Classification performance of sEMG and kinematic parameters for distinguishing between non-lame and induced lameness conditions in horses.

Despite its proven research applications, it remains unknown whether surface electromyography (sEMG) can be used clinically to discriminate non-lame from lame conditions in horses. This study compared the classification performance of sEMG absolute value (sEMGabs) and asymmetry (sEMGasym) parameters, alongside validated kinematic upper-body asymmetry parameters, for distinguishing non-lame from induced fore- (iFL) and hindlimb (iHL) lameness. Bilateral sEMG and 3D-kinematic data were collected from clinically non-lame horses (n = 8) during in-hand trot. iFL and iHL (2-3/5 AAEP) were induced on separate days using a modified horseshoe, with baseline data initially collected each day. sEMG signals were DC-offset removed, high-pass filtered (40 Hz), and full-wave rectified. Normalized, average rectified value (ARV) was calculated for each muscle and stride (sEMGabs), with the difference between right and left-side ARV representing sEMGasym. Asymmetry parameters (MinDiff, MaxDiff, Hip Hike) were calculated from poll, withers, and pelvis vertical displacement. Receiver-operating-characteristic (ROC) and area under the curve (AUC) analysis determined the accuracy of each parameter for distinguishing baseline from iFL or iHL. Both sEMG parameters performed better for detecting iHL (0.97 ≥ AUC ≥ 0.48) compared to iFL (0.77 ≥ AUC ≥ 0.49). sEMGabs performed better (0.97 ≥ AUC ≥ 0.49) than sEMGasym (0.76 ≥ AUC ≥ 0.48) for detecting both iFL and iHL. Like previous studies, MinDiff Poll and Pelvis asymmetry parameters (MinDiff, MaxDiff, Hip Hike) demonstrated excellent discrimination for iFL and iHL, respectively (AUC > 0.95). Findings support future development of multivariate lameness-detection approaches that combine kinematics and sEMG. This may provide a more comprehensive approach to diagnosis, treatment, and monitoring of equine lameness, by measuring the underlying functional cause(s) at a neuromuscular level.

Riders' Effects on Horses-Biomechanical Principles with Examples from the Literature.

Movements of the horse and rider in equestrian sports are governed by the laws of physics. An understanding of these physical principles is a prerequisite to designing and interpreting biomechanical studies of equestrian sports. This article explains and explores the biomechanical effects between riders and horses, including gravitational and inertial forces, turning effects, and characteristics of rider technique that foster synchronous movement with the horse. Rider symmetry, posture, and balance are discussed in the context of their relationship to rider skill level and their effects on the horse. Evidence is presented to support the feasibility of improving equestrian performance by off-horse testing followed by unmounted therapy and exercises to target the identified deficiencies. The elusive quality of harmony, which is key to a true partnership between riders and horses, is explored and described in biomechanical terms.

Electromyographic and Kinematic Comparison of the Leading and Trailing Fore- and Hindlimbs of Horses during Canter.

This study compared muscle activity and movement between the leading (Ld) and trailing (Tr) fore- (F) and hindlimbs (H) of horses cantering overground. Three-dimensional kinematic and surface electromyography (sEMG) data were collected from right triceps brachii, biceps femoris, middle gluteal, and splenius from 10 ridden horses during straight left- and right-lead canter. Statistical parametric mapping evaluated between-limb (LdF vs. TrF, LdH vs. TrH) differences in time- and amplitude-normalized sEMG and joint angle-time waveforms over the stride. Linear mixed models evaluated between-limb differences in discrete sEMG activation timings, average rectified values (ARV), and spatio-temporal kinematics. Significantly greater gluteal ARV and activity duration facilitated greater limb retraction, hip extension, and stifle flexion (p < 0.05) in the TrH during stance. Earlier splenius activation during the LdF movement cycle (p < 0.05), reflected bilateral activation during TrF/LdH diagonal stance, contributing to body pitching mechanisms in canter. Limb muscles were generally quiescent during swing, where significantly greater LdF/H protraction was observed through greater elbow and hip flexion (p < 0.05), respectively. Alterations in muscle activation facilitate different timing and movement cycles of the leading and trailing limbs, which justifies equal training on both canter leads to develop symmetry in muscular strength, enhance athletic performance, and mitigate overuse injury risks.

