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

Effects of pacing strategy on metabolic responses to 2-min intense exercise in Thoroughbred horses

Evidence suggests that positive pacing strategy improves exercise performance and fatigue tolerance in athletic events lasting 1-5 min. This study investigated muscle metabolic responses to positive and negative pacing strategies in Thoroughbred horses. Eight Thoroughbred horses performed 2 min treadmill running using positive (1 min at 110% maximal O2 uptake [V̇O2max], followed by 1 min at 90% V̇O2max) and negative (1 min at 90% V̇O2max, followed by 1 min at 110% V̇O2max) pacing strategies. The arterial-mixed venous O2 difference did not significantly differ between the two strategies. Plasma lactate levels increased toward 2 min, with significantly higher concentrations during positive pacing than during negative pacing. Muscle glycogen level was significantly lower at 1 and 2 min of positive pacing than those of negative pacing. Metabolomic analysis showed that the sum of glycolytic intermediates increased during the first half of positive pacing and the second half of negative pacing. Regardless of pacing strategy, the sum of tricarboxylic acid cycle metabolites increased during the first half but remained unchanged thereafter. Our data suggest that positive pacing strategy is likely to activate glycolytic metabolism to a greater extent compared to negative pacing, even though the total workload is identical.

Changes in muscle activation with graded surfaces during canter in Thoroughbred horses on a treadmill

Understanding how muscle activity changes with different surface grades during canter is essential for developing training protocols in Thoroughbreds because canter is their primary gait in training and races. We measured the spatiotemporal parameters and the activation of 12 surface muscles in the leading limb side of 7 Thoroughbreds. Horses were equipped with hoof strain gauges and cantered at 10 m/s on a treadmill set to grades of -4%, 0%, 4%, and 8%, randomly, for 30 seconds each without a lead change. Integrated electromyography (iEMG) values during stance and swing phases were calculated and normalized to mean iEMG values during stride duration at 0% grade in each muscle. The iEMG values at each grade were compared using a generalized mixed model. Stride duration significantly decreased due to shorter swing duration on an 8% grade (P < 0.001) compared to all other grades, where no significant changes were observed. Compared to a 0% grade, the normalized iEMG values during the stance phase on an 8% grade in five muscles significantly increased (Musculus infraspinatus; +9%, M. longissimus dorsi (LD); +4%, M. gluteus medius (GM); +29%, M. biceps femoris; +47%, M. flexor digitorum lateralis; +16%). During the swing phase, the normalized iEMG values in six muscles significantly increased on an 8% grade compared to a 0% grade (M. splenius; +21%, M. triceps brachii; +54%, LD; +37%, GM; +24%, M. semitendinosus; +51%, M. extensor digitorum longus; +10%). No significant changes were observed in iEMG values on -4% and 4% grades compared to the 0% grade. Although +/- 4% grades had little effect on neuromuscular responses, 8% uphill canter reduced stride duration due to decreased swing duration and required increase of muscle activation during either stance and swing phase. Canter on an 8% grade might strengthen equine muscles to increase propulsive force and stride frequency.

Effects of Fatigue on Stride Parameters in Thoroughbred Racehorses During Races

Exercise intensity during races is considerably high. To understand how Thoroughbreds adapt to fatigue conditions, stride parameters for the first and second lap of the race (2400-m, turf) were compared. A high-speed video system was set in a right lateral position about 20 m before the finishing post, with a field view width of about 16 m. The stride frequency, the length between each limb (hind step, diagonal step, fore step, and airborne step), and stride length were measured and analyzed using a generalized linear mixed model. Compared with the first lap, the mean ± standard deviation values in the second lap for running speed (17.3 ± 1.3 to 16.0 ± 0.9 m/s, P < .01), stride frequency (2.34 ± 0.08 to 2.21 ± 0.09 strides/s, P < .01) and stride length (7.42 ± 0.52 to 7.25 ± 0.38 m, P = .04) significantly decreased. Furthermore, significant changes (P < .01) were observed in the diagonal step length (2.32 ± 0.34 to 1.88 ± 0.23 m), hind step (1.19 ± 0.09 to 1.26 ± 0.10 m) and airborne step length (2.43 ± 0.25 to 2.61 ± 0.18 m). When controlled for speed, stride frequency (P = .02) and diagonal step length (P < .01) decreased, while the length of the hind step (P < .01), fore step (P < .01), airborne step (P < .01), and stride (P = .02) increased with fatigue in the second lap. These results suggest that horses could not extend their body when fatigued.

