Mind over muscle? Limits to Endurance Performance | Professor Samuele Marcora | Think Kent

Mind over muscle? Limits to Endurance Performance | Professor Samuele Marcora | Think Kent


Hello ladies and gentlemen, my name is
Samuele Marcora and I am Professor of Exercise Physiology
at the University of Kent in the School of Sport and Exercise Science and also
member of the Endurance Research Group. Today I’m going to talk about the limits
of endurance performance in humans and the basic question is, are we limited by
our own muscles or by our own mind? First of all, let’s define endurance
performance: it covers a variety of sports and human activities, we define it
as any whole body physical tasks such as running, cycling, rowing, lasting more than
75 seconds up to several hours or even days in the case of the Tour de France and of course the most iconic events are the Tour de France or the
marathon but there are many more. And there are differences in terms of
tactical and technical aspects of the sports however, there is a very basic
feature of endurance performance that is trying to run or cycle at a speed over
the course of the of the of the competition that your competitors cannot
keep nd this is shown here in this graph, This is a graph of the speed
maintained by different athletes during the 2008 Beijing Olympic 10k men’s race.
In the solid line is the speed of the winner, and here you can see that about
half way through the race a couple of athletes started to drop the pace, they
couldn’t keep it going anymore, this one here here, in the end this guy
lost because he couldn’t keep the pace set by the winner. And the very basic
question in exercise physiology is why he couldn’t keep that pace, and the way we
measure it in the lab is by measuring what we call, time to exhaustion, which is
our basic test of endurance performance. Basically, it’s very simple we ask people to
cycle or run on a treadmill or a cycle ergometer at a certain speed that we fix
for as long as they can. We can also take a variety of physiological measures while
they’re doing this activity. But the basic question is is why do they
stop, why can’t they keep the pace that we set for them? And, just to give you an idea, at
top this is a top professional cyclist he could maintain a workload of 410
watts, next time you go to the gym try that power output, most of you may not
even be able to push it once, but he can keep it for 25 minutes. But the question
is why couldn’t he keep it for 30 or 40 or an hour. And the traditional answer is
because of muscle fatigue and traditionally I mean since the early
20th century when exercise physiology started to develop, we believed and it’s
still important, that the oxygen delivery to the muscle, insufficient delivery of oxygen to
the muscle is a limiting factor because it leads to the production of lactic acid,
which is supposed to kind of poison the muscle and make it weaker. However, over
the years of course we have done much more research and now we know that lactic
acid actually is not that important, there are even people that believe it is not
fatiguing at all, but there are a lot of other changes within the muscle that
make the muscle weaker over time during exertion. And one of them for example is
the depletion of glycogen which is the main energy substrate for muscle
contraction. However, now we know that there are things going on even in your
central nervous system that may cause muscle fatigue. For example, when it’s
very hot our brain becomes less able to activate the muscles, so the combination
of these muscular and brain changes reduces the ability of the athlete to
produce power and this will lead to a reduction in endurance performance. This
long-standing physiological model has led to a lot of innovations. For example
now top elite athletes like Chris Froome are routinely tested in the lab to
measure, for example, the maximal oxygen consumption. We also tell our endurance
athletes to consume a lot of carbohydrates before the competition,
such as pasta and rice, in order to make sure that their muscles are full of glycogen
so they can last longer. And also unfortunately these models also inspired
some of the doping techniques used by many of these athletes. For example
erythropoietin which is a substance that stimulates the production of red blood
cells, which are the cells that carry oxygen in the blood to the muscles. There
is however an issue and the issue is in the very basic assumption of this model.
So in this graph we see this is the power output fixed in the lab at which
we ask the subject to cycle or run and here is the progressive reduction in
maximal power output caused by exercise, that’s what we call fatigue muscle
fatigue. And the assumption is that when the maximum power output coincides with
the power gap were required by the exercise task the subject stops, because
despite the maximal voluntary effort is not able, their neuromuscular system
is not able to produce the required power output. However, this is an
assumption and actually only in 2010 we tested that and we found something very
surprising. The surprising thing was that yes of course there is muscle fatigue as
you can see here in the upper line there is a progressive reduction in maximal
power but even immediately after exhaustion when the subject decided to
stop, to cycle in this case at 242 watts, there was a significant reserve in power
output so the subject could exert almost three times the power output
required only a few seconds earlier, albeit for a few seconds. So, clearly
muscle fatigue was not the limiting factor, there’s been now more studies
including one where immediately after exhaustion researchers took a sample of
muscle from the from the leg muscles and measured how much ATP was in the muscle,
and ATP is basically the fuel, the ultimate fuel, for muscle
contraction and they calculated that with what was left in the muscles after
exhaustion they could have kept going at the very high intensity for
another seven to eight minutes. So there is now really mounting evidence that the
muscle is not a limiting factor. So then obviously the next question is what is
the limiting factor? And it seems to be the mind, specifically perception of effort. The
perception of effort is the conscious sensation of how hard and and difficult
exercise is and we use a very simple scales such as this one where we ask the
subject to tell us which is the number that corresponds to how hard exercise feels, very simple measurement. And if you use these measures doing exercise
this is exactly the same study as before, so cycling at 242 watts for as long as they
could and on average it lasted 10 minutes. Over the course of these 10 minutes even
if the power gap remains constant, there is a progressive increase in perception
of effort, to the point the effort is perceived as maximal and therefore this the the
athletes believe that it’s impossible to continue as exercise, because they’ve given