Towards an Evidence-Based Classification System for Para Dressage: Associations between Impairment and Performance Measures.

This study follows a previously defined framework to investigate the impact of impairment on performance in Para dressage athletes. Twenty-one elite Para dressage athletes (grades I to V) and eleven non-disabled dressage athletes (competing at Prix St. Georges or Grand Prix) participated. Data were collected in two phases: performing a two minute custom dressage test on a riding simulator while kinematic data were synchronously collected using inertial measurement units (2000 Hz) and optical motion capture (100 Hz), and clinically assessed using a battery of impairment assessment tools administered by qualified therapists. Impairment and performance measures were compared between Para and non-disabled athletes. Significant differences between athlete groups were found for all impairment measures and two performance measures: simulator trunk harmonics (p = 0.027) and athlete trunk dynamic symmetry (p < 0.001). Impairment assessments of sitting function and muscle tone could predict 19 to 35% of the impact of impairment on performance in Para athletes but not in non-disabled athletes. These findings provide the basis for a robust, scientific evidence base, which can be used to aid in the refinement of the current classification system for Para dressage, to ensure that it is in line with the International Paralympic Committee's mandate for evidence-based systems of classification.

Evaluating Overall Performance in High-Level Dressage Horse-Rider Combinations by Comparing Measurements from Inertial Sensors with General Impression Scores Awarded by Judges.

In the sport of dressage, one or more judges score the combined performance of a horse and rider with an emphasis on the technical correctness of the movements performed. At the end of the test, a single score is awarded for the 'general impression', which considers the overall performance of the horse and rider as a team. This study explored original measures that contributed to the general impression score in a group of 20 horse-rider combinations. Horses and riders were equipped with inertial measurement units (200 Hz) to represent the angular motion of a horse's back and the motions of a rider's pelvis and trunk. Each combination performed a standard dressage test that was recorded to video. Sections of the video were identified for straight-line movements. The videos were analyzed by two or three judges. Four components were scored separately: gaits of the horse, rider posture, effectiveness of aids, and harmony with the horse. The main contributor to the score for gaits was stride frequency (R = -0.252, p = 0.015), with a slower frequency being preferred. Higher rider component scores were associated with more symmetrical transverse-plane trunk motion, indicating that this original measure is the most useful predictor of rider performance.

Adaptations in equine axial movement and muscle activity occur during induced fore- and hindlimb lameness: A kinematic and electromyographic evaluation during in-hand trot.

BACKGROUND: The inter-relationship between equine thoracolumbar motion and muscle activation during normal locomotion and lameness is poorly understood. OBJECTIVE: To compare thoracolumbar and pelvic kinematics and longissimus dorsi (longissimus) activity of trotting horses between baseline and induced forelimb (iFL) and hindlimb (iHL) lameness. STUDY DESIGN: Controlled experimental cross-over study. METHODS: Three-dimensional kinematic data from the thoracolumbar vertebrae and pelvis, and bilateral surface electromyography (sEMG) data from longissimus at T14 and L1, were collected synchronously from clinically nonlame horses (n = 8) trotting overground during a baseline evaluation, and during iFL and iHL conditions (2-3/5 AAEP), induced on separate days using a lameness model (modified horseshoe). Motion asymmetry parameters, maximal thoracolumbar flexion/extension and lateral bending angles, and pelvis range of motion (ROM) were calculated from kinematic data. Normalised average rectified value (ARV) and muscle activation onset, offset and activity duration were calculated from sEMG signals. Mixed model analysis and statistical parametric mapping compared discrete and continuous variables between conditions (α = 0.05). RESULTS: Asymmetry parameters reflected the degree of iFL and iHL. Maximal thoracolumbar flexion and pelvis pitch ROM increased significantly following iFL and iHL. During iHL, peak lateral bending increased towards the nonlame side (NLS) and decreased towards the lame side (LS). Longissimus ARV significantly increased bilaterally at T14 and L1 for iHL, but only at LS L1 for iFL. Longissimus activation was significantly delayed on the NLS and precipitated on the LS during iHL, but these clear phasic shifts were not observed in iFL. MAIN LIMITATIONS: Findings should be confirmed in clinical cases. CONCLUSIONS: Distinctive, significant adaptations in thoracolumbar and pelvic motion and underlying longissimus activity occur during iFL and iHL and are detectable using combined motion capture and sEMG. For iFL, these adaptations occur primarily in a cranio-caudal direction, whereas for iHL, lateral bending and axial rotation are also involved.

