Center of Mass During the Pullup

Question

Hello,

I'm trying to figure out the physics behind different pullup techniques. I read an article online that stated if you change your COM, you can effectively make the pullup easier. Physics of Fitness Fridays - The Pull-Up — Jane Reaction Fitness

1. How does the COM change with the leg position here? Is this person accurate?
2. If changing the leg position changes your COM, can you effectively make the pullup "easier" by starting with your legs in one position and moving them into another position to decrease the distance the COM will travel through the pullup exercise?
3. Does decreasing the distance traveled by the COM have anything to do with the total load being lifted and is it even possible to make the pullup "easier," or is this just momentum at play and moving the legs from the back position to the front adds an acceleration thus making the pullup easier.

Thank you!

Answer 1

1. I believe the COM will change with the legs position change.
2. Pullup means moving body, not legs. Changing COM (moving legs) pre-pullup does not change COM travel distance during pullup (with no leg movement) and does not make it easier.
3. Say you raise your legs pre-pullup [which is a "work" in Physics]. DURING pullup you lower them WHILE raising your body - THIS will change COM travel distance and make it easier, by "trading" the pre-pullup work.