Exercise! - Am I working out too intensely?

I am not one of those women reading a book while walking on a tredmill. I never stay in the fat-burning zone as defined by the given heart rates on the machine but now I'm wondering if maybe I should?

A typical workout for me is 60 minutes. I use different machines but I'll give the Tredclimber as an example. So, 60 minutes on the Tredclimber with my heart in the mid-to-upper cardio zone (as defined by the machine- typically the 155-160 range). I will do intervals that are 2-3 minutes long with my heart rate up in the 165-172 range. I am 37 and about 50 lbs. overweight.

Am I doing too much? Would I see better results if I decreased the intensity? I'm not disatisfied with my weight loss but I am wondering if I'm really maximizing my workout time. Thanks!

The "fat burning zone" is a myth. Here is a great article explaining why:

http://health.usnews.com/blogs/on-fitness/2009/03/03/the-fat-burning-zone-a-fitness-myth-debunked.html

I do all of my workouts in the high end of my HR range. Doing so burns more TOTAL calories, and therefore, more calories from fat as well as from all other sources. My personal experience is that it doesn't make ANY sort of improvement to exercise at a lower intensity.

It depends on your Threshold really... Those HR formulas aren't accurate for most people. However 155 for most isn't really all THAT high it's more moderate intensity. (For me anyway as my threshold is 180) but a great zone to work out in for increasing fitness as well as calorie burn.

Like Manda points out You'll burn more overall fat just because you burn more overall calories.

Doing intervals like you mentioned is excellent too for increasing fitness even more. Will help you pick up speed etc. The only thing you want to watch out for is not working out at the interval intensity for a long period of time on a daily basis or it takes your body too long to recover, and your workout the next day may suffer.