Best way to determine when you should end the workout....??

[dehydromethandrotren]

Title pretty much says it all.

Is there any way of determining/estimating when you have stimulated the muscle fibers enough? A certain percentage decrease in strength after a given amount of time?

Just thinking.......

[kaberle_15]

I finish my workout and i feel like throwing up and going home so thats when to throw in the towel.

[xlxBigSexyxlx]

I finish my workout and i feel like throwing up and going home so thats when to throw in the towel.

That happens on my leg day.
By the time I get to calf raises, I feel like collapsing in my own puke lol

For other muscles, Im not sure. Like for chest, I get to the point where I can't do a push up, and I know Im done.

[Brown Ninja]

When every thing starts shaking and your muscles feel like they are going to burst....or atleast until I get bored