true dat...
Perhaps I should explain why I say your most intense rep, your last rep, is probably the safest rep in a set as it seems counter-intuitive. Again it is very important to emphasize that your form must be strict which is often not the case as you struggle with the last rep. For many, their form degrades considerably as they try to eke out another rep they are not capable of doing strictly. But that is an issue of training form and not intensity.
There is an inverse relationship between force and intensity. The force you generate moving the weight and how hard it takes you to do that. The amount of effort, intensity, you have to generate to complete that rep. Say you can curl 100 lbs for ten reps full complete strict reps but fail to do eleven. During the first rep it is very easy. You could easily do more than 100 lbs if you had to. So your ability to generate force is high and intensity is low. As the set progresses your ability to generate that 100 lbs of force starts to wane and it gets harder to do that next rep. Hence, intensity starts to increase. You have to work harder. By the time you get that last complete rep you are barely able to generate that 100 lbs and it takes a lot of effort, a lot of intensity, to do so. Your biceps are now fatigued and thus weaker.
You injure yourself when you exceed the tensile strength of the muscle, tendons, or ligaments. By the time you've done the last STRICT rep you are simply unable to generate that amount of force to exceed that tensile strength. You are simply too weak to hurt yourself.