To do it:Get into pushup position with both hands on the stability ball directly below your shoulders (your feet can be slightly wider than shoulder-width apart to give you extra stability). Contract your abdominals and try to bring your body into a straight line from your neck all the way to you toes (your butt should not be sticking out, so contract your glutes and keep your hips down). Once you are stable, lift your right leg a few inches off the ground and hold for 10 seconds. Repeat on the other side. Try to do three sets of a 10-second hold, and then advance to a 30-second hold.
But there's science behind this buzzkill. The rectus abdominis — the muscle that makes the stomach look defined as hell — is typically covered by fat (because that's how humans are made) and isn't affected by things like crunches and planks. "You can work your abs all you want, but if you have a layer of fat over them, the 'pack' can’t be seen," Ball says. And FWIW, that's not a bad thing or something to feel bad about. "It’s very unrealistic for most people to have body fat percentages low enough to see the abs."
Yuri Elkaim is one of the world’s most trusted health and fitness experts. A former pro soccer player turned NYT bestselling author of The All-Day Energy Diet and The All-Day Fat Burning Diet, his clear, science-backed advice has transformed the lives of more than 500,000 men and women and he’s on a mission to help 100 million people by 2040. Read his inspiring story, “From Soccer to Bed to No Hair on My Head” that started it all.
But instead of just trying to perform as many reps as possible, slow down and really focus on the quality of the movement—especially the eccentric, or downward motion, of the exercise, he says. “The eccentric contraction is the most important phase when sculpting any muscle.” Plus, focusing on quality over quantity will help protect your back (some experts say crunches can be potentially troublesome for guys with back issues.)