Today's is a Twofer.

Part 1: 4 mins of Tabata

Choose the toughest plank that you have done so far and do it in 20 sec intervals with 10 sec rest x 8 rounds. There are so many free tiners available to help you with this. My fav free app is Gymboss 

A regular stopwatch will do the job too. Rest for all the 20s and 50s. Pank until 20 and 50,  

00-20 Plank

20-30 Rest

30-50 Plank

50-1:00 Rest

1:00-1:20 Plank..... For 4 minutes. 

Part 2: 7 mins of forearm Plank hold: *for a total time of 7. Take as many breaks as you need in irder to get 7 quality mins of a plank in. Try it all in one attempt or do a min each hour ... Its up to you.  

Quality is the goal.