Does Neil DeGrasse Tyson NOT Know Physics

– The MOVEMENT Movement with Steven Sashen Episode 079

Listen to this informative The MOVEMENT Movement episode where Steven debunks the myth on energy return.

Here are some of the beneficial topics covered on this week’s show:

  • How energy return is a term created by big companies to make more sales.
  • Why anything that has a little bit of flexibility sucks energy out of you.
  • How a higher energy suck means your body has to work harder.
  • How running speed comes from your stride length and frequency.
  • How trampolines and foam slow down how much energy you have


Connect with Steven:





Steven Sashen:

Sometimes even really smart people can say some really not so smart things like Neil DeGrasse Tyson. Let’s talk about Neil on today’s episode of The Movement Movement, the podcast for people who want to know the truth about what it takes to have a happy, healthy, strong body, often starting feet first because those things are your foundation. We’re going to debunk the mythology, the propaganda. Sometimes the, frankly, lies that you’ve been told about what it takes to run or walk or hike or play or dance or workout, or do yoga or CrossFit, whatever you like to do and do it enjoyably, efficiently. And did I mention enjoyably? If you’re not having fun, please do something different so you are.

I’m Steven Sashen your host of The Movement Movement podcast. Well, if you’re watching this because they’re places you can watch this. You know I normally wear a Xero Shoes T-shirt. Right now I am wearing a Boulder Polar Bear Club sweatshirt because it’s minus two degrees outside. It is insane in the membrane. So by the way, if you don’t know how to find us, go to, you’ll find previous episodes, all the different places you can find us on the inter tubes, everywhere you enjoy podcasts.

And of course, spread the word. We say, this is a movement about natural movement. You are the ones who are making that natural movement move. Do that by sharing and liking and thumbs up and hit the bell on YouTube and subscribing, and all those things you know how to do. In short, if you want to be part of the tribe, please do subscribe. So what are we talking about and why am I going to say nasty things about Neil DeGrasse Tyson? Neil’s a very smart guy. Let me start by saying that. Love what he does. And he has a podcast called StarTalk Radio, and he recently had an episode that he did that is called a Materials World. Pardon me. I got something caught in my throat.

And in that he was talking to Georgia Tech engineer Jud Ready about material science and how that’s affected sports. And not too surprisingly, they got into a conversation about running and running technology. Now, if you want, I’ll put a link to the podcast below. And the conversation about running starts at about 22 minute, 28 second mark. And it starts off immediately with a thud, in my opinion, because they started using the phrase energy return. Talking about the surface that you can run on.

Now, energy return we’ve talked about on this podcast before is a marketing term invented by big shoe companies because what’s really going on is energy suck. So any pliable surface, the soles of your shoes, the surface that you’re running on, grass, concrete, asphalt, whatever it is will flex a little bit some amount, depending on how fast you’re running, your ground contact time, how much you weigh, how far you’re falling when you hit the ground like how much bounce you have in your hips if you’re jumping off a ladder. Various things that impact that.

Energy return is the opposite of what really happens, which is energy suck. Anything that has a little flexibility sucks energy out of you. But again, the big shoe companies called it energy return so they could say, “Look, we have better energy return” as if that’s something that you actually want. Now the joke about this, and again, I’ve talked about this before so I’ll do it really fast is if you want to see a perfect example of this, I’ll make a video of this later. In fact, I’ll probably link to this as well in the show notes. An engineer from Adidas talking about how there is no such thing as energy return, it’s just energy suck. And then talks about how they have this new boost foam that has incredible energy return. And they demonstrate this by bouncing a steel ball like a two pound steel ball off some concrete then off some other foam, which by the way, no other company uses ” that other foam.”

And then the new boost foam, and then the boost foam, you see the ball bouncing like maybe up to about 30% of its original height, 25% of the height that it was originally dropped from. And then it bounces like six times, which is four times more than what it did on the other foam and two times more, whatever. You’ll see. It’s it basically bounces better. Well, here’s the joke. I’ll include this video too. If you look, go to the Exploratorium Museum in San Francisco, which is a hands-on experimental museum. They have an exhibit where they have a steel ball that you can drop. It’s a smaller one, but that doesn’t matter. And it hits a steel plate with concrete underneath it.

Now you would think that these stiff things don’t provide “energy return.” But what they do provide is very little energy suck. In other words, from the physics perspective, elasticity is how much something stretches, but how much or how quickly it comes back to its original form after being compressed or stretched. And so a steel ball hitting a steel plate is highly elastic because the steel barely moves, it barely compresses and it returns to its original shape really, really fast. So in the Exploratorium experiment, you have a steel ball. There’s a plexiglass plate with a hole in it. You drop the steel ball through that hole. It hits the steel plate with concrete underneath it. And the first bounce back hits the plexiglass underneath and then it bounces 249 more times.

