After many years of programming, I have found that I can no longer avoid the fact that I spend most of my day sitting, which is absolutely horrible for my health. I started swimming a few months ago and am enjoying getting back into better shape, so I'd like to start adding in some workouts on a stationary bike. I have one long bike tour under my belt, but that was many years ago at this point, so though I'm not new to cycling I haven't ever really focused on cycling for physical fitness.
I have ready access to a boring bike at the gym. It just has flat pedals, but it does have a computer and controllable difficulty levels, along with a built-in pulse monitor. My question is, what sorts of workouts would be good to try for starters ? Should I just get on and pedal for half an hour ? What cadence should I aim for (in my mind I'm shooting for somewhere near 100) ?
I have two goals in adding a stationary bike workout: I'd like to increase my cardiovascular fitness (currently I can barely swim 100m in one go, because my lungs feel like they're going to explode), and I'd like to make my quads stronger. Hopefully these aren't at odds with each other.