You would classify a fit horse under its days last start.
Generally horses that have had there last start less than 28 days win around 76% of the races.

A couple of our trainers have said horses lose there fitness after 18 to 22 days of intense training.

Whereas horses generally after 3 runs only win 51% of races.

The difference lies with the distance. Stayers require the 3-4 runs in a prep where sprinters can go fresh or 2nd up.

Other factors include the coat, sweating at barriers or in the yard or even the head position when walking around before the jump.