Intro

• How does our psychology interact physiology?
• Physiological parameters governing running endurance = 1) aerobic capacity (VO2 max; size of your engine), 2) running economy (efficiency measure), 3) lactate threshold (how long you can sustain activity for long periods of time) → from these, "ideal human" should be able to run a marathon in ~1:56. So what's up with the gap?

Part 1: Mind and Muscle (and Part 2?)

• Endurance = ability to overcome instincts telling you to give up, stop, etc. Not as much distinction between physical and mental trait as one might think.
• We can't help but pacing ourselves— max effort depends on how much more we think we have left to do, we compare to our expectations.
• History... people figuring out fatigue = lactic acid; oxygen enhances performance
• How to measure maximal optimal performance, indep of factors like sleep, diet, motivation? Hill & colleague —> study on "maximal oxygen uptake," AKA VO2max!
• Lots of studies to try to predict max performance using just this metric, but people soon realized that the brain also had a role to play:
  • Anticipatory regulation, to slow down before reaching critical thresholds of physiological distress
  • Facilitates this by limiting amount of muscle recruitment possible → not conscious! Effort feels the same.
• Evidenced by the end burst of speed at the end of a race— trend across basically all running events; and clustering of finishes just under arbitrary round number times
• Perceived effort and motivation = key arbiters of endurance. Effort affected not only by physical factors, but mental fatigue... mental training can thus improve physical performance. Also vice versa: physical fatigue affects mental performance!
• Builds on other body-mind connections; facial feedback hypothesis, etc. all can influence perceived effort. Relaxing your face, self-talk ("Feeling good," etc.), even seeing flashes of smiling face → less perceived effort & better performance!
• Pain: Regular intense physical training correlates pain tolerance— but more complicated than that! Pain is a sensation, an emotion, a drive force (to compel some sort of action). But which way is causation? Probably training → tolerance— in season athletes have higher tolerance!
• Painkillers, adrenaline lessen perceived effort → better performance... but different nuances of pain, and complicated relationship with effort!
• Even with maximum strength exerted by a muscle, we "pace" ourselves. Lack of conclusive evidence on what the physiological most extreme exertion of a muscle is vs what we can voluntarily put forth; lots of tests with electrical stimulation.
• Impact vs non-impact plays a role- feedback from micro-tears in muscle
• Lactic acid & other metabolites = cautionary signal to brain, but "real" limit reached in shorter races (ex. 800 m, where second lap times plateau)
• Oxygen: Free-diving (in all its varieties) = the extreme test of oxygen deprivation. What's the difference between when we actually need O2 and when we think we need it?
• Mammalian dive reflex: face in cool water → heart rate plummets, veins and arteries in limbs constrict to keep blood in torso (heart and brain) & keep lungs from collapsing, "spleen vent" releases oxygenated RBC reservoir (in seals, up to 20 L!). Spleen reservoir also releases RBCs during exercise.
• Part of one of many layer of reflexes to prevent us from drowning, controlled by autonomic NS (not under conscious control), but... HR drops before diving in humans, esp in seals, even if you're then told not to dive! = Anticipatory regulation, where brain uses consciously-gathered info to activate or inactivate unconscious safety mechanisms
• Oxygen scarcity also encountered at altitude. Even at mild heights, athletes → exercise-induced blood hypoxemia, affecting VO2 max.
• But.. if in endurance events, we don't actually operate at/close to VO2 max (usually around 80%, otherwise too hard to sustain), why does it matter?
• Levels of oxygen in the brain may increase fatigue signals; being born at altitude & having active childhood actually physiologically better prepares you to maintain O2 levels (ex. elite Kenyan runners)
• Lactate paradox: normally, produce high levels of lactate when anaerobically exercising. Would expect to go anaerobic sooner at higher altitudes, because less oxygen... but the opposite happens! At 2300 feet, you can't raise your lactate levels at all: higher altitude cause brain to have less oxygen, so it signals to muscles to fatigue sooner, so the muscles don't actually go anaerobic at the usual perceived effort.
• Heat: Our bodies adapt to exertion in the heat over ~2 weeks: sweat more, blood volume increases, etc.
• Performance/endurance affected by brain temperature (drinking cold slushie helps), core temperature (what actually matters?), & perceived temperature (what the thermostat says, putting cold towel around your neck)
• Training, and even self-talk (not thinking about how hot it is, etc) affects heat perception and allows people to push core temperature above usual limit (104 F)! More flexible than once thought (thought just by half a degree or so)
• Heat stroke → gut releases toxins → inflammatory response that eventually kills you. Also, drugs that increase dopamine levels alter heat regulation, increasing risk of surpassing critical temperature.
• Thirst: Not actually a simple rel'ship between hydration & heatstroke!
• Body water levels don't really (shouldn't, at least) vary more than 1 L, but best marathoners are ones who lose the most water weight? Why?
• Difference between thirst— when we feel like we want to drink (brain signal) and dehydration. Many studies confound the two— drinking more or less than you want actually does affect performance, usually; drinking more to avoid "dehydration" may not.
• Actual cause of thirst is blood osmolarity, which is much more tightly regulated than blood volume. Losing weight from exercise can be only 20% water in some cases; also burning glucose and fats, which release stores of water back to circulation.
• Thirst also dictated, as all these factors, by perception: feeling of drinking, knowing you have water. In summary, drink when you're thirsty.
• Fuel: Ratio of carbs vs fats? What your body uses depends on relative intensity of exercise, but majority is always carbs — glycogen stored in muscles being used (2000 kcal per leg!?), ~500 in liver. Ratio can also shift based on what you eat.
• Reliance on fat in diet actually decreases ability to use carbohydrates by downregulating some enzyme in glycolysis!
• Consuming ratio of sugars (glucose AND fructose) → higher rates of absorption, bc uptaken by different mechanisms. People at Nike, etc. trying to "optimise" ratio for specific athletes to maximise palatability, uptake → avoid depleting glycogen stores... BUT gylcogen also helps individual muscle fibres contract efficiently, so reservoir will still deplete before fuel is used up (brain-independent "safety mechanism" for muscles)
• Perception once again plays a role: if you're already in a fuel-depleted state, just tasting sugars without consuming can enhance performance!
• Low carb, high fat (LCHF) at some levels increase fat-utilisation for endurance athletes— shifts HR upwards at which you switch from using fats to carbs, saving those stores for layer, but need carbs for max performance and races.

Part 3: Limit Breakers

(Guess I missed the Part 2 segue-way?)

• Integration of all the psychological and physiological cues = perceived exertion: doesn't wait for catastrophe, but rises as temp increases, glycogen stores diminish.
• Pacing = comparison of anticipated effort & current perceived effort
• Controversy over how conscious these "calculations" are; how much feedback occurs between brain & body
• Lots of stuff about electrical brain stimulation and potential effects of mental fatigue, endurance.. mostly inconclusive
• Distinctions between placebos and belief effects: if swishing sports drinks actually makes you faster, does it matter that it's not "doing" anything? Placebo refers more to trickery; giving someone an inert substance and saying its active. Belief effect more about building trust, evidence-backed approaches.
• Actually a genetic variant associated with how strongly people respond to placebo treatments! Study on a sham acupuncture tx for IBC
• Things like "lucky charms" actually do make you try harder, but also can have physiological effects: ex. telling a runner they look relaxed actually lowers their caloric expenditure.
• Ultimately, best advice is still classic haiku: Run lots of miles Some faster than your race pace Rest, once in awhile
• Relying too much on tech to track pacing, HR, etc actually weakens bond between perception and physical experience