exercising horses on woodchips

Question
hello sir, in the movie SEABISCUIT, the horse was exercised heavily on wood ships at stud farm. may i know the purpose of exercising horses on wood chips? dont they get cup injuries?

Answer
HI -- some training tracks are made of different types of surfaces, some are real dirt, turf, sand, muddy, synthetic, shredded rubber tires etc. wood chips ..if the type of soil is for the type of horses and type of training you are going to do to get ready for a race..  thanks ED HESS