Fatigue: A mechanistic breakthrough

Columbia researchers shed light on mechanism of muscle fatigue

First, thanks to many of you who sent us the article by Gina Kolata from the New York Times. It is a hot news week, first with this story breaking on Tuesday and also with Roger Clemens and Brian McNamee testifying before a congressional panel on Wednesday. This kind of story on fatigue is right up our alley here at The Science of Sport, and so let's take a look at this and see what it is all about before we get to the Clemens/McNamee hearings.

Why study fatigue?

Since its inception the profession of Exercise Physiology has focused on "fatigue." This is a broad term, and fatigue has many manifestations. We can fatigue during dynamic maximal exercise such as a peak power output test, and we can fatigue during sub-maximal (endurance) exercise. We can also produce muscle fatigue in the lab while contracting a single limb and muscle group, either repeatedly or continuously. So it has many faces, and exercise scientists have been interested in all of these areas for decades. In fact one of the first exercise labs in North America was the Havard Fatigue Lab, and one of their most famous investigations of fatigue involved two dogs, Joe and Sally, who were fed glucose or nothing while running on a treadmill. The scientists were the first to demonstrate in the lab that carbohydrate ingestion during this type of exercise enhances performance.

Great discoveries occur by accident

While a large number of scientists today are interested in what causes fatigue during endurance exercise, the more mechanistic studies focus on actual muscle fatigue---that is, what is actually happening inside the muscle and how that may or may not cause the muscle to stop working as well.

The clinicians at Columbia University were actually interested in congestive heart failure patients. The problem in these patients is that the heart begins to fail as a pump, and the consequence is that things get a bit backed up. The heart becomes more and more filled with blood, thus losing its ability to actually contract and to pump blood, and it was this weakening of the heart that interested Dr. Andrew Marks at Columbia University.

In their quest to understand their heart failure data, they came to realize that certain events at the molecular level contributed to the cardiac fatigue. The problem is that for muscle, either cardiac or skeletal, to contract, we must produce a successful chain of events. In short, a nerve signal reaches the muscle and stimulates the release of calcium (Ca2+). The calcium is what is actually causing the process of muscle contraction. A special part of the muscle called the sarcoplasmic reticulum, or SR for short, releases calcium, flooding the muscle cells with it. The calcium causes muscle contraction to happen, and when we want to relax the muscle the calcium is then pumped back into the SR, thus causing relaxation of the muscle.

The key to Marks' findings is that his group showed the calcium channels were "leaky," and so the calcium was not reaching its target of the muscle cells. The result was that the muscle could not produce the required amount of force, and in the case of the congestive heart failure patients the consequence of this is that the heart begins to fail in its job as a pump.

Translation - from the lab to the "field"

Calcium blocking drugs were originally developed to lower blood pressure, but Marks' lab altered a calcium-blocking drug so that it was a bit less effective. The result appeared to be a drug that shores up the "leaky" channels. Then they exercised mice for 21 days, with one group receiving the drug and one group a placebo. Both groups showed fatigue over the 21 days, which was measured with a continual treadmill run. However the mice that received the drug ran 13 min longer on the 21st day---77 vs. 64 min for the placebo mice.

To help support this finding, Marks' then collaborated with Dr. David Nieman at Appalachian State University in Boone, NC. The drug cannot be administered to human subjects as it has not yet been approved by the FDA, and so Nieman and Marks instead demonstrated that after cycling three days in row for three hours at 70% VO2max, the cyclists had leaky calcium channels. This suggests that, just like the mice during their 21 day training program, the cyclists were becoming fatigued.

The full pdf file is available to everyone and can be downloaded here. Be warned, however. . .even for scientists it is highly specific, and with all of the special abbreviations and acronyms it might take a while to sift thru!

What on earth does this mean???

So will athletes be taking an "anti-fatigue" drug in the near future? Not likely. . .it will take time before Marks' new drug will become available for use in humans. Clinical trails take years to complete, but more telling is the quote by Dr. W. Robb McClellan from UCLA: "In heart failure, there are three medications that improve mortality, but there have probably been 10 times that many tested." So the odds are against a new drug for this condition, and even if it is approved, WADA and other anti-doping organizations would likely include it on their list of banned substances.

For now what we all must do is follow the development of this drug and see how the clinical trials play out. The problem is that fatigue is such a complex event. . .even if the drug prevents the calcium channels from leaking, that is no guarantee that it will enhance performance during self-paced exercise such as road racing and cycling.

