Why we get Ker-knackered. Possibly.
Mark Thompson
you competitive types out there. Got a fair bit of relevence to
cyclists. If you want to see it in its proper home try:
http://archive.newscientist.com/secure/article/article.jsp?rp=1
&id=mg18124395.400
but it requires a free registration.
Running on empty
New Scientist vol 181 issue 2439 - 20 March 2004, page 42
Your lungs are bursting and your muscles are screaming at you to stop.
Can it really be possible that fatique is all in the mind? Rick Lovett
reports
TIMOTHY NOAKES will never forget the day he encountered the hill from
hell. It was 1976 and he was running the gruelling Comrades Marathon, an
annual 90-kilometre road race between Durban and Pietermaritzburg in
South Africa. About 20 kilometres from home he rounded a bend and saw a
steep incline he hadn't known was there. Even before he started
climbing, he suddenly began to feel overwhelmingly tired.
At the time it was just a case of gritting his teeth. But Noakes, a
professor of exercise physiology at the University of Cape Town, South
Africa, soon came to see that hill as an intellectual mountain, too. Why
had the very thought of it made him feel so tired?
Conventional wisdom on muscle fatigue can't explain what happened that
day. For the better part of a century, scientists and athletes have
presumed, not unreasonably, that fatigue originates in the muscles
themselves. Precise explanations have varied, but all have been based on
the "limitations theory". In other words, muscles tire because they hit
a physical limit: they either run out of fuel or oxygen or they drown in
toxic by-products.
In the past few years, however, Noakes and his colleague Alan St Clair
Gibson have taken a hard look at the standard theory. The deeper they
dig, the more convinced they have become that physical fatigue simply
isn't the same as a car running out of petrol. Fatigue, they argue, is
caused not by distress signals springing from overtaxed muscles, but is
an emotional response which begins in the brain.
The essence of their new theory is that the brain, using a mix of
physiological, subconscious and conscious cues, paces the muscles to
keep them well back from the brink of exhaustion. When the brain decides
it's time to quit, it creates the distressing sensations we interpret as
unbearable muscle fatigue. This "central governor" theory remains
controversial, but it does explain many puzzling aspects of athletic
performance, as well as suggesting some revolutionary approaches to
training and offering tantalising hints as to the cause and maybe even
the cure of chronic fatigue syndrome.
The hill from hell might have set Noakes thinking about fatigue, but it
was a more recent discovery that made him start researching it in
earnest. He calls this the "lactic acid paradox". Lactic acid is a
by-product of exercise, and its build-up is often cited as a cause of
fatigue. But when research subjects exercise in a decompression chamber
designed to simulate high altitude, they become fatigued even though
lactic acid levels remain low. Nor has the oxygen content of their blood
fallen too low for them to keep going. Obviously, Noakes deduced,
something else was making them tire well before they hit either
physiological limit.
Noakes and St Clair Gibson decided to probe further. For their first
study, published in 2001 (American Journal of Physiology - Regulatory
Integrative and Comparative Physiology, vol 281, p R187), they recruited
seven experienced cyclists and asked them to pedal 100-kilometre time
trials on stationary exercise bikes. On several occasions during the
time trial, they asked the cyclists to sprint for 1000 or 4000 metres.
Throughout the experiment, the cyclists wore electrical sensors taped to
their legs to measure the nerve impulses travelling to their muscles.
It has long been known that during exercise, the body never uses 100 per
cent of the available muscle fibres in a single contraction. The amount
used varies with the length of the endeavour, but in endurance tasks
such as the cycling test the body calls on about 30 per cent, spreading
the load by rotating in fresh ones as needed. And because separate nerve
filaments send signals to each fibre, sports scientists can determine
what fraction of the muscle is being used by measuring the electrical
impulse travelling to it.
Noakes reasoned that if the limitations theory was correct and fatigue
was due to muscle fibres hitting some limit, the number of fibres used
for each pedal stroke should increase as the fibres tired and the
cyclist's body attempted to compensate by recruiting an ever-larger
fraction of the total. But his team found exactly the opposite. As
fatigue set in, the electrical activity in the cyclists' legs declined -
even during the sprints, when they were striving to cycle as fast as
they could.
Plenty in the tank
To Noakes, this was strong evidence that the old theory was wrong. The
cyclists may have felt completely done in, he says, but their bodies
actually had considerable reserves that they could theoretically tap by
using a greater fraction of the resting fibres. This, he believes, is
proof that the brain is regulating the pace of the workout to hold the
cyclists well back from the point of catastrophic exhaustion.
