Plus, doing a pull-up properly requires intense engagement of your back muscles -- particularly your latissimus dorsi -- and as Erick Avila, the owner of Ergogenic Health, points out, pull-ups have a way of highlighting all the weaknesses associated with a sedentary lifestyle. Namely, poor back strength: "Typically because of work and school, we're in slouched positions with our back muscles unengaged. In addition to this, many people tend to overlook developing their back muscles and instead spend time training the 'beach muscles' like the chest and biceps," he says.
As much as I hate to break it to you, all those bench presses and biceps curls aren't going to automatically translate to success on the pull-up bar.
It's not just weight and poor muscle strength that make pull-ups hard; mechanics and physics play a significant role as well. Dr. Matt Tanneberg, a sports chiropractor and certified strength and conditioning specialist, points out that, "Pull-ups force you to control your body weight in multiple planes. During a pull-up, you're pulling your weight up in one direction, and you're forced to stabilize your core to reduce swinging motion. This means you're not only working your upper body's pulling muscles (lats and biceps), but also your core."