Originally Posted by
BlazingPedals
Under my definitions, a certain amount of discomfort is normal and good. Breathing hard, burning legs, sweating, etc. That's not pain. If you're really in pain, that's a sign of injury, and you should back off!
Although sometimes it's hard to be sure when normal burning quads starts to become something more serious. When in doubt, back off before trying again. There! you've just invented intervals!
It is pain, actually. Although I get your point. But there's a difference between pain associated with exercise and one that has to do with an injury or ailment. Hopefully, anybody that's exercised at any time in their life would know the difference.
Even so, there are times and cases when it can be difficult to tell (especially in the case of lingering pain) which is which, and a more professional examination is necessary to distinguished between the two.