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92 | The Four Things Slowing You Down


There are 4 things slowing you down when you start your ride: gravity from the weight of you and your bike, aerodynamic drag from you cdA and air resistance, rolling resistance from the tires (or friction), and of course braking. Some of these are trade-off, where improving one problem will make the other worse. Some can’t be fixed at all. Some problems are bigger than others. Listen in as we discuss how you can reduce external forces and improve your performance.


Dr Will O'Connor 00:07

Welcome to Episode 92 of the performance advantage podcast where we bring sports science to the people with myself. Dr. Will O'Connor and Dr. Matt Miller aka MTB PhD, we're both sports scientists with oodles of experience within the field of applying sport science, to the real world of mountain bike, triathlon, ultra-endurance trail running, track cycling. And everything in between. What we like to do on this podcast is bring sports science to the people. And today, we're going to touch on the four things that are slowing you down. And there, there are a plethora of things that actually slowing you down. But these, according to Mr. MTB PhD, are going to be some of the most important nemeses that you're going to face. So on this podcast, we're gonna get into that

Dr Matt Miller 01:10

right. So I've been like writing this article. It I guess, the reason why I wanted to write this, it's just gonna go on my blog, as I get kind of annoyed.

Dr Will O'Connor 01:22

As generally why you write articles.

Dr Matt Miller 01:24

Do you think Is that why you write them?

Dr Will O'Connor 01:29

Yeah, I think so. I'll get I'll read something, either a blog, or an Instagram posts, or I'll get a question over whatever, platform and I'm like, Oh, I just need to, I need to break this down.

Dr Matt Miller 01:48

Yeah, yeah. I guess when I say annoyed, I'm not like angrily typing 3000 words in the morning, just like, I'm totally blacked out from everything else, because I'm mad. It's just like, You know what, like, I think we need to be able to explain this. Because like, especially with this article, it's, I'm seeing people talk about these marginal, like, extremely marginal gains, when actually there's bigger things that we can be focusing on, we can get way more like performance gains, versus focusing on these tiny, tiny little things. So if we, the point of this article was to bring everything in and talk about at one time to see how big like, one thing slowing you down compares to another thing slowing you down. Because as you say, like there's a lot of forces slowing us down.

Dr Will O'Connor 02:34

Yeah, I think the other thing I write blogs like this for these more science based ones is the you go, someone asks you a question or something. And then you have a look, you just do a quick Google to send them something like Oh, no one's really explained this. Collectively. Yeah. That kind of man, the one that annoys me the most is why you should slow down. No, slowing down just makes you feel better. And you can train more consistently, you know, evil. What's the science anyway?

Dr Matt Miller 03:07

Yeah, well, you know, that is one of the problems because when I showed you this article, oh, that's pretty technical. Well, cool. I could just write it super basic, and then I wouldn't be MTB science, right. So I'm sure people have talked about these. Like, I call them the portrayal nemeses. I'm sure someone's written about these things, but without that little extra explanation. I guess we're not talking science, right.


So what are they? Okay,

Dr Matt Miller 03:38

so I got four things. If you know, like a fifth one or sixth lawn or something, let me know. But I got, let me scroll through this. Do you want to do a drumroll? Now or it is not that big of a deal? I'll try. Okay, that's not a drumroll. But that's okay. We got gravity, right. Gravity is one thing slowing us down. Another one is aerodynamic drag. Or you could call it air resistance, I'll probably use the terms interchangeably. We have rolling resistance, which actually, like if we're thinking about a bike, we're thinking rolling resistance, everything about runners, we're probably thinking friction. Or, yeah, would you call it something else when you're talking about running like the contact between your shoes in the ground? Ground contact time, ground contact time. Okay,

Dr Will O'Connor 04:30

it's it's one of those terms, that probably covers like three different things, you know, because it can be specific to the shoe. So if you had a really heavy trainer, it would absorb a lot with not a lot of recoil. So to increase ground contact time, then But then if you had that, like no shoes on this, essentially Nothing absorbing, you know, there's no cushion underneath absorbing any of your forces. But you were running in mud, you'd have a really long ground contact time.

