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Mind Over Muscle

12th October 2019, a day that will go down in history. Elliott Kipchoge becomes the first person to ever run a marathon in under 2 hours, clocking in a time of 1:59:40 in the INEOS 1:59 challenge. A finishing time that researches said only had a 10% chance of being achieved by 2032. A remarkable achievement that saw the Kenyan running a sub 4.34 mile pace over the 26.2 miles. To put that into perspective, he ran 5km splits in 14:13 and 10km splits in 28:26, a speed most of us would struggle to hold on the treadmill for just a few minutes. Unbelievable! Kipchoge said after the race “I am the happiest man in the world to be the first human to run under two hours, and I can tell people that no human is limited,”. But what actually are the limitations of human endurance?

There are different theories out there with the most traditional being that exercise is limited by chemical factors in the exercising muscle itself, a term known as peripheral fatigue. Simply put, this hypothesis suggests that during maximal exercise the heart is unable to supply enough oxygen to the muscles at a sufficient rate to prevent the development of skeletal muscle anaerobiosis. This then accelerates the production of lactic acid as a byproduct and ‘poisons’ the muscles resulting in fatigue. Below is a useful YouTube video to help explain.

Tim Noakes however has argued that physical exhaustion is not a consequence of peripheral fatigue. He instead implies that the body’s level of fatigue is guided by the brain, ‘the central governor’, a term that has caused plenty of controversy over the years amongst researchers. He argues the brain will override physical ability to ensure self preservation and will regulate performance in anticipation so you don’t cause harm to your body (anticipatory regulation). This can be demonstrated when exercising in an oxygen deficient environment (altitude) or in extreme heat. If you are exercising in heat, your brain will ensure you slow down well before the core body temperature hits a critical threshold of 40 degrees centigrade and will then maintain that pace. It has actually been shown that athletes start at a slower pace when temperatures are higher and the number of muscle units recruited is lower. What’s also interesting is that although these athletes were running at a slower pace and less muscle units were recruited, their perceived effort on a conscious level was still the same as it normally is (we will talk more on perceived level of effort later).

Conventional physiology would suggest that fatigue progresses over the course of a run, as muscle fibres fail and fuel stores are emptied. However, you may have noticed when out running, when you see the end is in sight, you are able to dig deep and muster a final surge to the finish line. You are not alone in this and if you look at the record holders for the mile, 5000m and 10,000m races, the pacing patterns are all very similar. The pace starts off quick before settling into a consistent pace before an acceleration to the finish line. Dean Karnazes, an ultramarathon runner, ran 200 miles in 46 hours and 17 mins. An absolute lung buster. The last mile of this race was completed in under 6 minutes, a pace which he states would be strenuous even on fresh legs.

This casts further doubt over fatigue being driven by peripheral factors and supports Noakes’ theory that the brain has a more regulatory effect. Maybe once the brain knows the body is not under any threat and there will be no catastrophic changes in the body’s homeostasis it will allow more muscle units to be recruited. Theories stating the accumulation of lactic acid inhibits muscle function and that exercise terminates when muscles become energy depleted have been disproven. It is believed that in reality, skeletal muscle ATP concentrations never go below 50% of resting value under all conditions of exercise, even maximal exercise. So we always have more energy in reserve.

Fatigue can be viewed as an emotion and even though you are feeling tired and want to stop it does not necessarily reflect your true physical condition. The brain generates and increases the perception of fatigue, increasing the levels of discomfort experienced to ensure you slow down and cease exercise. This perception of fatigue has similar features to the way we perceive pain (which will be covered in a separate blog). We know there are lots of factors that can influence the way we perceive pain and that it is not just driven by the tissues, it is likely that there are lots of different factors that influence our perception of effort and fatigue. For example, motivation and belief levels, the situation (does your life depend on you being able to run further and faster), the environment (is it a training session or Olympic final, is it wet and cold outside), what is the athlete’s mental state like, what is their pain tolerance, what is their exposure to high demanding exercise etc.

