Why Your FTP Changes Between Flat & Climbs | GCN Does Science

Why Your FTP Changes Between Flat & Climbs | GCN Does Science


– Emma and I looked up why
most riders can produce more power on climbs or on the
flat, but how the same rider can rarely produce the same
power for the same effort on both terrains. – Yeah. One explanation was that
the greater inertia that comes from riding at faster
velocities, i.e. on the flat, changes the way you transfer power from your legs to the pedals. Now the other theory
suggests that the gradient of the road itself changes your
relationship with the bike, specifically the position of your hips in comparison to the bottom bracket. – Two theories, then. But can we test it? (upbeat music) – It’s not gonna be the
glasses that do it actually. But this, this being the Leomo Type-R. Now, they got in touch with
us to ask, to see if we wanted to use this little gadget
to do some science. Now as you know, we need
all the help we can get, so the answer was a resounding yes. Thank you very much. Now, what this is is
firstly, five little wireless sensors that attach to
various parts of your body, and then give you motion
tracking data in real time. Firstly displayed on this
head unit, but then of course, also saved for further analysis later on. – So, it’s kind of like
a supercharged version of something you might find in
a really advanced bike fit, but you can use it at
home, and take it outside into the real world in
all sorts of conditions. – Yeah. So, you could use it if you
need to analyze your position, maybe check out your
time trial bike position, all sorts of stuff, really. But in this case, it’s
gonna allow us to keep a very close eye on our body
position, our technique, whilst riding at VO2 max, so full gas, both on the flat and on climbs, outdoors, in the real world,
but firstly simulated indoors. – Does this mean we’re gonna
get some really cool graphs? – Lots of graphs. – Yes, everyone loves graphs. – But it is gonna hurt first. – Ahh. – So firstly, what’s the protocol? How do we use this to
analyze how we produce power on the climbs or on the flat? We will start with a warmup,
and then ride at 420 watts on the flat for five minutes,
ease off, and then ride 420 watts again for
five minutes on a climb. Outdoors, it’s very simple. We will find a flat road
and we will find a climb. Indoors, how do you simulate gradient? Well, fortunately, it just
got a whole lot easier ’cause Wahoo has very kindly
sent us one of their new KICKR CLIMBs, which does exactly that, right up to gradients of 20%. As you can see, it angles the bike, but it also changes the
resistance at our smart trainer at the back, in this
case it’s a Wahoo KICKR. Now, it could do far more
immersive and exciting things like respond automatically
to what’s going on in Zwift, or respond to a route that we’ve downloaded onto our head unit. But in this case, we literally
need it to angle the bike and then increase the
resistance at the back. And that increased resistance
is gonna effect the inertia because we’ll be using
much, much harder gears when we’re riding on the flat, so, that’s gonna get that
really weighty flywheel turning faster to generate that inertia. (upbeat music) As you can see, Chris has
drawn the short straw, and so is doing his VO2
max intervals first. Why don’t you warm up, mate? Let’s do a quick introduction
to Mio, shall we? So, Mio is a sports
scientist, who works at Leomo, and very kindly came in to help us out. Basically, you do cool
experiments for a living, right? So, in this case, the five
sensors that we’ve got on Chris, can you talk us through what
each one is gonna tell us? So, maybe starting with the sacrum one? – Yep. So, Chris is wearing the
sacrum sensor which measures his sacrum angle as well
as it tracks the motion, the left, right, rocking
motion on the saddle, and it also outputs the rotation motion on the saddle as well. The rotation is about his central axis. And then he has two thigh
sensors, the left and the right, which measures the range of
motion, minimum and maximum, of how far the thighs travel up and down. And then he has left
and right foot sensors, which it’s tracking the
movement in the sagittal plane of the foot itself. So, how much heel’s
dropping, his foot drop. – Okay, and so, as an
overall picture then. Do you think that we might
tell a difference as the bike is inclined, and then also the resistance on the flywheel changes? – Yeah, so the incline
difference whether he’s doing the flat or a simulated climbing, that may show up on his pelvic rocking and pelvic rotation. I’ve seen that case before. And with the resistance on the flywheel, if the inertia is significantly different, then that might translate
to Chris pedaling slightly different. And that would show up
as a motion indicator on his foot sensors. – Okay, so fingers crossed then. If there is a difference
between climbing and riding on the flat, then the foot sensors should pick up different
pedaling technique, and then the sensor on his
sacrum could well show up, again in different pedaling
technique, but from the top as opposed to the bottom. All right. Okay mate, you probably
better find that 420 watts and give it some beans. (upbeat music) All right, Chris, are you ready, mate? – I am as ready as I’m ever gonna be. – Five minutes at 120% of FTP. – Yeah, which I recently
found out means 350 in Dawson. – Is that all? – Yeah, so. – Okay, mate, all right. Right, I’m gonna press
the select button on here, and then I’m gonna go on my phone as well. You ready? – I’m ready. – Okay, three, two, one, go for it, mate. (upbeat music) What a legend, come on mate. Good effort dude, good effort. Ready, there he goes. (upbeat music) Right then, Chris, you
should recover by now. I have. – I’m getting there. – Okay, good stuff. Right, I’m gonna increase the tilt then. So, one, two. – Going up. – Three, four, five, six, seven. – Oh, I’m slowing down. I’m changing gear. – There we go, right. So, 8% gradient simulated. (bike chain clicks) You ready? – I feel heavier than I did a minute ago. – Good stuff, mate. Okay. Read me the lap. – Yep. – Okay, three, two, one, go. (upbeat music) – That was nowhere near as
comfortable as the first one. It just felt like an
