I am 5'7'' and 151 pounds and am trying to lose some weight. I work out on a regular basis on a treadmill or an elliptical (usually around 30-45 minutes). Oftentimes the machines will tell me that my heart rate is in the low 180's. I know this is high, but if I try to lower it, I don't feel like I'm working very hard! Is it dangerous or ineffective to workout with my heart rate so high?
Your heart rate is too high but probably you are not in the danger zone unless you are having some kind of chest pains or heart palpitations. From your question I can tell that you do not have the aerobic capacity to keep your heartrate at fat burning heart rate levels (known as zones). You jump up to sugar burning levels. This is a very common problem with many of us. The best thing to do is get a test done to measure where your anaerobic threshold is; i.e. your aerobic heart rate levels compared to your anaerobic levels. You burn mostly fat in the aerobic zones and burn mostly sugar in the anaerobic zones. While it is ok to work in both areas, it is best to train 70-80% in the fat burning (aerobic) zones, especially for weight loss and to change your body shape. Training in the fat burning zones will help you build an aerobic base and with that big aerobic base, you will gradually increase your anaerobic threshold so you will be able to burn fat at higher heart rates. This will increase your caloric burn over time while using fat as your fuel! Make sure and cross train so along with your cardio training, incorporate weight training with moderate to heavy weights. Weight training puts you mostly in the fat burning zones and the calorie burn continues long after the workout. I would recommend hiring a personal trainer for a few sessions so you get started on a program that will be designed to meet your goals. You ARE worth the cost you know! Another alternative is to look into group weight loss classes that are coached by a personal trainer. Please keep me posted on your progress!