What, they are fleeing from their own excrement? Does the elimination of waste cause them to enter into a state of momentary euphoria?
The first theory is from a biological point of view, where some specialists in animal behavior suspect that the fact that cats behave so different when they poop is because of the fear that a predator might smell their droppings.
Another theory posits that cats are used to being licked by their mothers after defecation when they were kittens so they are just flaunting their grown-up independence. Some speculate that their strange behavior could also indicate that cats may experience discomfort from the pooping process so they run away from their litter box when they are finished.
Do you believe these theories? As well, there is another that explains that both humans and cats have a vagus nerve that exits the brainstem. In both species, the nerve can be stimulated by defecation, which leads to a pleasurable sensation, something which some have called the euphoria subsequent to the defecation.
When running, the cat may simply be expending all that excess energy caused by the stimulation of the nerve.
Less interesting is the theory that claims that cats have a peculiar hygiene and may just want to shake off to remove excess fecal matter out of their rear.
The main problem is that this curious mania of cats has been investigated so little that there is still no universally accepted theory. What is clear is that there is something that moves them to do so and it would be interesting to know what it is.