13 studies pooled 1,016 people to compare machines and free weights for muscle growth. The total difference was smaller than the measurement noise.
Zero difference across 1,016 people is not a gap that one more study is going to fill.
Every gym has a ranking nobody posted on the wall. Barbells at the top. Dumbbells in the middle. Machines at the bottom. The hierarchy doesn't come with a source or a study. It comes with something more persuasive: a social code that rewards visible effort over invisible outcomes.
Chalk your hands, load your plates, ask for a spot, and you're a serious lifter. Sit down at the leg press, and something about your status shifts.
You know this ranking. You've followed it. You've felt that quiet pull when you chose the chest press instead of loading the bench, or walked toward the leg press when the squat rack was open. Most lifters have. The hierarchy doesn't just rank equipment. It ranks the people who use it.
Haugen and colleagues wanted to know whether any of that is earned. They pooled 13 studies covering 1,016 people (789 men, 219 women, ages 18 to 60, trained and untrained) and measured one question: does training with free weights produce more muscle growth than training with machines?
The equipment hierarchy every gym teaches has no scientific foundation. Whether the data holds for longer training periods and more diverse populations is the open question the evidence has not yet closed.
- Machines and free weights produce identical muscle growth across 13 studies pooling 1,016 people, with zero disagreement between individual studies.
- For upper-body strength, a sub-analysis found machines actually outperformed free weights, though this exploratory finding needs more research to confirm.
- Training experience made no difference: experienced lifters showed the most perfect equivalence of any subgroup in the dataset.
- Equipment choice is a preference, not a performance decision. Consistency with whatever you enjoy matters more than which equipment category you pick.
The Total Evidence for the Hierarchy
The difference was 0.055 standard deviations. That was the total gap in muscle growth between free weights and machines across every study in the meta-analysis. The probability of seeing a gap this small by chance? About 75%. Every individual study pointed the same direction — zero disagreement between them.
To put that number in context: if two people trained for eight weeks with identical effort, one on machines and one with barbells, a researcher with an ultrasound could not reliably tell their muscles apart. The difference is smaller than the measurement noise. The hierarchy that made you feel like a second-tier lifter for choosing the leg press has no measurable foundation in human muscle growth.
This is not one study's conclusion. Thirteen studies across different countries asked the same question with different populations, different exercises, and different measurement tools. The answer was the same every time. Machines and free weights grow the same amount of muscle.
Where the Hierarchy Might Run Backwards
If the story stopped at parity, it would be useful but quiet. Many lifters already suspected machines were "good enough." The data went further.
A sub-analysis of upper-body exercises found that machines produced significantly greater strength gains than free weights. Not equal. Better. For the measurement where the hierarchy promised barbells would dominate, the equipment gym culture calls training wheels came out ahead.
That finding has honest limits. The overall comparison between upper and lower body was not statistically significant. This is an exploratory sub-analysis, not a settled conclusion.
But the data shows a direction: for upper-body strength, the numbers lean toward machines, not away from them. The hierarchy is not just unsupported. For one measurement, it might be pointing the wrong way.
The meta-analysis found machines and free weights build the same total muscle. But total muscle is not the whole story.
The researchers noted that different exercises recruit different parts of the same muscle. A leg press and a squat may produce identical total quad growth while building different regions of the quad. The study's authors speculated that combining both modalities could optimize complete muscle coverage, because each exercise loads the muscle through a different angle and range.
This is the practical insight hiding behind the headline: using both machines and free weights is not a compromise. It may be the strategy that covers the most ground.
What the Data Cannot Tell You Yet
The parity finding is consistent. It is also limited in ways the researchers themselves named.
Only 5 of the 13 studies directly measured muscle growth, using different tools: ultrasound, BodPod, circumferences, skinfolds. Study durations averaged 8.9 weeks, with a range of 6 to 12. The researchers wrote that "one should be careful with the interpretations of the results, especially for muscle hypertrophy."
