YOU PROBABLY THINK you know how to do a plank. The ab training staple is relatively simple, after all—boiled down to the basics, all you need to do is get down on the ground and hold in place.

You've probably done a plank or two in your time. Maybe even groaned through a shaky 30 seconds or challenged yourself to a two-minute burn. But a clear difference exists between a basic plank and a ...

"Hearst Magazines and Yahoo may earn commission or revenue on some items through these links." THERE'S A REASON people often refer to strength training simply as "lifting:" it almost always involves ...