I can’t tell you your perfect running form, as it cannot be fit into words.
We use ‘form’ as a noun — ‘your running form’ — unconsciously biasing ourselves to think it’s a thing, an ideal that we should try to approach. It’s not a noun, though.
Pace (think sprinting versus end-of-ultra shuffling), terrain, angle of ascent or descent, time of month for some of you, fatigue level, today’s weight, weather, shoes, clothing, how far you’ve already run, what you did yesterday, surface wetness or dryness, texture, slipperiness, hardness/softness; the reader can add her or his own variations for influences. When enthusiasts instruct on perfect running form, they’re perhaps thinking, ‘Your perfect form when running on a flat unpitted moderately elastic non-slippery non-canted surface with neither wind nor rain nor snow nor excessive heat or humidity, neither speeding up nor slowing down nor turning, with no ground-level impediments nor larger obstacles nor other people nor animals near, nor any tree branches you might bump your head into, and after warming up, but not fatigued, while moving at your mid-high sustainable-for-a-few-minutes pace.’ Click-bait for sure.
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Of course there are plenty of people who are certain they know what that ideal is, the universal truth of running, and will with complete sincerity tell you. The word ‘natural’ is likely to show up.
This is scientifically unsound: any argument from evolution (nature) is descriptive, not prescriptive; feet are densely innervated nonlinear nonequilibrium dynamical systems that we don’t understand. ‘We evolved to run barefoot’ doesn’t stand up to the evidence that our intermarriage cousins the Denisovans were living on the Tibetan Plateau at least 170 thousand years ago. Human (Denisovan or Neanderthal) tools dating to 300 thousand years have been found in Siberia. Homo sapiens were in Mongolia 45 thousand years ago. We’ve been wearing shoes for a lot of generations. (Noting as well that evolutionary pressure would be centered on standing, walking, squatting, and stabilizing our trunks for throwing far more than on running.) Yes, running is part of our evolutionary heritage. That does not mean constant running without walking is a dominant evolutionary determinant, any more than is dancing, another human universal.
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Running is a skill, like dancing, so while your ‘perfect’ running form is something you have to continually rediscover from inside, looking at expert practitioners to see whether there are consistent patterns can (possibly) be helpful.
Here is Zola Budd winning the World XC Championship in 1986, running barefoot. She is a heel striker. (The gear icon at the bottom right of the YouTube frame allows you to adjust playback speed; slowing it down makes it easier to see.)
Kip Keino—the most beautiful runner I have ever personally seen—winning the 1968 Olympic Gold in one of the most strategically brilliant races of those or any other Games. Also a heel-striker, even at that extreme-for-us speed.
Sifan Hassan, the dominant runner of 2019, is a midfoot striker.
You can pick any number of elite runners, athletes who have immense volumes of running in their bodies, and find every form imaginable. Please don’t cite the third-dumbest paper published in the modern era under the Harvard brand name. Watch World Champion Tim Cheruiyot.
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It seems to be human to want a One True Way. It’s heroin to our minds for things to be simple. So here’s the One True Way to Perfect Running Form: Don’t interfere. Let your feet do what they want. They’re virtuosos. Enjoy feeling them.