Free weights or machines: What's the difference and which should I use?
It depends on how much stability you want - and that's determined by your goals and your level of experience.
For beginners, the biggest advantage of weight machines is that they keep you from making mistakes. Each exercise station is designed to move in only one direction, guiding you through the motion with proper form. But that's also their biggest weakness - because when you call on your muscles in the real world, you won't have that support.
"Weight machines are very stable," says David Behm, an exercise scientist at the Memorial University of Newfoundland. "But if you're on a muddy football field or running across a tennis court hitting a forehand on one leg, that's very different."
The same is true for everyday challenges, such as getting out of a car seat for an older person. For that reason, free weights - dumbbells and barbells that aren't connected to pulleys or contraptions - are thought to provide a more functional training stimulus because they're less stable. You're forced to balance your entire body while performing the exercise.
Consider a simple exercise such as the biceps curl. If you use a Nautilus machine to perform the curl, you'll strengthen your biceps - which, presumably, is your goal. If, on the other hand, you stand up and do your curls one arm at a time with dumbbells, you'll also be using a host of other muscles such as your back extensors, abdominals and quadriceps to keep your body upright.
With free weights, "people 'cheat' by using other muscle groups," says George Salem, director of the exercise and aging biomechanics research program at the University of Southern California. That "cheating" is a problem if you're using poor form or too much weight and you wrench your back as a result. But it can also be beneficial if you learn to use your whole body to provide stability and added strength, Dr. Salem says.
In a quest for even higher levels of instability, some people perform their weights routine while balancing on an inflatable exercise ball. This requires greater effort from the core stability muscles of the trunk and back. But there is a downside, Dr. Behm cautions: "To get maximum strength gains, you have to lift as much weight as possible. But you can't lift as much when you're balancing on a ball."
As a result, a forthcoming position stand that Dr. Behm is writing for the Colorado-based National Strength and Conditioning Association will recommend using an exercise ball primarily for health and fitness, while athletes seeking performance gains are advised to rely more on free weights.
Weight machines do have other advantages, even for experts: They allow you to address specific weaknesses by isolating certain muscle groups and they're designed to provide a constant resistance through the entire range of motion of each lift. In gyms that stock these machines, the biggest draw may be that they're more time-efficient than fiddling around with free weights.
In general, machines are best for beginners, for both safety and ease of use. And once you've mastered them, Dr. Salem says, it pays to move on. "Free weights are more realistic."
Alex Hutchinson is a former member of Canada's running team, and has a PhD in physics.