Come back tomorrow for our analysis of Clemens' and McNamee's testimony!

A drug conspiracy? Growth Hormone test

Drug conspiracy? Or administrative bungling? How a potential test for growth hormone slipped through the cracks (and it's possible rescue)

Well, first off, apologies again for the long absence between posts - it's been a frantic period of travel and work (and nothing in particular) and as a result, we've slowed right down in our posting sequence!

I (Ross) spent a large part of the last week and a half working my way steadily across the USA, beginning in Boulder where I was lucky enough to meet some of the local running community and was also blown away by some of the ideas and technology emerging from what must be one of THE meccas for endurance sport - but more on that in a future post. Then I moved progressively along the Grand Canyon, down to Phoenix for the Superbowl (condolences to Pats fans) and ended up in Vegas (which is just untrue - could have sworn I was in a theme park).

In any event, the result of the travels is that we've beena bit slow off the mark on a couple of really interesting stories, but as they say, better late than never! And one of the most interesting ones was this report from last weekend's Telegraph, in which a possible improved test for Growth Hormone is discussed.

The test - 8 years in waiting, while drug cheats prospered

The story concerns Professor Peter Sonksen, an endocrinologist (an expert in hormones) from London's St Thomas hospital, who was working to develop a reliable test for growth hormone prior to the Sydney Olympics in 2000.

As regular readers and any other followers of sport will know, growth hormone is a huge problem among elite atheltes, precisely because it has never really been possible to test for it! The confirmed or alleged use of growth hormone has some high-profile athletes linked to it...think of growth hormone, and you may think of the following athletes:

• Marion Jones - it was one of the drugs in her "cocktail" at BALCO
  
• Lance Armstrong - never "proven", but it was testified at a court case that he'd admitted to its use (among other substances) when questioned by doctors during his treatment for cancer
• Willy Voet and the Festina cycling team - in 1998, the first of the current series of drugs tidal waves broke when Voet was arrested carrying hundreds of vials of growth hormone in his car
• Jan Ullrich - alleged to have been given growth hormone as part of his 'treatment' by doctors in the now infamous Operacion Puerto scandal
• Roger Clemens and Andy Pettite - most recently, baseball was rocked by a scandal involving growth hormone (and steroids), with two of its big name pitchers being named in the Mitchell report. Clemens, for his part, denies using, while Pettite and trainer McNamee have confessed and implicated Clemens. This one should be really interesting, because someone is committing perjury!

There are other big names, but the point is, growth hormone is one of the most widely used drugs, because of it's undetectablity! And the second point is that because there's never been a reliable test, athletes who are accused can simply deny its use to millions, without any fear of being caught out.

So, when the reports emerge that Professor Sonksen has basically perfected a test for Growth Hormone in 2000, prior to the Sydney Olympics, one has to wonder what sequence of events took place to keep that test off the "market" for 8 years!

Because that's the summary of what has happened - Sonksen perfected his test in time for the Sydney Olympics, and promptly had his funding and support from WADA and the IOC withdrawn, and they chose to use another test for Growth Hormone instead. The test they chose is able to detect Growth Hormone in the blood for up to 24 hours after its use. Sonksen's test is able to detect markers of Growth Hormone use for 2 weeks - clearly, given the fact that athletes are now so advanced in their use of doping, the two week option is the better one.

The reason - it may be valid, but why settle for a second rate test?

Now, it's speculative to guess why the IOC and WADA would have chosen the way they did. These stories and decisions are never as simple as they appear with the benefit of hindsight, and WADA and the IOC may have had very good reason to pull support from Sonksen and go with the (now recognised) inferior test. Perhaps they felt that the proximity of the Sydney Games meant the test would not stand up to their legal requirements for a valid test, who knows? This would certainly be a good reason not to use the test in Sydney.

However, what is a mystery is why would they not continue to support the research and the efforts of a laboratory which was clearly very close to the answer? It may not have been useful in Sydney, but they seem to have been so close to an answer, why not pursue it a little further after Sydney? Instead, they settled on a test that only detects Growth Hormone for 24 hours. As a result, we've had a situation where for nine years, all the athletes ever implicated as using Growth Hormone can deny, deny, deny, and only Jones' confession confirms her use of it!

If the Growth Hormone problem is that large, which anyone but for the willfully ignorant (and Pat McQuaide, president of world cycling) will acknowledge, then why not plough money into perfecting the test? Why settle for a test that works for 14 days? Perhaps with more funding, Prof Sonksen would have been able to develop the test that was effective for 30?

