Harvard Health Letter

Special section: Feet: How your feet work - and three steps for keeping them healthy

Special section: Feet

How your feet work — and three steps for keeping them healthy

Standing and walking on two legs has many advantages over depending on four, six, or even eight, but it does mean we ask a lot of our poor two feet. They need to provide a steady base for the rest of the body to perch upon. They serve as shock absorbers as we walk, smoothing out the impact of landing with a force that exceeds our body weight. Run, and there's even more force and a need for cushioning. They act as levers that propel us forward — and occasionally in other directions.

An engineering feat

Tall orders for two low-level body parts? Most of the time, our feet are up to the job because of some rather amazing anatomy and biomechanics.

Each of them has 26 bones, one less than in our hands. The phalanges form the bendable (and breakable) toes. The calcaneus (pronounced kal-KAY-nee-us) makes up the heel. In between are the slender metatarsals and the blocky tarsal bones, which could be the work of a master mason the way they're ingeniously put together into an arch.

Over 100 different ligaments are needed to lash together this elaborate bonework and its 30-odd joints. The scores of muscles and tendons that orchestrate the foot's movement are divided into two groups, extrinsic and intrinsic. The extrinsic muscles and tendons start in the lower leg and wrap around the ankle in various ways before attaching to some part of the foot. They form a kind of sock, constructed out of crisscrossing straps of muscle and tendon tissue, which joins the leg to the foot and enables the foot to move in several directions. The intrinsic muscles start and end in the foot. Most of them are arranged in several layers across the sole of the foot so they help form its graceful, lengthwise arch.

All of this intricate architecture comes into play every time we take a step. In a normal, healthy gait, the heel hits the ground first. The calcaneus and a layer of fatty tissue underneath it absorb some of the impact. As the foot rolls forward on its outside edge, the intrinsic muscles of the sole of the foot give way a little and a band of tissue along the bottom of the foot, called the plantar fascia, stretches out. Then the weight moves to the ball of the foot and over the joints formed by the metatarsals and the first, or proximal, phalanges. Finally, we get leverage by pushing off on our big toes, while the Achilles' tendon lifts our hee

illustration of bones and ligaments of the foot

Lucky for us, this happens without our having to think about it very much.

So what could go wrong? Plenty. Some people are born with irregularities like clubfoot (talipes equinovarus) or very high arches (pes cavus). In many cases, those problems can be corrected with surgery, particularly in young children.

There's another, larger group of us who have relatively minor defects. Age, weight, and time spent on our feet turn them into something more serious.

For example, 20% of adults have flexible flat feet — their arches flatten out when they put weight on them but keep their shape when they don't. Usually, flexible flat feet are more of a curiosity than anything else, but the age-weight-use triad can turn them into troublemakers for muscles and other tissues in the feet. The fix is sometimes easy: comfortable shoes with a good arch — the beginning of wisdom for much that ails the feet — or perhaps a pair of orthotics, replacement insoles that go inside the shoe to support the arch and provide some extra padding.

Another example is overpronation — the tendency to walk or run along the inside part of the foot. Many people overpronate, and neither they nor their feet are any worse off for it. But other overpronators wind up hobbled by sore knees and ankles, fallen arches, and inflamed, overtaxed foot tissues. The opposite problem, oversupination, or walking on the outside edge of the foot, is less common but can run a similar course.

Shoes wisely

Then there are the foot problems we bring upon ourselves by the shoe choices we make. Hammertoes and bunions are often a consequence of continually jamming five toes into narrow shoes. High heels are murder on the metatarsals and no kinder to the Achilles' tendon.

Even when we buy sensible shoes — a category that includes athletic shoes and casual dress shoes like Rockports — we make mistakes that our feet wind up paying for. We buy shoes that are too small, not realizing that as we age, our feet tend to grow by half a size or more because the ligaments and tendons stretch out. Even if the shoes are the right size, we often wear them too long, so the sole that helps with shock absorption is worn away and the heel counter that holds the back of the foot in place is swayed to one side.

So here's step one to having healthier feet: buy shoes that fit well with low heels and plenty of room for your toes — and replace them regularly. An obvious point? Maybe. But it's often not acted upon.

Step two: stay trim, and if you haven't, work on losing some weight. Your feet won't be the only body part to benefit.

And step three: take your feet for a walk. The heel-to-toe motion strengthens and stretches your feet. See step one if your shoes are old and worn.