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Posts Tagged ‘central governor’

When VO2max isn’t max

February 6th, 2012

This week’s Jockology column in the Globe and Mail takes a closer look at the recent study that produced “supermax” VO2max values by changing the test protocol, suggesting that the VO2max plateau isn’t really a physical maximum:

Eventually, your muscles can no longer get enough oxygen. It’s an immutable physical limit that kicks in during any sustained physical exercise and tells your body: “This fast – but no faster.”

At least, that’s the theory we’ve been working with since 1923. But a controversial new study from researchers on three continents suggests that the famous “VO2max” – the maximum amount of oxygen that you’re able to deliver to your muscles during hard exercise – isn’t really a maximum at all. Your heart and lungs don’t call the shots after all; your brain does. [...]

As usual, Trish McAlaster has a nice graphic that illustrates what’s going on with the new test:

Does heat slow you down if you don’t know it’s hot?

January 29th, 2012

Why do you slow down in the heat? This may seem like a painfully obvious question, but it’s a topic of heated (oops) debate among physiologists. There are two basic camps:

  1. You slow down because the increasing temperature in your body begins to cause some sort of physical problem — maybe it’s in your muscles, or your heart, or your nervous system; there are several theories;
  2. You slow down because your brain detects that your body is getting hot, so it forcibly applies the brakes to avoid letting you reach any dangerous system failure (in your muscles, heart, brain, or whatever).

To put it another way, do you slow down in response to problems, or in anticipation of problems?

The problem with many of the experiments on both sides of this debate is that they can’t separate out the conscious psychological factors that also regulate self-paced performance. (I say “self-paced” because that’s what we’re really interested in understanding. Putting someone on a treadmill at a fixed pace and forcing them to run until they fall off is an interesting way of studying our ultimate failure mechanisms, but it offers basically no insight into what happens during a real-life race, where your decision to slow down comes long before you’re at risk of collapsing.)

Anyway, a new study from Stephen Cheung’s group at Brock University, in the journal Physiology & Behavior, takes a clever look at this problem. They told a group of cyclists that they were studying how much power output changes when you try to maintain a constant perceived exertion. To do that, they asked the cyclists to do two 60-minute rides (on separate days) where they maintained their RPE at 14 out of 20 (between somewhat hard and hard). But on the second ride, they secretly manipulated the room temperature as follows:

Now, let’s not kid each other: as the chamber heated up to 35 C, the cyclists knew something was changing. But at this point, they had oxygen tubes in their mouths, and couldn’t communicate with the experimenters. And the point is, they couldn’t consciously regulate their pace in advance to take the hotter temperature into account. Here’s what happened to their power output:

So what’s happening? Well, the power output did go down as they got hotter — but there was no real-time match between power output and any of the other variables that the researchers measured, including skin temperature, rectal temperature, heat storage (a measure of how much thermal energy is accumulating in the body), sweat rate, or heart rate. The verdict seems to be that the brain isn’t using any of these physical cues to anticipatorily regulate power output.

There are some potential limitations to the study — for example, the RPE of 14 might have been too low to cause severe enough thermal stress to trigger a response. But overall, the message seems to be that conscious psychological factors play a role in our response to thermal stress. And that fits with earlier studies like the one I blogged about last May, where lying to cyclists about the temperature allowed them to go just as fast at 31.6 C as they did at 21.8 C. This new study may not support the “anticipatory heat storage” idea of the central governor model, but it certainly reinforces the idea that the brain calls the shots.

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When is VO2max not max?

December 30th, 2011

Last spring, I had the opportunity to visit the sports science research group at the University of Cape Town. While I was there, I heard about some very surprising new research raising questions about the definition of VO2max. Since the research hadn’t yet been published, I agreed not to write about it; that paper has now been published in the January issue of the British Journal of Sports Medicine, so here goes.

A little background to start. The concept of VO2max — the absolute limit on how much oxygen you can deliver to your exercising muscles — is controversial these days, because it implies a physical limit on endurance performance. That idea, entrenched for the last century, has been challenged recently by researchers led by Cape Town’s Tim Noakes, whose “Central Governor Theory” argues that we never actually reach our ultimate physical limits — instead, our brains hold us back to protect us.

