Height-adjustable apparatus using a spring to urge forward and rearward undulating whippy locomotion. A hand-crawling embodiment enables users to engage in all-fours crawling locomotion while the body is conventionally situated in a two-legged orientation. A foot-bounding embodiment enables walkers, joggers, runners and jumpers to engage in forward and backward whippy locomotion. A crutch embodiment enables crippled or injured users to likewise engage in whippy locomotion.
