Here is another alternative from Will Heffernan.
This is the first time James had done this exercise and he didn't do a bad job at all. You should try it...I like this exercise for a lot of reasons...it sort of combines a 'wall sit' without the wall...I like the resisted rotation...it is a great way to load the trunk. We pull the shoulders blades back and down and keep a good tight lower back arch.
As the athletes get better we both increase the loading and hold the plate further from the body...try it and tell me what you think.