When people do an incline bench press instead of a flat one, the upper part of their chest muscle gets more activated — the electrical signal in the muscle moves upward, showing the incline version works the top of the chest more.

When you do bench presses on a flat bench vs. a slightly angled one, different parts of your chest muscle get worked more — the lower chest works harder on a flat bench, while the upper chest works harder when the bench is tilted up.

When healthy guys lift weights on flat and slightly angled benches, their chest muscle movement and activation patterns don’t really change — so any differences in how the muscle fires are probably not because of how they’re moving.

If you're a guy who lifts weights and doing the bench press with a medium-heavy weight, setting the bench at a 30-degree angle might fire up your upper chest muscles the most compared to flatter or steeper angles.

When you do bench press on an incline, the upper part of your chest works harder. But when you do flat bench press, the middle-lower part of your chest works harder instead. Scientists measured this using muscle activity recordings.

When you change the angle of the bench press, it might make the different parts of your chest muscle work in uneven ways, potentially causing one part to activate differently than the other.