More evidence comes from the fact that fatigued muscles don't actually
run out of anything critical. Muscle biopsies have shown that levels of
glycogen, which is the muscles' primary fuel, and ATP, the chemical they
use for temporary energy storage, decline with exercise but never bottom
out. Even at the end of a marathon, ATP levels are 80 to 90 per cent of
the resting norm. And while glycogen levels approach zero, they never
get there. Post-marathon muscles also still have substantial reserves of
other fuels, notably fat.
Still more evidence in favour of the central regulator comes from
observations of the closing stages of distance races. Top athletes
almost always manage to go their fastest during the last kilometre of a
race, even though, theoretically, that's when their muscles should be
closest to exhaustion. In particular, Noakes says, the end spurt makes
no sense if fatigue is caused by muscles poisoning themselves with
lactic acid. If lactic acid build-up is the limiting factor, racers
would progressively slow down and would find it impossible to sprint for
the finish line.
But with the central governor theory, the explanation is obvious.
Knowing the end is near, the brain slightly relaxes its vigil and allows
the athlete to tap a bit of the body's carefully hoarded reserves.
But the central governor theory does not mean that what's happening in
the muscles is irrelevant. The governor constantly monitors
physiological signals from the muscles, along with other information, to
set the level of fatigue. A large number of signals are probably
involved, but the ones Noakes is most sure about include the body's
remaining stores of carbohydrates, the levels of glucose and oxygen in
the blood, the rates of heat generation and heat loss, and the rate at
which muscles are working. Where the central governor theory differs
from the limitations theory is that these physiological factors are not
the direct determinants of fatigue - they are just information to take
into account.
Conscious factors can also intervene. Noakes believes that the central
regulator evaluates the planned workout, and sets a pacing strategy
accordingly. Experienced runners know, for example, that if they set out
on a 10-kilometre training run, the first kilometre feels mysteriously
easier than the first kilometre of a 5-kilometre run, even though there
should be no difference. That, Noakes says, is because the central
governor knows you have farther to go in the longer run and has
programmed itself to dole out fatigue symptoms accordingly.
This can be verified by putting people on treadmills and telling them
they're going to run one distance when in fact you have another planned.
When the subjects are given the real story midway through the test,
their reported levels of fatigue suddenly adjust to account for the new
information.
It also explains Noakes's experience on the hill from hell. "The central
governor had been pacing me for another 20 kilometres," he says, "but it
had presumed it was going to be flat. Now, it suddenly had to take the
hill into account, and it forced me to slow down."
St Clair Gibson believes there is a good reason why our bodies are
designed to keep something back. That way, there's always something left
in the tank for an emergency. In ancient times, an emergency might take
the form of a lion or pack of wolves at the end of a long, gruelling
hunt. Today, the "wolf" might be a mugger hiding in an alley, or a
lightning storm near the end of a long hike. But the same concept
applies: life would be too dangerous if our bodies allowed us to become
so tired that we couldn't move quickly when faced with an unexpected
need.
Drugs and hypnosis
The team also believes the central governor theory helps to explain why
hypnosis helps block sensations of fatigue, allowing athletes to work
harder. If fatigue were merely the result of hitting the muscles'
physiological limits, this shouldn't be possible. But it is.
Amphetamines have a similar effect, and again it could be down to the
central governor. Blocking the sensation of fatigue with drugs, however,
makes it much easier to work yourself to death. Normally, fatigue will
force even the most iron-willed competitor to quit before they succumb
to heatstroke, but this didn't happen for the British cyclist Tom
Simpson, who died after taking amphetamine during the Tour de France in
1967, the year before drug tests started. Ecstasy, Noakes adds, is an
amphetamine-like substance that could have the same effect on clubbers.
The theory could also help to unravel the mystery of chronic fatigue
syndrome. Perhaps something has interfered with the brain's regulation
of fatigue so that you always feel exhausted even though you are not.
Successfully puzzling out the workings of the central governor might
open the door to a long-awaited cure, Noakes suggests.
St Clair Gibson and Noakes are presently trying to find where the
central governor is located in the brain by studying the
electroencephalograms (EEGs) of tiring cyclists. "We're finding that a
lot of areas of the brain are involved," St Clair Gibson says, "but we
haven't yet found the stop switch." However, the mix of such areas is
interesting, and includes the frontal lobe (which is involved in
decision making), the parietal lobe (which is involved in sensation),
and, for some reason, the visual and speech centres.
The central governor theory has found favour with other exercise
physiologists. George Brooks at the University of California, Berkeley,
for example, recently amended his textbook to include it. But for some
it remains controversial.
