zumba and HRM

mygrl4meee

I got a polar FT4 for christmas and I was surpised that an hour and half only resulted in 835 calories and someone else near me was over 1000 using one too. I notice that my heart rate is higher in the first half and is at about 130 for the rest. I been doing zumba since April and I am wondering if the calorie burn being lower that I have been logging is because I am slacking or my body is used to it too much. I am dripping in sweat but do feel during new songs that I have a harder time following.