Every day when sizing people for runners in +Amphibian King Galway , I would normally hear several suggestions that I'm telling fibs about the numbers.I also get quizzical looks about sizes I may be suggesting.
I'm used to it at this stage.
There's a couple of measurements I look at; your barefoot size (just standing there), your recommended shoe size (normal everyday shoes) and then your running shoe size.
Foot width, bridge height & foot volume are generally 'eye-ball' dimensions that are taken into consideration when selecting and recommending a pair of shoes for you to try out.
What is the reason for the running shoe size?
Well, depending on your arch which may be high, neutral or low your foot will do a certain amount of work when you are running. The arch is a flexible structure of joints, muscles, connective tissue all designed to be a mobile unit that helps the body absorb impact energy (when running) store it as potential energy (in the muscles of the lower leg) and re-use that force as kinetic energy (driving your forwards). A highly efficient use of energy systems.
So, let's assume you have a neutral arch, nicely flexible with good mobility. When you run, between strides you are airbourne so gravity starts having an effect on your landing. It multiplies the impact forces from 1-2 times your walking body weight to anywhere from 2-5 times of point load on landing.
To absorb and redistribute this impact energy (remember from school science class the Law of Conservation of Energy? Energy in a system may neither be created nor destroyed but can be changed from one form to another. ) the arch flattens as the impact energy becomes stored by the foot. As the arch flattens your foot becomes longer.
If you don't have space at the head of your shoe, you are going to lose toenails, simple.
With sandal season around the corner, tell me do you this this is a good look?
Didn't think so. :)
Don't believe me, want to test me?
Next time you get out of the shower stand on the floor with your feet shoulder width apart. Have a look at your footprints. Now place one foot alongside the prints and stand on one leg. The second footprint is larger both in length, width and surface area. This is how the body starts dealing with running impact energy.
So that's it in a nutshell. We're not trying to make you trip over your own feet, or turn you into a circus clown. We're not even making up the numbers for fun.
Your foot size is your foot size, but your running shoes size is a different thing altogether.