CfStrongman08 is right about overtraining. Overtraining specifically is when your losing strength. Whether overtraining actually exists is a whole nother arguement.
But if you are doing negative reps, with bad form or forced reps with bad form you can injure yourself.
I'll give you an example, this slightly older guys, maybe 30s, pretty skinny. He was sitting by me in one of the chairs used for bicep curls mostly, and I was using thirties, he was using thirty fives. To show me off he swang his body to rep the 35's out, while I was using proper form for the 30's. What did he do after he got a few reps? He held his back because he had hurt himself.
Personally I don't go to the point of a forced rep ever. Using a forced rep with bad form is the same ideal as dropping that weight and picking up a lighter one. When you twist, turn, bob, or move your body around during a rep the extra momentum helps you through it, effectivly lightening the load.
__________________ 
Team BRoLiC 
INJECT ME WITH THE BLOOD OF MY ENEMIES SO I CAN EVOLVE THEIR GENES Welcome to BRoLiC City.
Population: The very few
Brolicholic |