Thread by @anishmoonka

Right before you fall asleep, your hands and feet get warmer. That warming is the real trigger that switches your brain into sleep mode. A 1999 Nature paper tested it against melatonin, core body temperature, heart rate, and how sleepy people felt. The hand and foot warming won.

The drawing in the tweet works on this exact trigger. The pose has a name in Japan: Mōkan Undō, or "capillary exercise." Katsuzō Nishi designed it in 1927. He was the chief technical engineer on the Tokyo subway, Japan's first. It became one of six daily exercises in his system, still done in Japan today.

You lie on your back, point your arms and legs straight up, and shake them for thirty seconds. While the limbs are up, gravity drains the blood from them. When you lower them, the blood floods back into your hands and feet, warming them in seconds. Your brain reads that warming as a green light to sleep.

The shaking activates a separate reflex, the kind most mammals use after a scare. Dogs and rabbits shake themselves off after a fright for the same reason. Dr. David Berceli, a trauma therapist, built a whole method around it, with certified instructors now in 40 countries. The shaking flips your nervous system out of "I'm wired" mode and into "I'm safe to sleep" mode.

Nishi got the biology wrong. He believed capillaries, the tiny blood vessels at the ends of your veins, did the pumping. William Harvey, an English doctor, had shown the heart did the work, three centuries earlier, in 1628. The exercise still works, for entirely different reasons than Nishi thought. The drained limbs come back warm. The body reads that as a sleep cue, and the shaking calms the nervous system on top of it.

A drawing on X with millions of views just rediscovered a 100-year-old Japanese sleep exercise. A subway engineer designed it first, decades before sleep scientists figured out why it would work.

Thanks for going down this rabbit hole ❤️

Follow @anishmoonka for daily stories across science, history, psychology, culture & AI.

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Sources:

Kräuchi 1999 Nature — “Warm feet promote the rapid onset of sleep”
nature.com/articles/43366

Raymann 2005 Am J Physiol — “Cutaneous warming promotes sleep onset” (causal follow-up to Kräuchi 1999)
journals.physiology.org/doi/full/10.11…

Nishi Shiki — Wikipedia entry covering the six exercises including mōkan undō
en.wikipedia.org/wiki/Nishi_Shi…

Katsuzō Nishi — biography with Tokyo subway role
en.wikipedia.org/wiki/Katsuz%C5…

TRE Global — Dr. David Berceli’s Tension and Trauma Releasing Exercises
treglobal.org

Part 2. Japan has the shortest average sleep in the developed world, and the longest average life. Sleep: seven hours and twenty-two minutes a night. Life: eighty-five years. Japanese women have topped the global life expectancy chart for forty straight years.

The drawing in the tweet is part of something bigger. The Japanese have built small daily physical rituals into national life at a scale no other country matches. Each week, more than twenty million Japanese take part in a ten-minute calisthenics broadcast that airs every morning on national radio. The broadcast is called Radio Taiso. It has aired daily at 6:30 AM since 1928.

Radio Taiso came from America. In the 1920s, Metropolitan Life Insurance Company aired a radio calisthenics program for its policyholders. Japanese postal officials visited, brought the idea home, and built a national infrastructure around it. The Americans abandoned theirs decades ago. The Japanese still do theirs.

Sleep deprivation costs the Japanese economy fifteen trillion yen a year, about one hundred billion dollars. Thirty-nine percent of Japanese adults sleep under six hours a night. They are not sleeping well. But they are doing something the rest of the developed world has stopped doing: showing up, in groups, daily, for free, to move their bodies in the same way at the same time.

Japan has more centenarians per capita than almost any country on Earth, roughly three times the US rate. As of late 2025, the count was ninety-nine thousand seven hundred and sixty-three people aged a hundred or older, virtually identical to the US total in a country one-third the size. Japan has set a new national record fifty-five years running.

The US sleep aid industry runs to about forty-four billion dollars a year. Melatonin gummies, weighted blankets, sleep tracking rings, mattress brands, prescription sedatives. The Japanese counterpart is a drawing of someone lying on their back, flapping hands and feet for thirty seconds before bed, now at 5.3 million views on X.

Nobody is selling it. That might be why it works.

