Footsteps


Walking is usually thought of as a mechanism of getting from place A to place B, a movement that requires placing one foot in front of the other with little thought given to coordination or execution. Humans learn to walk in infancy, while some animals, like horses or giraffes, learn to walk within hours of being born. Gaits transform from unsteady wobbles to confident strides, allowing us to evolve our own versions of the hop, skip, and run.

At the Biomechatronics Group at the Massachusetts Institute of Technology, the physics of human walking are being explored to understand how to design and control leg prosthetics to more closely mimic the comfortable ease of the human gait. Historically, the earliest prosthetics bring to mind the solid and unyielding peg legs and hook hands on Captain Hook and his fellow seafarers, cumbersome and incapable of achieving any of the angles that a human joint can assume. Through studies of the skeletal-muscular system of cadavers and recent technological advances that allow for manufacturing of malleable and lightweight materials, today’s prosthetics are made up of many movable parts. It is often assumed that prosthetics are kind of like shoes, in that your height and leg-length are most important for a proper fit, the way that shoe size is dictated by the length and width of your foot. As it turns out, however, the flexibility of the tendons and muscles also play a large role in how each individual walks. In fact, if the lab models the human gait with factors including the tensile strength and stretch of each tendon and the reflexes in each muscle, they can account for the kinetics of human walking over various surfaces, without an autonomous control center, such as the brain, supplying any external information. Thus, walking doesn’t necessarily require conscious thought, which is why we can converse or eat or stare at our phone screens while we walk without too many horrific consequences.

If the design of a human leg has been fine-tuned for walking, then the individual quirks of our legs must factor into the equation. The length of our fibulas and tibias, the amount of cartilage and synovial fluid cushioning each joint, the flexibility of our Achilles tendons, and length and density of each muscle subtly impact the way that each of us takes a stride. Furthermore, our legs and feet assume movements that are developed by habit; hence, the turned-out stance of a ballet dancer or the swagger of a sailor. The way each person takes a step and shifts his or her weight from left foot to right foot is ultimately unique.

Although we often take our footfalls for granted, it is intriguing to consider how different the sound of each person’s walk can be. By simply listening, what can we determine about a person? What do a pair of shoes, slippers, or lack thereof tell us? What does the tempo of a step reveal?

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A yoga studio is supposed to be a place of calm and meditation. However, if the room is outfitted with creaky wooden floors and acoustically cold walls, even a bare foot makes a kind of amplified echo. You may find that every visitor to the room lowers his or her foot with a kind of deliberateness that is similar to the toe-first step of a dancer, and peels up that same foot with a sound that only human flesh can make. Together, the feet create a quiet rhythm, a kind of beat that makes you aware of the movements of the people around you. Whereas the footstep of someone sneaking past a sleeping being involves a quick patter of elusive tip-toes, these footsteps involve the rocking motion of an entire foot planted on the surface, as if to firmly declare the presence of a fellow human being in the quietest way possible.

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Those who reside in multi-level, non-soundproofed apartment buildings often have a “type” of story: an upstairs neighbor who has heavy feet, an unusual sleeping schedule, and a tendency to pace at 2am. This story, however, came from the upstairs neighbor himself, who had insomnia, self-described heavy steps, and wandered his bedroom at night. He was painfully aware that directly below, the toddler of a young family would wake to his ponderous footsteps, despite his attempts to tip-toe as he walked himself into a state of tiredness. To the young girl, the footsteps belonged to a massive monster who stomped in his lair, wielding claws and snorting smoke through frightful nostrils. No matter how many times her parents introduced the man upstairs to her during the day time, during the night, the entity transformed from human being to a creature of the dark.

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Most of my family wears indoor slippers, which serve to protect toes from accidental stubs and separate the sensitive footpad from the frigid cold of winter, particularly on granite or linoleum floors. As most slippers are loosely attached to the foot to facilitate an easy-on-easy-off movement, a slipper wearer subtly changes his or her foot to keep the slipper on. For some, their foot flexes and grabs at the sole, creating a slap whenever the slipper rebounds. Some people create a distinct pattern of sounds this way, their right foot perhaps slapping louder than the left, or every fourth step accentuated with a firmer smack. Other people shuffle their slippers to keep them from sliding off of their feet, and the shh-shh-shh becomes a kind of lulling shuffle that sends a child off to sleep. Some individuals become accustomed to a squeak from their slipper every time they turn their left foot a certain way, while others no longer notice the sound of that sticky patch on the bottom of their right heel from the sticker glue that never rubbed off. To a family, these sounds become routine, and it can be a surprise to realize that someone is right behind you, having abandoned the familiar sounds of their footwear to sneak over in their bare feet.

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