Dr Matt Miller 05:10

Interesting that is slightly different than this. I'm thinking you're running with trail running shoes on the track

Dr Will O'Connor 05:19

come, that's another thing. So that would be the third one. Right? So you kind of have three different points.

Dr Matt Miller 05:28

Of all related, I'm going to actually write that down three things related to one metric. Okay, hold on, I'm making a note three things.

Dr Will O'Connor 05:35

But you I mean, rolling resistance can be your tire or the it's the same, right? Because you can have, you can have the pressure, like the air pressure, and the tire, because you had flat tires. Or you could have the tire itself. Or you could have the ground the tires rolling on. Yeah, it's the same thing, right?

Dr Matt Miller 06:02

ground contact time is a little bit different. That's probably actually as closely related to braking, which is the fourth trail nemesis. It wouldn't be you it's the

Dr Will O'Connor 06:13

biggest the big difference, right? As you as a cyclist, you have continuous contact with the ground. Yeah, runners barely contact the ground. I mean, the difference what differentiates running from walking is flight. Is the point at which there is no, there's no contact with the ground. Yeah. Because of your race walking, you leave the ground you are now you get a red flag, or I

Dr Matt Miller 06:41

can be classified like lumbering. That's what I'd say. And I'm lumbering around the forest, or I'm in contact with the ground. But I look like my body. It looks like it's running. Now, actually, I'm getting better. I'm getting better at running. I've been running every week.

Dr Will O'Connor 06:57

It's like everyone at the end of an ultra. I'm running. Like, well, I can see both your feet on the ground. Like you're doing the motion of running. But what you're doing is walking. Yeah.

Dr Matt Miller 07:10

It wouldn't at that point. I think it's like, it's like, do I walk or do I run? And like either one hurts?

Dr Will O'Connor 07:17

Yeah. How do you just do what you do to move forward?

Dr Matt Miller 07:21

Yeah, just just get there. Okay, so we got rolling resistance, which maybe not totally like. Okay, well, we'll have to cover that another time. But then we also have braking. Okay, so obviously, I love talking about braking. Actually love talking about all these things. I wouldn't consider myself an expert on rolling resistance over aerodynamic drag, just because I think they're so tiny, which is going to be kind of a theme here when we're talking about these four trail MCs. So gravity, aerodynamics, rolling resistance and braking, the four things slowing you down. And when I think about these, I'm thinking about them in a loop, right. So you, you leave, let's say on a bike or on when you're running, you leave the car or your house, you go and you go up the hill, and you go down a hill, and you come back. And you might do that multiple times. Or you might do that only one time. And you might go all different places. But these four trail nemeses are all slowing you down at different points along that loop. And sometimes it's a trade off by where if you improve one, you're making the other worse. And some you can't fix at all. Some you can maybe throw money at the problem and make it a little bit better. You know, like a weight weenie or something, you just buy something a little bit lighter, but then that's a trade off for something else. And then others are like something is something that you're actually doing, and you're in control of it. And you can actually fix it.

Dr Will O'Connor 08:49

So okay, so I'm Yeah, standing on the start line or getting ready to my my training

Dr Matt Miller 08:57

in the car and you're about to like hit Go on your gun. Yeah,

Dr Will O'Connor 09:00

got an hour. And I'm going in back of the car. And what's what's happening? Like, what? Why am I sliding down?

Dr Matt Miller 09:11

Well, I'll tell you why you're not moving. Well, firstly, I guess it's inertia. But gravity. Gravity is probably the biggest one. You know, gravity is acting on us all the time. It's what's keeping you you glued to the ground? Yeah. When you're at the end of an ultra lumbering and he's not right, either. Yeah. So the whole what you have to do is you have to fight gravity.

Dr Will O'Connor 09:38

Okay, right. Yep.

Dr Matt Miller 09:41

Gravity is number one. And actually like this is, is a huge force that we have to overcome to maybe get up a hill. Right. And we know that if we've ever, like, left the car and gone up a hill, like it's hard work yet so you could push harder. that'll get you out faster. But the kind of the work that you have to do is related to the size of the hill and how heavy you are.

Dr Will O'Connor 10:09

So if gravity is a constant as at 9.81 meters per second squared, yes. Why is it harder to go up a hill has the same gravity?

