Someone who is a committed exerciser, maybe you work out 3-5 days a week—how much of that time should be spent doing vigorous-intensity exercise. I would say, for VO2 max and other adaptations we're going to discuss, including the brain, about half of that exercise training time, I think, should be spent in vigorous exercise. So, again, you want to be at least 80% of your max heart rate or more.