Planks are a simply awesome exercise for strengthening your core. Push ups are a great exercise for strengthening your main abs (Rectus Abdominis). Up & Down Planks is an exercise that combines the best of both worlds. You get to strengthen your arms, core and abs all in one go.
What's involved: Abs, core, lower back, triceps, glutes, quads.
Powered by: Abs and core, but also triceps and quads.
Tip: There is little point in doing this exercise fast. For maximum benefits do it in a steady rhythm that pays total attention to form: body straight, lower abs pulled in.