The new issue of BJSM actually contains eight different papers that could be interpreted as supporting Noakes’s basic thesis. And Noakes himself has an introductory article that offers a good overview of the debate and why it matters, for those who aren’t familiar with it. The full text of that intro is freely available here. Here’s Noakes’s somewhat oversimplified summary of the current status quo thinking:

In 1923, Nobel Laureate Archibald V Hill developed the currently popular model of exercise fatigue. According to his understanding, fatigue develops in the exercising skeletal muscles when the heart is no longer able to produce a cardiac output which is sufficient to cover the exercising muscles’ increased demands for oxygen. This causes skeletal muscle anaerobiosis (lack of oxygen) leading to lactic acidosis. The lactic acid so produced then ‘poisons’ the muscles, impairing their function and causing all the symptoms we recognise as ‘fatigue’.

We already know for sure that lactic acid doesn’t “poison” the muscles. But what about the idea of VO2max?

According to Hill, during the period between progressive exercise and exhaustion, whole body oxygen consumption reached a maximum value – the maximum oxygen consumption (VO2max) – ‘beyond which no effort can drive it’.

Two studies in the new issue of BJSM appear to show that VO2max isn’t actually “maximal” — you can get a higher value. As Noakes argues:

Had Hill shown this in 1923, he could not have concluded that maximal exercise performance is controlled by a limiting cardiac output. Instead a more complex explanation is required to explain why athletes always terminate exercise before they reach an ultimate oxygen limitation.

Okay, so much for intro. The study, by Fernando Beltrami and his colleagues in Cape Town, introduces a new VO2max protocol. VO2max is usually tested with an incremental design: you get on a treadmill (or an exercise bike), and the speed/workload gets higher/harder every minute or so until you reach failure. At some point before you reach failure, the amount of oxygen you’re using will have reached a plateau. Beltrami’s test is a decremental protocol. You start at a speed/workload slightly higher than what you were able to reach in a conventional incremental test, and then the speed is progressively reduced.

The subjects in the study all did a series of tests, as shown below. The key test was on visit number 4, when the experimental group did their decremental test:

Now, why would you expect a different result from a decremental test instead of an incremental test?

We reasoned that if subjects knew beforehand that the test would become progressively easier the longer it continued, the possibility was that any biological controls directing the termination of exercise might be relaxed, thus allowing the achievement of a VO2max higher than that achieved with conventional INC.

In other words, if the plateau observed in conventional VO2max tests is mediated by the brain in some way, rather than being purely physical, then it might be possible to change the plateau. And here are the VO2max produced in those multiple tests by the two groups:

Sure enough, the VO2 produced in the decremental test is higher by 4.4% (with p=0.004) than in the incremental test. Strangely, it stays at this new higher value in the subsequent incremental test — even though there were no related physiological changes. Heart rate, breathing rate, and ventilation at VO2max were the same in the different protocols. So what’s going on?

Emotional stress can affect blood flow during exercise and stimulation of sympathetic cholinergic fibres are thought to promote arteriolar vasodilatation and to induce changes in metabolism, producing a switch from aerobic metabolism to increased oxygen-independent glycolytic pathways… We propose the interesting possibility that an anticipatory difference in perception of the future workload might impact the sympathetic or parasympathetic drives and lead to differences in the metabolic response during exercise.

That’s just speculation. But what’s not speculation is that the subjects in this study did conventional VO2max tests and produced reproducible plateaus; then they did another test that just involved changing the order of the speed, and produced higher Vo2max values. Whatever is happening here, it’s not tenable to argue that the VO2max values measured in conventional incremental tests represent some absolute physical limit on the body’s ability to deliver oxygen to working muscles.

Pacing and cognitive development

July 20th, 2011

Here’s a bit of a loaded question: does your pacing strategy — even? positive splits? negative splits? — reveal something about your cognitive development? I blogged a few weeks ago about the perennial question of 1,500-metre tactics and whether going out a fast pace is smart or stupid, so I was interested (and amused) to see a new study from Dominic Micklewright at the University of Essex, just posted online in Medicine & Science in Sports & Exercise, called “Pacing Strategy in Schoolchildren Differs With Age and Cognitive Development.”

It’s actually a really neat and thought-provoking study. Here’s the gist: the researchers studied four groups of children (aged 5-6, 8-9, 11-12, and 14). Each group was asked to run a time trial over a distance that took them about four minutes to finish — so similar to the demands of a 1,500-metre race in adults, actually. Here’s what the pacing for each group looked like:

The basic conclusion from this data:

Younger schoolchildren with less advanced cognitive development exhibited a negative pacing strategy indicating an inability to anticipate exercise demand. Older schoolchildren at a more advanced stage of cognitive development exhibited a more conservative U-shaped pacing strategy characterised by faster running speeds during the first 15% and last 20% of the run.

