We see it all the time. We ask people to show us their pull-up, and then we typically see rounded shoulders, elbows flaring, and a lack of midline control. Reminder: True strength is the ability to go through a full range of motion with as much midline control as possible.
If you aren’t expressing that, then two things will probably happen:
a) You will pattern a faulty movement , which will translate into weaker movements in the future.
b) You will probably get hurt from a lack of body integrity.
Here at TLF, we are always about mobility and stability first. If that isn’t there, then your foundation is fudged up. And this means you feel the right musculature firing throughout the entire movement:
c) Lower abs, obliques
d) Posterior delts
e) Glutes and Quads
Without further a-do, here is a video tutorial on how to refine this movement.