Sunflogun said:
I prefer to use all my senses, so no mirrors and music as I ride. Swimming is great to correct posture and body issues, as for running, I think it's as aggressive to the body as cycling.
My experience with swimming, as a teenager, resulted in hyperextended knees, poor foot strength, and a deeply S-curved spine (head forward, upper back back with the shoulders curled forward, hips forward). When I was 13 I developed a debilitating back injury that my family doctor could not diagnose. Through the secret sports network we finally found a massage therapist who found the problem and got me on a program to get back on my feet and into the water. This was in 1965, a time when alternative therapies were truly underground.
Swimming and biking don't develop the load bearing tissue as "feet-on-the-ground" activities do. These days, while biking is my main activity, I swim when I have access to water, and I run for foot strength and posture. And if I'm feeling a persistent or recurring injury, I see a professional.
The goal of most fitters who work in shops is to get their clients riding comfortably and quickly on their new bikes--whatever it takes. Rarely have I heard a fitter say, "Your lack of flexibility (or core strength, or foot strength, or weight control, or sound posture) is interfering with your ability to be comfortable on your bike."