CONTEXTO: O relacionamento entre a movimentação toracolombar e a ativação muscular durante a locomoção normal e quando há claudicação é pouco compreendido. OBJETIVOS: Comparar a cinemática toracolombar e pélvica e a atividade do músculo longissimus dorsi (longissimus) em cavalos ao trote entre o momento inicial (baseline) e claudicação induzida no membro torácico (iFL) e pélvico (iHL). DELINEAMENTO DO ESTUDO: Estudo experimental controlado cruzado. METODOLOGIA: Dados cinemáticos tridimensionais das vertebras toracolombar e pelve, e eletromiografia de superfície (sEMG) bilateral do longissimus na T14 e L1 foram coletados de forma síncrona de cavalos clinicamente não claudicantes (n = 8) trotando no momento inicial (baseline), e durante iFL e iHL (2-3/5 AAEP), induzidos separadamente em dias distintos utilizando um modelo de claudicação (ferradura modificada). Parâmetros de movimentação assimétrica, flexão/extensão máxima da toracolombar e ângulos de virada lateral, e amplitude de movimento da pelve (ROM) foram calculados a partir dos dados de cinemática. O valor médio normalizado retificado (ARV) e início da ativação muscular, e término e duração da atividade foram calculados utilizando sinais de sEMG. Análise de modelo misto e mapeamento paramétrico estatístico compararam variáveis discretas e contínuas entre condições (α=0.05). RESULTADOS: Parâmetros de assimetria refletiram o nível de iFL e iHL. A flexão toracolombar máxima e a ROM da pelve aumentaram significativamente com iFL e iHL. Durante iHL, o pico de flexão lateral aumentou em direção ao lado não-claudicante (NSL) e diminuiu em direção ao lado claudicante (LS). Longissimus ARV aumentou significativamente para ambos os lados na T14 e L1 para iHL, mas apenas no LS para iFL. A ativação do longissimus foi significativamente retardado no NLS e precipitado no LS durante iHL, mas essa mudança de fase clara não foi observada no iFL. PRINCIPAIS LIMITAÇÕES: Esses achados precisam ser confirmados em casos clínicos. CONCLUSÕES: Adaptações significantes e distintas na movimentação toracolombar e pélvica e atividade do músculo longissimus ocorre durante iFL e iHL e são detectadas utilizando captura de movimento e sEMG. Para iFL, essas adaptações ocorrem primariamente na direção cranio-caudal, enquanto que em iHL, movimento lateral e rotação axial também estão envolvidos.

Adaptations in equine appendicular muscle activity and movement occur during induced fore- and hindlimb lameness: An electromyographic and kinematic evaluation.

