Does ability to lift weight also decrease in about a week? I was recently out of town for over two weeks and came back with the ability to lift roughly the same amount I was able to prior to leaving.
My DEXA scans seem roughly correlated with the amount of weight I can do in my regular sets, which has increased about 50-70% depending on which muscle group you are talking about.
This is with heavy resistance training 3 times a week and Pilates once a week.
A good portion of the strength related to any specific lift is CNS adaptation up until a certain point (and most new lifters won't hit that threshold for quite some time), so strength on a lift you've been doing regularly isn't necessarily a good indicator. Building muscle will of course increase your strength too, but I've doubled my squat since getting back into lifting while certainly not doubling the muscle mass of the respective muscles.