The Smith machine combines use of a bar bell free weight within a vertical track that controls movement similar to a weight machine to use with oblique exercises. The track ensures that the bar travels straight up and down. To further increase safety, most Smith machines have self-spotting pins that you can use to prevent the bar from being lowered beyond a certain point. This helps protect your hip and knee joints from bending too low.
The Smith machine is best for exercises such as squats, the overhead press, lunges, and the bench press. By using the Smith machine instead of free weights, you do not need to have as much coordination, balance, and control. The machine provides guidance and security. The disadvantage is that you are limited to a vertical up and down motion.
Many Smith machines use a standard Olympic barbell. The weight of the barbell is counter balanced by springs. This negates the weight of the bar. The only weight you lift is what you’ve added to the bar. You still need to use correct form when using the Smith machine. The features simply add greater stability and safety.