Hello, I've always had this problem (or can't remember when it stated) but can't find information about it because I just can't describe properly. I try to do push ups, and at one point the nerves on my left arm just go crazy. I can see it trembling, like when a cartoon character is trying to lift a huge weight, I wouldn't have a problem with that as that would mean my arm is too tired to do that exercise.
However that is not really the case, and also the feeling is not as expected, it doesn't feel like my right arm for instance, the left arm feels like pure electricity, a stronger sensation and effect the more effort I attempt to do with that arm, and the source feels like two centimeters above the elbow and it goes all the way to my shoulder and the base of my hand (its left side / the pinky's side). If I move all my weight to my other arm then the feeling stops and of course so does the trembling, although my arm becomes a bit hard to control since it has just come back from that state.
I have noticed that if I start with push ups then I won't get these until my last set, but if I come tired from other exercises then the first set will be impossible, I mean I get scared, it feels like my "wires" could fry at any moment.
Other types of exercise I have done do not have this effect, the arm might get tired and it might or might not tremble from it but I won't feel a high voltage running through my arm.