coming into this late but my hubby has an extremely low HR.

He's in the 40's sometimes.

Has had ER people totally FREAK OUT on him.

But, he's a marathon runner and in very fine shape.

My HR just getting out of the house is your average HR on the bike! My Max is 180ish. My resting is in the 60-70 range.

When I run with my husband, I get into the 150's while he's MAYBE at 100.

But when we bike, I average lower than he does as I'm a more efficient biker. (on a lighter bike too)

If you know your resting HR, it will tell you a lot about your results. If you are not working hard enough to get that HR up, you won't burn the calories. You are efficient. Your heart is strong. (as long as you have a good recovery HR too!) And the better you are at something, the less you will have to work at it.

You do sound like my husband, very low HR. And that's just what you have to work with. Make sure you enter your resting HR in the garmin as well. That will help change the calculations.