Plank punches introduce an inherent instability in the classic plank position that further challenges your core. Once you have mastered the classic plank position this should be next on your list. 

What's involved: Core, triceps, shoulders, quads, lower back, lower abs, abs. 

Powered by: Core, shoulders, triceps. 

Tip: Have your feet about shoulder-width apart when you perform this exercise. It places a greater load on your abs as you take one arm off the floor, to punch giving you better results, faster.