Lol at the 600 calories a week! ;-) I would have thought u would burn less than the 409 while on 600 a day simply because you wouldnt be able to push yourself as hard. Depends what the session is like and 409 in half hour sounds like its extreme! I used to circuit train and i used to have to stop if i got dizzy and nearly puked a few times the trainer was pushing me that hard and that was when i was eating normally and before i had my son
You need to read your own body so u can function. The maths on those calories doesnt sound good but u need to learn to find a balance that suits your own body.