It’s a platitude that ‘what a thing is’ depends on how you look at it. Usain Bolt speeding toward a victory in the 100 meter sprint, for instance, has been described as a man toppling forward while moving his feet just fast enough to catch himself from falling on his face.
Which is to say that – looked at as a matter of balance – running has a lot in common with falling.
To understand that thought, imagine yourself standing still, and lifting one foot. Thanks to the one-way-folding geometry of knees and hips, that foot comes up well in front of your body, causing your center of gravity to shift out beyond your torso, causing it (and therefore all the rest of you) to start to fall forward. Thanks to eons of collective evolution – and several months of individual toddling at an early age – we nominal grown-ups generally know enough to let that happen for only a brief time before stretching the leg out to hit the ground and keep us upright.
Do that again with the other foot, and you get forward motion. Do it over and over and over, and quickly enough, and you get running: falling forward, and using the feet to catch ourselves and convert that fall into forward motion.
Of course that’s only one way to look at it, and what’s to say it’s any better than a more common image of running – the act of pushing yourself forward with your feet and legs – they both end up meaning the same thing don’t they? Well, no. Not if efficiency is your goal; because ‘pushing’ is all work, while ‘falling’ benefits from free energy – in the form of gravity.
Physics-wise, the main ‘work’ we do in running is to push our body thru the atmosphere (if that sounds insignificant, try running into a headwind). But if you fall on your face, no personal effort need be involved, (something I happen to know from experience, which I will not share here). It’s gravity that pushes you thru the atmosphere, and not only without effort, but sometimes even against your best efforts!
Yes, there’s still the biological energy required to swing the feet, and then the arms to counter-balance them, and the diaphragm to contract and the heart to beat; but if we can reduce the effort required to move the body thru external space, those internal efforts will all be reduced in proportion, so we’re still way ahead.
We also have to accelerate at the start, but that’s only a temporary load (remember Newton: “a body in motion tends to stay in motion”), or climb grades, which is functionally quite similar, since the ‘work’ involved is to counteract an omnipresent accelerative force toward the Earth’s center of mass (otherwise known as – you guessed it – gravity). And any way we can find to use less energy running at a steady speed on level ground just means that much more is available when we do need to accelerate or climb.
Bottom line though, if we get just the right amount of falling forward, balanced with enough putting the feet out at just the right moment, we can take advantage of gravity to pull us forward and use less of our leg strength to push. Witness, Mr. Bolt.
You might want to give it a try sometime: running at a comfortable pace and a high cadence on level ground, lean your body just a little bit forward, so your chest is ahead of your hips, and see if you can feel the force of gravity pulling you forward just before your foot contacts the ground. Done right, it’s almost like adding half a percent of downhill gradient to whatever surface you’re running on.
And that is something any runner can use!
(Closely-related topic for another time: where to land ‘em…)