Heart Rate Discussion

The other day I read that Chris Froome had an average heart rate of 145 during his time trial victory in the Vuelta last year. This had me asking some questions, because when I am training I consider 145 an easy heart rate.

I have done a few triathlons/duathlons this year, and here are the heart rate results for the bike portion.

1.2 mile run - 15 mile bike - 5k run after - Average heart rate during bike was 180
5K run - 16 mile bike - 200 meter swim - Average heart rate during the bike was 183

So my question is why Chris Froome had such a low heart rate, or is that normal for a professional time trial. I always hear announcers talk about how hard time trials are, but 145 seems pretty easy to me. Any insight would be great. I would love to hear about other's heart rates during competition.