Check out Women’s Health’s Fitness Faceoff every week to learn which moves will best help you reach your fit goals. Here’s this week’s faceoff:

The real secret to a sexy stomach is carving out those lines to frame your budding six pack (a.k.a. your obliques).

And while you’re already well aware that planks help tone your entire core, there are also some variations that focus on working your side abs: plank knee taps and plank sweeps. But between the two, which one challenges your obliques the most?