Originally Posted by
DrIsotope
It's unlikely you've gained any muscle at all. You may have cut some subcutaneous fat, so there's the appearance of increased musculature. And as I and others have pointed out-- you're very new. Everybody sees real (and perceived) gains in the first few months as their body adapts. You are absolutely not going to gain muscle in the upper body on a bicycle. Look at any pro. They're scarecrows. Look at any track cyclist... oh, that's right-- they spend as much time in the gym as they do on the bike.
Trying to sustain that kind of training load indefinitely is gonna catch up with you-- ask me how I know.
You footnoted "typically" , but I think you really can't generalize validly from your experience. I don't think trained athletes are going to be the only exceptions to your general rule. I have been at this for years, riding a number of miles that is very similar to yours, do absolutely no working out on my leg muscles other than bike during riding season and elliptical machine in the winter. I put on huge muscle mass in my thighs and calfs and kept it on for years. Where I'm sure you and I are different is in our gearing choices. I ride habitually in the highest gears and do so while riding for miles at 20-25 mph on the flat. I also probably take hills on much higher gears than average. This is basically a hybrid between resistance and cardio training. I doubt many people can and will do that, but it does tend to make statements like yours really inconsistent with my experience.