SETUP: Take a dumbbell in one hand. Hinge forward at the hips to allow yourself to sit at an angle on the bench without rounding your lower back.
REP: Let your arm hang down in front of your knee and lower leg, then curl the weight up at a 90 degree angle, squeezing your biceps hard, before controlling the weight on the descent.
TIP: Don’t rest your elbow against your inner thigh/knee – this tends to encourage swinging.