In other words, young kids go out very fast and fade from the front, while older kids understand the pain that awaits them and hold some energy back until they’re sure they’ll make it to the finish. But there’s more to it than that. The researchers also administered tests to determine where the kids fit into Piaget’s four stages of cognitive development — and they saw roughly the same pattern: kids with a lower stage of cognitive development went out hard and got progressively slower, while the kids with more advanced cognitive development had the U-shaped curve — which, I should point, is exactly the pacing strategy adopted by world-record-setters at distances from 1,500 to 10,000 metres ever since the IAAF started keeping records.

I should clarify (before Rob Watson kicks my ass) that the link between pacing between cognitive development and pacing is mostly related to age. Once you’re a grown-up (and in particular, once you’re racing against other people rather than just against the clock), there are many different reasons to adopt different pacing strategies. Let me repeat: I’m not saying that going hard means you’re dumb!

What this research is really about is “anticipatory regulation of effort” — which is basically just a rebranding of what’s sometimes called the central governor theory. (Debate about the central governor has become so personal that many scientists seem unable to actually read new studies about it, instead criticizing the ideas that were proposed 10 years ago.) Here’s how the authors of the new study put the idea into evolutionary context:

The survival of certain animals is contingent upon the successful deployment of energy conservation strategies such as the regulation of feeding, physical exertion and rest. Such energy conservation strategies are imperative to successfully completing predetermined survival activities within biological and environmental constraints. Humans use similar energy regulation strategies to successfully conduct their daily living activities albeit with less emphasis than other animals on survival. This is particularly apparent in the way humans pace themselves during athletic activity to avoid premature fatigue.

What’s fascinating is that this anticipatory pacing strategy appears to be hardwired into us. By the time we reach the third Piaget stage, we’re already pacing ourselves in exactly the same (much-debated) way that the runners who set distance-running world records do: a fast start, a slower middle, then a fast finish.

Jockology: exercising in the heat

July 3rd, 2011

This week’s Jockology column in the Globe and Mail is a round-up of a few recent studies on exercise in hot weather: how the brain slows you down more than the body; how acclimatization does (and doesn’t) work; and how cooling your palms can make your workout feel easier.

[...] “Slowing down in the heat could be a subconscious regulation to protect us from damage, such as heat stroke,” explains University of Bedfordshire researcher Paul Castle, the lead author of the study.

In other words, you don’t slow down because your body has reached some critical temperature. Instead, your brain slows you down to prevent you from ever reaching that critical temperature. It’s a subtle difference – but as the cyclists in the study discovered, it means that our physical “limits” are more negotiable than previously thought… [READ THE WHOLE ARTICLE]

 

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Burfoot, Noakes, and the ultimate workout

June 14th, 2011

Fascinating post on Amby Burfoot’s Peak Performance blog about a recent Yale study on the mind and appetite hormones. Researchers gave subjects either a high-calorie or a low-calorie milkshake (and told them which one they were getting), then measured the change in ghrelin, a key appetite hormone:

As you would expect, the subjects’ ghrelin levels dropped after the indulgent, high-calorie shake. After all, this thing contained more than 600 calories. It would fill up anyone. When the subjects drank the low-cal shake, their ghrelin levels stayed basically the same.

Here comes the twist: The shakes were identical; they were all moderate-calorie.

So what does this mean? Amby goes on to discuss other phenomena like “sham arthroscopy” and the”world’s best running workout.” The whole post is worth a read, but I found his suggestion for a workout particularly interesting: 5 x 1 mile as hard as possible… then when you’re done, your coach makes you do one more at the same pace:

From this workout, you’ll learn forever that you’re capable of much more than you think. It’s the most powerful lesson you can possibly learn in running.

I agree. And it also made me think of something Tim Noakes told me when I interviewed him last summer. I’d asked about the origins of his “central governor” model, and how coaches might actually apply its lessons in practice. Here’s what he said:

I think all the great coaches always work on the brain anyway. And they get you to run faster because they teach you that you can… I remember the compelling moment in my own rowing career was we used to do 6 times 500 metre repetitions. And one afternoon, we did our sixth and turned around rowing back to the boathouse, and the coach says, ‘No, go to the start again. You’re doing another one.’ So we did another 500. And he said go back. And we did another four. And you know, no one would have believed that we could do that, if you’d asked us… That taught us that you have to teach athletes, somewhere in their careers, that they can do more than they think they can.

