(cont) The same position is then transferred onto the chair - with hands on the seat and feet on the pedal for the pull up. A heavier weight is more supportive to help with the lift, but the important thing is that it is the two-way stretch of the hands pressing down into the seat and the feet pressing down on the pedal with the abs lifting up and away from the hands and feet. Even hovering the pedal off of the floor in this position is good. Watch for the student overly rounding her thoracic spine. Think hip bones reaching toward the chair so that the curve is more lumbar than thoracic. Also watch for shoulder stability - on both standing press down and the pull ups, make sure the shoulder blades are broad and down the back.
(cont) Another exercise that is a good prep is spine stretch forward on the chair. Sit on the floor with your legs framing the chair and hands on the pedal (medium weight - one spring). Press the pedal down slightly by engaging the lats and then round up and over to push the pedal down further. It's tough because you shouldn't have your back move backwards. You are folding OVER to push the pedal down, essentially creating a similar shape as a pull up. I hope that helps!!
I'm an instructor but for my own workouts, I'm always looking for great lower body work. I usually turn to Tracey Mallet's booty barre for that ;) but I really love this chair workout and how Mariska incorporated a great amount of lower body work.