body pump calorie burn?

so when I do body pump, I don't burn a lot of calories. I can't add more weights and still be able to do the moves effectively. I am shaking by the end of the tracks, I am breathing heavy, I am getting "sweaty" (I don't really sweat ever but I get sweaty hands, red face, etc) I only do the modified tracks for the abs because I am slowly rebuilding my core after 4 c-sections but other than that, I do all the regular moves.

is that normal? some people post they burned 500 calories doing body pump. I am no where near burning that many calories. I did the pump and burn track this morning and used my HRM and was at like 100 calories total.