Are you comfortable at that pace? Meaning, are you used to it and feel it is "light" by Tig's examples? If so, increase your pace to "moderate". You will burn more calories at a 4 mph pace. It doesn't have to happen overnight, just work up to it.
p.s. That is so cute, "just started walking the hubby" When I say "let's walk" mine runs in the opposite direction!