One critic is Jere Mitchell, a cardiologist at the University of Texas
Southwestern Medical Center, Dallas. He points to treadmill tests in
which people run up ever-steeper slopes while having their oxygen
consumption measured. Shortly before the subjects collapse in
exhaustion, their oxygen consumption reaches a plateau beyond which it
won't increase, no matter how hard they try to work.
This maximum rate of oxygen consumption, called VO2 max, can be boosted
by increasing the number of red blood cells in circulation - for
example, by re-injecting blood that was taken several weeks earlier.
This proves that fatigue has nothing to do with any central governor,
Mitchell argues. Instead, it kicks in at the point at which the body has
bumped into a very real physiological limit - the amount of oxygen the
blood can transport.
Peter Wagner of the University of California, San Diego, concurs. He has
conducted treadmill tests in which athletes are tested under two
different conditions: on normal air, and on pure oxygen. That is enough
to produce an 8 to 10 per cent increase in the amount of oxygen going to
the muscles, he says, producing a measurable increase the VO2 max in
well-trained athletes.
Noakes and St Clair Gibson, however, argue that the central governor
theory can explain both studies. The brain, they say, senses the
elevated amount of oxygen in the blood and then "resets" the pace to
allow the athlete to work harder, while still maintaining a reserve. "So
there is a ceiling of oxygen use," says St Clair Gibson, "but at a level
decided by the brain, with a wide margin of reserve for error."
If the central governor theory does prove to be correct, can coaches use
it to improve athletes' performance? Noakes's experience on the Comrades
Marathon underscores the importance of knowing the course beforehand -
particularly its later stages. Top athletes and coaches figured that one
out many years ago. In fact, says Brooks, trainers are often ahead of
the science. "Coaches, by experience, have discovered things which
scientists take longer to understand," he says. But Noakes argues that
the central governor theory helps make sense of interval training, a
"sharpening" technique in which athletes do repetitive bouts of
high-intensity exercise interspersed with recovery breaks (see Graphic).
In a recent experiment, Noakes took a group of cyclists who had never
done intervals before and asked them to add them to their normal
training, once or twice a week for six weeks. At the end of this
programme the cyclists, who were fast recreational riders but not
professional racers, had shaved a startling 15 minutes, or approximately
10 per cent, off their previous times on a 100-kilometre time trial.
Similarly dramatic improvements are often observed when runners are
introduced to interval training. Traditional theory says that the
improvement is due to physiological changes in the muscle cells that
make them better able to use oxygen or tolerate the build-up of
metabolic waste products. But Noakes doesn't see how major physiological
improvements can occur so quickly. And in any case, he says, interval
training seems to induce very little, if any, biochemical change in the
muscle. He believes that interval training works largely by teaching the
central governor that going faster won't do you any harm.
Perhaps, then, the central governor idea can be used to give athletes an
important mental edge. Simply telling them that even when they are
feeling completely exhausted their bodies actually have a lot in reserve
should provide an incredible psychological boost, says St Clair Gibson.
"When athletes know that," he says, "it's going to be exciting."
Simon Mason
"Mark Thompson" <pleasegive...@warmmail.com> wrote in message
news:Xns94B78E10913DCpl...@195.92.193.157...
> Just found this in last weeks new scientist. Should be useful for all
> you competitive types out there. Got a fair bit of relevence to
> cyclists. If you want to see it in its proper home try:
> http://archive.newscientist.com/secure/article/article.jsp?rp=1
>
Thanks -read this at work this morning, as well as the interesting piece
about what happened before the Big Bang.
--
Simon Mason
Anlaby
East Yorkshire.
53°44'N 0°26'W
http://www.simonmason.karoo.net
Niv
>
> Thanks -read this at work this morning, as well as the interesting piece
> about what happened before the Big Bang.
>
Isn't that contrary to all current cosmology/physics/whateever?
i.e. "before" has no meaning 'cos the space-time continuum didn't exixt.
Oh well, that's what "Q" & Trek does for you.
Niv.
Simon Mason
"Niv" <niv.nosp...@ntlworld.com> wrote in message
news:XoF8c.126$D3...@newsfe2-gui.server.ntli.net...
I think the gist of it was that god was at a loose end scratching his arse
and was bored with nobody to worship him. ;-) He only had to wait about 13
000 million years for us to evolve.
Simon M.
Paul - xxx
> Just found this in last weeks new scientist. Should be useful for all
> you competitive types out there. Got a fair bit of relevence to
> cyclists. If you want to see it in its proper home try:
> http://archive.newscientist.com/secure/article/article.jsp?rp=1
> &id=mg18124395.400
> but it requires a free registration.
That's a very interesting piece, especially the bit about how coaches have
worked using this theory, but without really knowing why or how.
