Russian Lean

Prerequisites: 
Ball Leg Curl
Target Muscles: 
Body Position: 

Person A knees on the floor in upright position, keeping legs close together at all times. Person B keeps lower legs of person A on the floor throughout entire motion. Person A slowly leans forward, back remains straight, until lean can not longer maintained and upper body falls towards the ground. Person A uses arms to absorb the fall and pushes upper body back into starting position.

Common Errors: 

Instead of controlled forward lean, upper body rapidly moves towards the floor.
Hips flex on the return.

Video: