They are fasciculations and they are brought on by weight lifting/exercising. I have had them over a year. I think that when you get in shape and have more muscles... then when normal hormones circulate throughout the body which is a normal process... in people with more muscle mass than fat... the receptors are a little worn... so the receptors are wide open and sensitive to these circulating acids and hormones... thus the muscle quivers or "fasciculates". This is extremely common amongst athletic people. I have had them over a year. I talk to a lot of people that have had them for years and years. There is nothing dangerous about them... it just means you are in shape and it's just something you are going to have to live with. Things that make them worse are anything that the worn receptors have to deal with such as caffeine, lactic acid after a workout or something simple like a 20 minute walk, hormonal changes such as when women have more circulating prostaglandins before their period, preservatives and chemicals in food, stress/cortisol... so basically you want to try to stay calm... meditate... eat fresh healthy whole foods... avoid chemicals... avoid foods high in neurotoxins or bacteria like shrimp and crabs... That;s basically all you can do. Welcome to the club.