Difference Between Bench Press Weights & Smith Machine Weights

"How much do you bench?" is often a question among hardcore gym rats, and the barbell bench press is a primary exercise for building a strong chest. However, the free-weight bench can be daunting, and gym staffers tell stories of solo lifters who became trapped under a heavy bar. On the other hand, some hardcore lifters may not even consider the Smith machine for bench presses. While the two stations have distinct differences, experts agree you can use both, depending on your situation and training goals.

Stabilizers

Both free weight and Smith machine bench presses engage your pectoralis major as well as your anterior deltoid and triceps brachii muscles. However, to horizontally stabilize the bar, a free weight press also engages your lateral deltoids. That means you'll work your shoulder stabilizers in addition to your chest. The Smith machine's fixed track prevents horizontal movement, so your lateral deltoids aren't engaged. If you're training for a sport or job that requires functional strength for a broad range of movement, the free-weight bench press is the superior exercise.

Safety

When you lift to failure for muscle building, a free-weight press requires a spotter to ensure you don't become trapped under the bar. The Smith machine offers self-spotting features such as its spring-loaded hook and a set of tabs you can position at the bottom of your range of motion, so you can perform a chest press with a heavy load even when a spotter isn't available. Because of the unnatural linear motion of the Smith bar, however, expect that your loads will be slightly lighter than on the free-weight bench.

Isolation

While the free-weight press may help to build the stabilizer muscles desired for athletics or highly physical tasks, it isn't always necessary or desirable to employ the stabilizers. With its strict linear motion, the Smith machine bench press isolates the chest and the front of the shoulders very well. If you've fatigued your shoulder stabilizers performing free-weight presses, you can finish your chest session with Smith machine presses to ensure your pecs are fully exhausted as well.

Research

Multiple studies have confirmed the value of each version of the bench press, finding that both fully engage the pectoralis major and anterior deltoid muscles. In addition, a 2005 study in the "Journal of Strength and Conditioning Research" found that the average one-rep maximum on a free-weight bench was 16 percent higher than that on a Smith machine, primarily because of the more natural "reverse C" lifting motion of the former. Michael Harper writes in the Cooper Institute blog, "This confirms that both exercises are good options in the weight room, but depend on the goal of the exerciser."