Hi Cherry,
I was still quite heavy when I got into kick boxing. I think I was about 29 stone or about 400 lbs roughly. Its not a good weight to start at as my body paid for what I was asking of it, however, it did mean that I lost weight a lot quicker, and it wasnt long before my performance had caught up with the others in the class.
Also by starting at a heavier weight I got a lot of experiance and got fit very quick as for each push up I was doing I was lifting 400lbs!! Not that I could do many to start with. For me it was the dojo, they pushed me but didnt make me feel bad when I couldnt keep up or do some of the exercises, it was a god send

)