---
title: 'How Running Completely Changes The Human Body'
source: 'https://youtube.com/watch?v=Q743HRn2_jM'
video_id: 'Q743HRn2_jM'
date: 2026-06-29
duration_sec: 1277
---

# How Running Completely Changes The Human Body

> Source: [How Running Completely Changes The Human Body](https://youtube.com/watch?v=Q743HRn2_jM)

## Summary



## Transcript

Running is cool as hell. Problem is, it
sucks. And everyone says doing too much
of it will kill your gains. But what if
I just sucked it up and ran every single
day for 30 days using MRI to measure
what actually happens to my muscles with
multiple other tests tracking every
change in my body and heart. I hate this
like
>> [laughter]
>> but I'm not just testing my progress in
the lab. At the end of the 30 days, I am
flying to London to compete in a race
against some of the best athletes from
around the world.
>> Great job. Doing well.
>> But first, I need to find out how good
my cardio currently is with a VO2 max
test. The higher you score on this test,
the better your cardio is. The average
gym bro typically lands in the mid 30s
to [music] 40s, whereas elite athletes
can get much higher with Cristiano
Ronaldo rumored to have scored as high
as 75. I'll see how close I get to that,
but I should probably explain why I'm
doing this.
>> You got it. Nice job. Great job.
>> So last month, this small YouTuber named
Brownie asked if I would compete in an
international race against some of the
top athletes and influencers from around
the world where I would represent Team
Canada with fellow Canadian YouTuber
Will Tennyson. And while I do lift
weights regularly, I can't say the same
about my cardio. I actually can't
remember the last time I went for a run
before this test, which means if I don't
want to completely embarrass myself in
front of a live audience of over 400,000
people, I've got a lot of work to do and
just 30 days to do it.
>> Well done.
>> Oh, yeah.
>> Yeah, it's tough.
>> So your VO2 peak was 58.3.
>> It's really good results.
>> So my day one score actually puts me
into the top 2% for my age, which is a
really good sign. And I'll explain later
on why I think my results were so high
despite not actually doing much cardio.
However, when we take a closer look at
the data, we found two serious problems
that I'll need to fix.
>> I heard you talking about me.
>> [laughter]
>> What do you got?
>> your respiratory exchange ratio could
start a little bit lower.
>> Basically, my body has become really bad
at burning fats for energy, but instead
prefers to burn through my carb stores,
which are limited and burn out much
faster.
So, even though I have a big engine, it
can't last very long.
Second, when we tested my blood [music]
20 minutes after, my lactate levels were
off the charts.
>> Pretty high.
>> 10.5
>> It's That's very high. Right after a
treadmill test, your body is still
clearing the lactate that you produced
during the test.
>> Lactate rises during intense activity,
and if your body isn't very good at
clearing it, hydrogen ions build up and
create a painful burning in your
muscles, and in extreme cases can lead
to vomiting, nausea, and even death.
>> But, even though I was able to push
through the burn, that was a 20-minute
test. And if I try that same approach
during the race day, I am just going to
quickly burn out. But, luckily, there is
a type of training that helps my body
handle lactate better and makes it
better at burning fat for fuel. And that
is exactly what I'm going to be doing
today.
>> To address these problems, part of my
training plan is to push myself to
actually slow [music] down and stick to
what's called zone two training. This
means training just hard enough to get
my heart rate up to 60 [music] to 70% of
my max, which for me is between 120 and
140 beats per minute.
>> A good rule of thumb is that you should
be able to hold a conversation without
too much heavy breathing. Now, the
downside of zone two is that you got to
do it for at least 45 to 60 minutes to
get the full benefit. And for me, that
is just painfully boring.
>> However, after just my first day of
running, I realized my body had a few
more weak points than I realized.
>> I just woke up, did my first run
yesterday. Every time I take a step on
my foot, there's like a super sharp pain
right on the outside. Like, it literally
feels like I fractured my bone. The
worst part, the race I'm training for is
called Hyrox. Known as one of the
toughest fitness races out there. You
run 1 km, immediately transition to a
brutal weights or cardio station, and
then go right back to the run and repeat
that a [music] total of eight times.
