cardio, smardio - can't I just get off my bum?

Learned all about the cardiovascular system - I really should have paid more attention in Ms Demith's 8th grade health class.

In case you are as clueless as I am, subtract your age from 220 and that is your maximum heart rate.  (Obviously, there is some room for variance.)  220-43=177

Once a week, I need to get my heart rate up to 177 during a cardio work out.
That is a lot of sweat.
I will do this with a mountain or treading class.
By doing this I will will burn complex carbs which is the body's fav food - which burns more calories.

Then, the rest of the my workouts should be ~60-80% of the maximum.  ~106-141
This burns less calories but is easier on the body.

I always feel I am at my max heart rate.