Consulting the website I use to study/review for the NSCA-cpt test because this site is not afraid of a biomechanical explanation I found an excellent explanation of how a chin up works. https://exrx.net explains why palms facing you/Palms Up is easier than palms away from you when pulling your body on a bar... Picture By Dima Goroziya at PixaBay.com Royalty Free Images https://bodybymargo.blogspot.com/2018/02/chinups-and-pullups-getting-it-done.html ...It’s interesting that the chin-up has a more dynamic resistance curve than the pull-up. Both movements allow the muscles to relax momentarily at the bottom of the motion. However, at the top of each movement, the lever arms are closer to the body’s center of gravity in the chin-up as compared to the wider grip pull-up. So it turns out that the Chin-up is relatively easier at the top of its motion. Also, the underhand grip of the Chin-up allows the Biceps Brachii to pull in a stronger mechanical position r