I've heard from many resources, snake owners I trust & suppliers that most snake owners overfeed their snakes to get them big fast not realizing what they are actually doing. I'm sure I'll get allot of flak for this but in the interest of your pets health here goes.
Many of the feeding amounts and weights of certain length snakes that most people boast, sound overweight to me. My burm is 8'10" & 25 pounds (Some claim 9 feet @ 60 pounds plus). His back muscles are still visible and his tail has a nice taper. I feed him 2-3 jumbo rats every 2 weeks and he seems just right. A few indicators of obesity I see are the spine dissappears, the tail is fat just prior to the vent, then gets skinny real fast to the end. You ever seen a snake in the wild that looks like that? The scales do not cover the skin properly (starting to spread apart from being to stuffed. Keeping things for the snake to climb on and giving them room to exercise will help them stay active.
Hope this helps.
DZ