Hello, i am a fit 28 yr old male, I normally train 2hrs a day and sometimes at the weekend I would run long distances, the past 2 months I have been taking it easy nothing to strenuous, yesterday i felt weak in my right bicep and thought it could have been from the few beers the night before however today i can hardly arm curl 5Kg when I normally curl 20Kg with ease, this is my right bicep only? no pain no injury all very sudden and isolated to this muscle? is there any reason for this is it common?