Regional muscle-growth differences might exist even when total hypertrophy is identical. A leg press and a squat could build the same volume of quad but in different regions of the muscle. Free weights may also transfer slightly better to explosive movements, though that trend did not reach statistical significance in most analyses.
These are real limits, not disclaimers. The parity data is consistent and the direction is unambiguous, but the evidence is not so extensive that the conversation is permanently closed. What IS closed is the hierarchy itself. Zero difference across 1,016 people is not a gap that one more study is going to fill.
Schwanbeck and colleagues tested the question independently in a 2020 trial. Forty-six men and women trained for eight weeks, one group exclusively on machines and the other exclusively with free weights. Biceps and quadriceps muscle thickness increased in both groups with no difference between them [1]. The meta-analytic parity held at the individual-study level.
Not Even for Experienced Lifters
The hierarchy has one remaining defense: "Machines are fine for beginners, but serious lifters need free weights." Haugen's data tested that defense directly.
Trained lifters showed a muscle-growth difference of 0.0005. That is the closest a number in exercise science gets to perfect equivalence. The untrained subgroup showed a slightly larger but still non-significant effect. The comparison between subgroups was not significant.
The most experienced lifters in the dataset showed the most perfect equivalence. The defense that machines are acceptable for newcomers but inferior for advanced trainees is not just unsupported. The data from the population it claims to protect produced the single most symmetrical result in the entire meta-analysis.
You didn't lose a single rep of muscle growth by using machines. You lost the peace of mind that should have been there all along.
What the Guilt Actually Cost
The data changes something more personal than a training program. It changes the feeling that went with it.
Every session where you chose the leg press and glanced at the squat rack, every chest day where you sat at the machine press and felt like you were cutting corners, every time someone told you barbells build "real" muscle and you half-believed it: none of that guilt had evidence beneath it.
You didn\'t lose a single rep of muscle growth by using machines. You lost the peace of mind that should have been there all along.
Equipment choice is a preference now, not a performance decision. The machine section is not a lesser section. It is the same section, for the same purpose, producing the same outcomes across 1,016 people.
Train on whatever you enjoy, whatever is available, whatever your body responds to on any given day. The hierarchy said that choice mattered. Thirteen studies say it does not.
The equipment question is settled. But it opens a different one. If machines and free weights build the same total muscle, does the specific exercise matter? Does a leg press and a leg extension grow the same part of the quad, or do different movements build different regions of the same muscle?
Equipment choice is now a preference, not a performance decision. The evidence across 1,016 people leaves no measurable gap between machines and free weights for muscle growth.
When machines make life easier: crowded gyms where the squat rack has a queue, sessions where you want faster transitions between exercises, and days when a fixed movement path feels better than balancing a barbell.
When free weights make sense: you enjoy compound movements, you train at home with limited equipment, or you want the coordination challenge.
The variable that actually drives results is consistency. The equipment you enjoy enough to show up for four times a week builds more muscle over a year than the "optimal" equipment you dread and use twice.
What other research found
What this means for you
The trained subgroup in this meta-analysis showed a muscle-growth difference of 0.0005. That is the most perfectly symmetrical result in the entire dataset.
The script that says machines are fine for beginners but insufficient for serious lifters fails exactly at the population it claims to protect. Experienced lifters showed the most complete equivalence. The leg press is not a step down from the squat rack. It is a different path to the same destination.
The untrained subgroup showed no significant difference in muscle growth between machines and free weights either.
Machines have one practical advantage for newer lifters: they reduce the stability demand. A chest press guides the weight through a fixed path, so the muscles do the work instead of your coordination. That means more focus on the muscle you're trying to grow and less energy spent keeping the bar straight.
The evidence says machines build the same muscle as free weights. For someone building their first training habit, the simplicity may make it easier to show up consistently.
A sub-analysis of upper-body exercises found something the general parity data hides: machines produced significantly greater strength gains than free weights.
