The Capacity for Maximum Physical Performance In Humans – Do We Ever Really Go ‘All Out’

I read an article in the newspaper this week about a group of pedestrians who lifted a car off a lady that was trapped under it after the car crashed into her as they were walking by the scene of the accident. A few weeks ago I watched young world class cyclists in the Tour De France push themselves up miles of uphill road in some of the highest mountains in France, and who looked completely exhausted at the end of each stage. I have had some fun Twitter repartee recently with Samuele Marcora, Jeroen Swart, Andy Renfree, Ross Tucker and others – old science collaborators, friends and academic ‘sparring partners’ – regarding whether folk ever use their maximal physical capacity, and if not, whether their performances are regulated by processes in the body or brain, and if in the brain, whether algorithmic neural processes are involved, or rather more intangible mental motivation related processes are behind our maximal physical performances during races or athletic events. I spent a fair amount of time, particularly when working at the University of Cape Town a decade and more ago, examining these concepts, and developed a theory for them, along with colleagues Tim Noakes and Vicki Lambert, called the Central Governor theory, which caused some controversy then, and still does today, with folk either loving or hating it, as what happens with all theories in science.

For a long time, the concept of maximal performance, and what finally results in folk reaching the absolute limits of what they physically can do, could be described as a ‘catastrophic’ model of fatigue. In the catastrophic model, the body, when pushed hard during an athletic event, either runs out of key nutrients or energy fuels, or is ‘poisoned’ as a result of metabolites that cannot be cleared out of muscles quickly enough, either due to lack of oxygen delivery capacity of the lungs or blood supply which have been ‘overwhelmed’ by the demand placed on them by the physical activity. The lactic acid theory was the classical example of this – the ‘burning’ pain one feels in one’s muscle during extreme exercise was thought to be related to lactic acid build up, which eventually ‘poisoned’ the muscles to the point that they simply stopped working.

Most of these theories developed from animal studies, or isolated muscle studies, where muscles were removed from their normal anatomical environment and stimulated with electrical shocks until they stopped contracting completely (developed rigor for the scientists reading this). At this point of absolute fatigue, a variety of parameters such as lactic acid were measured, and given that the levels of these parameters were very high (or very low in the case of fuels), a cause / effect relationship between absolute fatigue in these isolated muscles and lactic acid for example was suggested to be occurring during these trials. But the action of muscles of human folk performing exercise does not occur in an isolated state or in a petri dish. We therefore did some work in the University of Cape Town labs, building on work by greats in the fatigue field such as Roger Enoka and Simon Gandevia, amongst others, and looked at how much muscle was recruited during real life endurance and sprint athletic activity, using fairly novel techniques (at least at that point in time!) such as electromyography (EMG), which indirectly measures muscle recruitment (though one could write a book on the merits of this technique to measure fatigue, or the lack thereof). In a breakthrough study for us, we found that the muscles of folks in the lab who pushed themselves to the point when they said they were absolutely exhausted still had reserve capacity / had not used their muscles absolutely maximally, which was both astonishing and exciting to us. We did muscle biopsies at the beginning and end of the trial, and also found that the levels of fuels such as muscle glycogen and glucose, essential fuels of the body, were low but not zero, indicating the presence of a fuel reserve capacity too. We repeated this type of study in a number of different population groups and types of athletic events, and found similar results, and concluded that the brain of an athlete ‘stopped’ an athlete in an anticipatory way prior to them ever being absolutely completely fatigued, even if they did ‘feel’ absolutely exhausted. So some process in the brain appears to ‘disconnect’ the sensation of fatigue from what exactly was happening in the body, likely as a protective mechanism to prevent the occurrence of either muscle damage or general circulatory failure which could (and occasionally does) occur during an athletic event in a very motivated athlete.

A number of other examples of this protective ‘central’ / brain protective mechanism came to light during our further experiments, or from experiments in other labs around the world. Derek Kay, Jack Cannon and Frank Marino in Australia found that in a lab study using race-like conditions, participants started fast, slowed down in the middle and sped up the last 10 percent (or so) of the trial. The EMG activity in their study tracked these increases and decreases in pace, which indicated that these changes were probably initiated and regulated by the brain. The increase in pace in the last 10 percent of the trial was described as an ‘endspurt’ – speeding up at the end of an event or activity – and of course if one’s muscles are being ‘poisoned’ by a continuous build-up of metabolites during a race, or if one did run out of a fuel completely, there would be no way that the trial participants could speed up and show an endspurt at the end of the race. A fascinating study performed in the 1960’s, which came to light when we investigated what we were finding, which perhaps would not have passed the muster these days from an ethical perspective, showed support for this concept. Trial participants were asked to contract their leg muscles as hard as possible in a leg strength testing device where the movement of the leg was resisted and the force output of the leg muscles recorded. The subjects were encouraged to keep on going until they claimed they were absolutely exhausted and could not continue for even a few seconds longer, and at this point a second researcher, who unknown to the participants had entered the room behind them, fired off a shotgun blank shell, without the participants seeing them do so. This obviously caused a massive shock to the participants, and the interesting finding from a study perspective was that the subjects put out between 20 and 30 percent more force after hearing the gunshot, despite saying prior to hearing the gunshot that they were absolutely exhausted. Again, this was strong evidence for the presence of the muscle reserve capacity at exhaustion and a ‘disconnect’ between the sensation of fatigue and the physical changes associated with the fatiguing process.

