|MadSci Network: Biophysics|
To tell you the truth I had never heard this said beore. I have never been in the air force though, and talk of pulling Gs outside of the airforce is rare apart from the aerobatic crowd.
You black out (or grey out) when pulling positive Gs beause the heart is unable to pump blood up to the brain. The two main ways of overcoming this are to increase the pressure through musclular squeezing/straining (hence the grunting you sometimes hear airforce pilots doing), or the wearing of a "G suit" that inflates and puts pressure on your legs and lower abdomen during positive Gs. Sort of like squeezing the bottom half of a balloon to force air into the top half.
I was unable to find much on the internet. A few sites made the statement without further elaboration. Some forums on women's issues mentioned it was due to the heart being closer to the brain and the smaller body mass.
Some slightly authorative references I could find
It however implies women have less g force endurance than men.
This article also implies slightly less g foce endurance for females http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=11506236&query_hl=2
And this article (near the bottom) says pretty much the same thing.
Finally this study says they perform similarly http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12433235&query_hl=8
Basically, there doesn't seem to be enough information to say one way or the other. There may be some factors that would theoretically help females, in terms of pulling Gs, but real world experiences, and some initial studies in airforces seem to be saying the opposite. However this could simply be due to the fact that "g suits" are designed for the male anatomy.
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