Barbell Curl

You swing the hips and lean back to start the bar moving, letting momentum do the bottom half of the curl.

You let the elbows drift forward at the top, turning the finish into a front-delt raise.

You stop the lowering phase early, never returning to fully straight arms.

You let the wrists curl back toward you at the top instead of staying straight in line with the forearm.

Glue your upper arms to your sides and treat the elbow as the only joint allowed to move.

Lower the bar for a slow count to a dead-straight arm; the stretch phase is where much of the growth stimulus lives.

Squeeze the biceps deliberately at the top rather than just arriving there.