This is an exploratory finding from a sub-analysis, not a settled conclusion. The overall comparison between upper and lower body was not statistically significant. But the direction is clear: for upper-body pressing strength, the data leans toward machines, not away from them.
The chest press may deserve a lead role in your upper-body training, not a supporting one.
If machines and free weights build the same muscle, the time-efficient option becomes the productive option.
Machines eliminate plate loading and unloading. No spotter needed. No waiting for the one squat rack. Transitions between exercises take seconds instead of minutes. A 30-minute machine circuit covers more total work than a 30-minute free-weight session where 10 minutes went to setup.
The parity finding turns time-efficiency into a genuine training advantage, not a lazy shortcut.
Before you change anything
Adults aged 18 to 60, both men and women, with and without prior training experience, free from chronic disease or injury. Recreational gym-goers seeking general muscle growth and strength.
Not studied: competitive athletes (none of the 13 studies included them), adults over 60, anyone under 18, and individuals with chronic disease or injury. Clinical rehabilitation populations were excluded.
One caution: 77% of the total participants were male. The meta-analysis may underrepresent female-specific responses, though the Schwanbeck satellite (with a majority-female completion group) showed the same parity pattern.
Only 5 of 13 studies directly measured muscle growth. The core muscle-growth finding rests on fewer studies than the full 13-study count implies.
Measurement methods varied across studies: ultrasound, BodPod, circumference tape, and skinfolds. These tools have different precision levels, which adds noise to the pooled result.
Study durations ranged from 6 to 12 weeks (average 8.9). Longer-term adaptations beyond 12 weeks remain unknown.
The free-weight strength advantage (F2) was fragile: removing a single study (Lennon 2010) shifted the p-value from 0.023 to 0.153. Any conclusion about free weights being stronger for free-weight exercises depends heavily on one dataset.
Regional muscle-growth differences between modalities are possible even when total muscle growth is identical. A leg press and a squat could grow different parts of the same muscle.
The parity finding carries moderate-to-high confidence. Thirteen studies, 1,016 participants, and zero heterogeneity (every study pointed the same direction). The limitation is that only 5 of those 13 measured muscle growth directly.
The upper-body reversal carries low confidence. It comes from an exploratory sub-analysis. The overall comparison between upper and lower body was not statistically significant (p = 0.104), and the parent analysis had significant heterogeneity. The direction is suggestive, not settled.
The training-status finding carries moderate confidence. The trained-lifter subgroup showed near-perfect equivalence (effect size 0.0005), but subgroup comparisons have lower statistical power than the main analysis. The result is compelling but rests on fewer people than the full meta-analysis.
The equipment question is settled. Machines and free weights build the same muscle. But that finding opens something more specific: if a leg press and a squat produce identical total quad growth, do they build the same part of the quad?
Burke's team put one leg on the leg press and the other on the leg extension in the same person and measured where the quad actually grew. The answer reshapes how exercise selection works.
What This Study Found
All findings from this paper, in plain language.
- Machines and free weights produced identical muscle growth across all studies, with a difference too small to measure reliably.
- People who trained with free weights got slightly stronger at free-weight exercises, but this advantage was fragile and depended on a single study.
- People who trained on machines showed a trend toward greater strength on machine exercises, though the result did not reach statistical significance.
- When strength was measured on neutral tests (not favoring either equipment type), there was no difference between groups.
- Isometric strength and jump performance showed no meaningful differences between machine and free-weight training.
- Training experience did not change the result: experienced lifters showed the most perfect equivalence between machines and free weights of any subgroup.
- For upper-body strength, machines significantly outperformed free weights in a sub-analysis, though the overall comparison was not statistically significant.
- The researchers suggested that combining both machines and free weights may optimize muscle coverage across different regions of the same muscle.
- Every individual study pointed in the same direction for muscle growth (zero disagreement), but the strength analyses showed more variability.
- The included studies were rated as fair to good quality on a standardized assessment, with five scoring fair and eight scoring good.