Contribution of the forelimbs and hindlimbs of the horse to mechanical energy changes in jumping

Muscle-Driven Predictive Physics Simulations of Quadrupedal Locomotion in the Horse

Musculoskeletal simulations can provide insights into the underlying mechanisms that govern animal locomotion. In this study, we describe the development of a new musculoskeletal model of the horse, and to our knowledge present the first fully muscle-driven, predictive simulations of equine locomotion. Our goal was to simulate a model that captures only the gross musculoskeletal structure of a horse, without specialized morphological features. We mostly present simulations acquired using feedforward control, without state feedback ("top-down control"). Without using kinematics or motion capture data as an input, we have simulated a variety of gaits that are commonly used by horses (walk, pace, trot, tölt, and collected gallop). We also found a selection of gaits that are not normally seen in horses (half bound, extended gallop, ambling). Due to the clinical relevance of the trot, we performed a tracking simulation that included empirical joint angle deviations in the cost function. To further demonstrate the flexibility of our model, we also present a simulation acquired using spinal feedback control, where muscle control signals are wholly determined by gait kinematics. Despite simplifications to the musculature, simulated footfalls and ground reaction forces followed empirical patterns. In the tracking simulation, kinematics improved with respect to the fully predictive simulations, and muscle activations showed a reasonable correspondence to electromyographic signals, although we did not predict any anticipatory firing of muscles. When sequentially increasing the target speed, our simulations spontaneously predicted walk-to-run transitions at the empirically determined speed. However, predicted stride lengths were too short over nearly the entire speed range unless explicitly prescribed in the controller, and we also did not recover spontaneous transitions to asymmetric gaits such as galloping. Taken together, our model performed adequately when simulating individual gaits, but our simulation workflow was not able to capture all aspects of gait selection. We point out certain aspects of our workflow that may have caused this, including anatomical simplifications and the use of massless Hill-type actuators. Our model is an extensible, generalized horse model, with considerable scope for adding anatomical complexity. This project is intended as a starting point for continual development of the model and code that we make available in extensible open-source formats.

Variability of Jump Biomechanics Between Horses of Different Age and Experience Using Commercial Inertial Measurement Unit Technology

The application of commercial inertial measurement units has become popular in equestrian sports, which may help to eliminate a gap of knowledge concerning many aspects of biomechanics in training. This study employed the Seaver IMU system to measure jumping characteristics of horses with differing age-competition experience during regular training. It was hypothesized that experience level results in lower variability of jumping parameters. Twelve Warmblood horses aged 5 to 6 years with/without competition experience and 7 to 11 years with experience were investigated during regular training in 2 training centers. Consistent number of 10 successive jumps of the individual chosen course of vertical and spread obstacles (5th -15th) were analyzed and the following parameters were measured: jump height, reserve and length; taking off angle, acceleration, velocity; jump spatial shifting, energy by landing, and frequency of approach strides. Preliminary analysis confirmed comparable physiological effort in 2 training center based on heart rate, distance and duration measurements. The multifactorial analysis of variance for biomechanical data included in the statistical model the random effect of horse and fixed effects of training center, age-experience group, successive jump number, obstacle type and height. Four parameters were significantly different between the younger, inexperienced group and experienced younger and older horses: height of jump (P = .01), frequency of approach strides (P = .005), acceleration of taking off (P = .01), and energy by landing (P = .0013). Standard errors for almost all the parameters reached higher values for the youngest, inexperienced horses. Variability of jumping parameters was lower for experienced groups of horses, suggesting higher precision on obstacle courses.

Characteristics of the Flight Arc in Horses Jumping Three Different Types of Fences in Olympic Competition

