I’ve recently started doing more pull-ups and noticed that I subconsciously start lifting or swinging my legs when things get tough. I guess it’s about shifting my center of gravity, but I don’t quite understand how that works. and explain like I’m adult please!
In: Physics
Because you’re using your core to carry most of the weight of your legs so less work on your shoulders / back/ arms.
It’s exactly all about raising your center of gravity (center of mass actually) up using muscles other than your arms and upper back. If your center of mass quickly rises 3 inches, then the same effort with your arms will pull you (more or less) 3 inches higher. There’s a type of pull up known as a [kipping pull up](https://www.youtube.com/watch?v=r45xLlH7r_M) that takes advantage of this phenomena intentionally, allowing someone to both do pull ups more rapidly and do far more of them than if they’re being strict in their movements. Leaving aside opinions on whether this is a “real pull up” (whatever that means), the idea is to intentionally use a controlled swing to raise the hips rapidly, leading to a far smaller energy expenditure on the arms. Basically getting the rest of the body involved in the pull up.
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