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Why do racehorses have an optimum trip?

By Dr Jeremy Naylor
First Published: 16 July 2009 - Issue Number: 13

Irrespective of where in the world Thoroughbreds are raced, individual horses are usually campaigned over a narrow range of distance and are often categorized as sprinters (5-6f/1000-1200m)), middle distance performers (7-10f/1400-2000m) or stayers (>10f/>2000m).

Whereas in the USA and Australia most races are run at up to and around a mile (1600m), in Europe there is a greater range of racing distances, from 5f (1000m) to 2 miles 6f (4400m) on the flat and from 2 miles (3200m) to 4 miles 4f (7200m) over jumps. 
So why is it, when the Thoroughbred breed arose from such a small gene pool, that individual horses seem to be suited by different and narrow ranges of trip? Here we shall explore the principal factors behind these observations and the genetic influences that might be responsible for them.
 

Performance determinants and optimum distance
The principal factors that determine a horse’s racing performance are its genetic potential, its training and its environment (including atmospheric conditions, nutrition, tactics, rider, shoeing, racing surface and terrain). The former factor is the responsibility of the breeder while the others are to some extent controlled by the trainer. The relative importance of these factors is still very much open to debate.  However, few would question the primary role of genetics: even when conditioned by the world’s best trainers, moderately bred horses rarely perform competitively in the highest grades.
A more in-depth look at what determines an individual’s performance reveals another array of essential elements. These are the physiological attributes of its muscles and cardio-respiratory system (its “engine capacity”), the biomechanics of how it converts muscle contraction into propulsion (its “transmission”), and very importantly its motivation (its “will to win”).
The principal physiological components are the muscle mass and the cardio-respiratory systems that play supporting roles in carrying oxygen and other essential fuels to the muscles. The elite status of the Thoroughbred horse among the mammalian species relates to all these components, with muscle being a greater proportion of their body weight and cardio-respiratory systems that have enormously superior capacity for carrying oxygen. It is clear from studies of racehorses and humans that maximal capacity for oxygen consumption (VO2max) is an important factor in determining peak performance.

Muscle Fiber Types
Absolutely central to the issue of optimal trip are the relative proportions of slow (type I) and fast twitch muscle fi...

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