Show jumping horses must execute fences of varying height and width, but the effect of this on jumping kinematics during the airborne phase have not been described. The aim of this study was to describe differences within- and between-horses in CM trajectory, trunk orientation and average trunk angular velocity in a group of elite horses executing three fences: vertical fence (1.60 m), spread fence (1.50 × 1.80 m), water jump (4.5 m) during an Olympic competition. Two-dimensional kinematic data (60 Hz) were collected from video cameras set perpendicular to each fence. After manual digitization, linear and angular variables related to the position and rotation of the CM and trunk were calculated. Linear fixed effects models evaluated within-group differences between fences and kinematic variables. Repeated measures correlation (rmcorr) evaluated within-horse associations between kinematic variables and fence type. Compared with the water jump, CM vertical velocity, CM peak height, and average trunk angular velocity were significantly higher (P < .05) and CM horizontal velocity was significantly lower (P < .05) for the vertical and spread fences. Peak CM height coincided approximately with the middle of the spread fence, toward the take-off for the water jump and landing for the vertical fence. The trunk was significantly more inclined at take-off for the vertical fence and significantly less inclined for the water jump at landing. Rmcorr analysis revealed that individual horses generally employ similar jumping techniques for each fence type. Findings provide original insight into the mechanical requirements for elite horses jumping different fence types.

Muscle Function and Kinematics during Submaximal Equine Jumping: What Can Objective Outcomes Tell Us about Athletic Performance Indicators?

Selection and training practices for jumping horses have not yet been validated using objective performance analyses. This study aimed to quantify the differences and relationships between movement and muscle activation strategies in horses with varying jump technique to identify objective jumping performance indicators. Surface electromyography (sEMG) and three-dimensional kinematic data were collected from horses executing a submaximal jump. Kinematic variables were calculated based on equestrian-derived performance indicators relating to impulsion, engagement and joint articulation. Horses were grouped using an objective performance indicator-center of mass (CM) elevation during jump suspension (Z_CM). Between-group differences in kinematic variables and muscle activation timings, calculated from sEMG data, were analyzed using one-way ANOVA. Statistical parametric mapping (SPM) evaluated between-group differences in time and amplitude-normalized sEMG waveforms. Relationships between movement and muscle activation were evaluated using Pearson correlation coefficients. Horses with the greatest Z_CM displayed significantly (p < 0.05) shorter gluteal contractions at take-off, which were significantly correlated (p < 0.05) with a faster approach and more rapid hindlimb shortening and CM vertical displacement and velocity, as well as shorter hindlimb stance duration at take-off. Findings provide objective support for prioritizing equestrian-derived performance indicators related to the generation of engagement, impulsion and hindlimb muscle power when selecting or training jumping horses.

Accelerometers Provide Early Genetic Selection Criteria for Jumping Horses

The aim of this study was to evaluate the genetic component of the locomotor jumping ability, via a wearable accelerometer sensor, and to estimate the genetic correlation with performance in competition, to introduce such criteria in selection schema. A sample of 1,056 young 3-year-old horses were equipped with a 3-dimensional accelerometer during a free jumping test, in regular breeding shows from 2015 to 2017. Seven variables were extracted from the dorso-ventral acceleration curve for the last three jumps over a double bar obstacle of 1.15 m for the front pole and 1.20 m for the back pole with a 1.20 m spread. Variables were the peaks of forelimbs, hindlimbs, and landing acceleration, the duration between peaks at take-off, the peak of forelimb acceleration and start of jump, jump duration and duration between the beginning of the impact of forelimbs and the peak at landing. During breeding shows, judges scored balance, strength, style, and reactivity for free jumping and jumping tests under saddle. Jumping competition results were recorded by logarithm of the sum of points earned in each competition. All horses in official competitions were included, i.e., 160,257 horses born in 1997 with a total of 649,491 annual performances. An animal mixed model with complete pedigree over four generations (353,236 horses) were used with fixed effects of jumping test location and date, morning/afternoon, gender, month of birth, rank of jump for accelerometric data, effect of year of competition, combined with age and gender for competition results. As a result, jump duration was the most heritable and repeatable for jump variables: h ² = 0.16 (0.06), r = 0.52 (0.02), while accelerations were moderately heritable (h ² = 0.05-0.09, r = 0.39-0.51). Judgement scores were heritable: 0.21 (0.07)-0.33 (0.09) and were highly correlated. Scores during free jumping were genetically correlated to jump duration: 0.71 (0.15)-0.88 (0.16). Both jump duration and judgement scores were genetically correlated to competition performance: 0.59 (0.13) for jump duration, from 0.60 (0.11) to 0.77 (0.12) for scores. Jump duration and judgement scores can be used as early selection criteria. The advantage of the accelerometric measurement is its objectivity and the ease of recording.