But, the hardest station is saved for
the very end, 100 wall balls. This is
where some people's legs will literally
stop working. The goal is to complete
the course [music] as fast as possible,
with the best athletes finishing in
under 60 minutes. But, with my foot
injury, I can't even run past 60
seconds. So, I made an emergency trip to
see my physiotherapist, Rajan, for help.
>> Does it hurt here?
>> Oh, yeah.
>> Base of the fifth metatarsal.
>> So, [music]
>> I think you're cooked, bro.
>> Actually?
>> No, no, I don't think you're cooked.
>> Rajan suspects I've been playing one of
the joints or tendons across the bottom
of my foot, which is why I've been
feeling so much pain ever since my first
run. Okay, tell me tell me what's worst
case, best case?
>> Worst case, amputation.
>> [laughter]
>> Best case scenario, it'll probably get
better in a couple weeks with a little
bit of rest.
>> That's best case, couple weeks?
>> Couple weeks. That's That's a pretty
good best case. Then, you got 2 weeks to
push through.
>> So, with my foot injured after literally
my first run, I'm realizing it's not
enough to just be in shape. My joints,
tendons, and even bones had never been
trained for running, and [music] I'm
starting to seriously doubt if my body
is capable of finishing this race, let
alone doing well. Like, I'm feeling
really down right now.
Like, at this point, I'm honestly
considering backing out from the event.
Um
I
Yeah. It's not going the way that I was
expecting it to, and I just don't want
to embarrass myself when it comes to the
time of the event. This moment in time,
I'm like, I'm 50/50 [music]
about continuing. I decided I would give
myself until the end of the week to make
my final decision. But, to make sure I
was still doing what I could with my
cardio, for the first few days, I'm
swapping [music] all my running for
cycling and the assault bike, which are
much easier on my joints, and in my
case, my foot. But, I still had one more
question hanging over my decision. Is
all this cardio going to eat my muscle?
And to test this question with the
highest scientific accuracy possible, on
day one, I got MRI scans of my upper and
lower body and measured the thickness
and cross-sectional area of my muscles.
And in 30 days, I'm getting a follow-up
scan. So, if I lose any muscle on this
plan, the MRI will not only tell me
[music] how much, but where exactly that
muscle loss came from. Now, although I
have no idea what'll actually happen
with my muscles, fortunately for me, a
2021 meta-analysis actually tried
answering this question directly.
[music]
They combined the results from 27
different studies where researchers
looked at whether cardio paired with
strength training negatively impacted
muscle growth. And when they tallied the
results, those who paired cardio with
weights saw essentially the same muscle
growth as those who stuck to weight
training alone. However, this was only
true for beginners. They actually found
a slightly negative effect for trained
individuals, which is not good news for
me. But luckily, the researchers did
find three rules that every lifter
should follow if they want to prevent
muscle loss. Rule one, no cardio before
weights. If it's long or intense, like
my sessions are right now, you can tire
your energy and nervous system, which
can affect your strength when you go to
lift weights. So, for me, cardio goes
after weights or later in the day. Rule
[music] two, refuel properly. So, I'm
already eating enough protein to protect
my muscle, but with all the extra
cardio, I am burning through way more
carbs than usual. It's actually already
making me feel empty in my weights
workouts. So, it's not just about eating
enough calories to stop myself from
losing [music] weight too quickly.
Pretty much all those calories need to
come from quick carbs, like bananas and
rice cakes before my workout, and
complex [music] carbs, like potatoes and
rice, immediately after. And finally,
rule three, protect my leg days. Long
runs are one of the most taxing forms of
cardio on your legs, and I'd feel it the
very next day as if I just did a big leg
workout. And since my legs are honestly
already a weak point, I need them as
fresh as possible when I go to train
with weights. But honestly, I had no
idea how my legs are going to recover
because in order to prepare for Hyrox,
I'll not only be running every day, but
I'll also need to practice the eight
brutal stations. Luckily, my foot is
finally feeling better and my
physiotherapist Rajan has actually
competed in HYROX before. So, today he's
going to show me the ropes.
>> You want to get super low and bring your
head over. So, that way you have more
drive.
