“Concavity” is basically the “curve” on the bottom of the shoe along the balls of feet section as pictured in the feature photo above. Pick up a traditional shoe. Hold it right in front of your eyes looking down the length of the shoe from toes to heel. On many shoes, you will likely see the bottom is concaved or “curved” with the lower portion being right in the center. Now look at the bottom of your own foot. You will see the natural foot is NOT concaved with a projected or pointed center, but rather, the foot is basically flat along the balls (metatarsals joints) so it can fully contact the ground and stabilize the upper body then propel the body forward in gait. Since the balls of our feet are designed to be FLAT on the ground for stability, a concaved shoe bottom completely alters position and function of the ball of foot joints as the concavity drops the middle joints down into a hole and out of optimal position.
Even more interesting is what is under our forefoot skin at the skeletal level of the foot. We actually have a curve going in the OPPOSITE direction of how most shoes are designed–our upward curve is called the “Metatarsal Arch.” This arch goes across our foot not lengthwise as with the more obvious arch on the inside or medial part of our feet. While you don’t see this Metatarsal Arch, you can feel it and see it working if you softly place your naked foot on the ground then firmly press down–as the balls of your feet compress into the ground, you will witness your foot “flattening” across the forefoot section as it widens. This part of the foot is critically important for shock absorption yet tradition shoes ruin this part of the foot’s ability to absorb and disperse ground forces! The end result is more force coming up into our knees, hips, back, etc. OUCH! This is NOT good.
Why are shoes designed with concavity? Tradition and fashion. Western culture places higher attraction on smaller feet–shorter and more narrow. A concave sole makes the foot appear narrower due to a “winged” effect as the edges are curled and lifted upwards while pulling outer joints away from ground. In opposition, this “narrowed foot” is not widened like “working class” barefoot peasants. Sex and attraction win again while feet lose. Also note the possibility of “inside” concavity as the bottom sole surface of the shoe might be flat while the “inside” of the shoe liner can be concaved from design or from heat and pressure–this is called “creep” and will be addressed in a future post. For more information, visit my “Products Section.”