Is There a Border Between Low and Moderate Intensity?

There are two intensities, separate intensities, at which there's like an abrupt spike. The first of them is this first ventilatory threshold. When you're just below it, the exercise is not at all stressful to your autonomic nervous system. But when you cross over that threshold, am, it becomes a lot more stressful to your nervous system and it takes longer to recover from it.