so how it's possible that some athletes are swearing
that it makes them recover faster and make them
makes them better athletes yeah so there is a
bit of a difference in the context so for example
cold kind of like an analgesic effect so it can
reduce pain so and because of that it also has
quite a strong placebo effect probably. So if
you look at, for example, next day performance,
quite often you can see indeed sometimes a bit
of a better performance, but that increase in
performance doesn't really seem to be very different
than just normal placebo effect. So it's a bit
difficult to really say whether it's really the
cooling that has any beneficial effects on, let's
say, next day performance or... It's just because
they think they will have better performance.
You go into the ice bath and you think, okay,
this will help my recovery and tomorrow I can
deliver better, I can perform better. Yeah, it's
difficult to really say that. Hi Milan, it's
my pleasure to have you on Evidence Strong Show.
If you could briefly introduce yourself. Thank
you. Thanks for having me. So my name is Milan
Metz. I'm a PhD researcher at Maastricht University
at the M3 Research Group, Muscle Metabolism Maastricht.
Let's say the main focus of my research is the
muscle microvasculature, so like the smallest
blood vessels in the muscle, and specifically
how they, or like their role in muscle adaptation.
or muscle recovery. A big part of my PhD work
is also actually focused on the elderly, so age
-related muscle loss. But I had the opportunity
to do a little bit of a sidestep, side project
to look at the cold water immersion and more
muscle recovery in young, active people. So that
was actually quite a nice... Kind of like a side
project. Excellent. Very grateful for side projects
of M3 group. We're talking cool water immersion
and recovery from exercise. So let's go through
some kind of definitions so we are on the same
page. So what cold water immersion is? Yeah,
so for us, it really just means that you are
submerging into very cold water. And in this
case, we used eight degrees, which is definitely...
Very, very cold. So to do that, we also had like
a big, big ton full of water. And you just have
to like dump like five big buckets of ice in
to get to the eight degrees. So it's definitely
cold. Let's start with what was the aim of the
study? Because cold water is one and recovery.
But like, how were you thinking what you were
the most interested in? Yeah, I mean, one of
the main reasons to do research in this topic
is still because it's very, very popular. and
a lot of people are still doing it. And there's
still, yeah, this idea that it can improve muscle
recovery. But yeah, more and more work is now
showing kind of the opposite effect, that it
could maybe be bad for recovery. And that's also
what my colleague Kas Fuchs shown, that if you
put one leg into the cold water immersion, so
ice water, compared to just thermal neutral water,
you see a reduction in muscle protein synthesis.
And this is the essentially kind of like... an
underlying process that helps muscles to adapt
to exercise. So it's also one of the main, let's
say, mechanisms behind muscle growth. So we think
that's an important part of muscle recovery.
Could you explain a little bit more about the
hypothesis, how you think the adaptation and
recovery works on the muscle level? Yeah. So
you mean specifically with cold motor immersion
or just in general? Maybe let's start in general.
It's probably good to realize that our muscles
are not static. And what I mean by that is that
they're basically constantly turning over. So
all the building blocks of your muscle, so the
muscle proteins, they're essentially... every
day at every moment they are breaking down and
building back up and because it's doing that
if you stimulate muscles for example with exercise
or with nutrition it responds by building more
than it's breaking down so then because of the
balance the balance would then be positive then
you can build muscle over time and that is what
we think is just like an important concept from
muscle adaptation also for example if you want
to grow muscles or get stronger, you would like
to be in a positive balance. So you want the
synthesis to be larger than. the breakdown that's
kind of the idea of muscle protein synthesis
and then yeah we have already shown a couple
years back that cold water immersion can reduce
muscle protein synthesis and that actually also
aligns quite well with some work from from other
people showing that if you do cold water immersion
frequently during let's say i think they did
a 10 week 12 week resistance training program
you also see less gains in muscle mass and muscle
strength So yeah, it does definitely seem that
cold water immersion can have some kind of negative
impact on recovery and adaptation. And from the
study that my colleague did, we weren't really
sure what was the main mechanism behind it. So
we saw a reduction in muscle protein synthesis.
but we weren't really too sure about what was
really causing the effect. So that's why we came
up with this follow -up study. And it's actually
kind of a coincidence because for another project
that I've been doing at the start of my PhD,
we introduced a new method in our lab. And it's
a method with using ultrasounds. Using that method,
you can assess blood flow in the microvasculature.
