There’s a pecking order in the gym: Experts hoist the barbells and other free weights, while beginners stick to the machines. This makes sense. The machines are, after all, explicitly designed to minimize your risk of getting pinned under a heavy load or accidentally dumping weights all over the floor.
But this pattern has also led to the assumption that free weights are better than machines – that, pound for pound, you get more benefits from bench-pressing a barbell than you do from the same exercise on a machine.
“This idea has become a widespread belief,” says Jesús Garcia Pallarés, a researcher at the University of Murcia’s Human Performance and Sports Science Laboratory in Spain, “snowballing unchallenged.”
There are, indeed, some reasons to suspect that free weights might be better. Studies have found that they trigger higher levels of muscle activation, and the need to keep them balanced forces you to recruit additional stabilizer muscles.
But the primary goal of most people lifting weights is to build muscle and get stronger. So Pallarés and his colleagues decided to put conventional wisdom to a rigorous test, with muscle size and strength as the primary outcomes. The final results of their five-year research project, published this month in the journal Medicine & Science in Sports & Exercise, suggest that free weights and machines work equally well.
They assigned 38 volunteers to an eight-week program using either free weights or machines. The subjects trained three times a week, doing three sets each of four key exercises: full squats, bench presses, prone bench pulls and seated shoulder presses. The load and recovery were carefully balanced so that each group did precisely the same workouts using different equipment.
The outcomes weren’t identical. The free-weights group saw bigger gains when they were tested with free weights, while the machine group saw bigger gains when tested on machines. That’s the principle of specificity at work, Pallarés points out: You get better at the tasks you train. But the overall changes in both muscle size and strength were indistinguishable for the two groups.
There are still some situations in which one approach might be preferred. If you’re a competitive powerlifter, Pallarés says, you should stick with free weights because that’s what you compete with. Conversely, if you’re rehabbing an injury and need to isolate a specific muscle, machines give you maximum control.
The argument that instability is an advantage for free weights is the same logic that leads some people to lift weights while lying on exercise balls or standing on deliberately unstable surfaces. The problem, according to a Canadian Society for Exercise Physiology position stand authored by Memorial University researcher David Behm, is that you can’t lift as much weight when you’re unstable. As a result, gains in balance and stability come at the expense of maximizing strength and muscle growth.
One solution to this dilemma is to include a mix of free weights and machines in your exercise routine, in order to get the best of both worlds. That’s the approach suggested by Lehman College researcher and strength-training guru Brad Schoenfeld – at least for serious lifters intent on squeezing the most out of their workouts.
In addition to activating stabilizer muscles, free weights are easier to adapt to different body shapes and sizes, Schoenfeld says. They’re also more space-efficient if you’re equipping a home gym. Machines, on the other hand, can target individual muscles and movement patterns, don’t require a spotter, and enable you to push closer to failure without danger.
Resistance training is a crucial component of overall fitness, but it often plays second fiddle to aerobic exercise in public-health guidance, in part because the equipment and know-how required make it seem more daunting. Pallarés’s findings join a growing body of research suggesting that it doesn’t need to be complicated. Light weights and heavy weights produce similar outcomes, as researchers at McMaster University have shown; single sets and multiple sets both get the job done.
The same is true for strength-training equipment, it turns out. Choose whatever is most convenient, safe and enjoyable for you – and if you put in the work, you’ll get the results.
Alex Hutchinson is the author of Endure: Mind, Body, and the Curiously Elastic Limits of Human Performance. Follow him on Twitter @sweatscience.