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Free Weight Squats vs. Smith Squat Machines

Quick Hit Summary

There are many types of squat variations (back, front, Bulgarian, etc), all with their unique place in the workout plan. One of these variations is the machine based Smith squat which purportedly is safer than free weight squats and leads to greater activation of the quadriceps. However, in a recent study, this was found to be untrue. When using the same relative load on each lift (8 Rep Max), it was found that back squat led to an overall 43% greater muscle activation of the 8 major muscle groups tested. Additionally, a 49% greater activation was seen in the quadriceps (vastus medialis), disproving the theory that Smith machines work the quads harder. On a final note, the training effect of free weight squats transfer much more effectively to real world settings than the Smith machine.

Squat Variations

A popular weight lifting exercise amongst many athletes is the squat. Except for deadlifts, nothing quite gets the blood flowing for me quite like a good squat session. Additionally, it’s easy to always keep the exercise “fresh” due to the many variations that exist. These include the back, front, Bulgarian and split squats. Even more possibilities exist if you consider stance width and use of barbell or dumbbells.

Smith Machine Squat

Figure 1 Smith Machine Squat3

Another squat variation that I commonly see at fitness centers is the Smith machine squat (SMS). As its name implies, this squat variation differs from the aforementioned exercises as the squat bar is connected to a machine. The user can only move the bar in a straight vertical line. Proponents of the exercise claim that it’s safer than a free weight squatting (FWS) exercise. In addition, they also point to evidence presented by Anderson and Behm which indicated that greater muscle activity (measured via EMG recordings) of one of the quadriceps (thigh) muscles could be achieved when using a SMS (bar on back) vs. FWS (bar on back)1. However, the same absolute amount of weight was used while completing both exercises. In real life situations, many individuals are capable of lifting significantly more weight with SMS than with FWS. Furthermore, when exercising, people generally like to use a weight that they feel is “pushing” them. Thus, when comparing the effectiveness of each lift, its important to look at muscle activity while training at the same relative intensity (ie- %Rep Max).

Differences in Muscle Activation between Smith and Free Weight Squats

In a recently published study, Schwanbeck et al. compared differences in muscle activity (measured via EMG) in 6 resistance trained individuals (3 men, 3 women; mean age 23 years) while performing SMS and FWS2. In contrast to the work of Anderson and Behm1, who used the same absolute amount of weight for each exercise, Schwanbeck et al. had their subjects perform both exercises at the same relative intensity (8 rep max load)2. Muscle activity was recorded in the following 8 muscle groups: tibialis anterior (shin muscle), gastrocnemius (calf muscle), vastus medialis (quadriceps- inside portion), vastus lateralis (quadriceps- outside portion), biceps femoris (hamstring), lumbar erector spinae (support muscle around the spine), and rectus abdominus (abdominal muscles).

The researchers found significantly greater muscle activation of the gastrocnemius (34%), vastus medialis (49%) and bicep femoris (26%) muscles when performing FWS vs. SMS. Although the other muscle groups did not reach a statistical significance, they all tended to be higher with FWS vs. SMS. Furthermore, overall muscle activation (combined EMG recordings of all the aforementioned muscle groups) was 43% greater when performing FWS. There was no significant difference between genders on overall muscle activation.

Are Smith Squats Really Any Safer?

As mentioned above, various proponents of the Smith machine claim that it is safer (especially if one has a history of back or knee problems) than free weight squats. Although I’ve never seen any data to support this claim, I can somewhat understand this logic while performing the lift. If you take someone who has never done a squat (Smith or free), load them up with weight and tell them to start lifting, then yes I would agree that those using the free weights are probably more likely to get hurt. However, with any practice using proper form, this “safety” logic quickly falls apart. Based off my experience playing with SMS, I actually find this exercise to be harder on my back and knees, simply because the bar is in a fixed plane of motion. Due to anatomical differences, everyone moves slightly different while squatting. However, a machine that predetermines the movement cannot account for these anthropometric differences. Thus, I can’t adjust the squatting motion to account for my personal anatomical structure. As a result, added stress is put on my joints in order to conform to the movement plane predetermined by the SMS. About the only thing one can do to make it smoother is manipulate one’s foot position

I’d also argue that those who use SMS, in place of free weight versions, are more likely to injure themselves during activities of daily living (i.e. lifting a box from the ground, etc) and other athletic activities (running, etc) for a couple of reasons. First off, the “guide” bars on the Smith machines only allow the user to resist forces in a vertical plane of motion. In other words, they’re not forced to use the stabilizing muscles of their body that prevent motion in the frontal (think of side to side or lateral movement), sagital (think of front/back movement) or transverse (think of rotational movement) planes. Obviously, in FWS, there are no guide bars. Therefore, one’s muscles are forced to take the place of the guide bars and stabilize this movement. Lets apply this to a real world setting.

