Sure, I think I started off averaging 11mph on my long commute (32 miles each way, twice a week) and was shattered when I got home, you know, showered, sitting in front of computer with a glazed look and stiffening limbs.
Now, I'm mostly averaging 16 (depending on wind which is a big factor on coastal road and autumn) and arrive feeling brisk, get showered and crack on, no mucle aches, nothing.