Many popular curl exercises are just variations of the same theme. If you do these exercises in the same workout, you’re not really stimulating more growth or hitting the muscle in a new way. You’re mostly just wasting your time.
For example, let’s compare the lying cable curl to any standing curl variation (dumbbell curls, EZ-bar curls, or barbell curls).
Sure, the lying cable curl is performed with a cable instead of a free weight, and it’s also performed while lying supine on the floor instead of standing upright. However, when you look at how the lying cable curl places force across the biceps and elbow joints, it becomes obvious that they’re not much different.
During all standing free-weight curls, you have the most mechanical tension on the biceps – provided you don’t cheat by allowing your elbows to drift forward – when your elbow is bent at 90 degrees. The trouble is, we see the very SAME thing happening when you do lying cable curls.
What this means in practical terms is that not only are lying cable curls redundant to standing free weight curls, but unless you’re using different grips, standing free-weight curls are redundant to one another. Although these exercises may appear different, they basically load the biceps in the very same way.
If you’ve already gotten everything you can from a barbell curl, there’s no reason to add lying cable curls or other standing curl variations. You just aren’t stimulating the muscles any differently. You’d be far better off using less redundant exercises like preacher curls, for example.
During preacher curls, the forearm is perpendicular to the load vector (gravity), but at a different angle, thus loading your biceps in a different manner.