The relationship between lameness-related adaptations in equine appendicular motion and muscle activation is poorly understood and has not been studied objectively. The aim of this study was to compare muscle activity of selected fore- and hindlimb muscles, and movement of the joints they act on, between baseline and induced forelimb (iFL) and hindlimb (iHL) lameness. Three-dimensional kinematic data and surface electromyography (sEMG) data from the fore- (triceps brachii, latissimus dorsi) and hindlimbs (superficial gluteal, biceps femoris, semitendinosus) were bilaterally and synchronously collected from clinically non-lame horses (n = 8) trotting over-ground (baseline). Data collections were repeated during iFL and iHL conditions (2-3/5 AAEP), induced on separate days using a modified horseshoe. Motion asymmetry parameters and continuous joint and pro-retraction angles for each limb were calculated from kinematic data. Normalized average rectified value (ARV) and muscle activation onset, offset and activity duration were calculated from sEMG signals. Mixed model analysis and statistical parametric mapping, respectively, compared discrete and continuous variables between conditions (α= 0.05). Asymmetry parameters reflected the degree of iFL and iHL. Increased ARV occurred across muscles following iFL and iHL, except non-lame side forelimb muscles that significantly decreased following iFL. Significant, limb-specific changes in sEMG ARV, and activation timings reflected changes in joint angles and phasic shifts of the limb movement cycle following iFL and iHL. Muscular adaptations during iFL and iHL are detectable using sEMG and primarily involve increased bilateral activity and phasic activation shifts that reflect known compensatory movement patterns for reducing weightbearing on the lame limb. With further research and development, sEMG may provide a valuable diagnostic aid for quantifying the underlying neuromuscular adaptations to equine lameness, which are undetectable through human observation alone.

Hoof Matters: Developing an Athletic Thoroughbred Hoof.

Conformation of the hooves and distal limbs of foals and factors influencing their morphological development have not been reported in detail for the Thoroughbred breed. In this paper we explore morphogenesis of the equine distal limb in Thoroughbred foals with emphasis on adaptations in response to weight bearing early in life that prepare the foal for an athletic career. Novel data from four studies are presented chronologically during key time periods to illustrate specific aspects of distal limb growth and adaptation. Dorsal epidermal thickness increased from 2.84 ± 0.41 mm in utero to 4.04 ± 1.10 mm by 4 months of age. The increase in thickness was accompanied by decreased tubular density, increased inter-tubular material, and an increase in number and size of tubules at the quarters, which provided a malleable hoof capsule to allow for skeletal growth. Between 4−6 months of age, the hoof widens, and higher loading on the medial side (>60%) vs. the lateral side (<40%) may be factors that influence mature asymmetric hoof shape. Shortly after 12 months-of-age, the dorsal hoof wall angle and dorsal parietal angle of the distal phalanx become parallel, thus optimizing the functional capacity of the hoof capsule in the weanling Thoroughbred.

An exploration of stakeholder perceptions to inform the development of an evidence-based classification system in para dressage.

In dressage, horse-rider combinations must demonstrate harmony whilst performing a test of gaits and movements, scored by judge(s) using predetermined criteria. The para dressage governing body is working towards compliance with the International Paralympic Committee's mandate for evidence-based classification, which requires a comprehensive understanding of key performance determinants. This study aimed to explore stakeholder perceptions surrounding the key determinants of, and impact of impairment on, para dressage performance. Semi-structured interviews with 30 para dressage stakeholders (athletes, classifiers, judges, coach) were analysed using the Framework method. Themes relating to the equine and human athlete were associated with overall dressage performance and discussed within the context of impairment and horse-rider partnership. Key performance determinants were summarised as the athlete's ability to maintain dynamic postural control for absorbing the horse's movement and coordinating leg, hand, and seat aids, which directly influence the horse's quality and accuracy of movements during dressage. Thus, muscular coordination, joint mobility that influences rider posture, and personality traits that influence the horse-rider partnership were considered performance determinants. These themes will inform the development of an evidence-based classification system, through the establishment of standardised, sport-specific performance measures for assessing the relationship between impairment and activity limitation in para dressage.

Rider Skill Affects Time and Frequency Domain Postural Variables When Performing Shoulder-in.

