Everyone's genetics are different. Your friend may hold more body fat in their glutes and thighs, while you may hold extra body fat in your arms or in your hips. We're all different. We're all unique little snowflakes and we hold our body fat in different areas. But, no matter who you are, if you get a low enough body fat composition, we guarantee you that you're going to lose body fat everywhere including your arms.
Sweating it out in the gym is a known de-stressor. Harvard Medical School has shown that aerobic exercise helps curb stress hormones like cortisol and adrenaline (as long as you're not overdoing it), while also flooding your system with feel-good endorphins. It also ups the calming, good-mood brain chemicals serotonin and dopamine. So while exercise itself is actually putting low-level physical stress on the body, it can be pretty mentally relaxing.
Whether we’re fully conscious of it or not, we’re always looking for how to be happy. And exercise is one of the most obvious steps to take, as it’s not a coincidence that you feel better after a good workout: It’s science. A Penn State University study found that people who exercised, whether it was a mild, moderate or vigorous workout, had more pleasant feelings than those who didn’t. (1)