The point is to do is to be worn out. Initially, you start with 3 days a week. As your body adapts its energy levels you increase. I ride 20 miles a day on a bi

The point is to do is to be worn out. Initially, you start with 3 days a week. As your body adapts its energy levels you increase. I ride 20 miles a day on a bike (10 to work, 10 from). On weekends I ski moguls for 6+ hours in the winter and hike 12ish miles in the summer. The only time I feel a lack of energy is when I _stop_ regularly working out. You can be very efficient and get the same effect doing 20 minutes of HIIT. When the weather is marginal or I just don't have time that is what I do.