Running the curves: Thoroughbred limb dynamics explored

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Sharp turns have been shown in research to increase the risk of ligament-related injuries in the foot, and catastrophic injuries are more likely to occur in racing on a curve than on a straight segment of track.
Sharp turns have been shown in research to increase the risk of ligament-related injuries in the foot, and catastrophic injuries are more likely to occur in racing on a curve than on a straight segment of track. Photo by Pietro Mattia

Researchers have charted the limb dynamics of Thoroughbred horses running curves in training, saying a better understanding of the effects of lean and torque on the lower limbs is required to better understand injury mechanisms.

During racing, injuries are more likely to occur on a bend than on a straight section of track.

In nature, the negotiation of curves is important during locomotion, for example, during predator-prey interactions where speed alone may not be enough to escape.

Rebecca Parkes and her fellow researchers, writing in the journal PLOS ONE, noted that domesticated horses negotiate curves and bends frequently, both in racing and other disciplines.

It has been suggested that increased limb force associated with galloping on a curve may be associated with increased injury risk.

Sharp turns have been shown in research to increase the risk of ligament-related injuries in the foot, and catastrophic injuries are more likely to occur in racing on a curve than on a straight segment of track.

Despite a high incidence of musculoskeletal injuries during training, no study has yet assessed the changes in gait associated with galloping at training speeds on a curved track.

Parkes and her colleagues set up an experiment involving seven Thoroughbreds galloping at training speeds on large radius curves.

Each horse was equipped with a sacrum-mounted inertial measurement unit with an integrated GPS, two hoof-mounted accelerometers, and retro-reflective markers on the forelimbs.

The horses galloped 2 to 4 circuits anticlockwise around an oval track and were filmed at 120 frames per second using 10 cameras.

the authors said curve running is complex and not yet fully understood.
The authors of the study say curve running is complex and not yet fully understood. Image by H. Hach

Speed and curve radius was derived from the GPS data and used to estimate the centripetal acceleration necessary to navigate the curve.

Stride, stance and swing durations, and duty factor (the percent of the total stride cycle in which a given foot is on the ground) were derived from accelerometer data.

Limb markers were tracked and whole limb and lower limb angles were calculated.

For horses galloping on the correct lead, the duty factor was higher for the inside (lead) leg on the straight and on the curve. For horses galloping on the incorrect lead, there was no difference in duty factor between inside and outside legs on the straight or on the curve.

Limb lean angles increased as predicted, and lead limb function was found to mirror the functional requirements for curve running.

Discussing their findings, the authors said curve running is complex and not yet fully understood.

“This study does not take into account the hind limbs and therefore does not account for the differing functions of the fore and hindlimbs,” they said.

“In horses the hindlimbs mainly act to propel the centre of mass forwards, while the forelimbs apply vertical impulse to the centre of mass.

“This is also likely to be the case for curve running in the horse, as other quadrupeds such as greyhounds and mice show similarly differing roles for the fore and hindlimbs during curve running.

“Further work should take into account the role of the hindlimbs and bend along the long axis of the body when galloping at high speeds on curves representative of those used in training.

“Additionally, a more comprehensive understanding of the extent and effects of torque about the long axis of the limb would aid in understanding injury mechanisms during curve running.”

The study team comprised Parkes, with the City University of Hong Kong in Kowloon; and Thilo Pfau, Renate Weller and Thomas Witte, with the Department of Clinical Science and Services and Structure and Motion Lab, part of the Royal Veterinary College in South Mimms, Hertfordshire, England.

Parkes RSV, Pfau T, Weller R, Witte TH (2020) The effect of curve running on distal limb kinematics in the Thoroughbred racehorse. PLoS ONE 15(12): e0244105. https://doi.org/10.1371/journal.pone.0244105

The study, published under a Creative Commons License, can be read here.

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