I do high intensity training to build mass. I usually get muscle twitching after a hardcore training session. Usually in my Glutes, Triceps, Shoulders, Chest and Quads. I am genetically more gifted with my shoulders and back - but I have never gotten any muscle twitching in my back.
My last training was a shoulder training composed of several supersets. My shoulders were so pumped it felt as if lactic acid was going to ooze out of them. About four hours after my training my anterior deltoid started twitching. It has been doing this for about 18 hours now and almost prevented me from sleeping.
I don't think it's related to stretching because I stretch a lot (I'm a male and can do the splits easily). I'm extremely flexible and use great caution when stretching and lifting. I prefer quality over quantity.
What makes the muscle twitch? Does it mean it is overworked?