Mental Toughness: A Physiologist’s Perspective

A few of you may know that I began my college studies with a view to a career in sport psychology. After a few years of study it became clear to me that my mechanistic mindset was far better suited to exercise physiology and so I left matters of the mind behind. Or so I thought…

Recently, the brain has made a significant appearance in the scientific study of fatigue, a topic of particular practical significance for the ironman athlete. For the bulk of the 20th century it was assumed that physical fatigue in endurance performance was the exclusive result of physiological depletion of one kind or another. Specifically, the “peripheral model of fatigue” proposed by AV Hill in the 1920s suggested that in a very literal sense, the muscle stops when the fuel runs out. In this case, “the fuel” being oxygen or glycogen. However, in practice, we know that this never occurs. Unsurprisingly, it is a very bad idea to deplete a muscle entirely of oxygen or glycogen. Living things tend to die when they are deprived of these things!

As it turns out, our subconscious is a little sharper than the early physiologists and it simply won’t allow complete glycogen depletion to occur. Even in exhaustive exercise, there is still some glycogen present within the muscle. For example, Asp and colleagues performed muscle biopsies on runners following the 1998 Copenhagen marathon and found that despite maximal competitive performances, muscles were only 56% depleted of glycogen, begging the question: “If we’re not out of fuel what causes us to slow down?” This is the million dollar question of 21st century exercise phys.

The prevalent theory is that it is the brain that shuts us down before we do any real damage. It has been suggested that it “turns down the volume” in both a real time and an anticipatory manner. Real time: as energy stores are depleted, exciter neurotransmitters are also depleted, that is, our “go to sleep” messengers within the nervous system begin to outweigh the “will to win” messengers. We get tired, we get grumpy and all of a sudden we start to really question just how committed we are to continuing this painful effort. With this contribution, the give up point becomes a bit of a grey area — it’s no longer purely physiological and binary. This would seem to be confirmed by the “end spurt phenomenon” of seeing the finish line resulting in something extra no matter how physiologically depleted we may have felt just a corner or two before. Essentially, at least to a point, we quit.

In concert with this psychological contribution to fatigue, St Clair and Noakes have proposed that not only does our brain hold us back at the end, but also at the beginning of exercise. Noakes and his colleague Ross Tucker have done some interesting studies to confirm this position. In one study he looked at running pace in cool versus warm conditions and found that runners essentially (consciously or sub-consciously) paced their rate of heat gain so that they all finished at a similar core temperature of approximately 40 degrees Celsius. Bigger runners would begin more slowly in warm conditions, despite the fact that their body was not yet under any significant heat stress, implying some sense of anticipatory pacing. A similar phenomena has been shown In altitude studies, obviously despite no initial hypoxia.

Of more practical significance, that “cut off core temp” of around 40C while uncomfortable is far from life threatening, suggesting that, particularly for more experienced athletes, the brain becomes very good at pushing to — but not beyond — a safe point.

The individual definition of this safe point then becomes important. What if athlete A is able (willing?) to tolerate 5% more glycogen depletion than athlete B? Or a 5% higher core temperature? Or 5% lower PO2 levels? In fact, in the muscle glycogen study mentioned above, while the mean was 56% glycogen depletion after the marathon, the range of depletion for the runners was 45-67%, implying some runners were able to push a little harder, dig a little deeper than others. The impact on performance of an approximately 20% higher carbohydrate output is material!

The above should be applied cautiously. It’s certainly not my intention to conclude that “it’s all in the head.” We’re talking about degrees lying in and around the point of physiological depletion. But in a sport where small degrees over long periods can amount to significant differences in performance, it’s worthwhile to recognize the role that mental toughness plays.


Categories: Mind

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Alan Couzens

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