The reason the athletes are "one step ahead" of the testers

Of course, in times like these, rumours will abound, ranging from administrative bungling to "conspiracy and cover-up". And while only those within WADA and the IOC know the true extent, what we will say is that given the battle on our hands to save the sport's credibility, and given that we are continuously bemoaning the fact that the athletes seem to stay one step ahead of the testers, it's astonishing that it takes 9 years for part of the SOLUTION to make its way to the testers!

In this particular case, it's not that they were one step ahead, it's that the governing body of the sport and it's anti-doping regulators were simply fast asleep or looking the other way! It's hardly surprising that athletes are a step ahead, when it takes 9 years and the intervention of the UK Sports authorities to push the test back into the spotlight.

But now, thanks to those efforts, the test MIGHT be ready in time for Beijing. Currently, WADA and UK sport are involved in meetings to get the test through the obvious legal requirements.

Sadly, however, it's likely that this test, if it's passed, will simply mean that athletes and their "support teams" will have to work a tiny bit harder to come up with the alternative to Growth Hormone. One gets the impression, based on this sequence of events, that it won't be too difficult to do...

Other sports news - some tiny soundbytes

And then finally, just to wrap up today's post (and to make up for lost posting!), some very brief sports stories that grabbed my attention in the last day or two.

First of all, in Men's Hurdles, Cuba's Dayron Robles is having a spectacular start to the 2008 Indoor season. The reason this is interesting is because at this Summer's Beijing Olympics, one of THE BIG EVENTS is going to be the Men's 110m Hurdles final. That's because it involves the Chinese favourite Liu Xiang. Liu has been the poster boy for the Beijing Olympics - he is China's huge hope for a track and field medal, and has been under massive pressure for about the last 3 or 4 years.

But towards the end of last year, his "lead" over the rest of the world has started to erode, and in particular, it's Robles of Cuba who now poses a huge threat to him. The significance of Robles' early form is that in indoor racing over 60m, the athlete with the fastest start tends to dominate. So Robles' ability indoors suggests that his start and first 40m is a strength. This, in turn, will put pressure on Liu (assuming Robles produces that form in Beijing) and should make for a great race. Liu is already carrying a billion people's hopes on his shoulders - the prospect of Robles 2 m in front of him at the 60m mark is one to look forward to! In our "Review of 2007" post, we gave Liu Xiang the tongue-in-cheek "Losing sleep over the future award". Well, given Robles' early season form, he might yet retain that award in 2008!

Bekele going for indoor 3000m record

Then, in other news, this weekend sees Kenenisa Bekele gunning for the world indoor 3000m record in Valencia, Spain. The record currently stands at 7:24.90, by Daniel Komen of Kenya.

The reason this is so interesting is not only because Bekele is shooting for a massive PB - his current outdoor PB is only 7:25.79, so he's going to have to run faster indoors than he ever has outdoors - tough ask!

Rather, the reason this is interesting is because it suggests that Bekele's focus early in 2008 has again been on the shorter distance, speed-oriented events. Last year, I think it was really noticeable after his loss at the World Cross-country championships, that he came back and reeled off a string of fast times over 3000m and 15000m, running PB's in both distances. However, I feel his longer distance form was not quite as good - his victory in Osaka, while spectacular, was a 'fragile' one, and then he didn't look as strong in some other 10000m events.

So my suspicion is that after his loss, his focus changed to shorter events and perhaps his training to include more speed. It would appear that this remains a goal. That will be encouraging to Tadese and the Kenyans who take him on in Beijing over 10,000m, since they may well be able to find a vulnerability in the longer race. At least, in theory, that's what might happen!

But we'll let you know the results of his world record attempt - my prediction, by the way - he will run 7:27, maybe a low 7:28!

Ross

NFL, Gatorade and bananas

It must have been the bananas

Superbowl Sunday has come and gone, and New York Giants played the part of giant slayers by upsetting the New England Patriots, a team that steam-rolled the competition during the regular season, and even when against the ropes always seemed to be able to pull out a win from somewhere. Not in Superbowl XLII however, and Manning (the younger one, amazingly) led the Giants to two fourth quarter scores to win the title.

There are plenty of talking heads and pundits on the web, television, and in print to provide you all the detailed analysis of the game you need. Neither of us have tremendous insight into the game of football, and so we will leave the breakdown to the other guys. However, there is one story that emerged from the Superbowl that does fall within our "playbook", so we thought we'd spend some time on that instead!

