Mind, Body, and the Curiously Elastic Limits of Human Performance

By: Alex Hutchinson

Published: 2018

Read: 2021

Summary

Endurance. The struggle to continue against a mounting desire to stop, to overcome our physical and mental limits. We tend to analyze and train our physical limits (VO2max, lactate threshold, etc.) Mental limits are often overlooked.

But the brain plays a central role during prolonged physical activity. It monitors the state of the body and it combines the body’s signals into an overall sense of effort. This sense of effort slows us down (anticipatory regulation, pacing) or shuts us down (consciously or unconsciously) to avoid critical injuries.

Many factors influence our sense of effort. Some are trainable (pain and heat tolerance). Some are preventable (dehydration and lack of fuel). Some don’t matter as much as we think (muscle fatigue).

Much of our training is directed at managing the brain’s sense of effort, even if we don’t realize it. High intensity physical training accustoms the brain to higher levels of perceived effort. Self-talk “tricks” the mind into a lower sense of effort. Mindfulness inhibits or redirects the brain’s automatic responses to increasing levels of perceived effort.

The more we “train the brain”, the more we build the belief necessary to test and surprise ourselves. Improving our mental fitness helps us realize we are capable of much more than we think.

Practical Takeaways

• On training: stress the system to allow for adaptation.
  • Train on depleted fuel resources (without breakfast) to develop metabolic flexibility.
  • Train after a hard day at work to improve mental resilience.
  • Train with high intensity (suffer…) to improve pain tolerance.
• On racing: simple hacks.
  • Drink crushed ice drinks to lower core and brain temperature.
  • Consume caffeine (gum, drinks) to block fatigue receptors.
  • Relax jaw (floppy lips) / smile to ease sense of effort.
• On pacing: consider the trade-offs.
  • Pacing produces good results on average and lowers risks of a blow-up.
  • But, puts a ceiling on performance and doesn’t allow for break-throughs.
  • Consider pacing based on “how it feels” versus relying on technologic aids.

Worth Reading

A fun read. There are plenty of “aha” moments. Many of the book’s observations resonate with personal experience and hard lessons learnt over the years, such as:

• Relying less on technological gadgets and more on how the body feels.
• Surprising yourself when you throw pacing out the window.
• Muscle fatigue matters less than mental fatigue – many times the legs are unwilling rather than unable.
• Switching to a low carb diet can sharply reduce the need for fuel intake during races – perhaps due to higher availability of fat burning energy pathways.

Reading this book changed my perspective on one of the biggest lessons I learnt from endurance racing: the fact that your body (almost) always has a second wind. And a third wind. A fourth wind, etc. A lesson you typically only learn through experience. And a lesson that, once learnt, provides a dramatic confidence boost in any subsequent race (or in any other prolonged stressful or tiring situation). I always assumed that ebbs and flows in your performance are driven by physical issues (and sometimes they can be). This book made me realize it’s probably driven by mental, rather than physical, fatigue. And maybe, the more you aware of your mental fluctuations, the more you can try to even them out with the tools suggested in the book.

Overall, the book has a nice and neat structure. It covers a variety of factors influencing endurance. Many of these topics are incredibly complex. It’s not always clear that science fully understands what is going on yet. Theories change constantly and it is tough to untangle the complexity. Debates are heated and ongoing. The author does doesn’t get lost in the weeds too much and provides useful introductions to topics. For a deeper dive, you’ll have to go elsewhere.

Key Concepts

Endurance

• Struggle to continue against a mounting desire to stop.
• Need to for a prolonged period of time override your instincts.
• Requires conscious or unconscious decisions to “pace yourself”.
• Links physical and mental effort.

Physical limits: the body as a machine

• “Machinery” of the body.
  • The body’s limits expressed in physical and chemical terms.
  • Parameters that determine the “objective” limits to endurance capacity.
  • For instance, size or efficiency of the “engine”.
• Aerobic versus anaerobic limits.
  • Aerobic: low speed activities, muscles use oxygen to convert energy.
  • Aerobic: faster speed activities, generates lactic acid.
• Aerobic capacity limits:
  • VO2max.
  • Size of the engine: heart, lungs, circulatory system.
  • Maximum volume of oxygen uptake during exercise.
• Anaerobic capacity limits
  • Lactate threshold.
  • Ability to tolerate accumulating lactic acid.

