To perform an effective side plank for back strengthening, make a fist with the hand on the floor, push hips off the ground, and actively push the floor away.

“what you're going to do for the side plank in order to generate the strongest and most efficient side plank for strengthening and hopefully depainting your back is to get on the side Bend those knees put the hand down in a fist position okay then you're going to push the hips off the ground so the upper body is indeed in a plank position then you're going to raise the hips up and you're going to have to put some considerable effort into pushing the floor away from you that's really the key here pushing the floor away from you”