I'm 5'10, 160lbs, slightly muscular, I recently bought this shirt to wear to the pool so I don't have to put on as much sunscreen. The fit is good and very similar to most medium sized shirts I own. The material is very light, breathable and very comfortable. I'm probably a little cooler wearing this long sleeve than even a short sleeve because I wore it in the pool for about 3 hours and didn't notice an extra tan on my skin as a result. I'm wearing it in Mexico next week so I'm hoping the UPF will last 50. runs too but haven't worn it for runs yet but my pool experience tells me it will keep you cool as it is very breathable.