Staying in your target heart range

Today in my spinning class, I wore my heart rate monitor. I was able to see what my heart rate was while I was riding. Ryan would tell us to turn up the tension on the bike, but if I had continued to do that, I would have gone way over my maximum heart rate. I figured that they did not want to call 911 so I just kept my heart rate in my zone. Also, when you go over your 90%, you are no longer in the fat burning zone, but you are burning muscle. And this is what will make you feel bombed out when you finish. Ryan has given me a formula to determine what my 65-90% maximum heart rate is, so I know where I should be. When I finished today, I was red-faced, my hair was wet, and I was breathing hard- but, I was not exhausted- I felt good! Determine your heart rate range and stay in it when you do your cardio workout and see if you feel the same.