Physics of falling says professional athletes are running wrong
Physics of falling says professional athletes are running wrong
Enough angular momentum to go round? (Image: Walter Iooss Jr./Sports Illustrated/Getty)
Runners may be doing it all wrong. A slightly different posture could let runners and walkers get a gravity-driven boost – and potentially break world records.
To most runners and coaches, running is a series of jumps, says Svein Otto Kanstad, a physicist and former competitive runner based in Volda, Norway. Gravity isn’t considered helpful, because its force is perpendicular to the direction a runner is moving. But this mindset neglects the concept of angular momentum, Kanstad says. Rather than thinking of running as a series of jumps – leaping off one foot and landing again on the other – runners should view their sport as a series of falls, aided by gravity, he says.
“We are falling forward, and our legs catch us,†he says. With each footfall a runner’s body actually rotates forward, pivoting on the foot in contact with the ground. “It is not a series of jumps, it is a series of rotations.â€
A hula hoop illustrates how this rotation provides angular momentum. If you simply throw a hula hoop vertically into the air, it will fall flat when it lands. But if you spin the hoop as you launch it, it will roll away after it hits the ground because it has angular momentum.
“We are clever at using angular momentum without really knowing that’s what we’re using,†he says. But for many runners there is room for improvement.
Best foot forward
As a runner’s hips rotate to bring each leg forward, he or she gains angular momentum. But most runners don’t make the best use of this. At the moment their leading leg hits the ground, the second leg is usually stretched out behind. In Kanstad’s revised gait, the second leg will already have rotated forward again before the leading leg hits the ground. By doing this, the runner’s centre of mass is tilted far forward allowing for more forward momentum, but the recovery leg is there to stop a fall.
It’s tricky to do, but Kanstad has taught himself to run this way. He says that retired US sprinter Michael Johnson – who has held the world record in the men’s 400 metres since 1999 – uses the same technique.
“The arms become very important as a counterbalance to the leg movement,†says Kanstad. “You have to change to almost opposite the way you are used to using your arms and legs.â€
He trained distance runners from Tromsø to run using this technique on treadmills, while using straps that anchored them to the ceiling in case they fell. In one test, a male sprinter running at 14 kilometres per hour was making an energy saving of 10 per cent compared with his usual gait, as measured by his consumed oxygen volume per minute. As he ran, he shouted, “I’m flying!†Kanstad says.
Kanstad believes training distance runners and sprinters to run in this fashion would shave minutes off race times, resulting in a rash of new records.
“Gravity is there, and it drives us forward, but we immediately kill it by the way we run,†he says. “Just by not being that killer, you can have 10 per cent more energy for free.â€
Journal reference: Proceedings of the Royal Society A, DOI: 10.1098/rspa.2015.0287
Didn't they already have a name for this years ago?
A sprinter flying at 14km per hour. That will rewrite the record book.
Could you not just lean slightly forwards?
Did he really say Michael Johnson, who has almost 0 forward lean, uses this technique? How...??
I don't have access to the full text of the journal article but from the abstract the finding seems to be the usual advice: don't overstride.
waitwaitwait wrote:
Did he really say Michael Johnson, who has almost 0 forward lean, uses this technique? How...??
Someone must have pointed out the basic flaw in the falling forward hypothesis using MJ as an example. So the author tries to turn that around by saying that MJ uses this technique.
Just anothe fool trying to re-invent the wheel. We all know how to run. Racing faster comes from greater skill in speed endurance. There is no real mystery to it. But telling people they don't know how to run????
You are probably right about why they put the bit about Michael Johnson in there but to a physicist there are far deeper flaws in the falling forward hypthesis. Gravity is a conservative force which is a another way of saying that you can do anthing at all but if you end up back where you started (for examply by running one lap around a track) then gravity can have contributed none of the work. The only way gravity can help propel you forward is if you are running down hill or diving across the finishline and the only reason it can help in these cases is that you aren't ending up where you started. In the case of running down hill, you end up at a lower altitutide than where you started and have to fight gravity to get back to the start line. The case of the dive is similar where you have to fight gravity to pick yourself back up. In other words, you absolutely can derive energy from gravity by falling forwards, but it only works for a few meters before you fall on your face.
Gravity pulls stuff down, not across.
The Force wrote:
Gravity pulls stuff down, not across.
Dang, now there's a revelation!
If only AlSal the heel striker had known this. He could have been the first sun 2 hour marathoner.
fred wrote:
If only AlSal the heel striker had known this. He could have been the first sun 2 hour marathoner.
Well, let's hope he's got some seriously heat resistant shoes!
It's deceptly simply physics but many experts have been fooled:
"The Pose Method of Running consists of three elements: Pose – Fall – Pull and it accepts gravity as the primary force for forward movement instead of muscular effort. To achieve the optimum running technique, the key is to make the greatest possible use of terrestrial gravity. A skilled, knowledgeable runner should be able to work with the force of gravity just as a yachtsman gains energy from the wind."
-https://posemethod.com/running/
"With the ChiRunning technique, instead of holding your posture upright and in line with the pull of gravity, you allow yourself to cooperate with the pull of gravity by lettering yourself fall forward. Your body will then become a forward-falling object (like a tree that's just been chopped down). Because your center of mass (your pelvis) is just ahead of your point of contact with the ground (your feet), your upper body falls forward...and all you have to do is pick up your feet to keep up with your fall."
- Dreyer, Dreyer. "ChiRunning: A Revolutionary Approach to Effortless, Injury-Free Running," Simon and Schuster, New York, 2009, p27.
Ya, with a weight vest, duh.
MJ ran that way due to his natural spine angles. He is strong enough to be a sprinter. I have been using him as an example of the speed and strength of his 'recovery' from the drive to the knee lift. But its not anything you can learn without the natural structure already in place.
However when you have a guy who suddenly spends more time working on something than he ever did when running before, its suddenly due to the breakthrough and not the extra work.
MJ was great. Bolt is as great or greater. They run with their natural abilities buffered by hard work
That's Great! Keep us updated!
bad_stats wrote:
"With the ChiRunning technique, instead of holding your posture upright and in line with the pull of gravity, you allow yourself to cooperate with the pull of gravity by lettering yourself fall forward. Your body will then become a forward-falling object (like a tree that's just been chopped down). Because your center of mass (your pelvis) is just ahead of your point of contact with the ground (your feet), your upper body falls forward...and all you have to do is pick up your feet to keep up with your fall."
Gee, how does your center of mass get back up for the next "fall" in the next stride? Shockingly, whatever energy you gain with this "fall" is (assuming your legs are 100% efficient, which they're not) exactly equals the energy required to lift your center of mass back up for the next fall.
You'd think that would have occured to them when they wrote "like a tree that's just been chopped down." But no, it didn't.
There actually is a better way of running but it involves growing an extra pair of legs up front.