It's not planks or sit-ups — the starburst plank is torture on your abs, obliques and shoulders (so I tried it, and here's my verdict)

The starburst side plank variation strengthens the shoulders, abs and obliques. Here's why we love it at Tom's Guide.
Yahoo

Your Step-by-Step Guide to the Perfect Side Plank

How to do the perfect side plank, and how to make it easier (and harder). Planks are hard. Even just 30 seconds in plank position can feel like an eternity. But as challenging as planks are, side ...
Well+Good

If You Want a Stronger Core, Don’t Skip This Important Step While Holding a Plank

A strength and conditioning coach breaks down the proper way to start and hold a plank to prevent injury and strengthen your abs. Chip Coleman, CSCS, is the co-founder of Motus Performance in Tucson, ...