The shape of a racehorse’s hindquarters gives a clue to his potential as a stayer or a sprinter. Horses destined
to excel over shorter distances need to generate explosive power from the muscles of the quarters, principally the
gluteals and the hamstring group. So they build strong, rounded quarters which give them the required leverage
behind the saddle.
Strong, rounded quarters
Horses that are more suited to racing over a distance of ground tend to be lighter in their quarters and often
longer too, as measured from the point of hip to the hock.
Lighter, longer quarters
Differences in muscle contour between sprinters and stayers are largely due to the type of muscle fibres that
predominate in the horse’s physiological make-up. Sprinters have a high proportion of ‘fast twitch’ fibres, which
are physically bulkier, more rounded and shorter than ‘slow twitch’ fibres. Fast twitch fibres contract quickly and
provide a short but intense burst of pre-stored energy which can’t be replenished during a race. The staying type
of horse has a higher proportion of slow twitch fibres, which contract more slowly and can function for a longer
time without getting fatigued.
Whether the horse has the powerful quarters of the sprinter or the more spare shape of the stayer, there should
be clear evidence of muscle definition in the hamstrings (a group of three muscles: biceps femoris, semitendinosus
and semimembranosus). These are the muscles you can see as the horse walks away from you, down the back of the
quarters, roughly from the base of the tail to a few inches above the hock. Horses that are backward or still weak
will lack this definition, which derives from serious work on the home gallops or from several racecourse outings.