Do Machines Build as Much Muscle as Free Weights?

A 2023 systematic review and meta-analysis pooled 13 studies spanning 1992 to 2021. Over a thousand people trained with either free weights or machines under controlled conditions. Five of those studies measured muscle growth, and pooled, they showed no significant difference in muscle growth between the two.

The gap was close to zero, an effect size of -0.055. But with only five studies, the margin of error still leaves room for a small-to-medium difference either way, and the authors call the evidence tentative. The five results varied no more than chance would predict.

One of those five, a 2020 trial, included both men and women, one of only two studies in the review to do so. Biceps and quadriceps thickness grew in both groups with no difference between free weights and machines, and men and women responded similarly.

The hierarchy your gym operates on found no support in the muscle-growth data.

Why your squat PR is lying to you

Ask anyone who has trained with both barbells and machines, and they will tell you the same thing: free weights feel stronger. That feeling is real.

But the conclusion most people draw from it is wrong.

Strength gains are specific to whatever you practice. If you spend three months squatting with a barbell, your barbell squat numbers go up, not because barbells sent a superior growth signal, but because the barbell squat is a skill you rehearsed.

In the review, when both groups were tested on free weights, free-weight training gained more strength; on machine tests, machine training tended to gain more. Each group got better at the thing it practiced.

When researchers tested each group on the equipment it trained with, they found no significant difference in strength gains.

The feeling was real. The conclusion was wrong. Free weights feel superior because gyms measure strength through barbell movements, and people who practice barbell movements naturally score higher on barbell tests. The perception of superiority is a measurement artifact, not a physiological one.

Where machines came out ahead

When the researchers tested each group on the equipment it trained with and separated upper-body and lower-body results, machine training gained more upper-body strength than free-weight training (p = 0.003), while the lower body showed no difference.

On that measure, the hierarchy ran upside down.

This came from one slice of the data, not the main comparison, and the upper-body result did not differ significantly from the lower-body one (p = 0.104). But its direction runs opposite to what gym culture predicts.

And when the researchers checked whether training experience changes the strength comparison, whether machines really are something you "graduate from," it did not. Tested on the equipment they trained with, lifters in the studies the review classed as "trained" by strength showed almost no difference between machines and free weights, an effect size of 0.0005, though leaving out one study tipped that result toward machines. The review did not split muscle growth by training experience.

The idea that serious lifters outgrow machines found no support here.

What the evidence points to for you

Based on the five studies in this review that measured muscle growth: the equipment people trained with made no significant difference to how much muscle they built. The guilt you might feel for choosing the leg press over the barbell squat is gym culture talking, not the evidence.

Use whatever you enjoy and will actually show up for. That is the evidence-based answer: for muscle growth, the authors say individual preference should decide. If your gym has both options, the authors speculate that combining them could give more complete muscle growth, though no study in the review tested it. If your gym only has machines, the review found no muscle-growth gap you would be leaving behind.

The one place equipment genuinely matters is strength: you get stronger at whatever you practice. A barbell squatter's squat numbers tend to outpace a leg presser's squat numbers, and the review found no muscle-growth difference behind that: the barbell squat is a skill they rehearse every week.

Most people in these studies were men, 789 of the 1,016, training for six to twelve weeks. Four of the 13 studies included women, two of them women only; a 2020 trial that included both found men and women responded similarly, but the evidence there is thinner. Past age 60 or beyond twelve weeks, the data runs out.

And the Smith machine counts. The analysis covered machine-based exercises with a fixed movement path, which includes Smith machines. If it loads the muscle, the muscle responds.

The question that stays with you

For total muscle growth, the review found no significant difference between the equipment types. Its authors call that evidence tentative.

But the specific exercise you choose within that equipment category is not settled at all. Research on trained lifters found that two exercises targeting the same muscle grew different regions of that muscle, one built the outer portion more, the other built the front portion more. The map of where the growth landed was not the same.

The machines-versus-free-weights debate was never the question that mattered most. The real question is which exercises you choose, regardless of what equipment delivers them. And the evidence on that front is specific enough to change the way you program your training week. Six studies that mapped which exercises grow which regions — alongside three other training variables — tell the complete story.