Which is better for building muscle: free weights or machines?
This debate has been going on in gyms for decades, and one of the most common examples is whether you should use the barbell bench press versus the Smith machine bench press.
Smith machine proponents claim that it’s easier to learn and it lets you use more weight (especially as a beginner).
So … what’s the catch?
That’s what scientists from California State University wanted to find out in a study they published in 2010.
Let’s see what they found.
On average, the subjects were about 20 years old and about half had at least 6 months of bench press experience and half were completely new to strength training.
Everyone was split into 2 groups:
Next, everyone performed a one-rep max (1RM) test to gauge their maximal strength.
The researchers placed probes on the pectoralis major (pecs), anterior deltoid, and medial deltoid (front and side shoulder muscles), and used electromyography (EMG) to measure how well each exercise activated the muscles.
EMG measures the electrical impulses from the brain to the muscles, and is the most reliable way to see how hard a muscle is working when lifting weights.
Then, everyone performed 2 reps with either 70% or 90% of their 1RM, which is more representative of the rep ranges most people use when training.
Finally, everyone returned to the lab on a separate occasion to perform the opposite exercise: the people who used the Smith machine used the barbell bench press and vice versa.
This reduced the chances that individual differences could skew the results.
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Muscle activation was the same in the pecs and anterior deltoids, but the barbell bench press increased medial deltoid activation by 50% more than the Smith machine bench press.
On the whole, this study backs up what experienced lifters have been saying for years:
The traditional barbell bench press is better than the Smith machine bench press when it comes to muscle activation, especially for targeting smaller muscle groups that help stabilize your body when moving heavy weights.
This is because when you do a barbell bench press (or any other free weight exercise), you have to work hard to keep the bar from deviating too far in one direction or another, and that requires many other small muscle groups to pitch in.
When you use a Smith machine, though, the machine guides the path of the bar and reduces the need for stabilizing muscles to work hard.
During the barbell bench press, for example, the medial deltoids had to work about 50% harder to stabilize the bar.
Remember too that the researchers only measured 3 muscles in this study. There are many other muscles that also indirectly work to help stabilize your body when bench pressing, including your lats, legs, and even your abs.
It’s quite possible that the barbell bench press also caused more muscle activation in these muscle groups.
This study also casts doubt on another argument for benching with a Smith machine, which is that because you don’t have to stabilize the bar, you can more effectively overload the other, primary muscles like the pecs.
That’s not what happened in this study.
The Smith machine didn’t cause any more muscle activation in the pecs or anterior delts, as you can see in this graph of muscle activation in the experienced lifters:
Finally, the last argument in favor of using a Smith machine is that it’s easier to learn, which means newbie lifters can start using heavier weights sooner.
In this case, though, new lifters got just as much muscle activation from the barbell bench press as people who’d been practicing for 6 months.
Does this mean you’ll gain more muscle if you bench with a barbell instead of a Smith machine?
EMG measurements only tell us overall levels of muscle activation, and while it’s reasonable to assume that should lead to more muscle growth over time, we don’t know that for sure.
If you had to bet on which exercise was better for muscle growth, though, the smart money would be on the barbell bench press.
Anecdotally, many people find they plateau sooner when they start bench pressing with a Smith machine. They’re able to use heavier weights sooner (because it’s easier), but they also get stuck in more frequent and severe ruts.
That’s often when people roll up their sleeves and invest some time in learning how to barbell bench press, which pays greater dividends over time.
This doesn’t mean using machines is entirely without merit. They can be good for adding volume to stubborn muscle groups after you’re fatigued from your heavy compound lifting or for when you’re recovering from an injury.
Armistead Legge is the Editor-in-Chief for Muscle for Life and Legion Athletics. He has completed over 100 triathlons and cross-country, cycling, and adventure races, and has researched and written for over a dozen organizations, including the National Institutes of Health. When he isn't helping people get into the best shape of their lives, he's lifting weights, riding his bike, hiking, camping, reading, and making delicious food.