Is there any value in training biceps one arm at a time?

Q: Is there any value in training biceps one arm at a time, rather than both together?

A: More important than whether you train both arms together or one at a time is how you do the curling exercise in question. If you’re guilty of incorrect exercise technique, not training hard enough, overtraining or not increasing your exercise poundages, then neither the one-arm nor the two-arm option will build any muscle. If, however, you use correct exercise technique, train hard enough to stimulate growth, don’t overtrain, fully attend to the components of recuperation and gradually increase your curling poundages as the months go by, both options can help build your biceps.

Even so, what you do with the rest of your training may be of greater importance than what you do specifically for your arms. If you’re on a brief overall routine of just a handful of big, compound exercises, you may have a good chance of growing all over, including your arms, but if you’re using routines focused on isolation exercises—or even a mixture of compound and isolation exercises but in an excessive quantity—you won’t have a chance of achieving any substantial growth on your arms no matter what you do specifically for them.

Comparing one-arm curling with two-arm curling, keeping all other variables the same—technique, effort, training volume and so on—I doubt there would be any noticeable difference in results, but use one-arm biceps training in some of your routines, if you like it, for the sake of variety.