it all and they are not capable of continuing, even if physiologically they
are. The progressive increase in perception of effort is also depending
on muscle fatigue because we never have to compensate the muscle fatigue by
exerting more effort because the muscle get weaker. However, we are now
demonstrating that there are a variety of other factors that can affect perception
of effort and therefore performance. One of them, quite surprising, is mental
fatigue, that I’m sure you guys, students here and fellow academics are very
familiar with, if you exert mentally for a prolonged period of time, you will feel
tired after a few hours. However, this kind of fatigue according to the
physiological model shouldn’t really affect your endurance performance because it
doesn’t affect your muscle, it doesn’t affect your heart, doesn’t affect your
blood. However, we did an experiment where we experimentally fatigue a group of
subjects with the 90 minutes with a very demanding cognitive task and immediately
after that they were asked to do our endurance performance task which was a
time to exhaustion test and we compare the performance in this mentally fatigued
condition with this performance of the same group of subjects when they were not
mentally fatigued, when they just watched documentaries for 90 minutes. What we
found was a significant reduction in endurance performance measured by time
to exhaustion in a mentally fatigued state. However when we look at the
physiological responses, such as oxygen delivery, heart rate, blood lactate, we
couldn’t find any effect of mental fatigue whatsoever. So if I look at this
data, for me it’s impossible to explain why their performance was decreased from
a purely physiological point of view. However, when I look at the negatives of
perception of effort, the reason for the impaired performance is pretty evident.
When they were mentally fatigued, their perception of effort was increased and
as a result they reach their maximal effort earlier than in the control
condition when they were not mentally fatigued. Another experiments that we did
was using so-called motivational self-talk, this is a well-established
psychological technique that consists of statements, positive statements, such as
I’m going in there, go for it, dig deep, push it, you can do it. So try to avoid
negative thinking and give yourself motivation to keep going and this very
simple psychological technique has been taught to a group of subjects and
another group served as control and was not taught any psychological skill.
And again, we measure performance with a time to exhaustion test. Of course in the
control group I suspected there was no change in performance over a period of
two weeks but in the subject who practiced self-talk during their training
and they used it in the endurance performance test, there was a significant
improvement. And again this was associated with a significant change in
perception of effort, of course this time there was a reduction in perception of
effort which means that they reach their maximum effort and decided to stop exercise later than in the control condition. So clearly those previous studies
suggest, demonstrate experimentally that perception of effort is the
limiting factor. So, what can we do about it?
In terms of practical suggestions, the first one is to avoid mentally
fatiguing condition before a competition, so, for example avoid sleep deprivation,
so try to sleep well before a competition, which is not always easy
because you’re anxious about the competition and avoid things like video
games or other mentally fatiguing tasks but also avoid, for example,
controlling too much your own emotions. Controlling emotions is very mentally fatiguing,
mentally draining, so my advice to English athletes may be before
competition do not keep a stiff upper lip because that maybe have a negative
effect on your competition. The other one is to use in a systematic way these
psychological skills, such as motivation self-talk or goal setting or imagery
which are being found to be effective in improving and endurance performance. In terms
of testing, the suggestion is to include not only measure of the cardiovascular
system such as heart rate monitors during training but also measure that
such as questionnaires or the ratings or procedures ratio scale that measure
basically how the athletes feel and track the other time to understand when
when an athlete is fatigued and needs to rest and recover. We are also developing in
collaboration with the School of Computing here in Kent some objective
measure of mental fatigue such as electroencephalography which is a
technique to measure the electrical activity of the brain – so maybe in the
future we’ll be able to use these techniques to see whether an athlete
needs to recover from a brain point of view. Also nutrition, caffeine is widely
used by endurance athletes originally because they thought that was going to
improve the utilization of fat and improve performance that way. In reality
the performance is improved because there is a direct effect on the brain
which reduces perception of effort and we are now investigating other nutrients
such as tyrosine which is a precursor of a neurotransmitter dopamine to see
whether we can improve performance using this nutritional supplement.
In terms of training we are developing collaboration with the Minister of
Defense a new kind of training which combines classical exercise training
with the mentally fatiguing task on a computer, so this additional, if you like
brain workload, should make, there is actually evidence now they makes people
more resistant to mental fatigue and as a result improve their endurance
performance. But of course as for the previous physiological model
there is also scope unfortunately for doping. Amphetamines and more recently this
stimulant called Modafinil are banned substances and they improve performance
because they reduce perception of effort. And ourselves and also other
groups are researching brain stimulation which at the moment is not considered a
doping method but maybe in the future especially because there is evidence
that may be effective in improving endurance performance may be banned. The
research we are doing can not only benefit endurance athletes, hopefully a better understanding of fatigue and how to reduce it will help
other populations for example breast cancer patients receiving chemotherapy
which is a condition associated with very profound and debilitating fatigue
as well as in other conditions and of course this is not just about athletes
it’s about any human performance that requires endurance. For example soldiers
are required to work physically but also mentally for prolonged periods of time
and obviously there, a reduction in performance may mean the difference
between life and death or having a very serious injury.
So, hopefully this research will lead to improvement in many areas which are
affected by fatigue. Thank you very much.

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