New York coach Tom Coughlin does not read The Science of Sport

Back in October of 2007 we did a series on muscle cramps. In it we looked at the different theories of cramps, looked at the prevailing and perhaps dogmatic theory, presented a novel theory to explain cramps, and finally used the debate around cramps to demonstrate how science and knowledge evolve as new evidence comes to light.

The gist of this debate is that for years cramps have been attributed to dehydration and electrolyte imbalances and deficiencies. We suspect many of you who played youth sports were told, when playing in hot weather, to eat lots of bananas. The hypothesis there is that potassium depletion causes muscle cramps, and it is commonly accepted that bananas are a food stuff that is rich in potassium. So, quite simply, to stave off cramps one must just eat plenty of bananas - elementary school knowledge (or so we thought), and it turns out that even in the Superbowl, they adhere to that same dogma!

So in the big game, late in the first half, the crack Fox TV broadcast team crossed to their onfield reporter, who informed the watching nation that as a result of the high humidity in the stadium (the roof was closed), the Giants players were having problems with cramps, and that the coaches, sharp as they are, immediately had boxes of bananas brought to the sidelines. Sure enough, a couple of minutes later the cameras spotted it---a pile of bananas on the Giants sideline!

The first important (though tongue-in-cheek) point here is that Tom Coughlin and his coaching staff clearly do not subscribe to The Science of Sport. . .or perhaps they do, but they missed our series on muscle cramps? The second interesting point is in spite of all of the technology the NFL teams and coaches have at their disposal, all the high-tech strategies they employ, their wealth of human resources---19 coaches for the Giants and 14 for the Patriots---they rely on techniques that are entirely unproven and which no scientific evidence supports.

And then thirdly, and perhaps most thought provoking, is that Gatorade are the Official sports drink of the NFL, and copious amounts of it are available on the side of the field. Yet for some reason, the Giants were not told this - they chose the banana instead of the Gatorade! So calling for the banana backup is an indication that...the Gatorade wasn't working...? That wasn't an ad you saw in the Superbowl! Imagine the tagline..."Gatorade appears NOT to prevent cramps. Try bananas instead..."

No, science does not always have the answer

Admittedly, science does not always have the answers. Human performance even in individual events is incredibly complex. One only has to look at our previous post for some insight into will power and motivation to understand that many factors, perhaps too many and too complicated to measure, predict performance.

But it is still fascinating that at what many consider the pinnacle of professional sports---the NFL---the coaching staff turns to bananas during a game to alleviate muscle cramps. This is a sport in which assistant coaches, perched high above, take moving and still pictures, analyze them, and relay information about their opponents down to the coach on the sidelines. It is a sport that makes exstensive use of video analysis as players watch hours of game film of opposing teams to "get to know" them and their offensive and defensivee formations. They appear to be on the edge of technology. . . or are they? The bananas suggest otherwise, and give hope that maybe there is room for basic science.

In any case, it was a cracker of a game, and in our honest opinion the better team on the day won the match. Somehow the Patriots never really looked like the team that dismantled their opponents 18 games in a row. The Giants found a way to get to them, and came out ahead as a result of their efforts.

Be sure to come back later this week as we move on to Part III of our series on exercise in the cold.

Marathon survival: Courage and physiology

Marathon survivorship – physiology of some courageous marathon finishes

Last week, we featured the debut marathon of Kayoko Fukushi of Japan. As the fastest Japenese woman ever over the HALF MARATHON, much was expected of Fukushi’s debut marathon in Osaka, but in the end, she left the world with memories of a different kind – 15 minutes to cover the final 2km, three falls in the final 300m in the finishing stadium, and testament to the challenges posed by the marathon distance.

In the aftermath of the race (you can watch the final 400m, as well as our analysis of the race at our previous post), Fukushi’s final 400m was a hot topic on discussion boards and running websites. So in this follow up post, we thought we’d look back on other famous marathon finishers. We tip our hats, and our physiological paintbrush, at the following three famous “Marathon survivors”.

Gabrielle Andersen-Scheiss

In 1984, for the first time, women were allowed to run the marathon at the Olympic Games. The race was won by Joan Benoit, in a remarkable time of 2:24:52, beating off a stellar field including Weitz, Kristiansen, and Rosa Mota. The time was remarkable for a number of reasons. Not least of all, conditions in LA were hot and heavy – ahead of the Games, there was a great deal of anxiety over potential problems caused by the pollution – much as there are around the Beijing Olympic Games this year.