Limb dynamics in agility jumps of beginner and advanced dogs

A considerable body of work has examined the dynamics of different dog gaits, but there are no studies that have focused on limb dynamics in jumping. Jumping is an essential part of dog agility, a dog sport in which handlers direct their dogs through an obstacle course in a limited time. We hypothesized that limb parameters like limb length and stiffness indicate the skill level of dogs. We analyzed global limb parameters in jumping for 10 advanced and 10 beginner dogs. In experiments, we collected 3D kinematics and ground reaction forces during dog jumping at high forward speeds. Our results revealed general strategies of limb control in jumping and highlighted differences between advanced and beginner dogs. In take-off, the spatially leading forelimb was 75% (P<0.001) stiffer than the trailing forelimb. In landing, the trailing forelimb was 14% stiffer (P<0.001) than the leading forelimb. This indicates a strut-like action of the forelimbs to achieve jumping height in take-off and to transfer vertical velocity into horizontal velocity in landing (with switching roles of the forelimbs). During landing, the more (24%) compliant forelimbs of beginner dogs (P=0.005) resulted in 17% (P=0.017) higher limb compression during the stance phase. This was associated with a larger amount of eccentric muscle contraction, which might in turn explain the soft tissue injuries that frequently occur in the shoulder region of beginner dogs. For all limbs, limb length at toe-off was greater for advanced dogs. Hence, limb length and stiffness might be used as objective measures of skill.

Whole-Genome Signatures of Selection in Sport Horses Revealed Selection Footprints Related to Musculoskeletal System Development Processes

Selective breeding has led to gradual changes at the genome level of horses. Deciphering selective pressure patterns is progressive to understand how breeding strategies have shaped the sport horse genome; although, little is known about the genomic regions under selective pressures in sport horse breeds. The major goal of this study was to shed light on genomic regions and biological pathways under selective pressures in sport horses. In this study, whole-genome sequences of 16 modern sport and 35 non-sport horses were used to investigate the genomic selective signals of sport performance, by employing fixation index, nucleotide diversity, and Tajima's D approaches. A total number of 49 shared genes were identified using these approaches. The functional enrichment analysis for candidate genes revealed novel significant biological processes related to musculoskeletal system development, such as limb development and morphogenesis, having been targeted by selection in sport breeds.

Measuring Volumetric Changes of Equine Distal Limbs: A Pilot Study Examining Jumping Exercise

Simple Summary

When horse athletes exercise, forces are applied to their legs during each step. Repetitive loads applied during training and competition contribute to stress of leg structures. Swelling (i.e., local fluid accumulation) in the legs is a sign of increased stress in these structures. Currently, horse riders and trainers make training decisions based on visual observations of horse leg swelling, which are potentially subjective and imprecise. The aim of this study was to develop a low-cost, noninvasive method to measure lower leg volume in horses, as well as to assess the ability to detect differences before and after exercise. The tablet-mounted scanner measured increased lower leg volume after jumping, compared to scans before exercise. This method may serve as an objective tool for horse riders and trainers to prevent injury by modulating horse training frequency and intensity in response to physiological signs of stress, like leg swelling. Scans may also be used to seek veterinary consultation and treatment, as well as to guide rehabilitation from injury.

Abstract

Equine athletes can incur musculoskeletal injuries due to repetitive loading during training and competition. Prior to signs of lameness, horse trainers and veterinarians may observe swelling in the distal limbs, where injuries most frequently occur. Early observations may guide modulation of training to manage physiological stress and mitigate risk of injury. However, these observations of changing limb volume can be subjective and imprecise. The aim of this study was to assess the accuracy and applicability of a tablet-mounted, 3D scanner to measure and record distal limb volumes of horses before and after exercise. Users recorded scans of a cylinder of known volume with errors up to 8%. Experienced users’ measures were biased (i.e., consistently overestimated). The scanner was able to detect statistically significant increases in volume for both fore and hind limbs after one jumping session (310–2058 cm³). Age and intensity of workload may play a role in magnitude of limb swelling, but had mixed conclusions between fore and hind limbs. More studies with additional horses must be performed to solidify these relationships. The evaluated 3D scanner is a low-cost, accessible tool that was able to detect changes in limb swelling as a result of exercise and mechanical stress. With continued research, this information may guide training programs to decrease injury and maximize performance of equine athletes in the future.