Mental limits: the brain as the central governor – unconscious and conscious control

• Body as a machine mind-set acknowledges role of the brain.
  • The body sets the limits.
  • The brain dictates how close you get to those boundaries.
• But, concepts like VO2max can’t explain the limits of endurance.
  • Physical exhaustion is not caused by the heart’s inability to pump enough oxygen to muscles.
• Also, there is the “end spurt”…
  • If you’re body becomes progressively more fatigued, muscle fibers fail and fuel stories empty.
  • But what then explains your ability to go faster when the end is in sight?
  • Evidenced by the distribution of finishing times: spikes around whole hour marks.
• The brain alone, not the body, sets the limits during prolonged exercise.
  • The brain anticipates future energy needs and holds something in reserve.
  • Through experience and training, the brain learns how to pace.
• Two stages:
  • First: through anticipatory regulation.
    • Limits imposed by the brain to ensure we never reach “true failure” (death).
    • Brain may sense distress elsewhere in the body and “shuts things down”.
    • Example: you run slower from the start in heat (brain anticipates the build-up of core temperature).
  • Second: through controlling how much muscle is recruited at a given effort level.
• Central Governor theory (controversial).
  • Difficult to find or pinpoint specific brain regions involved.
• More practical “theory”.
  • Endurance isn’t simply a switch or dial in the brain.
  • It is a complex behavior involving many parts of the brain.

Mental limits: quitting is voluntary – conscious control

• Fatigue resides in the brain.
  • Any decision to speed up, slow down or quit is always voluntary.
  • Never forced on you by the failure of your muscles.
• Traditional model:
  • Muscle fatigue directly causes you to stop.
  • Your mental “sense of effort” is an incidental by-product.
• Psychobiological model:
  • Sense of effort “sits in between” muscle fatigue and the decision to stop.
  • Muscle fatigue, but also other (psychological) factors, influence your sense of effort.
  • Altering your sense of effort (subliminal messages, etc.) can alter your endurance.
• In other words, anything that moves the perceived exertion dial (sense of effort) is what matters most.
  • If effort feels easy, you go faster.
  • If it feels hard, you slow down or stop.
  • Driving factors includes physical cues: dehydration, tired muscles, pounding heart.
  • But also mental factors (concentration, boredom).
• Train the brain for endurance.
  • To become accustomed to mental fatigue.
    • Similar to training the body to become accustomed to muscle fatigue.
  • To alter your sense of effort
    • Alter your physical cues:
      • Emotions trigger a physical response, but the physical response itself then amplifies the emotion.
      • Use this feedback loop from “physical” to “mental”.
      • For instance: facial feedback.
      • Smile, relax your face, relax your jaw (floppy lips…)
      • Smiling face -> feeling of ease -> lower perception of effort.
    • Use motivational self-talk.
    • Consume caffeine:
      • Shuts down receptors in the brain associated with mental fatigue.
  • To increase your response inhibition.
    • Essence of pushing to your endurance limits is learning to override your instincts.
  • Best athletes have superior minds as well as muscles.
    • Superior response inhibition and resistance to mental fatigue.
    • Probably partly genetic and partly due to years of training.

Endurance limits: pain tolerance

• Pain tolerance is a trainable trait.
  • Linked to the type of training you engage in.
  • Simply getting fitter doesn’t automatically improve your pain tolerance.
  • How you get fit matters.
  • You have to suffer…
  • Pain in training -> better performance.
• Blocking pain can boost endurance.
  • Less pain makes the effort feel easier -> lower sense of effort.
• But, not blocking pain can also boost endurance.
  • Pain allows you to manage your fatigue and pace yourself.
• Side note: gate control theory of pain.
  • If you whack your shin, first instinct is to rub it with your hand.
  • Nonpainful rubbing sensation competes with the pain of the bruise.
  • Both share the same neural pathways back to the brain.
  • The more you rub, the less bandwidth is left for the pain signals.

