This is a test of commonsense. Complete the next sentence:

How to post while trotting on a horse
Understand why posting is done.
The main reason to post while riding is to avoid being jostled around in the saddle during a particularly bumpy gait-the trot. This makes things more comfortable for the rider and is easier on the horse's back.
Once you become more experienced with the rising trot, it is also possible to change the horse's rhythm simply by posting more quickly or slowly. The horse will alter his rhythm to match with your own, thus sometimes eliminating the need for hand and leg signals.