>> All my glutes.
>> You're a bodybuilder. You haven't been
an endurance [music] athlete before. So,
you haven't done hybrid training. So, I
think that transition for you is going
to be tough.
>> Is it weird that I get offended that he
calls me a bodybuilder?
>> All I'm saying is I'm going to prove you
wrong bro.
>> Okay. Okay.
>> I do I do a little bit of cardio. I stay
in shape.
>> And while I'm still not training at 100%
[music] just to be safe with my foot, so
far my training with Rajan actually felt
pretty good.
>> I'm used I'm used to this.
I'm not going to lie, it feels great.
>> Feels good?
>> Yeah, dude.
>> That was like only like 10 reps, though.
>> So, my plan is to use two long, easier
cardio sessions a week to build up my
zone two conditioning.
>> Where's
>> Three times a week, I'll be doing more
intense training sessions including
what's called the Norwegian training
method, which has been used to help a
small country of just five and a half
million people produce countless of the
top endurance athletes in the world
[music] with one of them holding the
highest VO2 max score ever recorded. And
one of the protocols I swear by is this.
Using the cardio type of your choice,
push yourself as hard as you can for
minutes. Then, take it easy for three
minutes and you repeat that a total of
four times. It is a brutal 30 minutes,
but it's actually quite similar to how
I've always done cardio. So, even though
I only used to do cardio maybe a couple
times a week, it might explain why my
VO2 max score was still so high on day
one. And after my first day of actual
HYROX training, I've already won over
one of my haters.
>> Honestly, I'm shocked. You did pretty
well.
>> Yeah?
>> I'm really surprised in like one week.
Like, that was crazy.
>> You serious?
>> That was crazy.
>> But, although Rajan's words of
encouragement did make me feel more
hopeful about the final race, that
completely changed. Once I was sent the
full list of people Will and I are
competing against. Dude, I'm cooked.
They just sent me the list of the people
who are going. Do you know the show
Physical 100? They take the fittest
people from every country, they put them
in a race to do a bunch of crazy stuff.
People that won that show, Team Korea,
those are the people that are competing
in the race that [music] I'm at. This is
insane. Fortunately, my foot was good to
go, and I was already back to running
and training pain-free.
Even if I still had a long way to go.
But so far, at least from the eye test,
[music] it looked like I hadn't lost any
muscle. If anything, I'm starting to
look a bit leaner, and my strength
[music] hasn't been negatively affected
at all. And there was even one benefit
to my cardio work that I never expected.
It was tough, but like I feel
incredible. Something about like pushing
yourself with cardio,
it just like gives you a high that
you can't replace with weights. All
right, like I now know what people mean
about the runner's high. Feels
incredible. There's a reason, despite
running sucking so much,
>> [music]
>> that people love to do it. Turns out,
your body releases a compound that acts
on the same brain receptors as cannabis.
[music] But in order to feel that, you
need to train a certain way. So when you
do cardio, especially at moderate to
high intensity, your body gradually
releases a compound called anandamide,
which is often called the bliss
molecule. It attaches to the same
receptors in your brain that respond to
THC, just like cannabis does. And once
you hit about at least 20 to 40 minutes
of cardio, is when enough of these
molecules are released for you to fully
experience the runner's [music] high,
which is chemically actually quite
similar to literally getting high. And
the reason you don't get this quite as
much from lifting weights is because
you're doing short, intense bursts,
>> [music]
>> and then resting. So you never actually
sustain consistent effort for long
enough to feel that effect. And so for
me, this healthy way of getting high
actually became one of the biggest
motivators for my training. If my MRI
scans show I haven't lost any muscle, I
can actually [music] see myself sticking
to running even after the race. But
there was still one thing I was
struggling with.
I always created this [music] pressure
in my head that I always had to just
like over-perform and there would be
moments where I'd have opportunities,
but [music] just the fear of of failure,
you know, not exceeding expectations, it
would be enough for me to just like back
out. And I think that's what's kind of
going on with this event. I don't want
to let that fear of failure [music] and
embarrassment stop me from experiencing
this.
