Speed and efficiency: The horse has got it all, research shows

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Poet’s Word. [file image] © Racingfotos.com
The remarkable efficiency of horses at a gallop have been demonstrated in a British study, which revealed muscle efficiencies of 37 to 46% and highlighted the importance of elastic cycling of energy in limb tendons.

Researchers from the Royal Veterinary College made use of force-plate technology to accurately measure the external work of galloping in Thoroughbred racehorses.

This technique, which has never been used for such large animals at high speed before, showed that horses had much lower levels of external work – that is, how much work the horse has to do to move relative to its environment – than had previously been reported when studied using different methods.

Sensors were planted under a section of the racing surface at the British Racing School in Newmarket for the experiment, organised by academics who work in the college’s Structure and Motion Laboratory.

Area of the track showing where sensors have been planted under the surface
Area of the track showing where sensors have been planted under the surface at the British Racing School in Newmarket, for a Royal Veterinary College study.

A professional jockey then rode seven thoroughbred racehorses over this specialist equipment, allowing the researchers to directly measure the external mechanical work of galloping by measuring the forces they exerted on the runway.

The study, the findings of which have been reported in the journal Biology Letter, produced lower values than those previously reported for external work in galloping horses.

Those earlier studies reported high external work values, estimated via different methods, which are at odds with the fact that horses evolved to move at high speeds over long distances. High external work values would make moving over long distances much harder.

The college research team has now been able to calculate the apparent muscle efficiency of galloping horses by combining the external work values from this latest study with published values for metabolic work (the conversion of food into energy used by muscles) and internal mechanical work (how much work is needed to move the limbs relative to the body).

They found that the horse’s efficiency values were between 37 and 46%.

The findings are expected to provide useful insights into the movement of racehorses and will contribute toward explaining how racehorses can gallop so efficiently over long distances.

“This was really challenging data to collect and, to our knowledge, it is the first time high-speed galloping force plate data have been collected from such a large animal,” said Dr Zoe Self Davies, a postdoctoral research associate at the college involved in the study.

Professor Alan Wilson, who specialises in locomotor biomechanics and contributed to the study, said: “This data provides fresh insights into these remarkable animals.”

Collecting data from the sensor array as the horse gallops over it.
Collecting data from the sensor array as the horse gallops over it.

The researchers were able to record 26 full strides of force data, which was used in their calculations.

The findings highlight the remarkably economical nature of horse locomotion, and provide insights into the mechanics of galloping from both an evolutionary and performance standpoint, the study team said.

The horse, they noted, has a very low metabolic cost of transport (COT) – that is, the amount of energy consumed to cover a given distance – meaning they can move very efficiently.

They have been selectively bred for increased speed and endurance.

Adaptive specializations for running in the horse include a lower limb that is slim and light, with an extended single digit and no musculature below the carpus and tarsus.

The reduced mass of the lower limbs reduces the energy required to swing the limbs between stances.

“Further, long, elastic distal tendons allow elastic energy storage and return, contributing to economical locomotion.”

The upper portion of limbs are made up of large, bulky muscles which allow rapid limb swinging and propulsion, with the further aid of a large tendon within the biceps muscle of the forelimb that acts as a catapult to give rapid limb protraction.

These adaptations underpin the metabolic and mechanical factors affecting – and limiting – athletic performance in racehorses, they said.

Discussing their findings, the authors said they factored in the use of a rider: “With regard to this study being performed on ridden horses, 13% of the total mass is the rider who, in racing posture, will add weight but limited inertia.

“As the rider can move horizontally somewhat out of phase with the horse’s centre of mass, horizontal work (by the horse) on the rider is reduced while their weight is still supported.

“Calculating mechanical works for horse mass alone would result in an 11% increase in mass-specific work.”

Z. T. Self Davies, A. J. Spence and A. M. Wilson. External mechanical work in the galloping racehorse 15 Biology Letters doi.org/10.1098/rsbl.2018.0709

The full study can be read here

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