As Amby points out, the problem is that you can’t prescribe a workout like that to yourself: you need a trusted authority telling you what to do. This is a really interesting and important point. We keep on discovering that the brain is more powerful than we’d suspected in regulating performance (and even appetite hormones) — but it’s still not clear how we can actually harness these powers.

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More evidence that heat is in your head (or neck)

May 27th, 2011

In the last month, I’ve posted about palm cooling, face-warming, and a study that suggested that some of the slowdown we experience in hot weather is attributable to the brain rather than body overheating. The latest addition to this theme: a study on neck cooling, published online in Medicine & Science in Sports & Exercise a few days ago.

The gist: Seven cyclists performed a 15-minute time trial in 30 C heat, after riding for 75 minutes to heat themselves up. They did it once as a control, once while wearing a “cooling collar” (essentially an icepack that fits around their neck while riding), and once with the cooling collar being replaced every 30 minutes to keep it colder. As expected, the cooling collar improved performance in the time trial by about 7% (this has been demonstrated before); but replacing the cooling collar didn’t produce any further gains, even though any cooling effect had disappeared long before the time trial started.

What’s most interesting is that there were no differences between groups in any of the physiological variables they measured — rectal temperature, hormones like seratonin and dopamine, lactate levels, etc. The differences appeared to be purely perceptual:

It has been proposed that during self-paced exercise the intensity is regulated by a complex network of feedback and feed-forward systems regarding the physiological state of the body to allow for the completion of the task within homeostatic limits. The data from the current study and from a previous investigation using the same protocol suggest that cooling the neck enhances preloaded time-trial performance in a hot environment by masking the extent of the thermal strain…

Or, to put it simply, it’s in your head. That doesn’t mean that heat doesn’t have real physiological effects — just that, in most cases, our brains take the heat into account to slow us down prematurely.

strain9The critical core temperature and central governor theories are the two main theories proposed to
explain the impairment in sporting performance observed in hot temperatures and both models propose that there are
mechanisms in place to prevent the onset of a dangerously high internal temperature

Palm cooling for endurance sports

May 13th, 2011

A reader sent me a link to Bex Runner’s “core cooling device” — essentially a small gel pack that you freeze and strap to your palms. So is it a useful device, or a stupid gimmick? Tough call.

There has actually been a fair amount of research on palm cooling over the last decade or so. I blogged last year about a study that found people lifting weights were able to lift more if they cooled their palms between sets. In that case, the palm-cooling device was a fancy one that also applied negative pressure to the palm to help prevent blood vessels from constricting with the cold. That ensures that lots of blood flows through the open vessels, past the cool palms, in order to better cool the rest of the body.

Still, the total cooling power of these devices is rather limited. Another study published last year compared the same palm cooling device to an Army cooling vest, and found that the palm cooling didn’t reduce heat strain during treadmill walking. They estimate that the vest was able to extract 55% of the heat generated during the trial, while palm cooling was only able to extract 14% of the heat.

The palm-cooling stuff is just one, small branch of the “ergogenic cooling” literature, and all sorts of theories have been proposed about how it does or doesn’t work. The crucial message that the weight-lifting study tells us, is that it doesn’t work by altering local muscle physiology. The chest muscles weren’t cooled, and yet the weight lifters lifted more weight. As the authors (from Robert Robergs’s group at the University of New Mexico) wrote:

[O]ur findings can only be explained by the central processing of peripheral input from afferent nerves and/or changes in core blood temperature and as such these results fit within the theory of the [Central Governor Model] of the regulation of fatigue and the final cognitive decision to end exercise.

If that’s the case, the palm-cooler doesn’t need to actually alter your physiology to make you run faster — it just needs to convince your brain that your body is in less distress than it would otherwise be. Does this particular Bex device do that in way that makes a practical difference to running performance in the heat? I have no idea — they need some independent studies to demonstrate it. But the mechanism is plausible.

(If it does work, there are still some questions. At a race, you’d have some logistical difficulties keeping it frozen until the start. For training, we get back to the question: is it really useful to use devices that make training easier? Or is that sort of self-defeating, because the whole point of training is to challenge yourself? If you run a tempo run in 30 minutes unaided, or 29 minutes with cooled palms at the same effort, do you actually get any superior benefit from the faster pace at the same effort? Or do you lose an opportunity to adapt to heat?

