I've always equated my ability to maintain a certain heart rate as a measure of the effectiveness of aerobic exercise, and that's one reason I've always loved cycling. It has always been easy to elevate my heart rate. When I'm walking on a flat surface, though, I don't get the same increase in heart rate - and I walk pretty fast. I've discovered that in order to get a "biking level" aerobic workout, I have to walk up hills. Fortunately my city has plenty of hills to choose from, so I can get the workout I want.

But when you bike up a long hill, at least you get to roll down. With walking, there's no coasting lol -

If you were forced off the bike, do you think walking could provide the same health benefits as cycling? I would think yes.