9 Efficient Cardio Planks To Work Your Core *and* Spike Your Heart Rate

Cardio planks will work your core *and* spike your heart rate. Oh, and they'll make you extra sweaty, too. Here are the best ones to try.

alt
Photo: <a href="http://www.stocksy.com" target="_blank" rel="noopener noreferrer">Stocksy</a>/Guille Faingold