But in the end, the heat caused the problems, and the biggest problems of all were encountered by Gabriela Andersen-Scheiss, of Switzerland.

Andersen-Scheiss entered Olympic Games AND Physiology folklore thanks to her performance over the final 400m of the race. This video, shown below, is often shown at physiological conferences as a demonstration of what happens to the physiology when the body temperatures rises to reach a ‘critical threshold’.

What you will see in the video below (apologies for the poor quality – if anyone has a better version, let us know!), is that Andersen Scheiss enters the stadium clearly in distress, and over the next 400m, staggers around the track, taking an incredible 5 minutes to cover the final lap! The video edits out much of this last lap (again, let us know if you know where a better version exists), but you can get a good idea of just what is wrong – it seems as though the left side of her body is dragging the “paralysed” right hand side behind it. And this is typical of what happens when the core body temperature rises to above 40 degrees Celsius.

The role of the brain

We’ve brought this up before, but it bears repeating – until the mid to late-1980’s, the theory for exercise in the heat was that you fatigued because the body was unable to provide sufficient blood to the skin for cooling AND the muscles for exercise. In this theory, dehydration was a problem because it meant less blood, which only worsened the problem. But in 1979, Ethan Nadel found the first evidence that the blood flow was not the problem. This finding was repeated in numerous studies, where they found that the body was perfectly capable of getting enough blood to muscle and to skin.

However, the body temperature can still rise (this is a function of exercise intensity and the environment), and when it happens, the evidence began to suggest that the brain was involved. Why? Because scientists started to observe that when people in LABORATORIES hit a body temperature of 40 degrees, they started to display symptoms of neurological problems. Which is exactly what you see in Andersen-Scheiss – “paralysis” of one half of her body, inability to control the limbs, and so forth. This classic symptom was strongly suggestive of the neural contribution to fatigue.

It was later found that when the brain gets too hot, it actually recruits less muscle (Nybo and Nielsen, 2001). Of course, when you exercise in the heat, it’s not quite as simple as a brain the stops activating muscle when you get too hot – I (Ross) did a study in 2004 that found that the activation of muscle actually goes down BEFORE you get too hot. In other words, the brain slows you down by activating less muscle IN ADVANCE of hyperthermia, specifically so that you don’t reach this point of complete exhaustion and ‘paralysis’.

However, as the video above testifies, it happens, with dramatic consequences. Andersen-Scheiss, for her part, became something of an Olympic legend as a result of her courage. She ended up finishing in 37^th place, some 20 minutes after Benoit. She was treated and released within 2 hours, showing how even the most intense effort is probably still within the reserve capacity for the body.

Jim Peters – the Vancouver 1954 marathon

Jim Peters of England was the Paula Radcliffe of his generation - he had broken the world record four times and was the first man to run under the 2:20 barrier, taking the record down by an astonishing eight minutes to 2:17:39!

So when he lined up in the 1954 Vancouver Empire State Games (today called the Commonwealth Games), he was the overwhelming favourite. This was the same Games, incidentally, that Roger Bannister and John Landy raced in what would later be called “the mile of the century”, with Bannister outkicking Landy to win. That race actually happed while this marathon was being run, and so Bannister actually sat in the stadium waiting for the men to finish.

Anyway, the marathon that day was particularly hot, and Jim Peters staggered into the stadium in first place, but was looking like he'd had too much to drink. He was swaying from side to side, and it looked as though one half of his body had been paralysed – much in the same way as Andersen-Scheiss would look 30 years later.

The conditions in Vancouver were pretty warm with starting temperatures in the shade in the high 20's Celsius. Reports were that the sun was so warm that the tar melted during the race! The temperatures may not jump out as being exceptionally high for those in the hotter parts of the world right now, but given that most of the athletes were not adapted to the heat, it was a tough day in the marathon. The conditions were so severe that out of 16 starters, only 6 finished the race.

Jim Peters was not one of them. After entering the stadium, with only 385 yards to run, Peters fell SIX TIMES within the first 200 yards. He took 11 minutes to cover that distance (making Fukushi look like a greyhound in her race!), before eventually collapsing for the final time – 200 yards SHORT of the finish line! He was taken to hospital, where he spent 7 hours being treated intensively before being released.

