Running is such an innate human movement that we rarely think about how it works. But as you run, your body constantly calibrates with dozens of small adjustments to prevent you from falling flat on your face. It’s so complex, in fact, that it requires a mechanical engineer to explain it.
“You might think running is just a repetition of identical steps,” says Nidhi Seethapathi, PhD, the author, with Manoj Srinivasan, PhD, of a recent engineering study published in the journal eLife. “But actually, you have to constantly correct to avoid falling down. Our muscles and our senses are not perfect, and that leads to errors. If we didn’t correct for these self-generated errors, we would fall.”
1. Each stride includes a stance phase, when one foot is grounded, and a flight phase, when you’re in midair. “Flight” accounts for about 25 percent of each cycle, depending on your speed.
2. When you’re in flight, your body moves in a parabolic trajectory and you have no control over this motion.
3. While in midair, your body compensates for imperfections in your balance and stride as well as changes in terrain by making small alterations in your core’s mass center.
4. To make these corrections, you unconsciously use input from your eyes, nervous system, proprioceptive sensors in your feet, and vestibular sensors, which control your sense of balance and spatial orientation, largely via the inner ear. “The correction happens almost continuously throughout the step,” says Seethapathi. “So you can think of it as one long correction or many small corrections.”
5. Small changes are transferred through your foot as you strike ground again and propel yourself forward.
6. Your arms counterbalance the movement of your legs and body.
7. Though running may seem like a series of repetitive, identical strides, each step is different and unique.
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