A simple model predicts energetically optimised jumping in dogs

It is generally accepted that animals move in a way that minimises energy use during regular gait and there is evidence that the principle might extend more generally to locomotor behaviour and manoeuvres. Jumping during locomotion is a useful manoeuvre that contributes to the versatility of legged locomotion and is within the repertoire of many terrestrial animals. We describe a simple ballistic model that can be used to identify a single unique trajectory of the body's centre of mass that minimises the mechanical work to initiate a jump, regardless of the approach velocity or take-off position. The model was used to show that domestic dogs (Canis lupus familiaris) demonstrate complex anticipatory control of locomotor behaviour by systematically using jump trajectories close to those that minimised the mechanical energy of jumps over raised obstacles. It is unclear how the dogs acquired the complex perception and control necessary to exhibit the observed behaviour. The model may be used to investigate whether animals adopt energetically optimised behaviour in any similarly constrained ballistic task.

The deep fascia and retinacula of the equine forelimb - structure and innervation

Recent advances in human fascia research have shed new light on the role of the fascial network in movement perception and coordination, transmission of muscle force, and integrative function in body biomechanics. Evolutionary adaptations of equine musculoskeletal apparatus that assure effective terrestrial locomotion are employed in equestrianism, resulting in the wide variety of movements in performing horses, from sophisticated dressage to jumping and high-speed racing. The high importance of horse motion efficiency in the present-day equine industry indicates the significance of scientific knowledge of the structure and physiology of equine fasciae. In this study, we investigated the structure and innervation of the deep fascia of the equine forelimb by means of anatomical dissection, histology and immunohistochemistry. Macroscopically, the deep fascia appears as a dense, glossy and whitish lamina of connective tissue continuous with its fibrous reinforcements represented by extensor and flexor retinacula. According to the results of our histological examination, the general structure of the equine forelimb fascia corresponds to the characteristics of the human deep fasciae of the limbs. Although we did find specific features in all sample types, the general composition of all examined fascial tissues follows roughly the same scheme. It is composed of dense, closely packed collagen fibers organized in layers of thick fibrous bundles with sparse elastic fibers. This compact tissue is covered from both internal and external sides by loosely woven laminae of areolar connective tissue where elastic fibers are mixed with collagen. Numerous blood vessels running within the loose connective tissue contribute to the formation of regular vascular network throughout the compact layer of the deep fascia and retinacula. We found nerve fibers of different calibers in all samples analyzed. The fibers are numerous in the areolar connective tissue and near the blood vessels but scarce in the compact layers of collagen. We did not observe any Ruffini, Pacini or Golgi-Mazzoni corpuscles. In conclusion, the multilayered composition of compact bundles of collagen, sparse elastic fibers in the deep fascia and continuous transition into retinacula probably facilitate resistance to gravitational forces and volume changes during muscle contraction as well as transmission of muscle force during movement. However, further research focused on innervation is needed to clarify whether the deep fascia of the equine forelimb plays a role in proprioception and movement coordination.

Comparison between specific and nonspecific tests for evaluating the physical fitness of show jumping horses

Show jumping is a century-old Olympic sport performed worldwide. However, despite the prominence of this sport, there is currently no satisfactory evaluation of the physical fitness of its horses. Our study compared two standardised exercise tests (specific and nonspecific for show jumpers) to determine the importance of a show jumping specific evaluation test. Sixteen horses were divided into two performance groups (high and low performance), and all horses performed standardised exercise tests without jumps (SET1) and with jumps (SET2). Heart rate, blood lactate, glucose, blood gas, haematological parameters, and plasma ions were measured before and after the tests, and performance indices were calculated. Both exercise tests (SET1 and SET2) resulted in changes in nearly all measured variables that were expected, based on other studies, for the duration and nature of the exercise performed. Differences between the two performance groups were observed for lactate and glucose, as well as some blood gas variables and performance indicators. These differences might have been the result of better cardiovascular and metabolic adaptation of the high performance group to the show jumping exercises. For the SET1, differences between groups were mainly noted for variables related to aerobic capacity, which suggests that this measurement is important for the evaluation of equine performance in show jumping. The SET2 was capable of detecting different horse performance levels that could not be detected by the SET1, which indicates that a specific test for show jumping (that includes jumping movements) could provide important information for the evaluation of show jumpers. Based on our findings, we recommend that the SET2 be included in future protocols for evaluating jumping horses.

