I recently started going for the Elliptical at my school's gym because I feel like it gives me a harder workout than the treadmill. Are the heart rate monitors on those things accurate? Mine told me last night that I had gotten up to 180 a couple times during my workout, and I'm really not sure if that's healthy or not. I'm a 22 year old female, 5'4 and weigh about 229lbs, if that's relevant info for that.