Training aside, I suppose if it enhances comfort on a hot day so that you can simply get your run in, that’s a plus.)

Carbo-loading with a “hyperglycemic-hyperinsulinemic glucose clamp”

February 19th, 2011

In search of the ultimate carbo-loading protocol, I stumbled across a paper in the European Journal of Applied Physiology that was posted online a few weeks ago. Researchers at Liverpool John Moores University in Britain investigated the use of a “hyperglycemic-hyperinsulinemic glucose clamp” as a sort of super-accelerated way of stuffing your muscles full of glycogen (the form in which carbs are stored in the body).

What the heck does that mean, you ask? Basically, the subjects spent two hours the day before the big exercise test, lying around with needles stuck in their arm delivering elevated levels of glucose and insulin. (The “clamp” means they picked a specific level of blood sugar and infused exactly enough glucose to maintain the subjects at that level for the two hours.) Glucose is carbohydrate, and insulin is one of the signals that initiates the storage of carbohydrate in your muscles, so the subjects were able to pack about 198 grams of carbohydrate into storage during the two-hour protocol.

The next day, the subjects did a 90-minute steady-state bike ride following by a 16K time trial — and sure enough, the clamp improved time-trial performance by 3.3% (49 seconds over ~24 minutes) compared to when the subjects received a placebo saline infusion. So yes, you can carbo-load in two hours the day before a race without any special dietary or training intervention (though it doesn’t show whether this method is better or worse than standard carbo-loading protocols). Of course, this really doesn’t have much practical significance. I suppose you could imagine Tour de France riders having the resources and incentive to undertake a protocol like this, but insulin is banned by WADA. (Oh wait…)

The most interesting part of the paper is buried near the very end, and it’s written very confusingly — it sounds very much as if the paper’s peer reviewers have insisted on a bunch of caveats and rephrasings, which wouldn’t be surprising as the topic is Tim Noakes’s highly controversial “central governor” theory. It relates to a somewhat confusing quirk in the data:

[D]espite the evidence of alterations in substrate availability (higher glucose and insulin), the patterns of substrate oxidation were no different.

In other words, carbo-loading makes more carbohydrate available, but it doesn’t seem to change how much carbohydrate (versus fat) is actually burned. A number of other studies have found similar anomalies, which has made some researchers question whether we really understand why carbo-loading works to improve performance:

The essence of this theory, supported by appropriate findings, is that muscle glycogen may have a signalling function that influences pacing strategy. Subjects who start exercise with elevated levels of muscle glycogen would be able to exercise at a higher pace due to signalling between muscle and the brain than when in a glycogen depleted state.

In this picture, carbo-loading is just another version of the carbohydrate mouth wash, whose function is to convince your brain that you have enough fuel. It’s hard to imagine that this is always the limiting factor, but it’s an interesting area of research.

Sports performance and the brain on Ritalin, Wellbutrin, etc.

December 19th, 2010

Of the sessions that I attended at the Sport Nutrition Conference in Canberra last month, the one that was most unfamiliar to me was about nutrition and the brain, presented by Romain Meeusen of the Free University in Brussels. He covered a lot of ground about the various ways that the brain interacts with the periphery, but what caught my attention the most was a series of experiments using anti-depressants.

The original experiments tried giving substances like bupropion (Wellbutrin), reboxetine and Ritalin to cyclists, and didn’t see any improvement in 30min time trial performance after a 60min warm-up. BUT when they increased the temperature from 18 C to 30 C, all of the sudden these drugs produced massive improvements in performance — from 39.8 to 36.4 minutes for (I think) bupropion. Ritalin was even bigger — a seven-minute improvement.

At 18 C, most of the cyclists hit a maximum core temperature of about 39.5 C, but at 30 C they were up over 40.0 C when taking the drugs — almost to the point where the trials had to be halted for ethical reasons. As Meeusen put it, their “safety brake” didn’t work, so they were capable of pushing into the danger zone without feedback from the central nervous system. This is essentially what happened to Tom Simpson (who was taking amphetamines) on Mont Ventoux in 1967, he said.

So what does this mean? Well for starters, buproprion, which was recently taken off WADA’s banned list, should be put back on it. To Tim Noakes, this would undoubtedly sound like evidence that fatigue is governed by a “central governor.” Meeusen, as far as I can tell, doesn’t see it that way. He says “fatigue is likely to be an integrated phenomenon with complex interaction among central and peripheral factors.” Which basically means “it’s complicated.” Hard to disagree with that.