences in relation to velocity and incline were identified using two-way ANOVA andpost hocStudent–Newman–Keuls tests (P≪0.05). The degree of association between timing of peak EMG intensity and the timing of maximum protraction/retraction angles was assessed using ANCOVA. Increases in velocity led to an increase in stride length and reduction in stride duration. Exercise on the incline increased stance duration and decreased swing duration, while limb protraction/retraction increased. The time of peak EMG activity in thebrachiocephalicuswas highly related to time of maximum limb retraction (r2=0.84). The time of peak EMG activity in the long head of thetriceps brachiiwas highly associated with time of maximum limb protraction (r2=0.87). Increases in velocity and incline both caused an increase in the intensity of the EMG signal from each muscle. Duration of EMG activity was prolonged in the long head of thetriceps brachiimuscle and in thebrachiocephalicusmuscle as velocity increased. Treadmill speed and slope therefore both alter the workload placed on forelimb muscles.

Centre of mass movement and mechanical energy fluctuation during gallop locomotion in the Thoroughbred racehorse

During locomotion cyclical interchange between different forms of mechanical energy enhances economy; however, 100% efficiency cannot be achieved and ultimately some mechanical work must be performed de novo. There is a metabolic cost associated with fluctuations in mechanical energy, even in the most efficient animals. In this study we investigate the exchanges between different forms of mechanical energy involved in high-speed gallop locomotion in Thoroughbred race horses during over-ground locomotion using innovative, mobile data collection techniques. We use hoof-mounted accelerometers to capture foot contact times, a GPS data logger to monitor speed and an inertial sensor mounted over the dorsal spinous processes of the fourth to sixth thoracic vertebrae (the withers) of the horse to capture trunk movement with six degrees of freedom. Trunk movement data were used to estimate the movement of the centre of mass (CoM). Linear(craniocaudal, mediolateral and dorsoventral) and rotational (roll, pitch and heading) kinematic parameters (displacement, velocity and acceleration) were calculated for seven horses at gallop speeds ranging from 7 to 17 m s-1 during their regular training sessions. These were used to estimate external mechanical energy (potential energy and linear kinetic energy of the CoM) as well as selected components of internal energy (angular kinetic energy). Elastic energy storage in the limbs was estimated from duty factor, sine wave assumptions and published leg stiffness values.

External mechanical energy changes were dominated by changes in craniocaudal velocity. Potential energy change, which was in phase with craniocaudal energy during the front limb stances, was small. Elastic energy storage in the limbs was small compared to the overall amplitude of fluctuation of external mechanical energy. Galloping at high speeds does not therefore fit classical spring mass mechanics.

The role of the extrinsic thoracic limb muscles in equine locomotion

Muscles have two major roles in locomotion: to generate force and to absorb/generate power (do work). Economical force generation is achieved by short-fibred pennate muscle while the maximum power output of a muscle is architecture independent. In this study we tested the hypothesis that there is an anatomical and structural separation between the force-generating anti-gravity muscles and the propulsive (limb/trunk moving) muscles of the equine forelimb. Muscle mass and fascicle length measurements were made on the thoracic limb extrinsic muscles of six fresh horse cadavers. Physiological cross-sectional area and maximum isometric force were then estimated. Maximum power was estimated from muscle volume and published contraction velocity data. The majority of extrinsic forelimb muscles were large with long fascicles arranged in parallel to the long axis of the muscle. Muscles arranged in this way are optimised for doing work. The architecture of serratus ventralis thoracis (SVT) was unique. It had short (48 +/- 17 mm) fascicles, arranged at about 45 degrees to the long axis of the muscle, which would suggest a force-generating, anti-gravity role. The muscle belly of SVT was sandwiched between two broad, thick sheets of aponeurosis. Hence, SVT could make a significant contribution to the overall elastic properties of the thoracic limb.