i have recently starting working out in a group fitness class. i don't lift heavy weights, maybe 5 to 8 lbs, but there are high repetitions. my muscles are not too sore post workout or even the next day, but recently, if i have used my arm to hold a water bottle (say between my upper arm and body in order to have hands free, etc.) for an extended period of time, when i go to put the water bottle down and release my arm, i feel extreme pain from my elbow into my forearm and tricept/bicept muscles. is this just muscle fatigue from holding my arm in a 90 degree position for an hour or so?