Cass H ~ Thank you so much! For Short Spine, they might not be able to reach the stopper due to tight hamstrings or a tight low back. If this is a struggle for them, they can also do the more traditional version that doesn't bring the carriage all the way in. It requires a lot of strength from the powerhouse but it is very effective! Also, it will still allow them to get the benefit of the stretch on the way down. I hope this helps! Feel free to reach out if you have more questions!