One trainer shares what a simple plank challenge did for his mental and physical strength.

Add Yahoo as a preferred source to see more of our stories on Google. Forget crunches and sit-ups. One of the best ways to blast your core is the oh-so-simple plank. When performing a plank with good ...

Add Yahoo as a preferred source to see more of our stories on Google. Whenever you're feeling a little stagnant in your training, taking on a new fitness challenge is the quickest way to snap out of ...