More ideas from eirini
I think I'm going to have to try this exercise for core strengthening... adds difficulty to a normal plank.  3x10.

7 exercises that will have you losing 2 lbs. a week. Do it three times a week, on alternating days, to tighten up exercises that will have you losing 2 lbs. a week. Do it three times a week, on alternating days, to tighten up everywhere.