Machines and free weights: the two pillars of weight training. Machines refer to fixed, standalone pieces of equipment that use pins, pulleys, cables and weight stacks. Free weights refer to dumbbells and barbells. You’ve used them both—perhaps as recently as your last workout. But questions persist about the pros and cons of machine training vs. free weight training. Which is better for building muscle? Which translates better to sports performance? Which one is safer?

To help you find out if you’re training the right way, STACK talked with Daniel Buck, CSCS and certified sports performance coach at Vantedge Performance, and Tony Bonvechio, CSCS and owner of BonvecStrength, to get their expert opinions on these questions.

RELATED: STACKletes Speak: Training With Free Weights

Which One Is Better for Muscle Activation?

It seems that both machines and free weights do an adequate job of activating major muscles. Take the Bench Press, for example. In a study from Illinois State University, researchers measured the amount of muscle activity among participants who performed a machine Bench Press and a free weight Bench Press. The loads were identical, and the difference in muscle activity in the pecs and triceps was statistically insignificant. However, the anterior and medial deltoids exhibited significantly more muscle activity during the free weight Bench Press—an average of 50 percent and 33 percent more activity, respectively, when participants were lifting 60 percent of their one rep max.

“Higher IEMG values for the anterior and medial deltoid muscles suggest that shoulder stabilizing muscles are more active during the Bench Press performed using free weights compared to a machine,” the study stated. Given the static, controlled nature of machine exercises, this makes sense.

“Machines are great at working the major muscles they are designed to work, there’s no doubt about that,” Buck says. “The problem is that machines only work in one plane of motion. They go front to back, side to side, or up and down.” Machines don’t challenge your stabilizing muscles as much as free weights, which are not limited to one plane of motion. Your body must completely control the load, and move it in the correct way. This stabilization actively recruits more muscle groups than machine lifting.

“In the machine Bench Press, the weight stack is located on a pulley system attached to two handles that the user grips while performing the exercise. The only motion that can occur with these handles is straight up and down,” Buck says. “When performing the same exercise with a dumbbell in each hand, you’re forced to use all of the little muscles in your chest and arms to keep the weight moving up and down without falling forward, backwards or to the side.”

RELATED: 3 Machine Exercises to Avoid

Which One Translates Better to Athletic Performance?

The dynamic nature of free weights is naturally better for athletic performance. During practice or a game, you rarely move your body in just a single plane. You’re constantly bending, turning, pushing, pulling, running, stopping, starting and jumping in various angles, speeds and directions.

“Athletic movement is dynamic, occurring in many planes simultaneously,” Buck says. Due to the wide variety of movements required for athletic performance, the fact that free weights require more balance, coordination and stabilization makes them more transferable to the court or field. Think of it like this: with a machine, the load you move is locked in place; it cannot wiggle, it cannot fight, it cannot get away. In contrast, the stabilization and variable range of motion needed when you use free weights “create an overall stronger and more dynamic athlete who is capable of moving in ways that sports demand,” says Buck.

Which One is Safer?

Most people think that machines are safer than free weights. If you fail to lift a load on a machine, odds are that no damage will occur. You simply stop pushing or release the handles, and the weight stack drops down (perhaps with a loud clang, but really nothing more). With free weights, failure can be dangerous. The bar can land on your head, neck or toes. There’s no “controlled” way to fail like there is with machines. Plus, stabilizing and balancing the load present another set of dangers (think about when you can only get one hand up on the Bench Press, for example).

But although failing might be safer on a machine, when it comes to how you move the load, the answer is not so clear cut. Obviously, there is a proper way to move a load during an exercise (generally known as your lifting form). Since a machine forces you to move the load in a strictly controlled manner, doesn’t that mean it forces you to use the correct form?

Well, not exactly.

“It’s a common misconception that machines are safer because they allow for a more controlled movement, because oftentimes machines won’t let you get into a good position from the get-go,” Bonvechio says. A machine might not let you get into a good natural starting position. For example, perhaps you want to move further back on the bench but the machine’s presets won’t allow it.

“One might argue that a machine Chest Press is safer than a barbell Bench Press, but good luck getting every athlete into a position on the machine that allows for a safe and strong position for the shoulders and back,” Bonvechio says. “You have much more freedom on the barbell Bench Press to alter an athlete’s setup, starting position and bar path to accommodate his or her needs.”

Buck agrees that the bar path on a machine cannot be appropriate for all athletes. He says, “Machines that were designed to move in one very specific way—such as straight up and straight back down—can be an issue for athletes who have injuries, limitations or just different body types, which don’t allow for that precise movement.”

This doesn’t mean that free weights always provide safer types of movement. Bonvechio says, “On the other hand, sometimes an athlete can’t get into a safe position to Deadlift because of limitations at the hips or ankles, so doing a Cable Pull Through with a cable machine is a better option.”

Bottom line: you need to understand how your body moves and what you’re trying to accomplish, then consult with a strength coach to determine your best overall option. A balanced program will likely include both machines and free weights.

To read more from Tony Bonvechio, check out BonvecStrength.com. To learn more about Daniel Buck and VantedgePerformance, check out VantedgePerformance.com.