Says a lot for the old adage of getting out what you put in as well .. check
exactly what you're going to do and where the course is and _know_ you can
do it before you start, and you're already partially there .. ;)
Thanks .. ;)
--
Paul
(8(|) Homer rocks .. ;)
Mark Thompson
Yeah, there's loads of different theories. People seem to be coming up
with new ones all the time. AFAIK they are all entirely wrong apart from
possibly one, which is probably only half wrong.
Pete White
"Mark Thompson" <pleasegive...@warmmail.com> wrote in message
news:Xns94B78E10913DCpl...@195.92.193.157...
Wonderful. I get blown out because some mangy mongrel chased an ancestor.
There must be someone I can sue!
Seriously though, I'm not surprised at this. I've often wondered if my
emotions have an impact on how well I cycle at any given time. If I'm happy
then I'm better able to concentrate on pedal-rhythmn/wether I need a
drink/cor that bird looks nice(!) etc. When I'm pissed off my legs feel
about 90 tonnes!
Hmm, require some thought on this...
Pete White
Just zis Guy, you know?
<petewhit...@ukonline.co.uk> wrote in message
<40632c35$0$10250$afc3...@news.ukonline.co.uk>:
>Hmm, require some thought on this...
Pete, please trim when replying.
Thanks
--
Guy
===
May contain traces of irony. Contents liable to settle after posting.
http://www.chapmancentral.co.uk
88% of helmet statistics are made up, 65% of them at Washington University
Mark Thompson
> ancestor. There must be someone I can sue!
That's nothing, I get knackered just scrolling to the bottom of your posts!
> Seriously though, I'm not surprised at this. I've often wondered if
> my emotions have an impact on how well I cycle at any given time. If
> I'm happy then I'm better able to concentrate on pedal-rhythmn/wether
> I need a drink/cor that bird looks nice(!) etc. When I'm pissed off
> my legs feel about 90 tonnes!
>
> Hmm, require some thought on this...
Dunno about being pissed off, but when I'm a bit drunk I can run much
further than normal before I start to feel tired. I really should do some
experiments to see if there are performance benefits as well, though I
can't imagine it being much cop for any endurance events - any benefits
would be used up by popping into the bushes every couple of pints but it
could be the incentive I need to get me jogging again.
MSeries
Not sure I understand the reasons why nor care for that matter but I have
been convinced for years that it is possible to let a big hill or long ride
out-physc one. If you think its going to be tough - it will be. I am
convinced I go up hills better in the dark that when I can see what is ahead
of me.
David Martin
"MSeries" <skank...@hotmail.com> wrote:
I used to do a 16 mile commute and as with any commute in a remotely hilly
place there is always The Hill. It is not particularly hard on paper but it
always manages to psyche you out.
It took several months before I knew that I could beat it any time and every
time without having to stop. I'm pretty sure it was all in the mind.
Likewise with my current bete noir, City Road in Dundee. It is quite steep
but I know I can ride up it. Most of the time though I can't be arsed so I
get off and walk. I'm sure it is all in the mind, but it does give me a
chance to look through the fence and check on the allotment.
..d
Iain Jones
> Just found this in last weeks new scientist. Should be useful for all
> you competitive types out there. Got a fair bit of relevence to
> cyclists. If you want to see it in its proper home try:
> http://archive.newscientist.com/secure/article/article.jsp?rp=1
> &id=mg18124395.400
> but it requires a free registration.
>
> Running on empty
>
> New Scientist vol 181 issue 2439 - 20 March 2004, page 42
Very interesting thanks, makes sense of a lot of my own experiences. If I'm
riding in an area I know well and thee's a hill near the end, it's hard
work but I can still manage OK. But if there's a hill I didn't know was
there, click click down into bottom gear, crawling along wishing for it to
end (as per today - why did they put so many hills on the Wirral). Like
someone has already mentioned as well, if I'm riding in the dark I find the
whole ride far easier, possibly because I can't see my computer - when it's
showing a slower speed I find myself urging myself on which surely doesn't
help.
Iain
James Hodson
<niv.nosp...@ntlworld.com> wrote:
>What! Something happened BEFORE the big Bang?
Certainly, Niv: the countdown.
James
Tony Raven
What's Carol Vorderman got to do with it?
Tony
James Hodson
<ju...@raven-family.com> wrote:
>>> What! Something happened BEFORE the big Bang?
>>
>> Certainly, Niv: the countdown.
>>
>
>What's Carol Vorderman got to do with it?
Eeeeek, I did hope that neither Carol nor Richard would be mentioned.
So be it.
James