Riding position for training/fitness?
I started another thread in General about what makes a bike well-suited to fitness riding. I got a lot of answers that basically said "any bike." So I'm asking my question here about how I can train better. I'm looking for cardio benefits, and an increase in muscle strength. I want to maintain and improve my performance backpacking, climbing, paddling, and cycle touring. I'm 50 yo., 5'8", 135 lbs, with no fat, so I'm not looking for weight loss. I work out at the gym 3 days a week. In the winter, I was doing weights as well as time on the elliptical, stair machine, or rower. I intend to keep up the resistance training with weights at the gym, but I want to work on cardio and build muscular endurance cycling outdoors because I enjoy the outdoors more than the gym.
My bicycles are upright recreational style, almost cruisers. That's how I like to ride when I tour -- not face down focused on pedaling. Now according to the other thread, this kind of bike would be good for fitness. I'm not sure I believe that but I'm not just looking for confirmation or validation. I'm not convinced either way. If I ride upright, am I not mostly developing the quads? I'm sure I can do the cardio irrespective of the seating position. Would I get any muscular benefit from putting drop bars on the bike or am I unlikely to involve the glutes even if I changed my position? For a non-competitive casual cyclist, does seating position matter for anything but aero?