In equestrian sports the novice rider learns first to follow the movements of the horse's back and then how to influence the horse's performance. One of the rider's challenges is to overcome inherent horse and/or rider asymmetry patterns when riding in straight lines, mirroring the movements on the left, and right sides when turning. This study compares the performance of novice and advanced riders when riding in sitting trot on straight lines and when riding shoulder-in to the left and right sides. Eight novice and eight advanced horse-rider combinations performed sitting trot in a straight line, shoulder-in left and shoulder-in right while wearing a full body set of inertial sensors. An experienced dressage judge indicated when the movements were being performed correctly and assigned scores on a scale of 0-10 for the quality of performance. Kinematic data from the inertial sensors were analyzed in time and frequency domain. Comparisons were made between trotting on the straight, shoulder-in left, and shoulder-in right. Advanced riders received higher dressage scores on all three movements, but significantly (P < .05) lower scores were found for shoulder-in right across the two groups. When riding shoulder-in, advanced riders had greater hip extension (advanced = -5.8 ± 17.7; novice = 7.8 ± 8.9 degrees) and external rotation (advanced = -32.4 ± 15.5; novice = -10.8 ± 13.2 degrees) in the outside leg compared with novices (P < .05), which reflects an important cue in achieving the required body rotation in the horse. Lower scores for shoulder-in right may be linked to significant (P < .05) changes in harmonics of trunk to pelvis rotation.

The Challenges of Equestrian Arena Surfaces: The Unprecedented Use of a Raised Platform at the 2012 Olympic Games.

The design of equestrian arenas can be challenged by time constraints and specific restrictions at a venue but are nonetheless a critical element to the success and sustainability of equestrian sport. The equestrian arenas for the 2012 Olympic Games were an example of a temporary arena constructed on a raised platform and supported by struts, a design unprecedented for equestrian activities. This study assessed the developmental stages of the Olympic surfaces from 2011 to the actual event in 2012 and aimed to confirm that accelerations and forces experienced by horses were comparable to those on solid ground. Assessment took place at (1) the Olympic test event;(2) a developmental mock-up arena; and (3) the Olympic venue in 2012. A Clegg impact hammer measured peak vertical deceleration and an Orono Biomechanical Surface Tester quantified peak load and peak loading rate. General Linear Models using the arena's structural features as explanatory variables highlighted surface heterogeneity. Peak vertical deceleration (P < .0001) and peak load (P < .0001) were significantly higher and peak loading rate was significantly lower (P < .0001) following iterative testing and modifications to the arena. Data were comparable with surfaces on solid ground by the final testing at the 2012 Olympic Games. Findings highlighted the importance of testing surfaces throughout their development and demonstrated the impact that surface composition, time elapsed since installation, water management, and type of construction have on surface functional properties, with relevance to future temporary arena initiatives.

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.

Ground Reaction Forces of Dressage Horses Performing the Piaffe.

The piaffe is an artificial, diagonally coordinated movement performed in the highest levels of dressage competition. The ground reaction forces (GRFs) of horses performing the piaffe do not appear to have been reported. Therefore, the objective of this study was to describe three-dimensional GRFs in ridden dressage horses performing the piaffe. In-ground force plates were used to capture fore and hindlimb GRF data from seven well-trained dressage horses. Peak vertical GRF was significantly higher in forelimbs than in the hindlimbs (7.39 ± 0.99 N/kg vs. 6.41 ± 0.64 N/kg; p < 0.001) with vertical impulse showing a trend toward higher forelimb values. Peak longitudinal forces were small with no difference in the magnitude of braking or propulsive forces between fore and hindlimbs. Peak transverse forces were similar in magnitude to longitudinal forces and were mostly directed medially in the hindlimbs. Both the intra- and inter-individual variability of longitudinal and transverse GRFs were high (coefficient of variation 25-68%). Compared with the other diagonal gaits of dressage horses, the vertical GRF somewhat shifted toward the hindlimbs. The high step-to-step variability of the horizontal GRF components is thought to reflect the challenge of balancing on one diagonal pair of limbs with no forward momentum.

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 (ZCM). 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 ZCM 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.