Dr Matt Miller 10:22

Why is it harder to go up a hill? Wow, that's like, such a basic question. But yeah, right. Okay. Because like to, to overcome to, uh, to get up the hill, we have to produce work with our muscles. Yeah, right. So that's measured in joules. Now, we can calculate how much work it takes to go up a hill, based on how, how much vert we're gaining, and how much we weigh. Right. So that's a set amount of work. Yeah. So if you weigh 100 kgs, and you're going up 100 meter Hill. Yeah. Okay. Now we're actually starting to talk about bigger numbers, but it's gonna take a lot of a lot of work. A lot of jewels to get you there. So you do. Dana J. Yeah. 100 meters times 100 kgs. times 9.81. Okay. Yeah, there's a lot. Like that's a lot of work. Obviously, like, you can do that really slowly. Right. So if you go up a hill slowly, it's not that hard. Right. Like if you walk up a hill, yeah,

Dr Will O'Connor 11:30

sure. I mean, it's all relative. But for the sake of we got a good amount of fitness. It's, it's fine. Yeah, it's it's not that hard. Like, the staff is themed. Yep.

Dr Matt Miller 11:42

Yeah, I mean, now we're starting to talk about fatigue, which obviously slows you down. I didn't put that in there as one of the four trail nemesis. So maybe that's number five. But it is like related a little bit differently.

Dr Will O'Connor 11:53

So you're not really you're not talking about physiological components. He talking about external forces? That's right. Yeah.

Dr Matt Miller 12:00

Yeah. So you got the hill, and it's a certain amount of work to go up the hill. So it doesn't matter. Like if you go fast, or you go slow. The the work required to get up this hill is set. Yeah. So that's the mass times gravity times the height. Okay. So it doesn't feel hard until you start to go faster. Right, so you have that set amount of work, and you decrease the time, which means your power goes up, because powers work divided by time. So our muscles kind of, you know, they get tired when we have to do a lot of work really quickly. You talked about that one, we talked about running to the donut shop. Remember that one? Yeah. I can't remember if I got the donut or you got the donut. But maybe we both got the donut.

Dr Will O'Connor 12:47

It was as dependent on Yeah. A lot of things anyway. So. So what you're saying is, it's not actually harder, you're not doing more work is just generally that you're trying to do the work faster. Yeah. And there is a minimum speed at which you need otherwise you just fall off your bike? The Yeah, well, I know it's still hard at because I can do 100 meters on the flat. easy

Dr Matt Miller 13:21

that you can, but I have athletes tell me this all the time, they say I get to a hill and I can't stay under 200 watts. Like you can. And I know you can because if you've ever tried to go up a hill totally blown. You're going at less than 200. You know, that's your your endurance pace. Like if you're totally blown. And you can't like get even close to your threshold. You're going at 200 watts.

Dr Will O'Connor 13:48

You got like usually rpm and the like, yeah, yeah,

Dr Matt Miller 13:52

I tried it the other day. I was like, totally blown from doing these hills as like, I was having a hard time staying under 200 Watts, right. And I've been getting this zone creep where my zone keeps like, suddenly my zone two becomes on three. That's yeah, a thing that we say you shouldn't do. I'm doing that. And like, wow, it actually I don't think I can stay under 200 watts here. And when I was tired I sure could. Right. So I was like yeah, okay, forget it, Matt. But yeah, so. But gravity is what causes that, like, you can ride at 100 watts on the flat, but gravity isn't really a huge factor that you have to overcome.

Dr Will O'Connor 14:35

You have to know especially not on a bike because you're being held up.

Dr Matt Miller 14:39

Yeah, like you runners would have to overcome gravity on flat like Yeah,

Dr Will O'Connor 14:45

yeah, so like it's, you can hold a constant pace when you start a hill or effort I should say quite easily, especially if you're running to heart rate or power because You're already fighting gravity every time you lift off the ground, and then now, you're still fighting gravity. But you're just you're striving shortens, and you're just not traveling as high. But if you want to maintain pace, I think part of it is you must be accelerating against a downward accelerating force. Right. So now now you're getting a multiple, it must be to the, to the quad.

