A plank isn't a passive hold. Make a fist and push away, pull your ribs down, tuck your pelvis, then squeeze your glutes and quads hard. That stiffness carries over to deadlifts and squats, letting you move more weight.
A plank is not passive. If someone is doing a plank and they're just kind of la-dee-da-dee-da, they're not doing it properly. Let's start from the hands. I make a fist and I'm gonna push myself away. You can see here, I'm not here pushing myself. Then I'm pulling my rib cage down. Now I've got my bum up purposely. I'm gonna tuck my bum down. My pelvis is tucked under. I'm trying to hide my tailbone and I'm pulling my rib cage down. Now I'm gonna flex my bum cheeks as hard as I can and then I'm gonna flex my quads as hard as I can. So right now I'm trying to get as stiff as I possibly can in the plank. That stiffness I'm going to carry over to a deadlift. I'm going to carry it over to a squat. I'm going to carry it over to every exercise I possibly can. I want to create as much stability in my body as possible. That is going to allow me to output as much weight on the bar as possible.
