One of the major benefits of the Smith is that eliminating balance concern lets you focus upon simply pressing the bar (especially useful if you don’t squat first). Research has shown you’re slightly stronger on Smith-machine squats than standard squats, probably because of your reduced need for balance and the fact that you can press both up and back against the bar. When your feet are almost directly underneath you during the Smith squat, you target the same muscles as in the standard free-weight version (quads, hamstrings and glutes).
Back ’N’ Forth
The most common way to perform the Smith-machine squat is with your feet beneath you as you likely would in a free-bar squat. Because you don’t have to worry about balance compared to the free-weight squat, however, with the Smith you can afford to adjust your feet to different positions – forward and outward.
Make This Change
Reposition your feet about 15-18 inches in front of the bar. When you use this technique, the hams and glutes become much more involved, automatically lessening (but never completely eliminating) the emphasis on the powerful quads. This effect can prove especially beneficial if your hamstrings and glutes are undertrained or underdeveloped when compared to your quads. That imbalance not only creates a lack of symmetry, but it can also be the source of low-back problems and other injuries.
Get the Benefits of Both
Alternate between the Smith squat and free-weight squat within the same workout or from one workout to the next. One of the reasons you’re stronger on Smith squats is that you don’t have to rely as heavily upon stabilizer muscles compared to the free-weight version. You want to put that benefit to proper use, but lack of stabilizer activity can prove to be a disadvantage as well. Therefore you need to master both. If you prefer to do Smith-machine and free-weight squats in the same workout, be sure to work the free-weight version first when your assisting stabilizers and low back are at their freshest and strongest. Then you can hit the Smith machine with your feet underneath you and way out in front of you (without worrying about balance) and zero in on the hams and glutes.