Dr Matt Miller 15:27

I'm not sure. Actually, I guess what I'm thinking though, is like when you're doing that, like a one way to make it easier is to be lighter. Right, since, like the, the work required overcome, well, we can calculate what the work that we would need to do mass times gravity times height, so we can't reduce gravity. And the height might be set. So that's when you're running. Like you're raising your center of mass, certain height, or you're going up a hill that is a certain height, but you can change mass, right. And that's by being lighter. So then you have to produce less power to go the same speed, because you don't have to do as much work. Yeah. Right. So when I'm thinking about these trail, nemeses, I'm thinking about weight weenies that are trying to make things as light as possible. Yeah,

Dr Will O'Connor 16:15

makes sense. So what that does is one of the variables that is contributing to their absolute number. So yeah,

Dr Matt Miller 16:22

it does make sense. Like so. But we did like this whole episode on bike weight. Like why bike weight doesn't matter? Yang's like that. And it's consequentially borrowed that article. And

Dr Will O'Connor 16:38

not by us.

Dr Matt Miller 16:42

Yeah, so like, you can you can kind of throw money at this problem of having to fight gravity to a certain extent, but then it's like a trade off where like, how, how light Do you want to be like, if you go for a run? And you're like, Yeah, I'm not gonna take water, which I know you did not long ago. And it was really hot. Like, I can run real fast, because suddenly, I don't have to fight gravity as much. Yeah, now I'm thirsty. Right. And same with your bike, you can put on lighter tires, or you could put on super lightweight handlebars that are potentially going to break. Like, well, there's actually not a ton of time that you can gain up this pretty long hill, just by, you know, saving 300 grams or something like that is not a huge deal. So sometimes that trade offs not worth it. So that's mostly what we talked about in that episode. But like, I think the example I gave from Palmach Dr. Paul McDermott's study was you can save one second up to two and a half minute climb by saving 335 grams. So

Dr Will O'Connor 17:42

yeah, I have to pull out some of the articles on running because they, they really done as they, it's hard to really to do it and run him because you can't just add weight to like a bike, you know, which is constant, but they did use sand vests and showed your general running pace economy was maintained for like a few kgs. But this is saying, you know, these these sayings, but it's like one kg of body weight is worth one minute for tea over 10 kg. And so someone I mentioned who, within our department, you say that to me? And I was like, that just doesn't even make sense. Like, otherwise, you know? It just it's just yeah.

Dr Matt Miller 18:30

Right? Like, how much do you weigh economy though, is like how its work per liter of oxygen, right? So if you suddenly have to do more work, because you weigh more, well, you're just going to go slower. It's not going to change how much oxygen you need. So economy, you wouldn't expect to change. But obviously, you'd be going slower. So that's really what you want is to like not go slower.

Dr Will O'Connor 18:57

You want to not go site. So just by losing weight as well doesn't necessarily mean you're like because you can get a greater appreciation of you know, the law league spring, which could increase recoil, like, if two of you know there may be kg either way, and which economy is not affected? Because you can compensate through the return of energy, which is gained, you know, at all like, like, where is where is that? Wait, where have you lost them? Yeah, right. Right. Right. Because it's like, dude, white is very different than, you know, I've got like, no body fat. So if I'm losing it on, I could potentially be losing functional muscle. Right? And that may just be negligible.

Dr Matt Miller 19:49

Yeah, yeah. So like, I guess when I think about weight, I think like, it's obviously super important, but you can't go to extremes, because then something's just Gonna go wrong, whether it's with your body or with your equipment.

Dr Will O'Connor 20:03

Yeah, Shoes Shoes are the same, because you can they sit at the bottom in the pendulum, you know, which is your law alum. So I mean, that's a very different place to have weight then and on your shoulders, say or like a handheld 30 mil bottle of water. But then yeah, what are they? But then you say you just run and be your feet and you get injured.

Dr Matt Miller 20:28

Exactly like that. That's an extreme, that doesn't make sense. Like you wouldn't do it. So, okay, we, we talked about weight, at length. So obviously, it's big, but just be careful. And that's kind of what I'd say is like, it's a huge thing slowing you down, be careful. So then we got this thing, aerodynamic drag, which I'm going to try and fumble my way through.

