Why aren't traditional physiological models enough to explain endurance performance limits?

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• The traditional physiological models account for maximum oxygen utilisation (VO2max) without producing too much lactic acid which results in muscle fatigue.
• These models assume that your muscles limit your capacity to maintain a given output (speed, power) for a prolonged period of time.
• Professor Marcora tested this assumption with a simple experiment: he showed that immediately after an endurance test to exhaustion, the body was still capable of producing much more power than the power that had been produced in the actual endurance test.
  
  In other words, the endurance performance was not limited by muscle fatigue.
• He suggests that what limited the performance was in fact the perception of effort in combination with the athletes' motivation. You slow down because you feel like you are unable to sustain the pace, not because you actually are unable to.
• Since professor Marcora's original study mentioned above, two more research groups, in Spain and the US, have replicated his findings.

Perception of effort and its effect on endurance performance

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• Perception of effort is usually measured using Rate of Perceived Exertion (RPE), a subjective scale.
• It has been shown that we are generally pretty good at rating our perception of effort. It correlates well with physiological measures like heart rate.
• Perception of effort increases over the duration of an endurance event, even if you maintain the same output. Eventually, you will reach a point that is the maximum amount of effort that you feel you can sustain. The key is this progressive increase in perception of effort.
• To illustrate, if you would start an event at an RPE of 8/10 but this perception of effort would never increase, you would feel like you could hold that pace forever. It would be hard, but not unsustainable.

More proof that physiological models are not enough...

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• It has been shown that you can improve or impair endurance performance using purely psychological interventions like self-talk or mental fatigue, that don't affect any physiological aspects of performance.
• This proves that purely physiological models are not enough to explain endurance performance.

The benefits of positive self-talk

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• Self-talk is basically talking to yourself, out loud or just in your head.
• Positive self-talk can be split into motivational and instructional self-talk.
• Professor Marcora and his lab has found that motivational self-talk ("You can do it", "You feel good") is more effective than instructional self-talk.
• Positive self-talk works to improve endurance performance since it reduces perception of effort. It's believed that this is related to self-efficacy.
• Professor Marcora has conducted a study that proved that it's very important to individualize statements. You need to find statements that work for you and practice them in training.

Mental fatigue and endurance performance

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• The first "study" conducted on this topic is a finger-lifting endurance test from 1891 (yes, really)!
• The subjects were two university professors who performed the tests on two consecutive days. The first day was a baseline. A regular, easy day. The next day, they repeated the test after giving lectures the entire day, which is very mentally fatiguing.
• Their endurance performance was significantly reduced on the day they were giving lectures.
• Until about 120 years later, when professor Marcora conducted a study on the same topic but using proper sample size and a cycling time-to-exhaustion test, this was the only data available on the topic.
• They induced mental fatigue using a demanding, 90-minute computer task and found a significant reduction of 15-20% in time-to-exhaustion compared to the control condition with no mental pre-fatiguing.
• In a previous study, they induced fatigue in the muscles prior to the cycling test by having the subjects do 100 drop jumps and investigated its effect on time-to-exhaustion.
• Incredibly, the reduction in endurance performance caused by mental pre-fatigue from a computer task was very similar to the reduction caused by 100 drop jumps!
• These findings can be explained by the fact that both mental and muscular pre-fatiguing have the same effect on perception of effort. It increases, and therefore the time required to reach maximum perception of effort decreases.

Summary of professor Marcora's model

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• Perception of effort in turn is affected by muscle fatigue, nutrition, mental fatigue, self-talk, and several other factors.
• But ultimately, it is their impact on perception of effort that limits endurance performance and not any of these factors in and of itself.
• As such, at this level of his model, there's no difference between psychological and physiological models.
• The great thing about this is that it gives you another avenue to improve your performance. Working on the psychological aspects may give you some quick wins that reduce perception of effort and therefore reduce perception of effort.
• That said, the best way to reduce perception of effort is still to train!
• If you want more, check out this excellent 15-minute video where professor Marcora explains the model. You'll see several useful charts to illustrate what we talked about on this show.

Brain Endurance Training and performance

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• The idea behind Brain Endurance Training (BET) is that by repeatedly induce an acute mental stress, you will adapt to this stress and be more resistant to mental fatigue.
• Since mental fatigue increases perception of effort and reduces endurance performance, you can decrease this performance reduction by an increased tolerance to mental fatigue.
• And you can gain this increased tolerance to mental fatigue trough BET.
• On a deeper level, you improve cognitive processes like inhibitory control and attention.
• It's still at an experimental stage. The first small study conducted was done with soldiers and not endurance athletes as subjects.
• In this first study, BET was practiced by performing a computerised task while training (indoor cycling). This is called concurrent BET.
• You can find some tasks online and try it yourself on the indoor trainer!
• Also, professor Marcora is involved in developing an app designed specifically built for this purpose.
• For running, he's involved in developing an audio-based program with mental tasks.
• In professor Marcora's BET-study, the subjects did either 3 regular cycling workouts per week, or 3 BET sessions which included the computerised task while training.
• In terms of fitness (VO2max), both groups improved by the same amount.
• However, in a time-to-exhaustion test, the non-BET group improved by 45-50%, but the BET-group improved by about 100%!
• An interesting finding is that during BET, the same brain areas that regulate perception of effort are activated. For this reason, specific cognitive tasks are required for BET to be effective. For example, solving math problems wouldn't be enough.
• His team has also done a small study suggesting that concurrent BET is more effective than doing cognitive tasks separately from endurance training.

Rapid-fire questions

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• Favorite book, blog or resource: "How bad do you want it" by Matt Fitzgerald and the Sweat Science blog by Alex Hutchinson.
• What's a good mantra for triathletes: Any positive, motivational statement that works for you and that you practice in training.
• What's a personal habit that's helped you achieve success? Going outside of his comfort zone and looking outside of his own field of research.
• What's a productivity-hack that helps you fit everything in: Multi-tasking is bad, so trying to allocating time to specific tasks, like setting a day aside to do deep work like writing and reading.
• A common but surprising trait of mentally strong endurance athletes: Professor Marcora has measured this in a study outside of endurance science, by just doing cognitive tests. The study showed that elite cyclists had much higher resistance to mental fatigue and much better inhibitory control.