10 miles is nothing really. Just give yourself extra time in the beginning. I dropped 20lbs my first year commuting (I have a 10 mile commute as well). I started out at a granny pace, chatting the whole way with a neighbor who also worked in the city. Now, a season later, I ride alone and try to beat my last "personal best" and arrive covered in sweat (26 minutes is the new time to beat). I have a gym in my building so I hit the showers when i get there.