A Smith machine guides the bar along fixed rails, and buyers of home racks often ask whether it can replace a free-weight setup. This article summarises the abstracts of three studies from the same research group, Marcos-Frutos and colleagues, published in 2025 and 2026. Two are eight-week training trials and one is a single-session force study. Each is small and used sport-science students or young volunteers, so the results describe those groups and do not settle the question for every lifter.
Study one: eight weeks of squat and bench press training
The first study, in the International Journal of Sports Physiology and Performance in 2025, assigned 37 sport-science students (14 female) to train with free weights or a Smith machine for eight weeks. Participants trained twice a week, doing four sets of back squat and bench press at 70% of their one-repetition maximum (1RM) with a moderate effort target of 20% to 25% velocity loss. The researchers measured load-velocity profile parameters, the cross-sectional areas of the vastus lateralis (a thigh muscle) and pectoralis major (a chest muscle), and repetitions to failure in the bench press, testing on both free weights and the Smith machine.
All variables improved in both groups, with the exception of the squat velocity-axis intercept. Two measures, the load-axis intercept and the area under the load-velocity line, improved more when the training and testing conditions matched. Repetitions to failure in the bench press and the muscle cross-sectional areas improved by comparable amounts in both groups. The authors concluded that people not concerned with the specificity of strength adaptations can choose between free weights and a Smith machine on personal preference.
Study two: does the machine change how force is applied?
The second study, published in the same journal in 2025, began from the observation that force is applied more in the backward direction in Smith machine squats than in free-weight squats. It asked whether eight weeks of training on either would change the horizontal forces later recorded in each squat type. Twenty sport-science students (nine female) trained twice a week with four sets of back squats at 70% of 1RM, and ground-reaction forces were recorded before and after during sets of 10 repetitions at about 45% and 70% of 1RM.
The abstract reports that squat type had minimal influence on longitudinal impulse, its components or the angle of the resultant force. The only significant difference was in the propulsive phase at about 70% of 1RM in the Smith machine squat: the free-weight group showed a reduction after training while the Smith machine group showed an increase. The authors concluded that eight weeks of squat training does not modify the effectiveness of force application, so both squat types can be used interchangeably without systematically changing the direction of force production.
Study three: force direction in a single session
The third study, in the Journal of Sports Sciences in 2026, involved 35 young volunteers (14 female) who completed two randomised sessions of one set of 10 back squat repetitions, at about 45% and 70% of 1RM, with a free-weight bar in one session and a Smith machine in the other. Force plates recorded the ground-reaction forces. Participants generated a larger posterior impulse in the Smith machine squat, during both the braking phase (-64.9 versus -8.1 newton-seconds) and the propulsive phase (-143.8 versus -18.0 newton-seconds), and the horizontal angle of the force differed between the two squat types. The differences grew with load and through the set.
The authors suggested that free-weight squats may be favoured over Smith machine squats for coaches aiming to improve vertical jump performance. That is an inference from the force data; the study did not measure jump performance.
How the three fit together
- In the short term, the Smith machine squat moves the body differently from the free-weight squat, with a larger backward force on the ground.
- After eight weeks of training, neither the choice of machine nor free weights changed how force was applied in the second study, apart from one measure at the higher load.
- In the first study, strength and muscle size in the thigh and chest improved in both groups, and the results were most specific when the training and testing setup matched.
What the studies cannot show
All three came from one research group and used young, mostly sport-science participants. The training trials lasted eight weeks with two sessions a week, so they say nothing about longer periods, older lifters or people with very different training histories.
What this means for choosing equipment
For a buyer, the practical reading is limited but useful. Where the goal is general strength and muscle, the first study found both options improved outcomes and treated the choice as one of preference. Where the goal is to be tested or to compete on a free-weight lift, matching the training tool to the testing tool gave larger changes in two measures. This site’s pages on Smith machines and multi-gyms and free weights against machines for home training cover space, cost and layout.
Frequently asked questions
Did the Smith machine group get smaller muscle gains?
Not in the first study, which reported comparable improvements in the cross-sectional areas of the vastus lateralis and pectoralis major in both groups.
Do these studies show which is safer?
No. None of the three abstracts measured injury or safety outcomes.
The bottom line
Three small studies from one group suggest that Smith machine and free-weight squats differ in the direction of force applied in a single session, but that eight weeks of training on either produced similar strength and muscle-size gains in the first trial and similar force application in the second. Lifters who want the specific skill of a free-weight lift are better served by training it, while those who simply want to get stronger can reasonably choose on preference, space and budget.
Sources
- Marcos-Frutos D, Miras-Moreno S, Marquez G, et al., “Comparative Effects of the Free Weights and Smith Machine Squat and Bench Press: The Important Role of Specificity for Strength Adaptations,” Int J Sports Physiol Perform, 2025
- Marcos-Frutos D, Miras-Moreno S, Marquez G, et al., “Free-Weight and Smith-Machine Squats: Do They Produce Selective Chronic Adaptations in the Effectiveness of Force Application?,” Int J Sports Physiol Perform, 2025
- Marcos-Frutos D, Miras-Moreno S, Morenas-Aguilar M, et al., “Anterior-posterior ground reaction forces in free-weight vs. Smith machine squats: Are differences modulated by load and volume?,” J Sports Sci, 2026