Weight machines work the larger muscle groups in your body. Most machines do this by offering constant resistance to an isolated muscle group or a couple of muscles working together. Machines do not work stabilizer and antagonist muscles like free weights do. For example, on a chest press machine you work the muscles of your chest but not the muscles in your back or shoulders.
Legs
Weight machines exist to train the muscles of your glutes, hamstrings, quadriceps, calves, adductors and abductors. The glutes are the muscles of your buttocks. The hamstrings are located in the back of your upper leg. The quads are the large muscles in the front of your upper leg. Your calves are the muscles of the back of your lower leg. The adductors are the muscles of your inner thighs and the abductors are the muscles of your outer thighs. Machines called adductor machines and abductor machines work your thighs. The leg press and leg extension machines train your quads and glutes. The glute kick machine and leg curl machines work your hamstrings.
Chest and Back
The muscles of your chest, called your pectorals or pecs, are worked by several weight machines. Chest press, chest flye, and pec deck machines all work the pecs. The latissimus dorsi and rhomboid muscles of your back are also able to be strengthened with weight machines. Row machines, lat pulldown machines, upright row machines, assisted pull up machines, and reverse flye machines will work these muscles.
Arms and Shoulders
Rear delt machine, lateral raise machines, bent arm lateral raise machines, and shoulder press machines all work your deltoid or shoulder muscles. Rear delt machines target your rear delts, or the part of your deltoid muscles in the back. The lateral raise machines target the middle portion of your delts. The shoulder press machines, or what are sometimes called overhead press machines, target the middle or medial delts too, but they also work your tricep muscles on the back of your upper arms. Tricep extension machines work the triceps, too. Bicep curl machines target the biceps, but they also work the muscles of your forearms.
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