The altitude tent buys you red cells and charges you sleep

Nobody puts the disturbed nights on the other side of the ledger, and for some athletes that column is the bigger one.

The pitch for a hypoxic tent is neat. You get the stimulus of living high without leaving home, without the flights, and without dragging your quality sessions up to a track where you cannot hit the paces. Live high, train low, from a bedroom in a flat city.

The mechanism is genuine. Spend enough hours a day in reduced oxygen and the kidney reads the signal, the hormone rises, and over weeks you make more red cells. The dose that matters is hours, and the number people quote is high. Twelve to fourteen hours a day for three weeks or more. That is not a nap. That is your whole night plus part of the evening, every night, inside a plastic box with a fan running.

Which brings me to the column nobody fills in.

Breathing at low oxygen destabilises sleep. Ventilation cycles, the athlete wakes more often, deep sleep gets fragmented, and the effect is worst in the first week, which is also the week people are least tolerant of the noise and the heat inside the tent. Meanwhile the entire recovery apparatus of an endurance programme runs on sleep. Tissue repair, the consolidation of motor learning, mood, appetite regulation, and the immune system that keeps a runner from losing ten days to a chest infection in March.

So the honest accounting looks like this: a modest gain in oxygen carrying capacity, set against a measurable degradation in the process that lets an athlete absorb training at all. For a sound sleeper with high tolerance, the trade is probably positive. For an anxious athlete who already sleeps badly before races, it is very likely negative, and no blood test will show you that.

I think the tents are oversold to the exact group they suit worst. Younger athletes, self funded, no sleep tracking, no medical support, buying a second hand unit online because a professional posted about one.

If you use it, do it properly. Baseline your sleep for two weeks before you switch it on. Ramp the simulated altitude slowly instead of starting at the number you read in an article. And accept the rule that should govern the whole thing: if the sleep has not recovered by the end of week one, the tent is losing you more than it is making.