Pull-ups and chin-ups are more different than you probably realize. That subtle change of turning your palms from inward facing (a chin-up) to outward swaps which side of your torso you target. A study in the Journal of Strength and Conditioning Research measured muscle signals during both exercises and found that the chin-up more heavily recruited the pecs and biceps, while the pull-up focused on your back's lats and traps. And to answer which one you should be doing, it's both, says James Fell, certified strength and conditioning specialist in Chicago. "You don't want to be unbalanced."
The moves should be mainstays in any strength routine. "They're complex, multi-joint exercises that attack a broader range of motion than something like a bicep curl," says Fell. Always perform them early in your workout, says Gunnar Peterson, a personal trainer to NBA and NFL athletes. "It's not like adding 20 crunches. They're big movements, and you've got to give them the respect they deserve and have the energy to execute them properly."
It's common for people to struggle with both moves at first, but there are a couple ways to make getting them easier. Peterson suggests working on chin-ups first, which typically come faster because you're using muscles that are likely strong already. "You get a lot more help from your biceps," he says, "but it still builds up strength for pull-ups." He also recommends adding reps of the lowering portion of a pull-up when you're building up to the move. To work the full movement, Fell says to use an assisted chin-up/pull-up machine to build up the strength to get your head over the bar. And for anyone needing a bigger challenge, he suggests adding weight. That can mean holding a 5- or 10-pound weight plate between your feet, or using a belt to loop the weights around your waist.