Trot

On June 29, 2014, at Pocono Downs in Pennsylvania the Swedish standardbred Sebastian K trotted a mile in 1 minute, 49 seconds (quarters were passed at 26:2, 55:3 and 1,21:4).

Eadweard Muybridge was the first to prove, by photography, in 1872 that there is a "moment of suspension" or "unsupported transit" during the trot gait.

Each time another diagonal pair of legs hits the ground, the rider can be jolted upwards out of the saddle and meet the horse with some force on the way back down.

Therefore, at most speeds above a jog, especially in English riding disciplines, most riders post to the trot, rising up and down in rhythm with the horse to avoid being jolted.

[1] To not be jostled out of the saddle and to not harm the horse by bouncing on its back, riders must learn specific skills in order to sit the trot.