Which muscles do pull-ups work?

Being able to do a pull-up is a common fitness goal but which muscles do pull-ups work and why are they so difficult?

Chin-Ups Vs Pull-Ups: How They're Different And What You Should Do

How to Do Pull-Ups: Muscles Worked & Proper Form – StrengthLog

Pull-Up Techniques for Everyone - The New York Times

Which muscles do pull-ups work?

Chin Up vs. Pull Up - What's the Difference and Which Is Better

How to Do Pull-Ups: Muscles Worked & Proper Form – StrengthLog

How to Train Your Chest with Pull Ups

What Muscles Do Pull-Ups Work?

Chin Ups: Benefits, Muscles Worked, and More - Inspire US

Pull-up (exercise) - Wikipedia

Australian Pull Ups, How to Perform an Australian Pull Up