Hacker News Reader

Comment by CobaltFire | Hacker News Reader

The fact that women, as a general rule, are more air efficient at the same mass is generally well known in diving.

I'm highly air efficient for a man, but only moderately more air efficient than the average of the women I've dove with (as in I've only dove with a couple men as air efficient as I am, but 20-30% of the women I've dove with are MORE air efficient than I am, sample somewhere north of 200 total with a roughly 33% female population).

I can't speak to the rest of the paper's conclusions.

View on HN

Does that "fact" hold up when you control for body mass and fat/muscle ratio? Because I suspect in reality this only means that we should send smaller people with fewer muscles into space. Life expectancy for example does not correlate with gender anymore once you account for body size.

That sounds very interesting, so you have a source for that? I could not find anything on Google searching for "life expectancy, gender and size".

I believe David Sinclair talks about this in detail in his book "Lifespan: Why we age"

Personally, I see this is less as a real research discovery and more like a cautionary tale on the pitfalls of statistics and the need for multivariate regressions with control variables.

That's an absolutely fascinating aside right there. Gonna have to look into that one.

This is an excellent point, and likely one of the main drivers.

How much that muscle mass means for the given mission is a separate, but relevant factor.

In diving, the main factor in determing air use (SAC rate if we want to use diving termonology) is work load. The more a person is relaxed and in rest, the lower the respitory rate will be. The more excertion a person do, like fighting a current, the higher it will be.

A smaller profile will also help in reducing drag. A smaller frame also need less air in their suit (both dry and wetsuit). This is likely however to impact resistance to cold.

While true this is orthogonal to the fact that for a given workload females seem to be more efficient.

That said, they generally have less capability for work at the same mass.

There seems to be a trade off between efficiency and power density, which is what this study is probably getting at.

Reading the article, it is unclear if they are comparing similar workloads. The article seems more focus on similar goals.

There are likely interesting differences based on density and base body functions that scale in non-linear ways. I expect however that all those would be minor gains compared to exertion rate, especially when it comes to oxygen consumption. If we use diving again as an example, a person just floating still will be using less than half the oxygen compared to a person swimming against a mild current. Heavy work can easily go past 4x or higher compared to the oxygen consumption of a person in rest, which is a major problem for rebreather divers who are limited by their equipment in term of scrubbing co2 (for every 1x of oxygen consumed, 0.9x of co2 is produced).

Reply on news.ycombinator.com