Was surfin the net and found this really great article. In it the author states that in as little as 15 secs per muscle group, you can build and/or preserve muscle through weight bearing exercises:
I believe this to be true, because I've only started weight training 2 weeks ago for about 2 days per week (1 upper/1 lower body). I already SEE progress. Also, I've been playing around with my pull up bar every other day. I went from ZERO pullups to 3!!! I think it's amazing how fast you can see results weight training with little effort! Hopefully, this article can motivate someone else to JUST DO IT!