When I bought Project Cheap Camaro—a $2,800 1968 coupe with a halfway attached roof and otherwise great bones—I was pretty sure I’d just scored one of the DIY deals of the year. Why was it so cheap?

“Dead bugs are great for basic core control, but the Zercher side bend trains your body to resist collapsing sideways, which is more transferable to real-life movement, lifting and sport,” says ...