As you sit on a roller coaster your heart rate begins to elevate due to the fact that you may feel both scared and excited. While you sit on that roller coaster and your heart rate begins to elevate, you are not getting any fitter. Same as when you walk into a haunted house, you do not come out any fitter just because your heart rate was up the whole time.
Heart rate, VO2 max, sweat, screams/grunts are correlates of intensity, not intensity itself. In CrossFit, we give definition to everything to include intensity. This allows us to be able to measure, observe and repeat it.
Click here and learn what intensity means in CrossFit and how we apply it: (Quick 90 second read)