Another 3 miles today, making this week a total of 6 miles.
I am running on smooth concrete sidewalks and relatively smooth asphalt trails, which are slightly rougher than sidewalks and good for toughening the plantar skin on my feet. It's amazing how much the surface you run on can make a difference in conditioning. I recommend new barefoot runners start on these seemingly hard surfaces because it teaches you good barefoot form more quickly than starting on cushy grass or even a track. Even when I have built up my miles on hard surfaces, running on soft surfaces causes me some twinges in my knees... my theory is there is some micro-stability compensation you have to do on soft surfaces because they are slightly more unstable. Kind of like running on foam and having to have the lateral stability in your joints to be able to take that. Also, you have a false sense of how hard you should land because your feet can take a harder landing on grass, even if your knees can't.
For example, last year I could run 14 miles on concrete sidewalks barefoot but during my Half Marathon on a trail I encountered a much larger variety of surfaces (soft dirt with a cushion of pine needles, hard packed dirt with roots, sticks and rocks, slab rock, rocky single track, and more!) and could only make it about 9-10 miles barefoot before I finished the race in Vibram Bikilas. I definitely recommend you train on the surfaces you are racing on if you want to have a good racing experience. Don't get me wrong, I really enjoyed the barefoot time I had during my Half, but it would have been a lot more fun if I had run more hills and trails during training and being able to finish the entire Half barefoot.
I have read a lot about form advice for barefoot running and kept several things in mind today that might help others in their barefoot running. It's a lot to keep in mind at once, but try thinking of one or a couple of these things while running and see how it impacts how your body feels after a run.
-Keep your legs relaxed and loose.
-Land lightly on your feet.
-Land on the ball of your foot and let your heel "kiss" the ground.
-Run with a short stride length, high cadence (how many times your feet hit the ground in a certain amount of time)
-Raise your knees.
-Bend your knees when landing.... almost like you are doing squats while running. You will be lower to the ground and be giving yourself the benefit of the natural shock absorption of your entire knee joint.
-Keep your hips forward and don't "reach" forward with your feet; Land under your center of gravity.
-Don't forget to use your hips and thigh muscles to lift your feet as the touch the ground rather than landing hard on them; Don't overuse your calves and lower legs by "pushing off" with your toes- you'll injure your calves or get blisters on your feet
There's a wealth of other advice around on what constitutes good barefoot form but the key is what helps you as an individual. Just listen to your body during and after a run and try to adjust if you are hurting or not able to increase your mileage.