There's a reason that the plank is such a staple of most exercises routines. The no-equipment-move strengthens your core, and all you need to do is hold the pose for a short while to see the benefits.
But, we'll admit, unrolling your yoga mat then staying put for 60 seconds or more can be a bit, well, boring. Fortunately, there are plenty of ways you can make this move more fun while still building a solid midsection.
