I have always heard that once you reach a certain point in size or strength, it is much easier to get back to that point. Some people believe that once the facia is stretched, it stays stretched, making it easier to regain the muscle. I have heard that if a bodybuilder breaks an arm, as someone else mentioned, and the cast comes off, he can easily regain his size. To answer the question, I would say about 10 days for me to start to lose strength. I took 8 months off a couple of years ago and I lost everything, but was back to my top strength in less than four months. That's just my 2 cc's, I mean cents.