This raises an interesting point about why we don’t just have steel shoes and run on steel. Well, you’re not a steel ball is the short version. Again, I’ve talked about that in the past. Find out on a previous episode. Point being that we’re starting off on a bad foot, if you will, if we’re talking about energy return and we’re not talking about the thing that’s applying the energy, which is the human body. The natural spring that you are because your muscles, ligaments and tendons help control how your joints bend and return energy.

And so they already start talking about trampolines. Wait, where do they do that? At the 30 minute, 40 second mark, they start talking about trampolines. Well, think about trampolines. You can bounce really, really high. You get a lot of “energy return.” And I’ll say how you get that in a second, but how long can you bounce on a trampoline? Not very. Not as long as it takes to run an average person going out for a five-mile run or a three-mile run, or even an 800 meters. Why? Because the thing that is applying the energy is your legs and they get tired after a relatively short amount of flexing and returning and flexing and returning.

So the more “energy suck” you have, the more your legs are doing the work, but your legs are always doing the work. As Eliud Kipchoge, the guy who ran a sub two-hour marathon in a pair of Nike shoes came out months later and said, “It’s not the shoes. It was my legs doing the running.” He was really kind of mad that people kept saying it was the shoes. And I’ve talked about why it probably wasn’t the shoes. Well, definitely wasn’t the shoes, in again, a previous episode.

So Neil DeGrasse Tyson. Gosh, pardon me. One more time with the coughing. So Neil keeps saying, “Well, why don’t we run on a trampoline?” And Jud he responds about how trampolines help you bounce up. And Neil says, “Oh yeah, you need friction to go forward.” And they get into this whole conversation about trampolines, where they completely miss the entire point about running and running fast. First, that trampoline thing, where again, your legs are applying the force. But most importantly, running speed comes from two things. Well, your stride length. How far you basically bounce from one foot to the next and your stride frequency, how fast your legs are turning over. The faster, the frequency with the same stride length, the faster you run. The longer your stride length, the same stride frequency, the faster you run. If you increase your stride frequency and increase your stride length, you’re running even faster. That’s it.

Why you can’t run on a trampoline is trampolines and every kind of foam slow down how much energy you have and often slow down your cadence compared to say running barefoot. Slow down, the what’s the word I’m looking for? I just said it seconds ago. Slow down your stride frequency because they’re sucking some energy out of you. Now there’s an argument about the new Nike shoe that because it is so lightweight and doesn’t decrease stride frequency compared to any other shoe. Because it’s basically again, just cushioning. Then because it’s so lightweight, it doesn’t change your stride frequency because it’s heavy. And it’s the same amount of cushioning as before so it doesn’t change your stride frequency because it’s not providing either more or less cushioning.

But what might be happening is just because it’s so high, because it’s taller than other shoes. You might be increasing your stride length in the same way that running on stilts would increase your stride length. This is not increasing it by that much, but a little bit makes a big difference. So the trampoline thing is also interesting because on a previous episode, I talked about the Harvard track. And the Harvard track is effectively a trampoline, which means it is supported outside of where your foot hits the ground. This will come back in a second. And it does bounce like a trampoline and they have some really cool physics that they talk about where basically the springiness of the trampoline is slightly springier than the springiness of the runner.

What that means is that when you hit the ground and you end up in midstance when your foot is underneath your body, and you’re starting to propel yourself forward. What happens at that point is you’re starting to apply less force on the ground. You’re basically starting to take off the ground. And if the floor underneath you is a little springier than the spring of your legs, then it’s going to recoil faster than you’re taking off and give you a little extra push. Here’s the rub. It only does this. If you are the right spring, if you are the right weight, if you’re running at the right speed, if you have the right spring in your body compared to the way the track is built.

So if you’re the wrong weight, the wrong speed, the wrong many other things, it won’t work. If you’re basically 135 pound, 140 pound 800-meter runner, that track is going to help you set personal bests. If you’re a 200 pound sprinter, it’s going to slow you down. If you are a super, super slow jogger, you’re probably not going to notice anything about it. So that’s the issue with trampolines. Then at about the 32:40 mark, once again they bring up the Vaporfly. Neil’s partner actually brings up the Vaporfly the Nike shoe. And again, a number of errors from these really smart people where one, the guy’s from Georgia Tech says that, “One of the reasons people are running faster in that shoe is because the carbon fiber plates act like springs.”

Steven Sashen:

No, they don’t. They’re not compressing in any direction that then gives spring back. And even if they are, again, like a trampoline, which they’re not. Because trampolines are supported outside of where your foot is. You can’t make a trampoline that supported just inside the width of your foot. It doesn’t work. Oh, once again, if there was a spring, then it would only work if you’re the right weight at the right speed, the right frequency, et cetera. There’s another footwear researcher Simon Bartold who said the carbon fiber acts as a lever.