Samuele Marcora formulated a new ‘psychobiological’ model of endurance which incorporates exercise physiology, motivational psychology and cognitive neuroscience. He believes that the ability to speed up and slow down or quit resides in the brain. You may have noticed that after a long, exhausting day at work, getting your running shoes on can be tough. Your legs may feel heavier than normal, you struggle to run as far or as fast as you normally do and your overall sense of effort generally feels higher. Marcora actually looked into the effect that mental fatigue has on physical performance. He got healthy volunteers to complete a ‘time to exhaustion’ (TTE) test on a stationary bike (cycling for as long as possible at a sustained power output of 230W). Prior to the test, the experimental group took part in a 90 minute mentally fatiguing test in comparison to the control group who spent the same 90 minutes watching ‘emotionally neutral’ documentaries. The results showed a significant reduction in TTE time in the experimental group, with no physiological difference between the two groups (heart rate, blood pressure, lactate levels, oxygen consumption). The only difference reported was their rate of perceived exertion, which was higher in the experimental group. When the brain is tired, the legs felt tired.

When out for a run it’s very easy stop. You’re feeling those heavy legs, you’re sweating, heart pounding. Why are you putting yourself through this pain? Your life doesn’t depend on it, you’re not running for gold in the Olympics. Intensity of motivation is a key factor. This is essentially the maximal amount of effort one is willing to exert in order to succeed in the task. It’s vary rare that PBs or records are set whilst out training. Another factor could include ones ‘response inhibition’ which is the ability to override your impulse (ie. to stop). How much are you prepared to suffer? Can you push harder? The answer is probably yes.

Marcora and his team did an experiment using a stroop test to assess response inhibition in a group of professional cyclists and amateur cyclists. The stroop test has words flash up on screen in different colours. So for example the word blue would flash but be coloured in green and the individual must say the colour and not the word. Both groups completed two 20 minute time trials. One was completed after the stroop test with the control being completed after staring at a black cross on a screen for 10 minutes. The results interestingly highlighted that the professionals demonstrated a significantly higher stroop test result than the amateurs. What’s also interesting is the effect the test had in performance between the two groups. The professionals did not slow down in their ride following the stroop test, however the amateurs demonstrated a 4.4% reduction in power output in comparison to their control ride. This demonstrates that the professionals have a greater resistance to mental fatigue but also greater response inhibition. Could this be a factor as to why they are the professionals? If this is the case, can mental fatigue be improved and will it have an affect on performance? Great question.

Well, Marcora looked into the effect brain endurance training (BET) had on levels of fatigue during an endurance exercise. He hypothesised that an increase in training load on the brain would induce adaptations in the brain, in particular the anterior cingulate cortex, and will reduce the perception of effort and improve endurance performance. He was right. The study compared a BET + standard training programme vs just the standard training programme alone over a 12 week period. The results showed that V02 max increases were similar in both groups. The ‘time to exhaustion’ test however significantly improved in the BET group and the rate of perceived effort was also lower in the BET group. Fascinating stuff.

Could this be something you incorporate into your training? Or could it be something that is used for athletes to complete whilst out injured or in the off season. Who knows? But maybe something to consider. When you are next out on a run and want to stop, can you try and suppress that desire and keep pushing on. Your muscles probably have the capacity to do so despite what you may feel.

What do you think when you are out on a gruelling run? Are you more of a positive or negative thinker? The reason I ask is because this has also been shown to have an effect on your effort levels. A study by Marcora (again) looked precisely into this and compared a cycling time to exhaustion test between two groups. One group were provided guidance on positive self talk and how to use certain phrases such as ‘feeling good’ and ‘push through this’. The results showed that the self talk group lasted 18% longer than the control group and the RPE (rate of perceived exertion) rose more slowly through the test. You may need to have a play around with different phrases to see what works best for you. In fact, even smiling can help improve your perception of effort. The following quote could be useful when you’re next out on the bike (or run).

I think the point of this blog is to open up the idea that there is more to fatigue than just what is happening in the muscles and it is vital to consider the role the brain has on the way we perceive the amount of effort we are putting in. It’s not to say that physiological demands don’t matter but it appears to be a complex topic. We need to look to find a balance between our physiology, emotional components (motivation and pain tolerance) and self preservation. A combination of all these factors is what leads us to how hard we are able to push during a race. Maybe see if you can put some of these theories to the test yourself and see if it helps.

If you’ve got this far through the blog then well done. Or you have just skipped to the end? Either way, thanks for reading. In another blog post we will look to explore the complex topic of pain and what affect this has on our performance.

By Josh Petty

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