A scoping review of determinants of performance in dressage.

As a first step in achieving an evidence-based classification system for the sport of Para Dressage, there is a clear need to define elite dressage performance. Previous studies have attempted to quantify performance with able-bodied riders using scientific methods; however, definitive measures have yet to be established for the horse and/or the rider. This may be, in part, due to the variety of movements and gaits that are found within a dressage test and also due to the complexity of the horse-rider partnership. The aim of this review is therefore to identify objective measurements of horse performance in dressage and the functional abilities of the rider that may influence them to achieve higher scores. Five databases (SportDiscuss, CINAHL, MEDLINE, EMBASE, VetMed) were systematically searched from 1980 to May 2018. Studies were included if they fulfilled the following criteria: (1) English language; (2) employ objective, quantitative outcome measures for describing equine and human performance in dressage; (3) describe objective measures of superior horse performance using between-subject comparisons and/or relating outcome measures to competitive scoring methods; (4) describe demands of dressage using objective physiological and/or biomechanical measures from human athletes and/or how these demands are translated into superior performance. In total, 773 articles were identified. Title and abstract screening resulted in 155 articles that met the eligibility criteria, 97 were excluded during the full screening of articles, leaving 58 included articles (14 horse, 44 rider) involving 311 equine and 584 able-bodied human participants. Mean ± sd (%) quality scores were 63.5 ± 15.3 and 72.7 ± 14.7 for the equine and human articles respectively. Significant objective measures of horse performance (n = 12 articles) were grouped into themes and separated by gait/movement. A range of temporal variables that indicated superior performance were found in all gaits/movements. For the rider, n = 5 articles reported variables that identified significant differences in skill level, which included the postural position and ROM of the rider's pelvis, trunk, knee and head. The timing of rider pelvic and trunk motion in relation to the movement of the horse emerged as an important indicator of rider influence. As temporal variables in the horse are consistently linked to superior performance it could be surmised that better overall dressage performance requires minimal disruption from the rider whilst the horse maintains a specific gait/movement. Achieving the gait/movement in the first place depends upon the intrinsic characteristics of the horse, the level of training achieved and the ability of the rider to apply the correct aid. The information from this model will be used to develop an empirical study to test the relative strength of association between impairment and performance in able-bodied and Para Dressage riders.

A Review of Biomechanical Gait Classification with Reference to Collected Trot, Passage and Piaffe in Dressage Horses.

Gaits are typically classified as walking or running based on kinematics, the shape of the vertical ground reaction force (GRF) curve, and the use of inverted pendulum or spring-mass mechanics during the stance phase. The objectives of this review were to describe the biomechanical characteristics that differentiate walking and running gaits, then apply these criteria to classify and compare the enhanced natural gait of collected trot with the artificial gaits of passage and piaffe as performed by highly trained dressage horses. Limb contact and lift off times were used to determine contact sequence, limb phase, duty factor, and aerial phase duration. Ground reaction force data were plotted to assess fore and hind limb loading patterns. The center of mass (COM) trajectory was evaluated in relation to changes in potential and kinetic energy to assess the use of inverted pendulum and spring-mass mechanics. Collected trot and passage were classified as running gaits according to all three criteria whereas piaffe appears to be a hybrid gait combining walking kinematics with running GRFs and COM mechanics. The hind limbs act as springs and show greater limb compression in passage and piaffe compared with trot, whereas the forelimbs behave more like struts showing less compression in passage and piaffe than in trot.

Collisional mechanics of the diagonal gaits of horses over a range of speeds.