Mechanical Energy and Propulsion in Ergometer Double Poling by Cross-country Skiers

PURPOSE

This study aims to investigate fluctuations in total mechanical energy of the body (Ebody) in relation to external ergometer work (Werg) during the poling and recovery phases of simulated double-poling cross-country skiing.

METHODS

Nine male cross-country skiers (mean ± SD age, 24 ± 5 yr; mean ± SD body mass, 81.7 ± 6.5 kg) performed 4-min submaximal tests at low-intensity, moderate-intensity, and high-intensity levels and a 3-min all-out test on a ski ergometer. Motion capture analysis and load cell recordings were used to measure body kinematics and dynamics. From these, Werg, Ebody (sum of the translational, rotational, and gravitational potential energies of all segments), and their time differentials (power P) were calculated. Ptot--the rate of energy absorption or generation by muscles-tendons--was defined as the sum of Pbody and Perg.

RESULTS

Ebody showed large fluctuations over the movement cycle, decreasing during poling and increasing during the recovery phase. The fluctuation in Pbody was almost perfectly out of phase with Perg. Some muscle-tendon energy absorption was observed at the onset of poling. For the rest of poling and throughout the recovery phase, muscles-tendons generated energy to do Werg and to increase Ebody. Approximately 50% of cycle Ptot occurred during recovery for all intensity levels.

CONCLUSIONS

In double poling, the extensive contribution of the lower extremities and trunk to whole-body muscle-tendon work during recovery facilitates a "direct" transfer of Ebody to Werg during the poling phase. This observation reveals that double poling involves a unique movement pattern different from most other forms of legged terrestrial locomotion, which are characterized primarily by inverted pendulum or spring-mass types of movement.

Swing phase kinematics of horses trotting over poles

REASONS FOR PERFORMING STUDY

Trotting over poles is used therapeutically to restore full ranges of limb joint motion. The mechanics of trotting over poles have not yet been described, hence quantitative evidence for the presumed therapeutic effects is lacking.

OBJECTIVES

To compare limb kinematics in horses trotting over level ground, over low poles and over high poles to determine changes in joint angulations and hoof flight arcs.

STUDY DESIGN

Repeated measures experimental study in sound horses.

METHODS

Standard motion analysis procedures with skin-fixed reflective markers were used to measure swing phase kinematics from 8 horses trotting on level ground, over low (11 cm) and high (20 cm) poles spaced 1.05 ± 0.05 m apart. Spatiotemporal variables and peak swing phase joint flexion angles were compared using repeated measures ANOVA (P<0.05) with Bonferroni correction for pairwise post hoc testing.

RESULTS

Peak heights of the fore and hind hooves increased significantly and progressively from no poles (fore: 13.8 ± 3.8 cm; hind: 10.8 ± 2.4 cm) to low poles (fore: 30.9 ± 4.9 cm; hind: 24.9 ± 3.7 cm) and to high poles (fore: 41.0 ± 3.9 cm; hind: 32.7 ± 4.0 cm). All joints of the fore- and hindlimbs contributed to the increase in hoof height through increased swing phase flexion. The hooves cleared the poles due to increases in joint flexion rather than by raising the body higher during the suspension phases of the stride.

CONCLUSIONS

The increases in swing phase joint flexions indicate that trotting over poles is effective for activating and strengthening the flexor musculature. Unlike the use of proprioceptive stimulation devices in which the effects decrease over time due to habituation, the horse is required to elevate the hooves to ensure clearance whenever poles are present. The need to raise the limbs sufficiently to clear the poles and place the hooves accurately requires visuomotor coordination, which may be useful in the rehabilitation of neurological cases. The Summary is available in Chinese - see Supporting information.

