Summer is right around the corner, and if you're looking for a challenge—and a six-pack—Jeff Cavaliere, C.S.C.S., of Athlean-X has you covered with an ab workout that’s built for all fitness levels.

It all began with two chilling words scribbled on a prescription slip: “Stop walking!” For most, those words would signal surrender. For entrepreneur, author, and content creator Ankur Warikoo, they ...