Flat ground. It's man-made, unnatural and constricting to feet. Combine that with the study that simply standing is harmful, and you have something. Taking this one step further, running on flat ground damages your feet and legs in two distinct ways: the absorption of repeated impacts and, more importantly, muscle atrophy from an unvarying motion.
First off, repeatedly slapping your feet against hard, flat surfaces is horrible for your joints and tendons. That's a no-brainer. Even wearing the most popular running shoes today, this continual impact is grinding. That's why we're seeing people taken out by injuries like Achilles tendon ruptures, knee ligament tears, shin splints and a host of ankle and arch issues. But this isn't even the primary concern.
Yes, the grind hurts. But the greater cause for concern is the muscle atrophy that sets in from a lifetime of living on flat surfaces. This artificial muscular degeneration sets athletes up for disaster.
Nature doesn't typically create flat surfaces. Generations upon generations of humans evolved on top of uneven, multi-planar surfaces, stepping over dirt, sand, pebbles, rocks, grass, roots and fallen leaves. The ligaments, muscles and tendons of our feet have adapted to this--the exact opposite of perfect planes--with muscles, ligaments and tendons accustomed to varied movements and constant adjustment.
Our feet need variety, to bend their arches, curl their toes and grip the ground beneath them. Spending all our time on tile, cement and hardwood floors, and strapped into flat-soled shoes, means our feet will never experience the full range of motion they were meant to. And without a full range of motion, parts of your legs and feet will remain underutilized, prime targets of atrophy.
When running, our feet, ankles, knees and hips will only adjust when we make turns or run hills. If we're running on a road or track, these shifts in gait are generally gradual and infrequent. So even for athletes and fitness buffs, atrophy will remain a constant threat when only a specific set of muscles are trained in a limited range of motions. This also leads the body to become susceptible to foot and leg injury when moving outside the accustomed set of motions.
Just look at the cumulative weight our feet endure from walking around every day. It can add up to several hundred tons for the average American. Then understand that while few people are born with any leg or foot issues, three out of every four Americans suffer from a serious foot or leg injury in their lifetime. The tissue atrophy from limited motion on a level plane, coupled with the pounding of feet every day on a hardened surface, makes it near impossible to avoid injury. This situation is simply based on lifestyle alone.
We need to change what we accept as "normal."
Don't throw away your shoes just yet, but it's time to start going barefoot for at least a portion of each day. Take your shoes off at home. Walk in the backyard. Add daily foot, ankle and calf stretches to your schedule. Embrace variety. Rather than exercising on a track or cement sidewalk, consider exploring a local hiking trail. Go off-roading.
We need to gently build up the muscles, tendons and ligaments we've misused for so many years. Or else we're setting ourselves up for failure: muscle, joint, tendon or otherwise.