The two men who made the final trek — Parrado and Canessa — were walking through snow and over glacier ice for ten days in conditions that posed ongoing frostbite risk. The improvised footwear they had — rugby cleats modified with metal — provided grip but not insulation. The sleeping bag they carried allowed them to survive overnight but did not make overnight stops comfortable. They were, throughout the trek, pushing against the physiological limits of what their bodies could sustain.
That they completed the trek is, from a purely physiological standpoint, remarkable. Both men had spent 60 days at altitude on a severely inadequate diet before they began walking. Their muscle mass had been significantly depleted by malnutrition. Their cardiovascular systems were stressed by altitude. Their immune systems were compromised by malnutrition and cold. The bodies they were asking to climb an 800-meter ridge and then walk 60 kilometers through difficult terrain were not in normal condition. They were, in the technical sense, seriously ill people who went for a very long walk.
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## The Mathematics of Starvation
The food rationing system the survivors used in the first weeks — before the aircraft provisions ran out — was precise in a way that reflects both the mathematical clarity of their situation and the collective discipline required to maintain it.
The aircraft had been stocked for a short charter flight: enough food for 45 people for a few hours, plus perhaps some modest extras. The survivors, working from what they could account for, estimated their total supply. Divided among 33 initial survivors, rationed strictly, they calculated they had perhaps a week’s worth of provisions — not in the sense of adequate nutrition but in the sense of something to distribute.