I've already questioned the plank.
Now let me question that if you're going to plank, why on elbows? Why not on hands?
First - if you have a wrist problem that prevents weightbearing through it, but you want training of the trunk that connects upper quarter and lower quarter, think chops and lifts. Or a large number of other exercises.
But, if you still want to plank, and the wrists aren't tolerant, there's always gripping a dumb-bell and planking.
Why am I strongly suggesting getting off elbows? Because if you don't include grip or weightbearing through the hand, you're missing out on stimulating large numbers of mechanoreceptors in the hand and wrist and fingers - all of these detect and respond to pressure, sending signals to the rotator cuff of the shoulder, as well as the muscles around the elbow, scapula and thorax and neck. So, if you leave the hands out, you're excluding so much useful information to challenge stability and motor control.
Then, as per my previous article on planking, get out of it after 10 seconds and progress. Read more.