If a guy does a chest muscle squeeze at a specific arm angle and twist, one part of his chest muscle lights up more than another — this might be the best way to test or train that specific chest area.

You can't fully work just the upper or lower part of your chest muscle when pushing as hard as you can — no matter how you position your arms, both parts end up working together.

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 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.

If you're a guy who lifts weights and doing bench presses, the flat bench works your chest muscles the most — especially the middle and lower parts — compared to when you use a bench angled upward, especially past 30 degrees.

When guys who work out regularly do a flat bench press with a normal weight, their chest and front shoulder muscles are working just as hard as each other.