Let’s assume that you’re picking up a heavy box off the ground. You squat down to pick it up. Who is more likely to bend funny and suffer an acute injury to their back or knee while lifting it? The individual who SMS or FWS? Obviously the guy who has trained their supporting muscles via FWS is less likely to get hurt. Besides acute injuries, like the situation mentioned above, I also feel that those who SMS are more likely to develop chronic musculoskeletal injuries. Since SMS do not require as much self generated stability (via muscle activity), muscle imbalances are more likely to develop as support muscles are underdeveloped in comparison to the muscles primarily responsible for moving the weight. Eventually, the primary muscles will become too strong in comparison to the support muscles, pulling funny on joints, kneecaps, etc.

What to do if Back or Front Squats Increase Low Back Pain?

I know what those with a history of back pain are thinking, “Back and front squats always bother my back/knee. The only squat exercise that I can do without bothering my back/knee is SMS. What lower body “pushing” exercise can I do FWS squats bother my back and you tell me not to do SMS?” Here’s my advice if you find yourself in that situation:

In general, assuming your back pain is not being generated by pinched disk or other nerve related problem (in this case, seek medical advice before starting any training program), most back pain is related to general weakness of the core muscles (abdominals, lumbar muscles, obliques, etc) which results in poor posture and thus pain. The same holds true with knee pain, just different muscles are involved. To solve this, I recommend including more front planks/pillars, side planks/pillars and glute bridges into your workouts to strengthen these muscles. In addition, I’d substitute single leg squatting exercises in for double leg squat variations. This forces the body to rely more heavily on core/support musculature to balance the body. Examples of single leg squatting exercises include split squats, single leg quarter squats, Bulgarian squats, lateral lunge/squats, back/front lunges, etc. In addition, I would switch to dumbbells. If the dumbbells are too heavy to hold onto, use some wrist wraps that you can also loop around the middle section (of the dumbbell) while holding them. The weight can be held at your waist for all those exercises (thus not putting any direct weight on the spine). In the case of the lateral squat, the weight can be rested on top of the shoulders with your elbows pointed directly in front of you. For this position, think of the final position in hang/power clean except with your palms facing each other such that your pinkie is toward the sky and your thumb pointed toward the top of your shoulder. Although this position puts indirect pressure on the spine, it does not come close to the compressive forces that squatting with a bar on your back will have on this region.

Bottom Line

Hopefully this article demonstrates to the advantages of using FWS vs. SMS. If you’re including SMS in your workout simply because traditional FWS aggravate your back or knees, focus on doing the exercises listed above. Also, have a trained professional test you for muscle and flexibility imbalances that may be contributing to the problem.

Stay healthy & don’t make the Smith machine squat your primary lower body pushing exercise!


1 Anderson K, Behm DG. Trunk muscle activity increases with unstable squat movements. Can J Appl Physiol. 2005 Feb;30(1):33-45.

2 Schwanbeck S, Chilibeck PD, Binsted G. A comparison of free weight squat to Smith machine squat using electromyography. J Strength Cond Res. 2009 Dec;23(9):2588-91.

3 Stepanek, George. Smith Machine Squat. Obtained May 17, 2010 from: http://en.wikipedia.org/wiki/File:Smith_machine.gif.

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Written on April 30, 2010 by Sean Casey
Last Updated: June 26, 2011

This information is not intended to take the place of medical advice.Please check with your health care providers prior to starting any new dietary or exercise program. CasePerformance is not responsible for the outcome of any decision made based off the information presented in this article.

About the Author: Sean Casey is a graduate of the University of Wisconsin-Madison with degrees in both Nutritional Science-Dietetics and Kinesiology-Exercise Physiology. Sean graduated academically as one of the top students in both the Nutritional Science and Kinesiology departments.
Field Experience: During college, Sean was active with the UW-Badgers Strength and Conditioning Department. He has also spent time as an intern physical preparation coach at the International Performance Institute in Bradenton, FL. He also spent time as an intern and later worked at Athletes Performance in Tempe, AZ. While at these locations he had the opportunity to train football, soccer, baseball, golf and tennis athletes. Sean is also active in the field of sports nutrition where he has consulted with a wide variety of organizations including both elite (NFL’s Jacksonville Jaguars) and amateur athletic teams. His nutrition consultation services are avalable by clicking on the Nutrition Consultation tab.