Yes- A huge study of high school and college athletes was done in the early 1960's - wish I still had the link. But anyways it showed that after a weight training program the muscle mass increases over 4 years was an average of about 10-15 pounds, with 30 pounds being in the top 1 % of gainers. That really was pre-steroid by and large- so it pretty much sums up what is naturally possible.
For advanced lifters who are over 25 years, it's about 5 pounds MAX of solid muscle a man can build in a year.
Once you hit 40 or so, it's pretty much impossible to build muscle without anabolic supplementation.
Women are lucky to build 2 pounds of solid muscle a year, if that.
That's why it's so easy to spot women juicing.
People claim DLB makes these gains because she trained 7 days a week and follows a strict diet. However they fail to understand basic Physiology. A female simply cannot build muscle like that without AAS of some sort. Nor can they get shredded lean without "help".
It defeats every aspect of how our bodies work. She is not a "genetic freak", she's been using AAS for a long time. I think she comes off from time to time, but it blows my mind that people are dumb enough to believe she is not on drugs.