Optimal speed in Thoroughbred horse racing

The objective of this work is to provide a mathematical analysis on how a Thoroughbred horse should regulate its speed over the course of a race to optimize performance. Because Thoroughbred horses are not capable of running the whole race at top speed, determining what pace to set and when to unleash the burst of speed is essential. Our model relies on mechanics, energetics (both aerobic and anaerobic) and motor control. It is a system of coupled ordinary differential equations on the velocity, the propulsive force and the anaerobic energy, that leads to an optimal control problem that we solve. In order to identify the parameters meaningful for Thoroughbred horses, we use velocity data on races in Chantilly (France) provided by France Galop, the French governing body of flat horse racing in France. Our numerical simulations of performance optimization then provide the optimal speed along the race, the oxygen uptake evolution in a race, as well as the energy or the propulsive force. It also predicts how the horse has to change its effort and velocity according to the topography (altitude and bending) of the track.

Variation in GPS and accelerometer recorded velocity and stride parameters of galloping Thoroughbred horses

BACKGROUND

With each stride, galloping horses generate large skeletal loads which influence bone physiology, and may contribute to musculoskeletal injury. Horse speed and stride characteristics are related, but the usefulness of using horse speed and distance travelled as a proxy for stride characteristics is unknown.

OBJECTIVES

We aimed to determine stride characteristics, their variance and their relationship with speed in horses performing maximally.

STUDY DESIGN

Retrospective cross-sectional analysis of archived data.

METHODS

Stride characteristics obtained using GPS and inertial sensors in Thoroughbred horses were retrieved. Data per 200 m race segment ('sectionals') for horses competing in races (N = 25,259 race starts) were analysed to determine if speed predicted stride parameters. Multivariable mixed-effects linear regression models were fitted.

RESULTS

Mean (±SD) stride length, stride count (number of strides per 200 m), duration and speed were 7.08 ± 0.39 m, 28.32 ± 1.56 strides/200 m, 0.43 ± 0.02 s/stride and 16.63 ± 1.04 m/s across all sectionals and starts. Speed and stride length decreased, and stride count increased with race progression (P < 0.001). Male sex, greater race distance, better finishing position and firmer track surfaces were associated with less strides per 200 m and longer stride durations.

MAIN LIMITATIONS

Lack of an independent party validation of the measurement system used in this study.

CONCLUSIONS

There was a substantial inter-horse variation in stride parameters, with speed predicting half or less of this variation. Speed alone does not fully explain stride characteristics in horses. Future studies aimed at investigating the impact of gait on bone biology and pathology would benefit from accounting for stride characteristics (eg length and duration).

Horseback riding pathways and harbors at the beginning of the colonial era in Mexico

The introduction of horses in the New World changed the way of traveling on complex terrains. This change reconfigured the land transport network connecting harbors in the region. However, data of horseback riding pathways among harbors is scarce. We analyzed the case of Mexico at the beginning of the colonial period to recreate routes that connected ancient harbors and to identify the network characteristics of a large-scale system of routes. We used the complex systems approach as a framework in which we applied the least cost path analysis to reconstruct a network of horseback paths, and we computed the node betweenness centrality to identify the most probable locations that controlled de flow of travels. Findings suggest that horses modified the transportation system by expanding the connections and increasing the speed of traveling across the New Spain territory. The node betweenness centrality suggests that some locations organized the flow of traveling based on a few harbors located at the central region. Therefore, the horse allowed the Spaniards to reshape the spatial organization in the colonial era in Mexico.

