Lets see if we can clear this one up,
So a persons max heart rate is 220 - age.
No. MHR is an actual number that is related to your own heart. It has a physical meaning.
When you exercise, your HR goes up. When you exercise harder, it goes up more. Harder, and it gets higher. But your heart has a maximum HR, when you get there, no matter how hard you push it won't go any higher. It's an inbuilt limit in your body, though it might vary with different exercises, and tends to decrease as we age. That number is your maximum HR.
As you can see, finding out your MHR is uncomfortable, and possibly dangerous if you have an underlying heart condition, so there are various formulas to
estimate it. But they are just informed guesses; they'll be dead on for some people, and wildly inaccurate for others.
Ignore weight loss zone. It's been debunked.
You burn a higher %age calories from fat at this level, but you burn more actually calories of fat at higher workout levels. Plus post workout you will continue to burn more calories if the effort was harder. IE, you will burn less fat if you stick to the so called weight loss zone.
Ah (checks google), that's 60-70%.
You should be working harder than that, if your body is ready for it. EDIT: Don't listen to me, listen to your doctor!