Concentration curl with a twist your forearms will feel.
Only the forearm moves. If your shoulder swings, the weight is too heavy.
Bracing your elbow against your inner thigh removes every trace of swing, so flipping the grip leaves the biceps curling from a locked position with the hand turned away, an angle that changes the demand through the whole arc. One arm works at a time, making it easy to find and fix a strength gap between sides. It earns its place as a strict finishing curl that feels completely different from its palm-up sibling, with the forearm working overtime to hold the grip.
Only the grip changes, but it changes everything. Turning the palm away puts the biceps at a disadvantage and pulls the forearm muscles heavily into the movement, so expect to lift meaningfully less.
The braced elbow removes momentum and the reversed grip removes leverage, leaving nothing but the working muscles. Light weight with a full stretch and squeeze is the entire point.
Staying locked in line with your forearm. If the wrist bends to sneak the weight up, drop the load, a bent wrist shifts stress somewhere it does not belong.
