After doing a few sets of overhead barbell presses, I noticed my right trap had gotten super tight to the point where it seemed almost flexed even though I was not flexing it. I typically have very good form when doing this movement so I am kinda suprised and not exactly sure why this happened. I am not in pain or anything but it's kinda weird when I look in the mirror and it looks like my right side is flexed while my left trap is totally relaxed. Anyone care to chime and tell me why my body is actin' funny?
It could be an arthritc muscle. When a muscle is arthritic it can stay contracted for a long period of time. This will in turn create a build-up of lactic acid. Usually this happens in older people but, as always, it can happen to everyone. It may or may not be that. But you can try to alleviate this by doing some light strecthing in that area. Roll your shoulder around for 20 seconds at a moderate speed in circles, rest and repeat. Then grab a bar or something thats secure at hanging hand height and slowly angle away from the bar stretching the trap. Don't go at 1000rpms on the rotations and don't over stretch the trap. Just keep it moderate. Hopefully this will help you.
Could be a muscle spasm, although pulling your trap usually hurts like hell and will cause a loss of mobility in your neck. Ice it for the first 24 hours or so if its inflamed then you can start to use heat, gentle stretching or myofacial release. ART can also work in this area.