Part 3. Your brain has a built-in cleaning system, and it only runs while you sleep. The researcher who discovered it calls it a dishwasher: it loads up during the day, runs at night, and you wake up to a clean brain. Skip a single night and the Alzheimer's protein in your brain rises by five percent.

In 2013, a neuroscientist named Maiken Nedergaard at the University of Rochester discovered the system and called it the glymphatic system. The name combines "glia," for the brain's support cells, and "lymphatic," for the body's normal waste-drainage network. When you fall asleep, the space between your brain cells expands by sixty percent, and spinal fluid floods in to pick up the day's metabolic waste and drain it out. The whole process pauses the moment you wake up. The system is so recent that doctors trained before 2013 never learned about it in medical school.

What gets washed out matters. One of the main waste products is beta-amyloid, the protein that aggregates into plaques inside the brains of Alzheimer's patients. Healthy older adults still have some. People with Alzheimer's have about forty-three percent more.

In 2018, researchers at the National Institutes of Health put twenty healthy volunteers in a PET scanner, kept them awake for thirty-one hours, and scanned them again. The Alzheimer's-related protein had risen by five percent overnight, concentrated in the hippocampus and thalamus. Those are the exact regions where Alzheimer's damage first appears.

The exercise in the source tweet works on the front end of this cycle. Falling asleep faster means more time for the cleaning system to work, since it is most active during deep sleep. Hours of insomnia mean hours subtracted from the shift.

Every minute you lie awake is a minute lost from the brain's cleaning shift. A 30-second bedtime exercise might be the cheapest way to start the shift sooner.

Part 4. A 2013 study at Henry Ford Hospital gave twelve people 400 milligrams of caffeine, roughly two strong coffees, six hours before bedtime. The next morning, their sleep monitors showed total sleep time had dropped by more than an hour. The participants said they had slept fine.

The reason: caffeine has an average half-life of five hours. That means if you drink a coffee at 3 PM, about a third of the caffeine is still active when you try to fall asleep at 11 PM. Caffeine is a stimulant by accident. The molecule happens to look enough like adenosine, the natural compound that makes you feel tired, to slot into the same receptors and block them. Once it does, adenosine cannot bind. Your brain stops registering that you are tired.

The five-hour average hides a huge range. Caffeine half-life across healthy adults runs from one and a half hours to ten, driven mostly by a gene called CYP1A2. A fast metabolizer clears half the dose in three hours. A slow metabolizer still has half of it circulating ten hours after the cup.

Drake's participants did not notice the disruption because caffeine attacks sleep quality more than total time asleep. A 2023 meta-analysis of twenty-four studies found that caffeine cuts deep sleep by about eleven minutes per night and adds twelve minutes of overnight wakefulness. People wake up feeling rested. The sleep was lighter than it would have been without the caffeine.

This is the part that makes the bedtime exercise in the source tweet useful or useless. A 30-second physical routine before bed can help your body slip into sleep mode, but it cannot un-block your adenosine receptors. If there is still caffeine in your system, your brain cannot reach the tired state.

The clean afternoon math: if your bedtime is 11 PM, your last serious caffeine should be by 3 PM. For a slow metabolizer, closer to 1 PM.

Coffee is fine. The hour you drink it matters more than the amount.

Part 5. A Virginia Tech historian named Roger Ekirch was reading a London legal deposition from 1697 when he noticed something strange. A nine-year-old girl described how her mother had awakened after her “first sleep” to go out. The phrasing was casual. Like it was the most normal thing in the world.

Ekirch began searching, and found more references, then more. He has now documented over two thousand mentions of “first sleep” and “second sleep” across a dozen languages. The oldest goes back to Homer’s Odyssey. In nearly every preindustrial Western society, people went to bed around nine or ten at night, slept for about three hours, then woke up. For the next hour or two they prayed, made love, smoked, worked, or visited neighbors. Then they went back to bed for a “second sleep” until dawn.

The eight-hour consolidated sleep most of us treat as natural is roughly one hundred fifty years old. It is the byproduct of artificial light, factory schedules, and industrial work.