So in the very, very smallest muscle vessels
of the muscle. So we now had this method and
then we... thought wow that's that would be perfect
to use in in this cold water immersion protocol
because yeah we do think that it probably has
to be related to to some kind of reduction in
blood flow just because yeah in the cold you
have you have vasoconstriction so blood vessels
they they go well they tighten up basically.
So this would then be kind of like a really nice
technique to really investigate like blood flow
within the muscle. And then again, how that relates
to recovery. And in this case, we wanted to look
at how, let's say the amino acids from a drink.
So that's basically just the building blocks
from protein. How they ended up in the muscle.
We just gave him a drink and it had also, we
call it a tracer. So it's kind of like a special
amino acid. So building block of muscle protein.
And then just after a couple hours, we take a
piece of muscle tissue out of the leg. And then
we can measure how much of that drink actually
ended up in the muscle. Okay, so we have your
goal of the study. You want to be sure. So you
asked people to drink a tracer. protein so traced
drink with traced amino acids so the building
blocks for the muscle as the to exercise yeah
So we did... Rest is first, then exercise? No,
we first did the exercise because we also wanted
to see just the effect of the exercise on blood
flow. Okay. So that's why we first started with
just... We did all the measurements from blood
flow with the ultrasound when they were just
resting in the bed. Then we did the exercise,
which was leg press and leg extension. And then
four sets of 8 to 10 reps with 80 % Bono Ram.
It was pretty heavy. And right after, we would
again measure all the blood flow measurements
just to see the increase in blood flow. And then
we would do the cold water immersion and then
again measure blood flow to see specifically
the effect of the cold water immersion. And then
they would have the drink and then they would
just lay in bed for another four hours. And then
at the end of the four hours, we would take like
the little piece of muscle and then... like from
both legs and then see if there were differences.
I love this design. Thank you. Awesome. So the
last piece of information we need is who were
the participants? Yeah, so I did actually similar
participants as Gus did, just to also make sure
that, yeah, we would again see a similar effect,
but then we could combine it with all the measurements
from blood flow. So it was basically just young
male adults that were active. So they were definitely
exercising a couple of times. I believe the average
was exercising four times per week and doing
all kinds of sports, but they were not doing
resistance training on a very structured regular
basis. So it was more like we had a lot of team
sport athletes. So people playing football or
something. And then they were familiar with going
to the gym maybe once in a while, but they weren't
really following a really structured three times
per week or even more resistance training program.
So did you test what the one repetition maximum
was? Did you test them? Yeah. Okay. Yeah. Yeah.
So that was at the very first time that someone
comes into the lab, we do a screening session.
So in that screening session, you also... have
like a medical questionnaire to see whether they're
really fit or fit enough to participate in the
study. And there's no maybe medical issues or
medical issues that maybe could influence your
results. And then also part of that screening
session was to test the 1RM on the leg press
and leg extension. And then we could use that
during the actual test day. I should think a
little bit more about the muscle samples for
people who are not familiar. How does that look
like? Yeah. It sounds quite, how do you say it?
It sounds a bit scary maybe, but it's not as
bad as it sounds. And I can speak from experience
because I've had 10 taken out of my legs. So
I have some experience with having muscle biopsies
taken from my leg. But so how the procedure works
is that it is performed by a medical doctor and
they put anesthetic. In the skin and in the muscle.
And that's usually the most. Let's say annoying
part. Because yeah putting an anesthetic in.
That can be painful. Just for maybe like a couple
seconds. Kind of like a sharp pain. But quite
quickly that goes away. Because then everything
is just numb. So actually the whole procedure.
Of then with the scalpel. Making a small incision.
Just a centimeter. And then putting like a hollow
needle in. And we're basically. Yeah, sucking
a little bit of muscle tissue into the needle
and then cutting it off. All of that you don't
really feel, actually, just because of the anesthetic.
So, yeah, actually, most people who participate
in our studies, after having the muscle biopsy
taken, they're like, oh, that actually wasn't
too bad. I expected worse. But then that piece
of muscle we can then freeze and later do all
kinds of analyses on. So these heroes, Gabe,
how many did you have? How many participants?