One of the goals of the neuromotor control system is to minimize the cost of locomotion by reducing mechanical energy losses. Collisional mechanics, which studies the redirection of the downwards motion of the center of mass (COM) by ground reaction forces (GRF) generated by the limbs, represents an important source of energy loss. The primary objective of this study was to compare collisional mechanics and the associated mechanical energy losses in horses performing diagonally-synchronized gaits over a range of speeds. It is to be expected that collisional energy losses will be high when the COM velocity vector is closely aligned with the GRF vector. This condition is achieved in piaffe, an artificial gait performed in dressage competitions that has a diagonal limb coordination pattern similar to trot but performed with little or no forward velocity. Therefore, we hypothesized that collisional energy losses would be higher in piaffe than in trot. Synchronized kinematic and GRF data were collected from three highly-trained horses performing piaffe, passage and trot at a range of speeds. Derived variables were vertical excursion and velocity of the trunk COM, fore and hind limb compression expressed as percentage reduction of standing limb lengths, range of limb pro-retraction, GRF vector magnitude and vector angle, collision angle (Φ), and mechanical cost of motion (CoMotmech). Linear regression was used to investigate the relationship between CoMotmech and speed for each gait. Partial correlation was used to seek relationships between COM excursion and limb mechanics for each gait. Piaffe, passage and trot were clearly separated on the basis of speed. In all gaits the trunk was high at contact and lift off and descended to its lowest point in midstance following the pattern typical of spring mass mechanics. Mechanical cost was significantly (p < .05) and inversely related to speed in trot and piaffe with the value increasing steeply as speed approached zero due to a near vertical orientation of both the COM velocity vector and the GRF vector. Limb compression during stance was significantly (p < .05) linked to trunk COM vertical excursion in all gaits, with a stronger relationship in the forelimb. Hindlimb compression was, however, large in piaffe where the force magnitudes are notably smaller. The study illustrates the potential value of studying artificial gaits to provide data encompassing the entire range of locomotor capabilities. The results supported the experimental hypothesis by showing a threefold increase in collisional energy losses in piaffe compared with trot. In all gaits, dissociation between diagonal limb contacts and lift offs was thought to be an important strategy in reducing in collisional losses. Piaffe, the most costly gait, has similar characteristics to hopping on the spot. It appears that greater hindlimb compliance and a lower step frequency are important energy conservation strategies for piaffe.

Ground Reaction Forces: The Sine Qua Non of Legged Locomotion.

Legged locomotion results from the feet pressing against the ground to generate ground reaction forces (GRFs) that are responsible for moving the body. By changing limb coordination patterns and muscle forces, the GRFs are adjusted to allow the horse to move in different gaits, speeds, and directions with appropriate balance and self-carriage. This article describes the typical GRF patterns in each gait, the adaptations that produce turning, and the GRF patterns used to unload the painful limb when the horse is lame. The intent is to provide information that is of practical interest and value to equine scientists rather than being a comprehensive review of the topic.

Orientation and location of the finite helical axis of the equine forelimb joints.

To reduce anatomically unrealistic limb postures in a virtual musculoskeletal model of a horse's forelimb, accurate knowledge on forelimb joint constraints is essential. The aim of this cadaver study is to report all orientation and position changes of the finite helical axes (FHA) as a function of joint angle for different equine forelimb joints. Five horse cadaver forelimbs with standardized cuts at the midlevel of each segment were used. Bone pins with reflective marker triads were drilled into the forelimb bones. Unless joint angles were anatomically coupled, each joint was manually moved independently in all three rotational degrees of freedom (flexion-extension, abduction-adduction, internal-external rotation). The 3D coordinates of the marker triads were recorded using a six infra-red camera system. The FHA and its orientational and positional properties were calculated and expressed against joint angle over the entire range of motion using a finite helical axis method. When coupled, joint angles and FHA were expressed in function of flexion-extension angle. Flexion-extension movement was substantial in all forelimb joints, the shoulder allowed additional considerable motion in all three rotational degrees of freedoms. The position of the FHA was constant in the fetlock and elbow and a constant orientation of the FHA was found in the shoulder. Orientation and position changes of the FHA over the entire range of motion were observed in the carpus and the interphalangeal joints. We report FHA position and orientation changes as a function of flexion-extension angle to allow for inclusion in a musculoskeletal model of a horse to minimize calculation errors caused by incorrect location of the FHA.