Never do Smith machine squats. If you do strength training, it’s important to understand why.
The underlying issue is: Should you use only free weights, only machines, or both?
My answer is: use what you have available. If you have both free weights and machines available, use both.
However, in general, I do prefer free weights to machines. There are two major problems using machines rather than free weights.
First, even when machines are somewhat adjustable, they don’t fit everyone. People come in all different sizes and shapes. A particular machine may or may not fit you well.
Second, even if a machine fits you well, it won’t work the stabilizing muscles, which are the muscles used to balance a weight through the range of motion. Since working stabilizing muscles is important for strength-related tasks outside the gym, in general free weights are better than machines.
(If you train at home, two other problems about machines are that they are expensive and take up a lot of room.)
Still, I have machines such as a lat machine, an angled leg press, a seated calf machine, a D.A.R.D. machine, and a leg raise machine in my home gym. (I’d love to add a pullover machine.) I use them at nearly every workout.
What about Smith machines? I don’t have one and I don’t want one. I have used them and find them dangerous.
That’s the opposite of what you might think. After all, the primary reason trainees use them to do squats is because, supposedly, they are safer than free weight squats.
Squats done on a Smith machine force the bar to travel either straight up or straight down. That is an unnatrual motion. If you want to hurt yourself, do Smith machine squats.
To convince yourself of this, from the side, just watch anyone who is squatting and you’ll see that the bar does not travel straight up and down as it does when doing Smith machine squats.
The best squatters are power lifters. Have you ever seen a power lifter using a Smith machine for squats?
Feel free to try them for yourself. My guess is that you’ll find them either awkward or very stressful on your knees.
Sometimes advanced bodybuilders do Smith machine squats to try to improve the shapes of their upper legs. You’ll see them doing them with their feet way out in front of them. If you really want to shorten your lifetime ability to do squats, do squats that way!
If you put your feet forward when doing Smith machine squats, you will prevent your knees from going too far forward near the bottom of the movement but you’ll also be putting your lower back at risk.
If you put your feet under your shoulders when doing them, you’ll find as you descend that the load will shift over the balls of your feet, which will increase the stress on you knees.
Not all exercises that can be done on a Smith machine are dangerous. However, there are so few of those exercises that, even if you have a relatively well-equipped home gym with lots of space, I suggest you avoid the expense of buying one.
Smith machine squats are dangerous. Even if you train in a commercial gym that has one, avoid doing Smith machine squats.
If, as I hope you do, you want to train safely for your whole life, avoid doing dangerous exercises like Smith machine squats, behind-the-neck presses or pulldowns, heel elevated squats, and so on.
Which exercises should you do and which should you avoid?
The best book on this is Stuart McRobert’s Build Muscle Lose Fat Look Great. Do only the exercises listed there and do them as he describes. (I don’t get a kickback of any kind for recommending it.)
Mastering the art of strength training includes learning which exercises not to do and learning correct technique for all the remaining exercises.
Strength training is an excellent hobby. If you do it at all, I want you be able to enjoy training safely for the rest of your life.
Either learn how to master free weight squats and the other basic exercises or don’t do them at all.