Serious question about Smith machine

[Peter Bex]

A buddy of mine who is somewhat interested in strength training got assigned Smith machine squats by the fancy gym he just joined.
He's enthusiastic about it because he says it allows him to squat without having to think about technique (he struggles especially with the grip).

I've searched the forum about Smith machines, but didn't find a lot of concrete info except the fact that it doesn't involve much balance, but I doubt he's very interested in that.
Another argument would be that not involving technique and requiring as much focus means he'll probably get bored.

At the risk of being branded a troll, I'd like to see some more non-dogmatic and non-snarky reasons why the Smith machine is to be avoided.
One of the things I like about Starting Strength is that we insist on being able to explain from first principles why we do things the way we do them, and why that approach is better.

My friend struggled with knee pain in the squat before with a different personal trainer who used high bar squat and bad technique.
I've seen offhand comments here that Smith machine squats can hurt your knees, so that's an argument he'll be interested to hear.
What's the mechanism by which that happens? Presumably it has something to do with the rigid bar path being forced on your body by the machine's design, but as we know a perfectly vertical bar path (which the machine enforces) is also the ideal bar path. So logically, I fee like I am missing something here.

[Mark Rippetoe]

Let's see what the board comes up with.

[Kitsuma]

Before discovering starting strength, I was squatting sets of 10 and 20 in Smith Machine. I ended up with a very scary nerve impingement in my neck. I lost the use of my right ring and pinky fingers and my right tricep atrophied to nothing. Surgeons recommended surgery (surprise).

I don't know if it was the limited motion of the smith machine, the stupid sets of 20 or just bad form that caused my problems. But, because of that experience, i would never recommend squatting in a smith machine. It's just not worth the risk.

I fixed my problems with traction and learning to lift correctly here at SS...in a rack with pins...and how to eat & sleep to build muscle around my spine/neck to support the space created by the traction.

[Jason Donaldson]

I've seen offhand comments here that Smith machine squats can hurt your knees, so that's an argument he'll be interested to hear.
What's the mechanism by which that happens? Presumably it has something to do with the rigid bar path being forced on your body by the machine's design, but as we know a perfectly vertical bar path (which the machine enforces) is also the ideal bar path. So logically, I fee like I am missing something here.

A few ideas:

The ideal bar path is vertical. That doesn't mean the bar path is exactly vertical. The Smith machine does not allow any sagittal (front-back) changes, and this is bad for multiple reasons. If the bar's not over the center of the foot, it cannot GET over the center of the foot, for example. The combined center of mass is what needs to be over the center of the base of support (i.e. the feet) - the bar acts as a useful proxy for this, especially as the bar gets heavier, but it does change slightly throughout the warmups, and over time. The Smith machine does not allow the lifter to adjust this naturally - it must be exact from the top down, and at the top is not necessarily the best place to figure this out. As a result, risk of injury goes up - there are no adjustments available on the fly.

Like it or not, this is also true with the more complicated ones that allow some lateral travel. You have to exert the lateral force to move the whole apparatus, not just the bar. This is not the same.

Having the machine keep the bar level also robs you of the need to exert force relatively equally. If you do a real barbell squat, and one leg is sandbagging, you'll know it. Having to keep the bar level for yourself entails a naturally balanced exertion. With a Smith machine squat, a lagging side doesn't have to catch up.

Yet another problem has to do with why people like it. The natural movement pattern for the whole body includes the stabilization of the load. The Smith machine makes it easier by taking much of that away from the lifter, so the lifter does not stress those capacities, and hence those capacities do not grow in concert with what is stressed and what does grow. (See the "Easy doesn't work" principle...)

These problems are easier to picture on a lift like the bench press, which most everyone can see does not have a vertical bar path, but it's there with other lifts, too. Robbing the body of the ability to respond as it should endangers the body in general, including the joints in particular. The lifter needs to learn to keep the bar in the right path himself. Having a machine exert the force for you is clearly not helpful, so why think that having a machine enforce the bar path for you is helpful, either?

Finally, speaking of first principles: Is a Smith machine squat using more or less muscle mass to move more or less weight through a greater or lesser effective range of motion?

[mbreuer]

Are you sure the bar path is perfectly vertical? Many machines are designed with a non-vertical path to accomodate bench pressing.

[FrankNJ]

(1) One of the key benefits of the barbell squat, as taught by the starting strength method, is that it requires the lifter to balance the load in multiple directions (forward/backward, side-to-side). The Smith machine does not require the lifter to balance the load in any direction, so the lifter losses this major benefit with the Smith machine.

(2) People also often place their feet too far forward with a Smith machine turning the movement into something like a leg press, so it’s no longer a squat movement.

(3) Barbell squat lifters need to train to maintain a vertical path during a lift, but the Smith Machine does that for you.

Overall, it’s a deficient exercise compared to the barbell squat. The Smith machine might be useful in an ocean-going ship where extreme sea motion could put a lifter at risk.

[Dr. Manhattan]

At the risk of being branded a troll, I'd like to see some more non-dogmatic and non-snarky reasons why the Smith machine is to be avoided.
One of the things I like about Starting Strength is that we insist on being able to explain from first principles why we do things the way we do them, and why that approach is better.

You followed up your request by providing the source of the answer. All you need to do is explain "why we do things the way we do them."

Snark often gets a bad rap. Snarky replies and general teasing of folks for doing silly things have served many generations well by keeping many of us from continuing to do silly things; particularly during formative years.

[Bluefan75]

This won't be a full explanation, but people's anthropometry (did I use the right word?) is very different from trainee to trainee. Some have longer legs, some have longer torsos. You're trying to gain strength throughout the body, and one of the things you gain is balance. With the barbell on your back, if you aren't balanced, you fall over. Where do you get that from a Smith machine? You are essentially forced into a specific form to match the path the smith machine moves, rather than doing a proper squat.

It's probably a terribly worded explanation but hopefully it gets the gist of that part of it. The word "selectorized" would be used here, but I wouldn't use it correctly so I haven't used it in my attempt at an explanation.

[Subby]

He's enthusiastic about it because he says it allows him to squat without having to think about technique (he struggles especially with the grip).

You've answered your own question.

A squat is loaded normal human movement which is a stress that causes a desired adaption. This is the best way to build strength.

Smith machines are not a normal human movement, they are on rails. Disrupting the normal movements of the barbell means it's no longer a systemic stress so the body can ignore it.

An analogy. Walking requires you to propel yourself forward against the ground. But it's also hundreds of other things that require practice and technique. If I put a baby in a harness attached to a rail on the roof and teach it to propel itself forward using it's feet while weightless due to the harness. Will he be able to walk? No, regardless of how many years he mobilises in the harness contraption.

A "squat" is a defined event, it has a definition in the same way "banana" has a definition. A smith machine is not that. Ergo it is not a squat.

[Mark Le Comte]

Instead of the "correct" answers:
1. The smith machine squat is not a functional exercise.
2. The fixed plane of motion and bar will promote muscle imbalances and joint instability.
3. The rolling motion to "unrack" the smith machine bar promotes an inconsistent grip and could pinch nerves in your neck.