Oooh I don't know Thompson. When I see cyclists on our Norfolk roads, they seem so vulnerable beside huge lorries and tractors etc. Our roads are narrow and twisting. I'm always worried about rounding a bend and finding a cyclist right in front of me.
In towns, they stop right beside the exhausts of vehicles and are presumably inhaling lots of diesel and petrol fumes.
It would be excellent if dedicated cycle tracks were provided everywhere (Holland has these) so one could bike in safety and without the air pollution.
I'm wondering if the static exercise bikes in gyms would be equally beneficial in preventing cancer? After all, the physical movements and energy output would be the same. My sister does an hour on hers in the house, and swears it keeps her in great shape.