Unlike barbell or dumbbells, where the resistance varies during the lift, the machine provides a uniform resistance throughout the movement. There’s one disadvantage all free weight and cable biceps curl variations have that a machine doesn’t – gravity! Preacher curl machine removes almost any opportunity to cheat and provides a perfect biceps contraction by separating the elbow movement from the rest of the body. At the beginning, the muscle tension is intense, so be sure to warm up properly using light weights. To avoid the risk of tendinitis, do not completely extend the arm.