Derby the dog, born with underdeveloped front legs that prevented him from running, was abandoned at a shelter and in danger of being put down, The Dodo reports, but he got a second chance with a foster mom who happened to be a director at a 3D printing firm.

Derby started out in a wheelcart, but it limited his speed and his ability to play with other dogs, so Tara Anderson and a team at 3D Systems designed and printed him some sweet custom prosthetics.

They started with a "running man"-style design like the ones used by human athletes, but rejected it because the blades could sink into the ground. After a few iterations, Derby ended up with a set of round treads that let him finally run for the first time—and he loves it.

His adoptive family says he was always a happy dog, but he didn't know what he was missing until he got his new legs. Now he runs 2 to 3 miles a day with his humans, and they can barely keep up.

What a good boy.

[h/t The Dodo]