A bare room at a Dutch university hospital, a steel tub, and a man sitting in it up to the shoulders.
The tub is packed with crushed ice, not cold water, so the shards are resting directly against his skin.
A swallowed capsule is reporting his internal temperature. Sensors on his skin report the outside.
He sits for 88 minutes and does not move.
Nothing about him shakes.
His inside barely cools.
What the cold is supposed to do to a person in that tub
A body in ice defends its core first and treats the skin as expendable, which is why the surface goes cold so fast.
Blood vessels near the skin clamp down within seconds. That pulls warm blood inward and leaves the outer shell to fall toward the temperature of whatever it is touching.
Once the brain sees the core itself starting to slide, it orders muscle to burn fuel by shaking, and shivering can lift heat output several times over resting level.
It is also expensive and unpleasant and it usually loses. Clinical hypothermia begins at a core of 95 degrees Fahrenheit, and in a tub like that most people are heading for it.
Shivering itself gives out somewhere around 86 to 90 degrees of core temperature, and after that the fall accelerates.
The skin is given away. The core is defended.
What the instruments actually recorded
His skin did what skin does. Sensor sites that started between 82 and 93 degrees ended the session between 39 and 59 degrees.
The coldest of those readings is a little over a degree above freezing, on living tissue, held there for most of an hour and a half.
His internal temperature went from 99.9 degrees to 98.6 over the full 88 minutes. That is a loss of about 1.3 degrees.
Oxygen uptake doubled, and heat production rose from 169 watts at rest to about 321 watts.
Heart rate peaked at 101 beats per minute and mean arterial pressure at 115, both unremarkable for a man under that much stress.
Skin fell 54 degrees. The core fell one.
Where the missing heat was coming from
Doubling your heat output while sitting perfectly still is the part that needs an explanation, and the usual one is brown fat.
Brown adipose tissue sits mostly around the collarbones and neck. It burns fuel to make heat directly, with no muscle contraction involved, which is exactly what this looks like from the outside.
So imaging was pointed at it. Scans during cold exposure found roughly 25 grams of brown fat active in him, which is below the range measured in untrained comparison subjects.
What lit up instead was the muscle between his ribs. Glucose uptake and sympathetic activity in the chest wall ran above the comparison range, and that tissue was working hard because he was breathing hard.
Forced deep breathing is muscular work, and muscular work makes heat. The heat is generated a few inches from the lungs and the blood leaving them carries it inward.
The chest is a furnace. Brown fat is a bystander.
The relative who did none of the training
The neatest test of whether any technique deserves the credit was run on him and his identical twin brother, who has no cold training at all.
Both men were scanned in the cold. Brown fat activity came out at 1,144 in the trained brother and 1,325 in the untrained one, so the difference ran the wrong way.
Cold induced heat production was 40.1 percent in one and 41.9 percent in the other, against a normal young adult range of roughly 7 to 18 percent. Neither of them shivered.
That result is awkward for everybody. The trained man is not physiologically special compared to his twin, and the untrained twin should not be able to do this either.
Genetics is the obvious suspect and it is not a new idea, given what ancient DNA appears to do to cold tolerance.
Two brothers, one training log, identical results.
What this does not license anybody else to try
The record this man is usually credited with no longer stands. The longest documented full body contact with ice now runs past five hours and belongs to a Polish athlete.
More importantly, the crushed ice is the safer half of the practice. The breathing that precedes it drops carbon dioxide so far that a person can lose consciousness without warning.
Doing that in or near water is how the method has accumulated its casualties, and there are dozens on record along with active litigation. The physiology here was measured on a single trained man under continuous medical monitoring.
Breath control changes what a body can survive, which is also visible in the 29 minutes a diver spent face down in a pool.
The temperatures, the oxygen uptake and the watts are all listed in the case study.
Eighty eight minutes in crushed ice is one data point, and the mechanism behind it is still partly open.
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