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.

The Effect of Training on Stride Duration in a Cohort of Two-Year-Old and Three-Year-Old Thoroughbred Racehorses

Simple Summary

Objective gait monitoring via GPS and motion sensors is becoming increasingly popular with racehorse trainers. This has the potential to assist in early detection of lameness and performance issues. This study sought to identify normal changes in gait in a population of two and three-year-old racehorses in order to inform future studies. We found that horses decrease their stride duration at a given speed over time with training. Stride duration appears to increase with increased distance galloped, but this effect is reduced over a training season and presumably increased fitness, so this may serve as a useful indicator for fatigue.

Abstract

Objective gait monitoring is increasingly accessible to trainers. A more comprehensive understanding of ‘normal’ gait adaptations is required. Forty two-year-old thoroughbred racehorses were recruited when entering training and followed for 22 months. Gait analysis was performed by equipping each horse with an inertial measurement unit with inbuilt GPS (GPS-IMU) mounted on the dorsum. Horses were exercised as per their regular training regimen. Data were analysed using a linear mixed model. For two-year-old horses, there was a non-linear pattern of stride duration (SD) over time (p < 0.001) with SD decreasing initially and then ‘flattening off’ over time (linear and quadratic coefficients −0.29 ms/week and 0.006 ms/week²). Horses showed an increase in SD of 2.21 ms (p < 0.001) per 100 m galloped, and over time, SD decreased by 0.04 ms (p < 0.001) with each 100 m galloped per week. Three-year-old horses overall showed no change in SD over time (p = 0.52), but those that had a period of time off showed a decrease in SD of −0.59 ms per week (p = 0.02). They showed an increase in SD of 1.99 ms (p < 0.001) per 100 m galloped, and horses that had a period of time off showed an increase in stride duration of 1.05 ms per 100 m galloped (p = 0.01) compared to horses which did not have time off. Horses demonstrate an adaptation to high-speed exercise over time. SD decreases with training when other factors are controlled for in naïve horses.

External mechanical work in the galloping racehorse

Horse locomotion is remarkably economical. Here, we measure external mechanical work of the galloping horse and relate it to published measurements of metabolic cost. Seven Thoroughbred horses were galloped (ridden) over force plates, under a racing surface. Twenty-six full strides of force data were recorded and used to calculate the external mechanical work of galloping. The mean sum of decrements of mechanical energy was -876 J (±280 J) per stride and increments were 2163 J (±538 J) per stride as horses were accelerating. Combination with published values for internal work and metabolic costs for galloping yields an apparent muscular efficiency of 37-46% for galloping, which would be reduced by energy storage in leg tendons. Knowledge about external work of galloping provides further insight into the mechanics of galloping from both an evolutionary and performance standpoint.

Track Surfaces Used for Ridden Workouts and Alternatives to Ridden Exercise for Thoroughbred Horses in Race Training

Little is known about the types of surfaces used during training of Thoroughbred racehorses or methods of exercise used in addition to ridden track-work. Our aims were to (1) describe the types of surfaces used in the training of Thoroughbred racehorses and to (2) identify alternative approaches used to exercise horses in addition to, or in place of, ridden overground track-work. Information regarding surface and alternative exercise methods was collected as part of an in-person survey of training practices of 66 registered Thoroughbred trainers in Victoria, Australia. Sand and synthetic surfaces were used by 97% and 36% of trainers respectively for slow-workouts, with galloping on turf training tracks used in training regimens by 82% and synthetic by 58% of trainers. Of those trainers utilising turf tracks, only 34% of gallop training was completed on turf despite turf being the predominant racing surface. Almost 90% of trainers used alternatives to ridden exercise. There is substantial variation in training surface used and alternative types of exercise undertaken by Victorian trainers. Future research should focus on how such practices relate to injury risk, particularly as it relates to the importance of musculoskeletal adaptation to specific race-day surfaces.

