When healthy people lift their arms out to the side, their shoulder muscles work in a very similar way no matter if they're lifting straight out to the side, slightly forward, or in line with the shoulder blade — their muscle patterns stay consistent.

When you lift your arm forward of the usual shoulder line, your upper trap muscle works about 6% less hard compared to lifting it along the normal shoulder path — at least in people with healthy shoulders.

People who play tennis don't use the shoulder blade muscles as much as other athletes when doing a specific exercise where they lie face down and pull their shoulder blades together, especially when their arms are raised high.

If you lift your arms out to the side at slightly different angles, it changes how much your shoulder muscles have to work — even small shifts can make one part of the shoulder muscle work harder or easier.

Lifting your arms out to the side or slightly backward, especially with your palms turned down, works your side shoulder muscles the most — this move might be the best way to build stronger shoulders.