Let's get one thing out of the way right now: There's not going to be any "one method is better 100 percent of the time" here. Both free weights and resistance machines can help you build strength, size, and generally get fit.

They do, however, each have unique sets of strengths and weaknesses. That's because free weights move freely forward and backward, side to side, and up and down, explains exercise scientist, Ed Hulit, CSCS, project manager at Technogym, which designs and produces top-of-the-line free-weights and machines. That's all three dimensions, my friends. Weight machines, however, are fixed to an axis, meaning their weights can only move in a specified way—generally in only two planes. Sometimes just one.

It's important to make that clear, not only because it affects how the muscles train and grow, but because some machines are not fixed and, by and large, actually belong in the free-weight camp, he notes. For instance, cable systems look like machines, but grab ahold of one and you can move its weight wherever you want. There's no track pre-determining your motion. Machines, however, are only going to let you move that bar up and down. There's nowhere else to go.

So, with that in mind, take a gander at the strengths and weaknesses of both free-moving and fixed exercises:

FREE WEIGHTS
They Train Several Muscles at Once

"You can't go wrong with using multi-joint compound movements that can only be done with free weights," says strength coach Chase Karnes, CSCS, NSCA-CPT. "They recruit more muscle mass than using machines since you not only are moving the weight, but are required to stabilize it. So when you're squatting, not only are your quads and hamstrings working, but so are your calves, glutes, spinal erectors, abdominals, and lats. In comparison, on the leg press you're only recruiting your quads and hamstrings."

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They're Functional
As of late, "functional fitness" has become something of a buzz-term—and for good reason. Movements that train your body using its natural biomechanics can actually help your performance outside the weight room, whether you're sprinting to a bus or trying to lift a definitely overweight bag into a plane's overhead compartment. Your body is trained and develops strength in movement patterns it was designed to perform, Hulit says. In daily life, you rarely, if ever, perform a movement that doesn't hit all three planes.

They Require Awesome Form
When you grab a barbell, you really need to know what you're doing, as improper form can lead to anything from so-so results to injury, notes Hulit.

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WEIGHT MACHINES
They Isolate Specific Muscles

When you're trying to train the most muscles in the least amount of time, or just build all-over strength, this is a huge con. But sometimes, you do really want to hone in on a specific muscle. "For instance, when you are pushing the handles away from you on a chest press machine, you are only going to move in one direction, which isolates the pectorals and makes them grow more dramatically," Hulit says. However, even if you aren't looking to make a certain muscle pop out like never before, isolating muscles can also come in handy if you suffer from any muscle imbalance and you need to shore up said muscle's strength, he says.

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They Let You Lift More Weight
Pound per pound, weight machines tend to be easier than free weights because you are only moving in one direction and don't have to work to keep the weight from falling to one side or the other. That means you can move more weight on a bicep curl machine than you could if you were wielding dumbbells. The more weight your bicep moves, the more it will grow.

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They Don't Always Provide The Right Fit
They have a reputation for taking the guesswork out of exercise, but if you don't understand how to adjust a machine properly, and don't take the time to move any pegs in all of the right places, you could still be using poor form, Karnes says. More machines, however, are making moves to make proper form easier. For instance, on many of its machines, Technogym includes QR codes that can be scanned with your phone to show proper form. Meanwhile, all adjustments can be made while you're on the machine, so you don't have to keep hopping on and off in order to find the right fit for you.

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In the end, for overall strength and conditioning, free-weight exercises—especially those that use compound movements—should be the bedrock of any strength-training plan. Still, machines can be great tools for helping you focus on and develop certain muscles (granted you use them properly).

For example, to get the most from the weight room, Carnes recommends starting your workouts with one or more multi-joint compound movements such as the squat, bench press, deadlift, and overhead press. Then, you can use a few carefully selected machines to strengthen any weak spots and craft the physique you want.

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