We, and other scientist folk, have had a long look at how this sensory / perceptual disconnect during the fatigue process and at the point of absolute ‘fatigue’ occurs. Clearly there is teleology behind this finding, and it is likely that it is a protective mechanism which uses ‘trickery’ to keep folk safe from their own motivational drives, but it is does ‘boggle the mind’ to think that one’s own brain in effect ‘lies’ to its own ‘self’ in order to protect ‘it’ from ‘itself’. The origin of sensations and the perception of emotional constructs such as fatigue, and how they develop in underlying brain structures (or indeed how they are even related to physical brain structures) is difficult to understand, given how little we unfortunately know about basic brain function, mental states, or indeed sensory awareness of anything. However, using indirect methods, we were able to show that the dissociation of the sensation of fatigue from the underlying physical fatigue processes can be fairly easily elicited. One of the most fun studies I have been involved with (though which has very relevant findings pertaining to this research area), was a study we (Rachel Winchester and others) did during my time at Northumbria University, where when young male participants who were running on a treadmill said they were feeling exhausted, we introduced either an attractive female or an athletic male into the lab who interacted with them while they were running. There were profound changes in the levels of reported sensation of fatigue by the athletes – when the attractive female interacted with them, they reported significant reductions in the level of fatigue they felt, but when an athletic male interacted with them, they reported being significantly more fatigued as a result of the interaction. So this was classic (and humour inducing) evidence showing that the sensation of fatigue can be actually fairly easily ‘dissociated’ from what is happening in the body itself, and that the sensation of fatigue has a psycho-social component, or at least can be ‘interfered with’ by psycho-social factors.

So what does all this tell us about the limits to performance and whether athletes, or indeed folk who perform recreational sport, ever really are ‘maximally’ fatigued, even if they do feel as if they are. The evidence described above would seem to clearly indicate that, at least in these scientific studies, one’s brain as a protective mechanism appears to limit ones activity to an always submaximal level, even if one ‘feels’ that one is pushing oneself to absolute maximum. How the brain (or mind) does this is currently not clear, but there is clearly some interplay or calculation between one’s motivations and desires for success, and one’s fear of damaging oneself during athletic, or indeed any, physical activity. Interestingly, in the wild, animals being chased by predators do occasionally push themselves so hard to not be eaten as prey, that even if they escape, they die as a result of their muscles becoming so damaged by overheating or over-exertion that they become necrotic, which results in kidney failure and death from multiple organ failure due to toxin build up from the badly damaged muscles. Clearly us humans are never in a situation in our routine lives that these animals face, and therefore perhaps this ‘reserve’ capacity is some relic of our ancestry where we were indeed potentially a larger animals prey, and there was benefit of always maintaining a reserve for this ‘death-defying’ challenge if it occurred, though of course it will always be nothing more than conjecture when speculating on ancestry or evolution as a cause for modern day behaviour or function, particularly when brain function or mental behaviour is involved. Though some athletes do collapse during and after events (and why they do so is still a mystery), the vast majority, even Tour De France winners, know that they need to leave a small level of physical capacity to allow them to be able to climb off the bike, have a shower, get their medal, or leave something ‘in the tank’ to race the next day. So when we think we are absolutely exhausted, we probably never are. When we see the person with the car on top of them in the middle of the road, we do have the capacity to perform life-saving feats (obviously within reason) and have ‘strength’ that we are not aware of. Whether it is wise to use this inherent reserve, and risk ‘all’, even one’s life, for that single instance of extreme use of strength or endurance capacity in whatever circumstance, is of course another story. As is persuading my scientific colleagues, who despite all this evidence described above, still think the concepts are baloney and nothing more than a good story!

Advertisements

About Alan (Zig) St Clair Gibson

Professor Alan (Zig) St Clair Gibson MBChB PhD MD - Deputy Dean (Research), Faculty of Science and Health, University of Essex, Colchester, United Kingdom View all posts by Alan (Zig) St Clair Gibson

2 responses to “The Capacity for Maximum Physical Performance In Humans – Do We Ever Really Go ‘All Out’

  • Yuri Motoyama

    Hello professor Gibson! I’m a big fan of your work about fatigue. Me and my colleagues develop studies about fatigue and central fatigue in a group called GEPEFEX (Brazil). Fatigue has been the big motivation in my academic life. I have a “guiding question” in this area that I would ask to you answer (you can use a kind of poetic licence to answer :P):

    Imagine that you had a magical power and this gift allow you to change any variable in human physiology (but just one variable). What do you change in this person to overcome fatigue or create a “non fatigable superhero”?

    Thanks for the excellent text!

    • Alan (Zig) St Clair Gibson

      Thanks for your kind words Yuri and hope you own work is going well! To be honest as some who has always looked at things from an integrative perspective, you question is a hard one to answer – if there was one thing I would change to become a ‘superhero’ it would be to be able to ‘tweak’ an athlete’s ‘will’ so he or she becomes capable of resisting fatigue processes at all levels in the body and brain and so go really fast, for a really long time! Sorry if its not a brilliant answer to what is a great question! (-:

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: