Is there any rule of thumb for how much muscle is lost as a part of the weight you've lost? My understanding is you will always lose muscle as you lose weight.
Recently I went on a four week tour and I've come back 15 pounds lighter. Is it 10 pounds of fat and 5 of muscle? Is it completely different for every person depending on their build? I can see were I've lost some fat on the torso and face, I can see more muscle/definition on my lower body, and the upper body looks about the same.
The main reason I'm wondering about this is because I was debating if I should start doing a bunch of upper body work outs again. If I've lost a bunch of muscle with the weight I'd be more inclined to do so, versus a regime of mainly cycling and jogging.
It's more than likely, that if you lost that much weight without doing resistance exercises, you would've lost some muscle mass -- I wouldn't like to speculate on the ratio, but (here i go anyway) I'd say 1/3 would be about the maximum.
Muscle gains and maintenance does depend on genetics.
I would say that if you continue to lose weight at any rate greater than 2lbs a week, you will continue to lose muscle mass off your upper body. You may even end up with arms like Lance Armstrong.
So, in other words, if you lift weights, and don't lose weight too quickly, you will most likely make muscle gains, especially if you haven't done weights for a while