Twelve. 12 male heroes agreed to the horrendous
protocol of doing it first, then freezing of
one of their legs and then lying flat for four
hours for you to punch them with the needle in
the thigh and take the samples. Was it vastus
lateralis? Yes. Also because that's just the
safest muscle to take biopsies from because it's
on the outside of the upper leg. There's like
no major arteries or major nerves close to it.
So that's actually the main reason also why we
usually take the vastus lateralis muscle. Excellent.
So after all that ordeal, you had the samples,
you processed them. And then let's talk about
the outcome measures. So what you were comparing
and what you were measuring and then comparing
in the study. Yeah. Yeah. So maybe one thing
we didn't really cover yet, what I think is also
really, really cool. of the study is the the
way how we measured blood flow because usually
when people measure blood flow it's often in
just the big artery of the leg for example so
in the artery you can just measure how many milliliters
per minute of blood is is flowing through it
and it's also quite easy to measure so it's being
done quite often but the artery basically supplies
not only the muscle but also all the other tissues
like the skin connect tissue, bone, also, of
course, the whole lower leg and everything. So
we wanted to go one step further and measure
the muscle itself. And even a little bit further
than that, we only wanted to measure the very
smallest blood vessels in the muscle, so the
microvasculature. And the only problem then is
that you cannot just pick up an ultrasound and
measure it because the signal of the blood flowing
through the micro... microvasculature is so low
that essentially you just cannot measure it without
a contrast. So that's why we had to infuse a
contrast basically directly into their circulation,
so in a vein. And this contrast, it sounds maybe
a bit weird, but this contrast was very, very
tiny micro bubbles, so kind of like very tiny
gas bubbles. They were so small, they are approximately
the same size as a red blood cell. So we infused
them. directly into the circulation. So then
they basically just go around the whole body.
Because they are so small, they also go through
all the tiny blood vessels. And because it's
essentially a gas bubble, it reacts to the ultrasound
waves, so the ultrasound signal, and it basically
enhances it. So we can actually see the blood
flow through the microvasculature. Well, now
I have questions. Wait, wait, wait. What kind
of gas did you use? There's a company, Braco,
who makes these micro bubbles. And it has already
been used also in just at cardiology departments
to really visualize certain areas of the heart,
for example, if they think there's some kind
of damage. So that's basically just like a prepackaged
vial with the micro bubbles in it that we would
get. And then over the time of six minutes, we
would then infuse it. So very slowly into the
circulation. And then in the circulation, it
goes around. So during those six minutes, then
we can do like all the measurements that we wanted
to do. You injected it to the, was it thigh vein
or how did you? Yeah, no, just here in the elbow.
Hey, come on. And then you inject it and in six
minutes it's everywhere. The bubbles are everywhere.
Oh, yeah, yeah, yeah. For sure. I think so. It
also kind of depends on the heart rate, of course.
So after the exercise, I would say within one
minute. you could already see the bubbles appearing
in the leg. But I think in rest, it takes a bit
longer because you do want to have like a steady
state from the micro bubbles in the circulation.
So we use, in rest, we wait three minutes. So
three minutes before we actually start the measurements.
And how much time do you have until the, are
they cleared? Are we, how did they get? Yeah,
that's also quite interesting. So because they
are just gas bubbles, you breathe them out. So
when, after the six minutes, We stopped the infusion
and then actually already after 10 minutes, there's
like barely any bubbles left in the system because
every time they pass the lungs, you just breathe
them out. Can you, can you smell that? No, no,
no, you can't smell it. No, that would be funny.
Like, ooh. Yeah. But I think also the, another
cool aspect from this study and this measurement
was that we had two of the ultrasound machines,
so we could measure it in both legs at exactly
the same time. then we could just infuse the
micro bubbles and then at exactly the same time
we could see how many of those bubbles were passing
through both legs so you did that you did exercise
then you did the cooling protocol did you check
again how the so did you inject them twice no
we we injected them five times yeah tell me so
we did it at rest at the beginning after exercise
after the the cooling and then two more times
during the recovery so what was actually also
cool is so we did some pilot testing and with
the with the pilot testing so before we would
actually we were doing the study we did some
we already did it with the two machines and we
had a person with one leg having the the ice
bath and then afterwards you could already see
on the screen well while we were doing the measurements
that there was like oh Almost no of the bubbles.
