There's a bunch to unpack in this move.

First of all, it requires some strong back muscles to lengthen through the spine.

Second, the length of your hamstrings is key. If you are tight, you won't be able to straighten your legs out all the way. Not only that, but tight hamstrings tend to pull your pelvis into a posterior tilt. That makes it harder to sit out of your hips and lengthen the back.

So if tight hamstrings are your lot in life at the moment, modifying this exercise is necessary. Do what Katie does by keeping your knees bent and just working on driving the spine straight and chest forward.

Balancing on the sits bones with your legs extended is also another good prep for this exercise. Keep channeling the strength in the core to help you find the strength in your back as well.