Incidentally, the athlete who was in second position with about two miles to run, Stan Cox, had also collapsed and ended up in hospital. At the 25 mile mark, he was so disoriented that he ran into a lamp-post, collapsing again. Eventually, police helped him to an ambulance, and he was taken to the hospital, where he’d later be joined by Peters.

And then finally, the eventual winner was a Scot, Joe McGee, who had actually collapsed five times on the course as well! But he heard that the two men who had been in front of him failed to finish, he picked himself up and went on to win! An attritional race if ever there was one!

The IronMan duel – Sian Welch and Wendy Ingram

And finally, for perhaps the most dramatic video we know of, we go to the IronMan Hawaii Triathlon of 1997, where Sian Welch and Wendy Ingram “race” over the final few hundred meters for fourth and fifth place.

This video, shown below, is difficult to watch, for the sheer agony that I’m sure most of you can relate to in some manner. It’s absolutely remarkable because it shows two elite athletes, both struggling with a combination of fatigue, muscle cramp and in the case of Welch in particular, hypoglycaemia. It’s quite clear that she’s in a disoriented state, and struggles to balance, find direction and stay co-ordinated.

Wendy Ingram, for her part, is cramping quite severely, and modifies her running style drastically in the final straight before the finish line.

What is most amazing, from a physiological point of view, is that the women move through different stages of what I would call “muscle activation patterns”. It’s as though there is a Plan A, which is to run absolutely normally, finishing strong (like some of the men who are finishing at around the same time as these two, you’ll see them in the background).

But given the difficulties both are experiencing, the brain quickly switches over the Plan B, which is this “modified running technique” – anything to keep going forward. Ingram’s “spider walk” is amazing, she’s clearly putting everything she has into what looks an incredibly uncomfortable running style!

Welch is unable to do even this – her muscles have simply been “switched off” and she has nothing left, mostly as a result of the low energy she has available and her fatigue – tired muscles with little fuel, and the brain says “No chance you’re running any more!” She’s unbalanced, uncoordinated and out of control. Eventually she staggers and walks to within meters of the finish line – she is on Plan C. But then she falls, taking Ingram down as well. And you’ll see in the video, the eventual winner between the two of them is the one who first realises the need for Plan D – Crawl!

So it’s an astonishing video, and you’ll hear reference to Julie Moss, a link you’ll find in the comments section of our Fukushi post from last week.

But this finish, and these two women, must surely go down as one of the bravest and most courageous, dramatic finishers in history!

Can you ever overcome the body’s limit through sheer willpower?

One question that is often asked when this whole area of “limits to performance” is discussed is this whole issue of “mind over matter”. What we are saying is that brain decides when “enough is enough”, and reduces the activation of muscle fibers BEFORE you even get near the dangerous levels of body temperature or fuel depletion, for example.

The logical question, however, is “Can an athlete, through sheer willpower, find that little bit extra, over-ride the brain’s protective reduction in muscle activation, and allow the athlete to go that little bit faster?” Professor Tim Noakes, who is one of the primary drivers of the theory of the brain protecting the body, often talks about the psychology and willpower aspects. And while they are relevant, I feel it’s not quite correct – it’s not simply a case that the guy who wants it most will win, which is unfortunately the spin that is often put on it.

So the answer is complex. Certainly, willpower and psychology play a role, and different people will tolerate different levels of discomfort. But I think that what these videos and stories show is that eventually, physiology wins the day. Peters, Welch, Andersen-Scheiss, and Ingram are all examples of athletes who have dug deep, found EVERYTHING their physiology has to offer, and quite literally run to the “edge of the limit”, but eventually, their physiology shuts down so completely that they simply could not run anymore. And yes, they survived. So in that sense, the brain did its job of protecting them, because all made recoveries, none “exercised themselves to death” (this happens, but it requires some special circumstances, we’ll discuss that in a future post).

So, to use a morbid analogy – no matter how badly you want to go, you cannot commit suicide by holding your breath – physiology wins. And similarly, during exercise, your willpower can take you that little bit closer to the limit. In fact, training takes you nearer that limit, since you learn what is tolerable and what is not. Motivation is of course important here too – given the right motivation, you might be prepared to tolerate a lot more than usual! But as you approach that “limit”, your body begins to progressively throw barrier after barrier in front of you. It becomes more and more difficult to hold the pace. Your brain is not activating muscle at the same level, and your perception of effort rises and rises. And eventually, physiology wins the day, and you stop, either voluntarily or because your legs fail to hold you up any more. This is human performance at the very extremes, but it’s still physiology!

Join us for exercise in the cold next post!

Ross