I take spin 1-2 times a week and in the class the instructor is high intensity pretty much the whole time, we do not dip below 80% of max heart rate. I'm in my 20's so mine is pretty high. Is this still effective for fat loss? I always hear everyone talking about "the fat burning zone" but I do not see how doing 50 minutes of spin at a high intensity could not burn fat. Thoughts please??