The Smith machine helps beginners learn how to perform the squat, a very difficult exercise. For advanced bodybuilders, the Smith allows lifters to squat with more weight than the free-weight version does. However, that doesn’t mean you should completely abandon free-weight squats in favor of the Smith machine version. University of Saskatchewan researchers measured muscle activity of the major leg muscles in trained men during free-weight squats and Smith machine squats. During the Smith machine squat, muscle activity of the quads and hamstrings were 50% and 25% less, respectively, than during the free-weight squat. Less muscle activity can limit growth. So use the Smith machine to squat with heavier weight from time to time, but keep free-weight squats as your primary mass builder.