Young horse response on changing distance in free jumping combination

The aim of the present study was to verify the influence of distance between obstacles in combination for free jumping test on linear and temporal kinematic parameters of the jump. Investigated groups of halfbred stallions being prepared for 100 days performance test (two groups, 36 horses in total) were filmed on different distances between main doublebarre obstacle and last cross-pole in the jumping lane. Both groups of horses were filmed during their regular work in the same training centre 1 week before performance test. Jumping parameters were obtained on the same size of the obstacle. Data were analysed separately for both groups by analysis of variance. On the basis of the conducted study, it is possible to conclude that in the range of the most popular free jumping distance horses may use different jumping techniques to clear the jump. The shorter distances between last two obstacles in the jumping lane in the range of 6.8 to 7.1 m stimulate higher jumps; however, the reaction of horses was not exactly the same for all measured jumping parameters.

The effect of induced forelimb lameness on thoracolumbar kinematics during treadmill locomotion

REASONS FOR PERFORMING STUDY

Lameness has often been suggested to result in altered movement of the back, but there are no detailed studies describing such a relationship in quantitative terms.

OBJECTIVES

To quantify the effect of induced subtle forelimb lameness on thoracolumbar kinematics in the horse.

METHODS

Kinematics of 6 riding horses was measured at walk and at trot on a treadmill before and after the induction of reversible forelimb lameness grade 2 (AAEP scale 1-5). Ground reaction forces (GRF) for individual limbs were calculated from kinematics.

RESULTS

The horses significantly unloaded the painful limb by 11.5% at trot, while unloading at walk was not significant. The overall flexion-extension range of back motion decreased on average by 0.2 degrees at walk and increased by 3.3 degrees at trot (P<0.05). Changes in angular motion patterns of vertebral joints were noted only at trot, with an increase in flexion of 0.9 degrees at T10 (i.e. angle between T6, T10 and T13) during the stance phase of the sound diagonal and an increase in extension of the thoracolumbar area during stance of the lame diagonal (0.7degrees at T13, 0.8 degres at T17, 0.5 degres at L1, 0.4 degrees at L3 and 0.3 degrees at L5) (P<0.05). Lameness further caused a lateral bending of the cranial thoracic vertebral column towards the lame side (1.3 degrees at T10 and 0.9 degrees at T13) (P<0.05) during stance of the lame diagonal.

CONCLUSIONS

Both range of motion and vertebral angular motion patterns are affected by subtle forelimb lameness. At walk, the effect is minimal, at trot the horses increased the vertebral range of motion and changed the pattern of thoracolumbar motion in the sagittal and horizontal planes, presumably in an attempt to move the centre of gravity away from the lame side and reduce the force on the affected limb.

POTENTIAL RELEVANCE

Subtle forelimb lameness affects thoracolumbar kinematics. Future studies should aim at elucidating whether the altered movement patterns lead to back and/or neck dysfunction in the case of chronic lameness.

Validation of vertical ground reaction forces on individual limbs calculated from kinematics of horse locomotion

The purpose of this study was to determine whether individual limb forces could be calculated accurately from kinematics of trotting and walking horses. We collected kinematic data and measured vertical ground reaction forces on the individual limbs of seven Warmblood dressage horses, trotting at 3.4 m s–1 and walking at 1.6 m s–1 on a treadmill. First, using a segmental model, we calculated from kinematics the total ground reaction force vector and its moment arm relative to each of the hoofs. Second, for phases in which the body was supported by only two limbs, we calculated the individual reaction forces on these limbs. Third, we assumed that the distal limbs operated as linear springs, and determined their force–length relationships using calculated individual limb forces at trot. Finally, we calculated individual limb force–time histories from distal limb lengths. A good correspondence was obtained between calculated and measured individual limb forces. At trot, the average peak vertical reaction force on the forelimb was calculated to be 11.5±0.9 N kg–1 and measured to be 11.7±0.9 N kg–1, and for the hindlimb these values were 9.8±0.7 N kg–1 and 10.0±0.6 N kg–1,respectively. At walk, the average peak vertical reaction force on the forelimb was calculated to be 6.9±0.5 N kg–1 and measured to be 7.1±0.3 N kg–1, and for the hindlimb these values were 4.8±0.5 N kg–1 and 4.7±0.3 N kg–1, respectively. It was concluded that the proposed method of calculating individual limb reaction forces is sufficiently accurate to detect changes in loading reported in the literature for mild to moderate lameness at trot.