Endurance limits: muscle fatigue

• Under normal conditions, we pretty much use all the strength our muscles have to offer.
  • Usually 100% voluntary activation of your theoretical maximum strength.
  • Voluntary activation: command signal from the brain.
• But, you can’t maintain 100% activation indefinitely.
  • Decline in muscle strength (muscle fatigue).
  • Decline in voluntary activation (brain fatigue).
• Brain and muscle fatigue difficult to separate.
  • Inseparably linked, signals going back and forth.
  • Muscle fatigue more likely to limit short duration performance.
    • Sprinters and 800 meter runners don’t speed up at the end.
    • Brain still calls for a sprint, muscles are unable to obey.
  • Brain fatigue more likely to limit prolonged activity.
    • In (ultra) endurance, legs are unwilling, not incapable.
    • Overcome brain fatigue at the finish and call for a sprint.
• Muscle fatigue and lactic burn.
  • Muscles overwhelmed by flood of lactic acid.
  • But, lactic acid itself can actually be an important energy source.
  • [See also Lactate Shuttle Theory.]
  • Lactate may be part of a feedback system that sends cautionary signals to the brain to prevent critical levels of stress.

Endurance limits: oxygen scarcity

• Limiting role of oxygen.
  • Supply of oxygen to the muscles.
    • Determines efficiency of energy conversion in the muscles.
    • Driven by circulatory system’s capacity (VO2max).
  • Supply of oxygen to the brain.
    • During exercise, you breathe more heavily.
    • Carbon dioxide levels in the blood increase.
    • Blood vessels in your brain constrict (same as hyperventilating).
    • Shortage of oxygen in the brain may interfere with muscle recruitment.
    • Driven by amount of blood vessels in the brain.
• Supply of oxygen to the brain may be the limiting factor in endurance.
  • Brain slows down muscle recruitment to ensure it doesn’t run out of oxygen itself.
  • Demonstrated by lactate paradox:
    • At higher altitude, due to lack of oxygen, you should go anaerobic sooner.
    • Anaerobic pathway produces lactate.
    • Therefore, at higher altitude, you would expect higher levels of lactate.
    • But, lactate levels are lower at higher altitude.
    • Likely reason: brain pre-emptively slows down muscle recruitment in low oxygen environment.
• The urge to breathe.
  • Driven by a build-up of carbon dioxide.
  • [See “The Oxygen Advantage“.]
  • Warning signal.
• Side note: the mammalian dive reflex:
  • Set of automatic responses when immersed in water.
  • Sensors appear to be primarily around your nose.
  • May start earlier: anticipatory regulation.
  • Objective is to conserve oxygen.
  • Dramatic drop in heart rate.
  • Peripheral vasoconstriction, sending blood to the core to ensure sufficient oxygen supply to the heart and brain.
  • Spleen vent infuses oxygen-rich blood from the spleen.
• Side note: four dive stages:
  • Awareness: conscious awareness of urge to breathe.
  • Contractions: involuntary contractions of the diaphragm.
  • Rush: fresh blood released from the spleen.
  • Black-out: standby mode to conserve energy.