Tracking Performance in Endurance Racing Sports: Evaluation of the Accuracy Offered by Three Commercial GNSS Receivers Aimed at the Sports Market

Advances in global navigation satellite system (GNSS) technology have resulted in smaller and more accurate GNSS receivers, which have become increasingly suitable for calculating instantaneous performance parameters during sports competitions, for example by providing the difference in time between athletes at any location along a course. This study investigated the accuracy of three commercially available GNSS receivers directed at the sports market and evaluated their applicability for time analysis in endurance racing sports. The receivers evaluated were a 1 Hz wrist-worn standalone receiver (Garmin Forerunner 920XT, Gar-920XT), a 10 Hz standalone receiver (Catapult Optimeye S5, Cat-S5), and a 10 Hz differential receiver (ZXY-Go). They were validated against a geodetic, multi-frequency receiver providing differential position solutions (accuracy < 5 cm). Six volunteers skied four laps on a 3.05 km track prepared for cross-country skiing, with all four GNSS receivers measuring simultaneously. Deviations in position (horizontal plane, vertical, direction of travel) and speed (horizontal plane and direction of travel) were calculated. In addition, the positions of all receivers were mapped onto a mapping trajectory along the ski track, and a time analysis of all 276 possible pairs of laps was performed. Specifically, the time difference between any two skiers for each integer meter along the track was calculated. ZXY-Go, CAT-S5, and GAR-920XT had horizontal plane position errors of 2.09, 1.04, and 5.29 m (third quartile, Q3), and vertical precision 2.71, 3.89, and 13.35 m (interquartile range, IQR), respectively. The precision in the horizontal plane speed was 0.038, 0.072, and 0.66 m s^-1 (IQR) and the time analysis precision was 0.30, 0.13, and 0.68 s (IQR) for ZXY-Go, Cat-S5, and Gar-920XT, respectively. However, the error was inversely related to skiing speed, implying that for the low speeds typically attained during uphill skiing, substantially larger errors can occur. Specifically, at 2.0 m s^-1 the Q3 was 0.96, 0.36, and 1.90 s for ZXY-Go, Cat-S5, and Gar-920XT, respectively. In summary, the differential (ZXY-Go) and 10 Hz standalone (Cat-S5) receivers performed substantially better than the wrist-worn receiver (Gar-920XT) in terms of horizontal position and horizontal speed calculations. However, all receivers produced sub-second accuracy in the time analysis, except at very low skiing speeds.

The effect of the A-frame on forelimb kinematics in experienced and inexperienced agility dogs

Limited research has evaluated the kinematics of agility dogs over different equipment despite the growing popularity of recreational and competitive agility. A-frames are associated with a higher risk of injury; these risks could be related to how dogs approach the equipment. We hypothesised that forelimb (FL) and spinal kinematics would differ throughout the different phases of negotiating the A-frame: incline, apex, decline, and between experienced and inexperienced agility dogs. Eight agility dogs of mixed breed and age, all trained on the A-frame participated in the study. Participants were divided into two groups: inexperienced dogs (ID: <4 years training; n=4) and experienced dogs (ED: >4years training; n=4), and undertook 3 runs over the A-frame. Reflective markers were placed on each dog’s carpus (Ca), radiohumeral (RH) and scapulohumerus (SH) joints, Atlas, C3 and L3. Video footage was transferred to Dartfish™ to enable FL joint angles to be calculated for the approach (last stride), incline (FL contact), apex (FL over), decline (FL touchdown and FL departure). The range of movement (ROM) for spinal markers was also calculated. Wilcoxon signed rank analyses, with Bonferroni correction applied (P<0.02), indicated if kinematics differed for ED and ID between the phases. Similar kinematic patterns were observed through all phases for C3 and L3, however a greater ROM was found for ED: C3 and ID: L3. For Atlas, ED stayed in flexion for all phases whilst ID movement varied: approach-incline extension, incline-apex: flexion, apex to decline extension followed by flexion. No significant differences in FL joint angles existed (P>0.02). No significant differences in kinematic measures were seen between ED and ID dogs in any phase of the A-frame. ED demonstrate consistent movement patterns; ID vary their head and neck position more, and exaggerate their apex jump. Rounding the A-frame apex could encourage a less-extreme technique in ID.

