I have the book and purchased a heart rate monitor and started in. I use it for my walks, hikes, and mountainbike rides which can be epic at times. We have many mountains here on the coast where you can jack your heart rate in a second. A couple of posters offered good advice, if you can't jack your heart rate walking, jog a bit, when you hit your max and go over, walk. My mountainbike rides send my heart rate all over the place, I just try to make sure the greatest percentage of my bike riding is under my age calculated target. I have noticed this is much more enjoyable than the constant killing myself that I used to do.
You'll never see the light if you're in someone else's shadow, or said another way, life is like a dog sled team, if you're not the lead dog, the scenery never changes