Endurance limits: excess heat production

• Human body is literally a furnace.
  • Transforms the energy from food into mechanical work.
  • This transformation generates heat.
  • The harder you work, the more heat you generate.
• Thermoregulation.
  • Sometimes heat is useful, sometimes it is an inconvenient by-product.
  • Blood carries heat away from the core and releases it through the vessels near the skin.
• Exercise produces excess heat, driving up core temperature.
  • In response, blood vessels dilate to allow for increased blood circulation.
    • Opposite happens in cold: blood flow to extremities is cut off.
  • You also begin to sweat: evaporation of water cools the skin.
    • Phase transformation from liquid to vapor consumes energy.
• Regular exercise (in hot conditions) allows the body’s protective responses to adapt.
  • Stress the system.
  • Sweat more heavily at lower temperatures.
  • Blood vessels dilate wider, blood volume in your body increases.
• Again, both brain temperature and core temperature matter.
  • Or even, perceived temperature.
  • Ice sponges cool the skin, but don’t actually lower core temperature.
  • They only alter how hot you “feel”.
• Heat doesn’t necessarily or only slow you down through physiological effects.
  • Instead, the brain moderates pace to keep your body below critical thresholds.
• Improve your perception of heat.
  • The right frame of mind may allow you to push beyond usual temperature limits.
• Drinking crushed ice slushies.
  • Lowers core temperature:
    • Phase transformation of ice to water in the stomach.
    • Stomach has temperature sensors.
  • Lowers brain temperature:
    • Ice passing through mouth and throat may also cool the brain.

Endurance limits: dehydration

• Human body is about 50-70% water.
  • It needs pretty much all of that.
  • Fluid balance fluctuates throughout the day, but regulated fairly precisely.
  • Need to replace water lost to through sweating (during exercise).
• Dehydration.
  • Kidneys begin to reabsorb fluid (that would have otherwise become urine).
  • Fluid will start draining from cells to maintain necessary level of blood.
  • Blood becomes so concentrated that brain shrinks.
  • Lower blood volume compromises body’s ability to regulate temperature.
• Thirst versus dehydration.
  • Thirst:
    • Feeling that you would like to take a drink.
    • Body’s way of ensuring that you top op fluids.
    • Brain monitors concentration of small particles (sodium, etc.) in the blood.
    • If concentration too high, brain signals thirst.
  • Dehydration:
    • State of having lost fluids relative to your normal levels.
• You can tolerate some level of dehydration, without getting thirsty.
  • “Born to run” theory: ability to tolerate some dehydration without negative performance effects.
  • Body also reacts by adjusting the amount of salt in our sweat to keep concentration stable.
  • Some of the fluids lost to sweating are replaced internally (by water “unlocked” and released as by-product when you burn carbs or fat).
• How much dehydration is acceptable?
  • Unclear how much fluid loss is acceptable without deterioration in physical performance (likely > 2%).
  • Collapses post finish line may be due to halting of exercise, not dehydration per se.
    • Blood pools in the legs, dizziness ensues.
    • Solution: elevate legs, re-hydrate.
• Suggestion: drink according to thirst.
  • Perception matters.
  • Thirst, not dehydration, increases sense of perceived effort.
  • Mere act of swallowing fluids fights thirst and improves performance.
• Hyponatremia.
  • Over-hydration.
  • Dilutes blood levels of sodium.
  • Lungs fill with fluid, brain swells.

Endurance limits: fuel depletion

• Fuel = energy.
  • Food contains energy stored in the form of chemical bonds between atoms.
  • As the food is metabolized, energy bonds are broken.
  • Energy released powers muscles and other organs.
• Performance depends on:
  • What (type of fuel is available).
  • Where (it’s stored).
  • How (quickly you can access it).
• During prolonged exercise, you mostly rely on carbs and fat.
  • Limited role for protein.
• Balance between carbs and fat depends on how hard you are working …
  • Easy exercise: mostly fat (supplied through bloodstream).
  • Speed up: add carbs to the mix.
  • Hard exercise: mostly carbs.
• … fitness …
  • The fitter you are the greater the proportion of fat you burn at a given exercise intensity.
• … and diet.
  • Eating a diet high in either fat or carbs tilts the preferred fuel mix in that direction.
• Using carbs as fuel:
  • Finite amount of carbs stored in the body.
    • Stored in the muscles: about 2,000 calories.
    • In the liver: about 400-50 calories.
    • Circulating in the blood: minimal amount.
  • Therefore, makes sense for endurance athletes to stock up on carbs.
    • General diet: 60-65% of calories from carbs.
    • Pre-race: top up couple days before.
    • During race: 60 grams an hour (250 calories) is maximum absorption from intestine into the bloodstream.
  • May offer instantaneous boost.
    • For example, only rinsing a sports drink in the mouth.
    • Mouth has carb sensors that signal to the brain that fuel is on the way.
    • Only works when you are low on fuel.
• Using fat as fuel:
  • Body stores much more fat (30k+ calories) than carbs.
    • Makes sense to try and tap into the bigger “gas tank”.
  • But, some caveats.
    • Requires time for the body to adapt to accessing fat stores.
    • Compromises speed (which requires anaerobic, quick-burning carbs) for endurance.
    • Likely less efficient (burning fat requires more oxygen).
    • Doesn’t work for everyone.
  • Makes sense for low heart-rate, aerobic endurance activities.
    • Reduces your dependence on external (or internal) carbs.
• Metabolic flexibility.
  • “Train to burn fat, race on carbs.”
  • Carbs as a fast fuel with limited storage capacity.
  • Fat as an inexhaustible but rate-limited alternative.
  • How:
    • Overall high fat, targeted carb use before and during key workouts and races.
    • Deliberately depleted carb store workouts (no breakfast exercise, bonking).