The workload of riding-school horses during jumping

REASONS FOR PERFORMING THE STUDY

As there are no reports on the real workload of horses that jump fences, this study was undertaken in riding-school horses.

OBJECTIVE

To compare the workload of horses jumping a course of fences with that of horses cantering over the same course at the same average speed without jumping fences. The workload variables included heart rate (HR), packed cell volume (PCV), acid-base balance (venous pH, pCO2, HCO3-) and blood lactate (LA), glucose, total protein and electrolyte concentrations.

METHODS

Eight healthy riding-school horses performed test A (a course of approximately 700 m with 12 jumps from 0.8-1.0 m high at an average speed of approximately 350 m/min) and test B (same course at the same speed, but without the rails) in a crossover study with at least 4 h between the 2 tests. Before each test the horses were fitted with a heart rate meter (Polar Electro). Blood samples were taken from the jugular vein at rest prior to the test, after warm-up before starting the course, immediately after the course and after recovery. All samples were analysed immediately.

RESULTS

The mean +/- s.d maximal HR (beats/min) during the course (184 +/- 17 and 156 +/- 21, respectively) and the mean HR after recovery (75 +/- 6 and 63 +/- 7, respectively) were significantly higher in test A compared to test B (P = 0.001 and P = 0.007 respectively). The mean LA concentrations after the course and after recovery (mmol/l) were significantly higher in test A (3.6 +/- 2.7 and 1.0 +/- 0.9, respectively) compared to test B (0.9 +/- 0.5 and 0.3 +/- 0.1, respectively), (P = 0.016 and P = 0.048 respectively). The mean PCV (I/l) after the course and after recovery was also significantly different between tests A (0.48 +/- 0.04 and 0.39 +/- 0.03, respectively) and B (0.42 +/- 0.04 and 0.36 +/- 0.03, respectively) (P<0.01). The mean pH and the mean HCO3- (mmol/l) after the course were significantly lower in test A (7.40 +/- 0.04 and 28.9 +/- 1.4, respectively) compared to test B (7.45 +/- 0.03 and 30.4 +/- 2.3, respectively) (P<0.05).

CONCLUSIONS

This study indicates that in riding-school horses jumping fences, even at a low level competition, provokes a significant workload compared to cantering the same distance and speed without fences.

POTENTIAL RELEVANCE

This study makes it clear that the extra workload of jumping fences should be taken into account in the training programmes of jumping horses. Further research with more experienced horses jumping higher fences will reveal the workload for top-level jumping horses.

Joint work and power for both the forelimb and hindlimb during trotting in the horse

The net work of the limbs during constant speed over level ground should be zero. However, the partitioning of negative and positive work between the fore- and hindlimbs of a quadruped is not likely to be equal because the forelimb produces a net braking force while the hindlimb produces a net propulsive force. It was hypothesized that the forelimb would do net negative work while the hindlimb did net positive work during trotting in the horse. Because vertical and horizontal impulses remain unchanged across speeds it was hypothesized that net work of both limbs would be independent of speed. Additionally because the major mass of limb musculature is located proximally, it was hypothesized that proximal joints would do more work than distal joints. Kinetic and kinematic analysis were combined using inverse dynamics to calculate work and power for each joint of horses trotting at between 2.5 and 5.0 m s(-1). Work done by the hindlimb was indeed positive (consistently 0.34 J kg(-1) across all speeds), but, contrary to our hypothesis, net work by the forelimb was essentially zero (but also independent of trotting speed). The zero net work of the forelimb may be the consequence of our not being able to account, experimentally, for the negative work done by the extrinsic muscles connecting the scapula and the thorax. The distal three joints of both limbs behaved elastically with a period of energy absorption followed by energy return. Proximal forelimb joints (elbow and shoulder) did no net work, because there was very little movement of the elbow and shoulder during the portion of stance when an extensor moment was greatest. Of the two proximal hindlimb joints, the hip did positive work during the stride, generating energy almost throughout stance. The knee did some work, but like the forelimb proximal joints, had little movement during the middle of stance when the flexion moment was the greatest, probably serving to allow the efficient transmission of energy from the hip musculature to the ground.