Well, this is interesting because for a lever you need a fixed point, a fulcrum, and then a flexible point. Think diving board. That is a lever. There is no fixed point. There’s no fulcrum in that shoe. In fact, ironically, Nike says that part of what makes that shoe work is how it has a curved rocker bottom that gives you extra spring. But the real joke there is, if you look at Kipchoge’s two-hour, sub two-hour marathon, he and all of his runners, his pacers especially at the beginning of the race, they don’t even touch the heel. They’re landing on their midfoot or forefoot. So they’re not rolling across this curved bottom.

Basically, it just debunks everything they’re saying. Speaking of which, then at about the 35:18 mark, they bring up this whole idea about how Nike says that shoe improves performance by three to 4%. Well, one is Neil actually does do a smart thing around there. He points out that Eliud Kipchoge, his sub two-hour marathon was only about 40 seconds faster than his regular marathon on a normal course. And the sub two was on a perfect course in perfect conditions with people he was pacing. With people he was drafting from so he didn’t have a wind resistance. And Neil kind of brings that up, but it goes right by the wayside.

And the other thing that isn’t brought up is that Nike makes that claim from studies that came from here at the University of Colorado from Roger Kram who actually said that what it did is it improved VO2 max, the way you can uptake oxygen, which is a measure of efficiency. How efficient are you at taking in oxygen and using that in your muscles? He said it gives a 4% improvement in VO2 max. But eventually claimed that that doesn’t equate to performance. It took him a while until he said that. And that was like the last sentence of the article that I read it. He was the one who really studied that shoe and came to the conclusion that he did not know why anybody would run faster in it.

The best he could come up with is maybe you’re not having to use your muscles as much, which is why you’re getting a VO2 max improvement and something else is going on that’s allowing you to run faster. It’s an interesting point. Well, here’s where it gets really fun. At the 35 minute and roughly I think 36 second point, they start saying, “Well, it’s all about lightweight and whatnot, and maybe it’d be better to run in bare feet.” And then they joke about that. They think that’s hysterical. Although again, Neil’s partner does bring up the point that there have been highly successful runners who either ran races entirely in bare feet. Abebe Bikila being one, Zola Budd being another or like had to kick off their shoes or accidentally lost their shoes in a race. They don’t bring that one up, but it’s happened and then run better.

Well, they think this is hysterical, not surprisingly over here at Xero Shoes world, we think that makes total sense. Because A. You don’t have foam. That’s getting in the way and sucking energy out of you. It’s the lightest shoe you could possibly wear bare feet. In fact, Ron Hill who won that, I think the 10K in Mexico City in bare feet said he ran in bare feet because it was the lightest shoes he could find. And our friend, Dr. Phil Maffetone has written an entire book called 1:59, where he suggests that someone can run a legit sub two-hour marathon without pacers, without drafting if they’re running in bare feet if they’re accomplished barefoot runners.

The reason we don’t have accomplished barefoot running marathoners is that almost any professional marathoner is getting paid a bunch of money by shoe companies not like Xero Shoes who have a bunch of money. Let me just say that sentence better. By companies who have a lot of money unlike Xero Shoes, who does not have a lot of money. The big shoe companies are paying those guys to run. It’s their livelihood. It’s also part of their identity. There’s a lot of money attached to it. We and other minimalist natural movement footwear brands don’t have the kind of cash to support the kind of people who arguably could run a marathon in bare feet and/or in a pair of Xero Shoes, which is just basically bare feet plus a little bit of protection, some of them.

Some have a tiny bit of cushioning if you’re like on trails. Our trail shoes have that. But the gist is we’re giving you the closest thing to a barefoot experience that you can get in modern footwear. And in fact, Phil Maffetone mentions that in his book. So all that said, so glad that Neil brought this topic up. So glad it’s a conversation, but it’s to see how really smart people can really miss the point about simple Newtonian physics. And unintentionally reiterate marketing nonsense from big shoe companies like energy return or like trampolines ignoring where trampolines have been used effectively and where they’re not. Or of course, making jokes about natural movement and running barefoot.

So I hope this is useful. And I hope that you can share this with people, well, who are big fans of Neil’s as well. I am also. Let me just start by saying that and end by saying that. And again, many of us who think we’re moderately or reasonably smart, we can be fooled too. So it’s always helpful, always important to look right underneath the surface of what we think we believe and see what might be true underneath that that we haven’t gotten to yet.

Okay. Hope that was useful. If so, drop a comment somewhere or drop me an email at In fact, if you have any comments, questions, suggestions, people you think you should be on the show, et cetera, just email And go to that website to find, again, previous episodes, all the places you can interact with us. You can find us wherever you enjoy podcasts. Most importantly, please go out, have fun once it’s not minus two degrees outside and live life feet first.


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