You can read more about how to do an up-down plank with perfect form here, but essentially ... in this exercise as you move ...

This week: low planks. You probably didn’t think planks could harder than the five-minute-hold challenge. But for a deeper (and arguably more useful) burn, try taking the plank into a low position.

One of the best ways to blast your core is the oh-so-simple plank. When performing a plank with good form, you’re working your midsection, shoulders, chest, lower back, quads, and glutes.