Facing the naked backs of those in front of them, the women sweated in a circle, each teetering on the ball of one foot. Their trainer, seeing the last one secured by her bridle to the overhead arm of the exercise machine, pulled a lever on its central column. Like spokes on a great horizontal wheel, the arms began to rotate, pulling the trainees irresistibly forward, and off-balance.

Instinctively stepping forward with her raised foot, Jean squealed through her gag, as the elastic cord stretching from one ankle strap, through her pussy ring to the other ankle, yanked her cunt lips earthward. In pure pussy preservation, her muscles twitched the planted foot off the ground, as the raised foot plunged down to catch her weight.

The clumsier captives screamed through the bits between their teeth, stumbling to avoid being dragged by their halters, while the taut cord stretched their sex flesh to impossible length. In seconds, pain forced all the harnessed women into this hopping gait, useless hands pawing the air. Their groans mingled with the metallic clank of the pitiless mechanism forcing them round and round, at steadily increasing speed.

Slow learners – including one girl who tried to hop along on one foot - felt the trainer’s lash across their asses. Even if they performed flawlessly, none could escape the tug of their flailing tit weights. Helplessly, Jean watched Sheree, just ahead of her, try to prance fast enough to spare her pussy, whose punished lips Jean could see protruding far below the poor girl’s whip-striped buttocks with each unsteady hop.

Ankles began to weaken, but the heel stingers in their hoofgear kept the ponies on their toes, building the powerful calf muscles they would need in service to their owners. Only the highest, quickest steps spared them labial agony. As their prancing improved, the girls’ tit and muscle strain was more than offset by the relief they felt in their groins. At last, the new fillies began to prance in rapid unison, conditioned by the pain in their heels, butts and crotches to the automatic obedience of trained animals.