Concentration curls are the “best” exercise for the biceps, according to a small 2014 study at the University of Wisconsin, commissioned by the American Council on Exercise (ACE). This method—done with your upper arm pressed against your leg for support as you lift the weight—resulted in significantly greater muscle activation of the biceps than seven other popular biceps exercises, including the cable curl, incline curl, barbell curl, and EZ curl. (Watch a short video by ACE about the study, including footage of each exercise.)
Concentration curls are more effective because they isolate the muscle, whereas the other exercises allow the arm or shoulder to swing with the lift, thereby reducing the total load on the biceps. You may also get better results because the position allows you to watch your biceps in action, so you can focus more on what you’re doing. Some gym machines also target just the biceps.
Biceps are used to pull open doors and lift and carry things, among other tasks. But other arm (and shoulder) muscles are also involved in these everyday activities— which is why it’s important to do a range of strength-training exercises that work all your upper body muscles, including your triceps, deltoids, and pecs. That is, you can do concentration curls a couple of times a week, but chin-ups and a tricep dips, for example, will round out your workout.