Physical limits in sports

Over exertion varies from person to person.  There are some days when I can only run 2 miles and other days I can run 7 miles. But I know I've reached a point of over exertion when I begin to feel pain such as a cramp, pulled muscles, or limping as I walk or run. Other points that alert me that I've exercise to much is when I grimace in pain, or make grunting noises.  Believe me, if you over do it, your body will let you know immediately or either you'll feel  the burn the next day.

When I get a head rush, headache or stomach cramp I know I've reached my limit. I don't over exert myself as it takes my body two days or even three to totally recover from it. I like to run 5 times a week with two days of swimming in between and if I over do it, I have no energy nor motivation and feel irritable. 

Please clarify whether you are referring to peak exertion over the course of a week(for example), or in a singular workout.