Barbell squats develop muscles in your back, hips, butt and thighs. The exercise starts with mounting a weighted barbell on your shoulders and across the base of your neck. You then repeatedly raise and lower your body, keeping your shoulders steady and bending at the hips and knees. Several types of resistance machines can mimic a barbell squat.
A Smith machine has a typical free-weight bar, but it is locked inside a track so that the movement will stay within a single plane. As with a barbell squat, you push upward with your shoulders by straightening your legs and hips. The chief advantage of a Smith machine is that the track ensures that the bar won't fall forward or backward. The disadvantage is that your body doesn't have to stabilize itself, as it does with a barbell squat, so you might not get the same range of muscle development.
A lever squat machine mimics a barbell squat with a lever-and-fulcrum design. Place your shoulders under the padded arms and push against the foot platform to lift the lever. Placing your feet slightly forward targets the gluteus maximus, and placing them slightly back increases the involvement of the quadriceps. Lever squat machines come in many varieties. Some are plate-loaded, meaning you adjust the weight by adding or removing round weight plates. Others allows you to adjust the weight setting by moving a pin.
A resistance machine that uses a cable-pulley system can help you mimic a barbell squat, provided you can grasp one handle in each hand from a low and close position. Not all cable-pulley machines offer this feature, so check your owner's manual or ask gym staff if you're not sure what options a particular model has. The movement you perform essentially is the same as a barbell squat, but you must keep your arms straight while extending your legs. Pulling upward by contracting your arm muscles detracts from the lower-body workout.
A major advantage of using a resistance machine is increased safety. Resistance machines help you emulate the movement of a barbell squat with less chance of deviating from proper form. For example, many Smith machines have a design that prevents the bar from falling too far, eliminating the risk of it collapsing under the weight onto the user.