Large circles, sufficiently deep dirt, short sessions
The hoof will always be parallel to (flush with) the ground surface, & so the tighter the circle, the more the breakover point shifts from the center of the hoof to the inside edge of the hoof. The tendons, ligaments, & joints on the outside will be stretched to accommodate the turn, which stresses the horse's body because it naturally has very slight lateral stretching capacity. Barrel-racers have very deep footing for their tight turns, race horses have sufficient depth & spring in the tracks, yet longeing is often done on insufficient footing, & done for too long a time, as well. The increasing instances in stifle, navicular, etc. nowadays are the result of humans mishandling their horses in longeing and other ways under saddle.