central governor – Sweat Science

February 6, 2012

When VO2max isn’t max

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My new Sweat Science columns are being published at www.outsideonline.com/sweatscience. Also check out my new book, THE EXPLORER'S GENE: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map, published in March 2025.

- Alex Hutchinson (@sweatscience)

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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:

January 29, 2012January 29, 2012

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

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- Alex Hutchinson (@sweatscience)

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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:

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;
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.

December 30, 2011

When is VO2max not max?

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- Alex Hutchinson (@sweatscience)

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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 (VO_2max) – ‘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 VO_2max 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.

July 20, 2011July 20, 2011

Pacing and cognitive development

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- Alex Hutchinson (@sweatscience)

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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.

July 3, 2011

Jockology: exercising in the heat

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- Alex Hutchinson (@sweatscience)

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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]