>> I'm being nervous today because today is
going to be the longest, hardest
training session I have done yet. I have
not ran this far, this hard ever yet,
but uh we'll see how I do.
>> So, I've asked my friend Jeff to test my
conditioning. He's actually competed in
HYROX four times, and I want to see how
I'll do running just 80% of the complete
race with Jeff as my partner.
>> We started at 4:30.
>> Jeff's scared that I'm going to go too
hard and crash and burn.
>> For this test, we'll be running 800 m
immediately followed by a station,
starting with a ski erg. Now, my goal
today is to get through the full circuit
in under 1 hour. That's because if the
top athletes are completing HYROX in
around 60 minutes, if I can't do 80% of
a HYROX in the same time, I'm going to
have no shot of performing well on the
final race. Now, this is a duo's race,
and even though each team has to run the
same amount, you are allowed to tag team
the stations. So, Jeff's advice is for
Will and I to play to our strengths.
Will is a strong dude, and he's [music]
probably going to have no problem taking
on more of the sled pulls and pushes,
while I'd probably be stronger [music]
taking more of the burpees, the ski, and
the rower.
>> Come on.
Ooh.
>> We're going to get through this.
>> But as we were closing in on our final
two stations, my body was hitting its
breaking point.
Oh [ __ ]
I might drop.
I'm okay.
>> Jeff's scared that I'm going to go too
hard and crash and burn.
>> But for the final stretch, everything
just became mental, and I knew all I had
to do was to push through the final
circuit.
>> I see
Let's go.
Our final time was 55 minutes and 21
[music] seconds.
I wasn't the whole thing. I had to make
some swaps, but
that was longer and harder than I've
ever pushed. And while I was feeling
[music] hyped about our first practice
run of the course, I was about to get a
call that would change everything. All
right, I have some bad news, guys. I
just heard from Will's team, and
apparently he has a scheduling conflict
and he's not going to be able to make it
to the race. I mean, I'm honestly pretty
frustrated right now, but I totally
understand. It's just that I was [music]
really excited to compete with Will
because I know he's such a strong
competitor, and now I don't even have a
partner. To make matters worse, and
according to the weight scale, I'm down
3 lb. That is not good.
I do not want to be losing weight that
quickly because that is most likely
going to lead to muscle loss if this
rate of weight loss continues. Even
though I've been eating roughly 2,600
calories a day, which is normally enough
to maintain my weight, with all my extra
activity, I was now in a pretty big
deficit. Fortunately, because I was
consistently logging my food and weight
into my Built With Science Plus app, it
sensed I was losing weight too quickly,
and it bumped up my calorie target to
2,800 calories per day. And we actually
designed our app to be able to adjust
your plan and based [music] on how your
body is changing, just like a real coach
would do. It even does the same thing
with your workouts. Every single week,
whether your goal is to get lean, build
muscle, or just start living healthier.
And it's why I've been trusting it every
step of the way in preparation for this
race. And if you want to try it yourself
for 2 weeks [music] completely free, all
you have to do is scan this QR code
right here, or head to
builtwithscience.com. [music]
That said, even though my muscles are
starting to look and feel a little bit
flatter than usual from all my training
and weight loss, something happened in
week three that started to give me hope.
Okay.
I actually managed to set a PR today.
That was a volume PR, so like most reps
I've done
at that weight, which is totally
unexpected
given all the extra cardio that I'm
doing. But how is that possible? Well,
remember how inefficient my body was at
getting rid of lactate back on day one?
Lactate also builds up when you're
strength training with relatively higher
reps. And these evil hydrogen ions come
with [music] it, which is actually what
creates that horrible burning sensation
in your muscles as you push closer to
failure. Cardio, especially
high-intensity cardio, it trains your
muscles to clear all that out. And at
the same time, it trains your cells
[music] to produce more energy, which
can help your muscles work harder,
recover faster between sets, and
ultimately lead to better workouts.
Which might explain why some new studies
are showing that cardio can actually
help rather than hinder muscle gains.
But [music] we'll see what actually ends
up happening after my final MRI scan.
Guys, so I got some really good news. I
just heard back from the organization,
and they are allowing Jeff to be my
teammate for the race, which means Team
Canada is my best friend and I training
at a local [music] gym.
