Single-Arm Cable Curl

Stand facing a low cable with a single handle in one hand, palm facing up. Curl the handle toward your shoulder while keeping your elbow pinned at your side, then lower it back down under control. Because the cable pulls at a constant angle rather than straight down like a dumbbell, you'll feel tension even at the bottom of the movement, where a free weight would normally go slack. Working one arm at a time also makes it easy to notice if one side is weaker or cheating more than the other — keep your torso square and resist rotating toward the cable to help the weight up.