Been doing alot of walking recently as an additional tool to my training. Due to knee problems I'm currently unable to run at the moment so that's what got me into the walking. I walk up my local hill, around my neighbourhood which is in the country so plenty of free space, inclines. What I've noticed is that, how much of a substitute is it? cause with the walking, I swear I actually feel slightly fitter. As I was doing other forms of cardio throughout the week with weight training also, I only run once per week but with my new approach things seem better. I try and walk every day for around 45mins brisk walking.