in the cooled leg versus the control leg. So
already at that point, we were like, wow, okay,
there seems to be something going on here. And
I think we can also see that, of course, now
when we did all the 12 participants, you can
see like a 60 to 70 % reduction in the blood
flow in the muscle after the cooling, which I
think is a really large effect. Wow. The main
finding is that after cool... cooling the leg
that was cooled had reduced blood flow through
capillaries to this leg. in mind is it possible
yes or no and why that this would actually elicit
bigger adaptation later because it would be more
stressful on the leg after so exercise is one
stress what should happen is the stress then
there is a recovery so kind of dipping with exercise
and then we hope for super compensations would
cooling be adding a stress so you drop exercise
then you drop lower and then you're building
maybe this Yeah, so that is actually also something
that someone once told me. That they thought
that maybe cooling would reduce blood flow. But
then only for a little bit or for a short period
of time. And then it would like shoot up. But
that's actually not what we saw at all. Because
after the cooling, it went straight down. And
then one hour after, it was still down. And then
even three hours after, it was still. like a
little bit down. So it looks like it just reduces.
And then while the muscle is basically just heating
up again, it also, you see the blood flow kind
of returning back to baseline. We don't, of course,
know what happens after the three hours, four
hours, but I would be surprised if somehow it
shoots up. It seems to be mostly related to just
the reduction in the muscle temperature. That's
what I think at least. All right. 60, 70%. That's
shocking. So how it's possible that some athletes
are swearing that it makes them recover faster
and makes them better athletes? Yeah, so there
is a bit of a difference in the context. So,
for example, cold kind of like an analgesic effect,
so it can reduce pain. So and because of that,
it also has quite a strong placebo effect, probably.
So if you look at, for example, next day performance,
quite often you can see indeed sometimes. a bit
of a better performance but that increase in
performance doesn't really seems to be very different
than just normal placebo effect so it's a bit
difficult to really say whether it's really the
the cooling that has any beneficial effects on
let's say next day performance or it's just because
they think they will have better performance
they you go into the into the ice bath and you
think okay this will help my recovery and tomorrow
i can deliver or better, I can perform better.
Yeah, it's difficult to really say that. Any
other, so you observed the less bubbles in the
cooled leg up to four hours after, still less
bubbles. So with the exercised leg, the blood
flow increased after exercise, I assume, then
the cooled leg would have the drop in the bubbles,
how the non -cooled leg would behave. That's
also one thing that we were really... happy with.
We were measuring, of course, blood flow in both
legs at rest and after exercise without any intervention
yet. And those values actually were pretty much
identical, which is of course what you would
hope, but you never know. So in both legs, you
saw a very large increase in blood flow and it
was like exactly the same. for uh for each leg
and then after the cooling you saw that the control
leg was still a bit elevated compared to rest
so of course it goes down after exercise but
it was still slightly elevated and the cold leg
was already actually uh i believe below resting
values there was quite a quite a substantial
drop did it happen for everyone or there were
some cases that that we had differently yeah
that's uh that's also a different point or an
interesting point There were, I think, 2 out
of 12. that didn't really show much of an effect.
So I would say 10 clearly showed an effect and
then two, like not really. Of course, you always
have some variation in your measurement. So that's
why we, of course, test groups and not only one
person. So you cannot really say too much about
it. But still, what was also interesting is that
those two people, if you looked at the incorporation
of the amino acid tracer into the... muscle also
in their muscle you couldn't really see a large
difference and in those other 10 you could so
It definitely seems that there's quite a good
relationship between the changes in blood flow
and then because of that, also how nutrients
from the diet actually get into the muscle. And
of course, it makes sense if you say it, but
it's still good to actually see that back in
the data, especially with actually a relatively
small sample size. All right, so let's go there.
