Questions about HRMs, target heart rate, and calories burned

SmileyFaceGuy

So I got a heart rate monitor for Christmas (well, technically I got it for my mom, but she didn't want to use it because it's "too complicated") and I used it for the first time while biking through the snow today. My HRM has an alarm that goes off if you below or above your target heart rate zone (I'm sure this is a common, if not universal, feature), and I was really surprised at how easy it was for my to go above my target zone (which is 137 - 167 for my 24-year-old self); my alarm was beeping almost the whole time, and my average heart rate over 78 minutes was 170 BPM. So my first question is: is it safe to sustain that high of a heart rate over such a long period of exercise?

Secondly, I used a calculator (http://www.shapesense.com/fitness-exercise/calculators/heart-rate-based-calorie-burn-calculator.aspx) that estimates calories burned based on avg. heart rate (mine HRM doesn't have a built-in calculator) and it says I burned 1,400 calories. How accurate are these calculators? People say the MFP calculator already grossly overestimates calories burned, yet this 1,400 figure is 240 more calories burned than MFP suggests.

Thanks.

SmileyFaceGuy

Bump.

KelsLovesRando

I just posted the same question and then searched for this... hope someone posts an answer! I just used my HRM for the first time today and I easily went over mine too.