This is an exercise I first saw done by strength coach Mike Boyle a couple months back. Looking at it, you make this this would be considered an upper body exercise since that’s where the movement is occurring. But actually this is an isometric anterior core exercise as you try to resist extension at the spine when pressing the weight out.
It’s also a great exercise to work on your squat depth and get you used to what coaches refer to as “sitting in the hole”.
The more you you can get out of any particular exercise,you should always consider that exercise to be part of your training arsenal.