One week out from the competition, I'm
realizing that there isn't much left I
can do to improve my conditioning. So I
need to instead focus a lot more at just
building an actual strategy for the
final race.
>> What's up, dude?
>> Yo. This is Cole Learn, a pro Canadian
HYROX competitor who set multiple
records and completed the race over 20
times.
>> The biggest thing for HYROX is
maintaining your heart rate off of the
start. If your heart rate is too high,
uh your muscles are not going to work
the way they should.
>> While I was burning myself out each
trial run on the rower, Cole's advice
was to actually do the exact opposite.
>> Just think like this is more of like a
recovery station. This is a station
where I'm not going to make up a ton of
time on my competitors, but I could lose
a lot of energy and really skyrocket the
heart rate.
>> Canadians have officially touched down.
We're about to go see Big Ben.
>> As we got into the stadium and saw the
competition from all 16 countries for
the first time in person, my stomach
dropped.
>> I'm not going to lie, the Americans
looked stronger than I thought.
>> Yeah.
>> They're not normal, man.
>> And in addition to [music] team Korea,
team France has arrived with a high
rocks champion on their team.
>> All right, we just got in. It is a
completely empty venue just for us.
This is insane.
>> But as intimidated as I feel right now,
I know that coming to this event today,
I am not the same athlete I was [music]
just 30 days ago. A few days ago, before
catching my flight, I retested my VO2
max.
>> Oh
god, there we go, there we go.
>> Good.
Awesome.
>> Oh,
yeah, you're good. You did great.
>> Oh.
>> Your VO2 peak was 61.32
>> Yes.
>> ml per kg per minute. So, you did great
job. Nice work.
>> You did great.
>> You worked 60. 61 is in the 99th
percentile. You did excellent.
>> What's even more promising is my body's
ability to burn fats rather than just
carbs for energy dramatically improved,
which should help me avoid burning out
halfway through the race. It's
definitely giving me a bit of
confidence.
>> There was one team that Canada has to
beat, it's us.
>> It's It's just us.
>> Oh, it's cuz of the hockey sticks.
>> All right, bro, you said it. The luck of
the Irish.
>> Now as for if I lost any muscle after 30
days of cardio plus weights, based on
the MRI scan of my upper body, there was
no change. The same was true for my
legs. I didn't gain muscle, but I didn't
lose muscle either. As for fat loss,
according to my DEXA scan, my body fat
dropped by 1%, which is pretty
surprising to me considering this is the
most calories I've ever eaten while
being able to lose weight. Now, while I
may may be the most jacked guy here, I
am hoping all my training will be enough
to make it [music] into the top three.
>> You know what? I I love you, dude. I
love your content, but
I have to beat you today.
>> Yeah, okay. You have to. You have to.
Okay. May the best win.
>> And they are off.
>> Coming out of the first lap and seeing
so many racers just take off ahead of
me, I honestly thought like that's it.
We are about to get crushed. I am going
to get completely embarrassed. And it
honestly took everything in me not to
just sprint ahead to catch [music] up.
But I stuck to the plan.
>> We have got some lovely pacing though
from Team Canada there.
>> Team Canada is catching up.
>> And the next after this is going to be
the sled push. This is really the one
where the lactic acid can build up in
[music] your legs.
>> This is just mainly just character.
>> Yeah, this is all mental.
>> And the more I stopped worrying about
where Jeff and I were in the standings,
the better we started doing.
>> Yes, and you can also see the Canadian
team moving into fourth now.
>> How's it going? How's it going, better?
>> South Korea, they are going to be
champions.
>> There they go.
>> So Anglo-French duo of
>> With South Korea locking in first,
France locking in second, there was only
one podium spot left and two countries
trying to win it.
At this point, my lungs and legs are
begging me to stop. But if training for
this race has taught me anything, it's
that when you're scared of failing, when
everything in your mind is telling you
to just quit, keep going.
>> May the best win.
>> It was a no rep, but they've got it
done. And Team Canada goes across the
line.
Jeff
and Charity for Team
Canada.
>> Oh, yeah.
>> a great job. That is a very good job.
[music]
>> Very good.