Dr Will O'Connor 20:52

But it's with gravity, it's constant. As well, like it's true, like, always gonna be there. But it's gonna I have these, these athletes are both doing the same race next weekend. And there's, if you know, Mount Maunganui, there's like the bass track, you know, which is undulating trail. And it's only about two and a half kilometers long. So what's that met like a one and a half miles of he do it twice as part of the half marathon, just like 13 Miles 21 case. So it's, it's like nothing in as like that I was going to be such slow course. I was like, well, you're actually like, you're only going to go slow on the oppose. And the apples are only going to be about a total of 5% of the entire race. And then you have a downhole as well. Right? So in the end, like you have what is it is going to be a slower section and if you're just on the flat pavement but it's not the be all and end all of like, a completely Yeah, throw away race, it is never gonna be news, it never has the potential to be fast. Because your while you have to go slower in terms of its, you know, in terms of PACE speed, because you've got to find the fixer gravity greater when you're traveling towards it. I guess. You give it on return on the down

Dr Matt Miller 22:29

gravity becomes your friend. Yeah. Yeah, it's,

Dr Will O'Connor 22:33

it's constant. So yeah, I think we yeah, we do think about these things as like, Ah, this is a you know, this is big uphill. And for mountain biking, especially. These this big downhill, which has this huge potential to be able to gain considerable amounts of time. If you, you know, took care of the fix of gravity on the way up.

Dr Matt Miller 22:59

Yeah. Yeah. Yeah.

Dr Will O'Connor 23:04

And Dr. Dynamics, yeah. Okay, so should we think about aerodynamics?

Dr Matt Miller 23:08

Um, they probably should, though. Why would they not think about aerodynamics?

Dr Will O'Connor 23:14

I think about this, because these, these are quite a few runners have long hear short distance runners, and hairy legs to German. But in this 2000 Sydney Olympics, Cathy Freeman, had the full body suit.

Dr Matt Miller 23:32

It headachy don't remember it.

Dr Will O'Connor 23:34

She's all men. Now I'm going to test myself with her. She's a 400 or 800 or both things. She went gold in both. And she had like the, like, full ankle to

Dr Matt Miller 23:48

do remember. There were a few people trying that. And they tried the same thing and downhill mountain biking, where, like everyone was rocking lycra, which just looks ridiculous. Like they had skin suits. Yeah, I'm gonna tell they got banned. They got like, because it didn't look cool. Which might be what happened in like track running. Because like, you know, lycra is cool, but if you don't wear lycra regularly, you don't think that looks cool. You're not

Dr Will O'Connor 24:18

a you know that. They're called, you know, gimp suits if you're buying them for a dress up party. Yeah, and that like no one wants to see that. No, like, you can't just you can't wait if it's not. It creates a pretty large shift in trend like tradition to just be seen like running shorts and a singlet vest to like a full on. lycra suit.

Dr Matt Miller 24:53

Well, you know, downhills kind of gone that way, right. So they went from full on lycra, were like obviously there Going at really high speeds or aerodynamics is really important. And they went to like just crazy baggy stuff in the early 2000s. Or, you know, when we wore shorts down to our ankles, and like three sizes too big tops, and there's just flapping in the wind, like that actually is slower.

Dr Will O'Connor 25:16

So because I asked I think I asked you about this a while back, is that why they're wearing such baggy clothes? You said they gotta have like two fingers.

Dr Matt Miller 25:24

Distance Yeah, I'm

Dr Will O'Connor 25:26

not sure like the rule is skin and the clothing Yeah, I I'm not sure actually that would that sounds like a UCI ro.

Dr Matt Miller 25:36

Sock length thing.

Dr Will O'Connor 25:38

Yeah, good cough

Dr Matt Miller 25:41

yeah yeah, I'm not sure what the rules are but like obviously there's this fine line between a nice look cool and we want to go fast. So there's, they're like kind of

Dr Will O'Connor 25:52

a fine line. This shouldn't be this shouldn't be right. Like it should just be we need to go fast. That's the goal.

Dr Matt Miller 25:59

Like yes, well, that's why like you see down there's now tucking in their shirts where they didn't really do that before. They're just like, let's look as cool as possible which means as baggy as possible, probably wearing Dickies. You know, that that's like an era thing. fashion. But now it's like a little bit tighter. Obviou