In 1992, a psychiatrist at the National Institute of Mental Health named Thomas Wehr tested whether the old pattern was still hardcoded into human biology. He took seven healthy men and locked them in a room for fourteen hours of darkness every day, for one full month. The first few nights, they slept eleven hours straight to repay sleep debt. By the fourth week, their sleep had naturally split into two separate blocks of about four hours each, with a one-to-three-hour wakeful gap in the middle. Their bodies had reverted to the pattern in Ekirch’s records from 1697.

Sleep researchers have started to take this history seriously. Charles Czeisler, Harvard’s sleep medicine chief, has called Ekirch’s research a major contribution. Johns Hopkins sleep specialist David Neubauer has said the modern eight-hour ideal of consolidated, unbroken sleep is itself an unstable invention of the industrial era. Waking up at 2 or 3 AM for an hour may not be a malfunction. It might be the original setting your nervous system has not entirely let go of.

The bedtime exercise in the source tweet addresses falling asleep, the easier half of the modern problem. Most sleep complaints today are about staying asleep through the entire night. The historical record suggests that part is fighting human biology.

Your middle-of-night wake-ups might be ancestral biology. The eight-hour standard is the modern invention.

Sources for Parts 2-5

Part 2 - Japan Sleep Paradox (Radio Taiso, MetLife, centenarians)

OECD 2021 sleep duration data — Japan’s 7h 22m average
fpcj.jp/en/assistance-…

AP report on Radio Taiso — 20 million weekly participants, 1928 origin, US insurance company source
kiro7.com/news/health/ja…

Japan MHLW September 2025 — 99,763 centenarians, 55th consecutive record
newsonair.gov.in/japans-centena…

Pew Research Center — US centenarian count and global per-capita comparison
pewresearch.org/short-reads/20…

Market Data Forecast — US sleep aids market 2024 valuation
marketdataforecast.com/market-reports…

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Part 3 - Glymphatic System (Nedergaard 2013, beta-amyloid, Alzheimer’s)

Xie et al. 2013, Science — “Sleep drives metabolite clearance from the adult brain” (original glymphatic discovery)
pmc.ncbi.nlm.nih.gov/articles/PMC38…

Shokri-Kojori et al. 2018, PNAS — “Beta-amyloid accumulation in the human brain after one night of sleep deprivation”
pnas.org/doi/10.1073/pn…

NIH plain-language summary of the 2018 study
nih.gov/news-events/ni…

Scientific American 2025 — “How Sleep Cleans the Brain and Keeps You Healthy” (Nedergaard’s dishwasher quote)
scientificamerican.com/article/how-sl…

Nedergaard and Goldman 2020, Science — “Glymphatic failure as a final common pathway to dementia”
science.org/doi/10.1126/sc…

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Part 4 - Caffeine (Drake 2013, half-life, CYP1A2, adenosine)

Drake et al. 2013, Journal of Clinical Sleep Medicine — “Caffeine effects on sleep taken 0, 3, or 6 hours before going to bed”
jcsm.aasm.org/doi/10.5664/jc…

AASM press release on Drake 2013 (with the “participants unaware” finding)
aasm.org/late-afternoon…

NCBI Bookshelf — Pharmacology of caffeine (half-life range, metabolism)
ncbi.nlm.nih.gov/books/NBK22380…

2023 systematic review and meta-analysis of caffeine effects on sleep architecture
sciencedirect.com/science/articl…

Mahdavi 2023, JAMA Network Open — CYP1A2 variation and caffeine metabolism
pmc.ncbi.nlm.nih.gov/articles/PMC98…

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Part 5 - Two-Phase Sleep History (Ekirch, Wehr 1992)

Ekirch’s faculty page at Virginia Tech with full bibliography and 2,000+ reference repository
sites.google.com/vt.edu/roger-e…

Wehr 1992, Journal of Sleep Research — “In short photoperiods, human sleep is biphasic”
onlinelibrary.wiley.com/doi/10.1111/j.…

CNN 2022 interview with Roger Ekirch on biphasic sleep history
cnn.com/2022/01/09/hea…

Harper’s Magazine 2013 — “Segmented Sleep” by A. Roger Ekirch (Neubauer quote on consolidated sleep as unstable invention)
harpers.org/archive/2013/0…

National Geographic 2024 — Background on Wehr’s experiment and modern segmented sleep
nationalgeographic.com/science/articl…