kick with hoof, horse's gallop
趹 centers on a horse's forceful leg action: kicking with the hoof and the resulting gallop. Both meanings describe the same powerful, rapid movement of a horse's legs.
趹 combines 足 (foot) with 夬, which likely contributes the sound. The character is associated with a horse's kicking and galloping, but the exact historical development of the 夬 component in this context is uncertain.
The left side 足 means foot, and the right side 夬 looks like a horse's hoof striking out. Picture a horse's foot kicking forward with force, then breaking into a gallop.
For ケツ, imagine a horse kicking so hard it leaves a deep ketsu (けつ, butt) print in the dirt: ketsu -> ケツ, and the hoof strike is powerful.