So we covered to rest, exercise. checking the
the blood flow after cooling and then we didn't
even talk too much about how the traces traveled
through the body and what have you found there
um could you move us through that yeah yeah so
that was so right after the cooling we had the
uh the drink which was essentially just a recovery
drink. So it was basically a protein shake that
also had some carbohydrates in it. But then we
also added the, let's say, the special amino
acid. So we call it the amino acid tracer. So
it basically behaves like a normal amino acid,
but we can find it back in the body. So they
drank. the drink and then you can also see that
the the amino acid tracer was like clearly went
into the circulation because we took quite some
blood samples and then also throughout the the
whole recovery phase you could see that this
tracer was essentially just going through the
circulation And then because at the very end
of the day, we took the muscle biopsy from both
legs, then we could see that in the cooled leg,
there was 30 % less of the tracer built into
the muscle compared to the control leg. Wow.
So how do you see the tracer? Is it glowing?
No, no. It's actually, it's basically just a...
The carbon atoms. So you have an amino acid.
It has basically like a whole structure made
of carbon atoms. And maybe if people remember
from back in the day, like chemistry, you would
have like all the C's, right? And you have like
H's and CO, whatever, like a whole structure
of a molecule. The amino acid tracer is essentially
just exactly the same as a normal amino acid,
but just the carbon atoms, so the Cs, they are
slightly heavier. So they have an additional
neutron. So basically it's not 12 carbon, but
it's 13 carbon. So technically it's slightly
heavier, but it still just acts normally like
a normal amino acid. But because it has those
heavier carbon atoms, we can... detect those
using all kinds of machines like very technical
machines and we can then see how much of that
yeah of the tracer is then back or then in this
case in the muscle or in the blood so you have
like the spike for c12 here and for 13 it will
be just slightly off yeah exactly yeah yeah all
right wow all right so that like there is no
no guessing here it's you saw it it's it's for
sure so you found two things one was blood supply
was very different, 60 -70 % difference of blood
supply between the cold leg and the hormone -neutral
leg, and 30 % difference in the special amino
acids bound into the muscle after you provided
the tracer. Yeah, exactly, yeah. And then also
one of the things that we saw was that there
was quite a good correlation between the two.
So like what I said about the two... participants
that didn't really respond in both. You could
definitely see a pattern that the people who
would, let's say, have the largest negative effect
of the cooling in terms of blood flow also had
the largest negative effect in the amino acids
incorporation into the muscle. Now, from your
expert to all the coaches and athletes, how would
you sum up the results of your study? What does
it mean for an athlete and a coach? So I would
be very careful with using cold water immersion,
especially during training phases where either
muscle growth or the gain in muscle strength
is important. I would say in those situations,
I would just not. do it or if you really want
to do it do it as far away from your exercise
as possible because yeah what we did now was
of course first the exercise and then immediately
after into the ice bath so of course it could
be that possible negative effects are much much
less if you just split split them up more yeah
and I think for some it can still be useful during
let's say competitions so if you have multiple
multiple competitions per day or a couple days
in a row. Yeah, on one hand, it could help for
some. But on the other hand, yeah, is it really
helping more than just a placebo effect? I think
that's the main thing where I'm still struggling
with is, yeah, still should people do it during
competition? I think that's still an area that
we can't really say at the moment. Because I
think in this case, in the study that we did,
the focus was more on muscle adaptation. And
I think if you look at performance, recovery
so let's say you had a an intense match and you
want to or a competition and the next day Again,
you need to perform. I think that's a very different
question than what we looked at in this study.
Also, there's an aspect of exercising in heat
or hot environment. Then we have to balance cooling
down, like literally dropping the body temperature
down, matching the sun for two hours in a tournament
that takes four days and so on. So there are
still some benefits we have to kind of keep.
the context in mind exactly yeah i agree yeah
awesome two more questions to finish the first
one is what is your favorite exercise yeah actually
i i did do quite some olympic weightlifting for
some time and i must say i really like the power
clean because it's just like just raw power just
like Pulling on something full force is just
a good feeling, I think. So yeah, I would definitely
say that the Power Queen is my favorite. All
right. And the last question is where people
can find you if they want to follow your research
or ask a question. Yeah. So research, I try to
kind of share on all kinds of platforms. So X.
Our Twitter, that's one. Also LinkedIn, of course.
But also on my Instagram, I post about my research
sometimes. So my handle is basically always just
my name, but with W in between. So it's Milan
W Betts. And yeah, with that handle, I think
you could find me on several platforms. All right,
Milan. Thank you so much for today. I learned
a lot. I hope that... The audience will enjoy
too. I hope so too. Thanks for having me.