uphill struggle, literally. (heavy breathing) – Well done, mate. That was two cracking efforts there. And the best thing is, that’s all the data we need apparently,
before now going outside. – Not quite. It’s sorta my data. Your bike’s in the next room. So, go and get your shorts on. (upbeat music) – All right, then Chris, let’s do this. Lower percent, five minutes. What was yours, 420? – 431 actually, Si, in the end. – All right. Ready. Okie doke. (upbeat music) (heavy breathing) – Three, two, one, stop. Good work, Si. That looked enjoyable. (heavy breathing) – Love it. (laughing) (upbeat music) – So, now that Si’s done his
five minutes on the flat, he’s convinced he can do a little bit more whilst going uphill at 8%. So, we’re gonna crank it up. – All right. – Get ready for another
five minutes at 120% of FTP. – Okay, one, two, three, four, five. – The suspense. – Six, seven. – Three, two, one, go. (upbeat music) Three, two, one, good work, Si. All right, well that’s
test number two done. Si’s gonna spin and catch his
breath, and then we’re gonna go over to the other side of the room and check out the results. (upbeat music) – Well Chris, we have a lot of
data to go through, don’t we? Two sets, of course, yours and mine, and for both indoors and outdoors as well. – Yeah, and a few things
jumped at us straightaway. Particularly Mio, who could
barely contain herself with the excitement when
she saw Si’s frankly, well, unorthodox pedaling. – Yeah, it turns out, that my
pedaling technique is bizarre, very asymmetric, not in
terms of power output, which left and right
balance was still 50/50. But it basically seems that
my left leg and my right leg do completely different things. So, actually we’ve got
three data sets, haven’t we? We’ve got Chris’, and then
we’ve got my left side, and my right side. – Yeah, and not only Si’s
left and right legs were doing different things, Si and I also differed quite significantly. – Yeah, so after all of
that, can we actually answer our initial question? Does power output vary because
of inertia or gradient? – Well Si, we’ve got to look closely. – We do. Firstly, at foot angular range. So, how much you move your ankles. Now, for both Chris and I, there
was a measurable difference in this, specifically, when
you look at us climbing, there was less range of motion in our ankles compared to the flat. So, it suggests, at the most basic level, that there is some kind
of difference in how we’re transferring power to the pedals between flat and climbing. – Well, that is a fairly
basic observation. – Thanks. – And to which Mio suggests
we look even closer to the data at the
individual pedal strokes. And at that level, you can
see that there is a difference in the initiating of the push down phase of the pedal stroke. – That’s right. So, when climbing, you can
see that that power transfer phase starts to happen at
about the one o’clock position. However, on flat riding,
you’ll see that that power transfer phase happens even earlier, even before potentially
the 12 o’clock position. – There’s also a difference
in the distribution of the dead spot score,
which hits at a different leg movement throughout the pedaling cycle. The greater disturbances,
in this case, were happening around and after the
bottom of the pedal stroke. – Yeah, with thigh movement,
which you can pick up on these graphs, there’s
little wavy motions on the orange and the yellow lines. Now, those were consistent
between indoors and outdoors, but there were a few very
interesting discrepancies between riding indoors and outdoors. Away from our original
question, if you permit us, a slight tangent just for a minute. – Pelvic rotation actually
decreased when outside, primarily because the
bike was no longer mounted to a rigid, well, turbo trainer. However, pelvic rock, so
the fore and aft movement, that did actually increase. – Yeah, there we go. The first one, you can
kind of understand because as you say the bike’s not
being held underneath you, but the second one,
that’s just kind of weird. Anyway, back to our
original question, although sticking with pelvises
just for one moment. One thing that was consistent
between indoors and outdoors, but that varied between
flat and climbing was the pelvic angle. So, when riding on the flat,
there was a lower pelvic angle, i.e. your pelvis
was closer to horizontal than when climbing. Now, you would think, wouldn’t
you, that if you angle the bike, then the pelvic
angle also increases. But remember, an 8% gradient
actually only equates to an angle of about four
degrees, which was admittedly the exact same difference
in myself, but less than the seven degrees that
we measured on Chris. Although potentially, that’s
just due to you trying to get more arrow on
the flat and therefore having a rotating pelvis compared to a different climbing position. – Yeah, that would make good
sense because naturally, when you’re going fast
on the flat, you do try and tuck out of the wind a bit. – Yeah, and naturally
on an indoor trainer, when going fast, you still get arrow. – Yeah. So, what does it all mean? Well, we can see that as
the gradient increases, the way we ride a bike changes. But gradient alone is not
the reason because we know the gradient increase was only
equatable to four degrees. – That’s right. And one of the most
significant differences, the power delivery initiation, was between one o’clock and 12 o’clock,
and that of course, equates to 30 degrees. When you combine that with
the change in the dead spot scores, it suggests, to us
at least, you’ll hopefully let us know in the comments
section what you think, that the changes were not due to gradient, but something else. – Something else, something like inertia? – Something like inertia. Chris, I think we just did science. (high five) – Yes. – Boom. Yes. – Feels good doing science, Si. – Yeah. We should do more science. – Do I get a badge for doing science? – You can wear the glasses, right. – Oh. – We would just like to
say, genuinely big thank you to Leomo for their help for this. Hopefully, we’ll be able to use this to do some more science in the near future. Now, if you would like to see that video where we mentioned earlier
about Chris and Emma going through the existing studies and the existing literature into this, then please make sure
you check that one out. – And give us a big
thumbs up before you do.