Limit breakers: training the brain

• Pacing: anticipatory regulation of performance.
  • Brain has access to and integrates psychological and physiological cues.
    • Indicators of body temperature, oxygen levels, fuel storage, mood, etc.
  • Brain compares the effort you feel to the effort you expect to feel at that stage.
    • Internal template that you develop and fine-tune through experience and training.
• Effort is what matters.
  • How hard it feels dictates how long you can sustain it.
  • Anything that moves the “effort dial” in your head will affect your endurance.
• How do you train effort?
  • Training the body: helps make the effort feel easier.
  • Training the brain: similar effects (caffeine gum to block fatigue receptors in the brain, self-talk, etc.).
• Training the brain.
  • In some sense, all training is brain training…
    • Physical training recalibrates the brain’s horizons (pain threshold, heat tolerance, etc.)
  • Train when mentally fatigued.
    • Not just when you are fit and ready.
    • Train after a hard day at work.
  • Train response inhibition.
    • By inhibiting responses over and over in a systematic way.
    • Insular Cortex is region in the brain that monitors sensory signals from within the body (interoception).
    • Subduing the natural (over)reaction to discomfort.
    • Mindfulness, non-judgmental awareness.
    • Monitor how the body feels, while suspending judgment.
    • [See “The Inner Game of Tennis”.]

Limit breakers: zapping the brain

• Brain is a giant electric circuit.
  • Web of inter-connected neurons that communicate by firing electric discharges.
• Transcranial Direct Current Stimulation (tDCS).
  • Sustaining a small trickle of current for 10-20 minutes to alter sensitivity of neurons.
  • Priming the brain to respond differently to a stimulus (more or less likely to fire).
  • Turn down insular cortex (brake signal), turn up motor cortex (keep driving).
• Promising, but complicated.
  • Many different feedback loops, many inter-related brain regions involved.

Limit breakers: belief

• Many supplements or training aids boost performance by 1-3% .
  • Beet juice, caffeine, altitude training, positive feedback, etc.
• Combine these approaches and you see: still only an improvement of 1-3%.
  • 1 + 1 + 1 = 1…
• Reason: training aids mostly have the same (mental) objective.
  • Objective is to raise expectations (placebo effect: if you think it will work, it will work).
  • Raised expectations also trigger beneficial brain pathways (activating endorphins, endocannabinoids, etc.)
• Over time, raised expectations develop and build strong belief.
  • Self-fulfilling belief in your own competency.
  • Awareness that you can do more than you think you can do.
• Acquiring justified and true beliefs about your own capabilities.
  • Requires testing yourself.
• Training is the cake and belief is the icing.
  • Helps you access your hidden reserves.
• Side note: drawbacks of “perfect pacing”.
  • May produce good results on average and lower risks of a blow-up.
  • But may be self-limiting by putting a ceiling on performance.
  • Takes away the opportunity to produce breakthrough or dramatic outperformance.
  • Especially when using technological aids.