Cardiorespiratory function in Thoroughbreds during locomotion on a treadmill at an incline or decline

OBJECTIVE To determine cardiorespiratory responses of Thoroughbreds to uphill and downhill locomotion on a treadmill at identical gradients. ANIMALS 5 highly trained Thoroughbred geldings. PROCEDURES Thoroughbreds were exercised for 2-minute intervals on a treadmill at 1.7, 3.5, 6.0, 8.0, and 10.0 m/s at a 4% incline, 0% incline (horizontal plane), and 4% decline in random order on different days. Stride frequency, stride length, and cardiopulmonary and O₂-transport variables were measured and analyzed by means of repeated-measures ANOVA and Holm-Šidák pairwise comparisons. RESULTS Horses completed all treadmill exercises with identical stride frequency and stride length. At identical uphill speeds, they had higher (vs horizontal) mass-specific O₂ consumption (mean increase, 49%) and CO₂ production (mean increase, 47%), cardiac output (mean increase, 21%), heart rate (mean increase, 11%), and Paco₂ (mean increase, 1.7 mm Hg), and lower Pao₂ (mean decrease, 5.8 mm Hg) and arterial O₂ saturation (mean decrease, 1.0%); tidal volume was not higher. Downhill locomotion (vs horizontal) reduced mass-specific O₂ consumption (mean decrease, 24%), CO₂ production (mean decrease, 23%), and cardiac output (mean decrease, 9%). Absolute energy cost during uphill locomotion increased linearly with speed at approximately twice the rate at which it decreased during downhill locomotion. CONCLUSIONS AND CLINICAL RELEVANCE Findings suggested that for Thoroughbreds, downhill locomotion resulted in a lower energy cost than did horizontal or uphill locomotion and that this cost changed with speed. Whether eccentric training induces skeletal muscle changes in horses similar to those in humans remains to be determined.

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

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

Gait as solution, but what is the problem? Exploring cost, economy and compromise in locomotion

Many studies have examined how legged mammals move, defining 'what' happens in locomotion. However, few ask 'why' those motions occur as they do. The energetic and functional constraints acting on an animal require that locomotion should be metabolically 'cost effective' and this in large part determines the strategies available to accomplish the task. Understanding the gaits utilised, within the spectrum of gaits possible, and determination of the value of specific relationships among speed, stride length, stride frequency and morphology, depends on identifying the fundamental costs involved and the effects of different movement strategies on those costs. It is argued here that a fundamental loss associated with moving on limbs (centre of mass momentum and energy loss) and two costs involved with controlling and replacing that loss (muscular work of the supporting limb during stance and muscular work of repositioning the limbs during swing) interact to determine the cost trade-offs involved and the optimisation strategies available for each species and speed. These optimisation strategies are what has been observed and characterised as gait.

Locomotion dynamics of hunting in wild cheetahs

Although the cheetah is recognised as the fastest land animal, little is known about other aspects of its notable athleticism, particularly when hunting in the wild. Here we describe and use a new tracking collar of our own design, containing a combination of Global Positioning System (GPS) and inertial measurement units, to capture the locomotor dynamics and outcome of 367 predominantly hunting runs of five wild cheetahs in Botswana. A remarkable top speed of 25.9 m s(-1) (58 m.p.h. or 93 km h(-1)) was recorded, but most cheetah hunts involved only moderate speeds. We recorded some of the highest measured values for lateral and forward acceleration, deceleration and body-mass-specific power for any terrestrial mammal. To our knowledge, this is the first detailed locomotor information on the hunting dynamics of a large cursorial predator in its natural habitat.