A fascinating question, which I thoroughly enjoyed researching...
The following article indicates that roller-coaster riders may have
to fear than astronauts:
"Can Roller Coasters Cause Brain Trauma?"
"While G-force gives riders the thrill they experience, it also can
injuries including bleeding in the brain and stroke, some researchers
"Space shuttle astronauts experience less than 4 G's during lanch and
re-entry. By contrast, a roller coaster in Houston has been measured
at 6.5 G's, the Times reports."
from The HealthScout News Service, via Arizona Central.com:
From the Australian Department of Defense:
"Large studies of fertility in pilots are limited. Responses to
questionnaires distributed to pilots of the German Federal Armed
Forces suggest that there is no gender bias in the off-spring of
transport pilots. During the first 1000 flying hours of their careers,
there was an over-representation of male offspring to jet pilots,
which reversed after 1000 logged flying hours. However, there
is a severe limitation to studies of this nature imposed by the
numbers of offspring required to provide suit-able statistical power.
Calculations suggest that about 2000 off-spring of these men are
needed to obtain valid answers. Jequier has reported oligospermia
in a fast jet pilot that reverted to normal once flying duties were
ceased. It was hypothesised that G-forces induced a varicocoele-
like situation, and possibly even testicular ischaemia, although this
could not be proven. Attempts at a wider study were abandoned
due to the small numbers, both of pilots and their offspring,
available for investigation (Anne Jequier, personal communication)."
"Unfortunately, there have been so few systematic studies with
appropriate design that the effects of military service on
spermatogenesis, or on fertility in general, are still not clear.
As with many environmental influences, extreme levels of
hyperbaric pressure, G-force and exposure to radiation may have
detectable biological effects on the semen. However, the basic
questions asked by servicemen cannot satisfactorily be answered
at the present time."
...both from an .html version of a .pdf file:
...or download the .pdf file:
On the other hand, horse spermatazoa are routinely centrifuged,
for a variety of reasons, including decreased storage space, and
are exposed to over 400Gs, with no degradation adequate to
motivate processors to discontinue the process, according to
this page, on equine-reproduction.com:
This article, from the August '99 Agrichemical Environmental
News site, mocks a study about the sex ratio of offspring among
fighter pilots being skewed toward girls:
"In a lighter vein, one critic of the JAMA article pointed out the
absurdity of taking the effects of a toxic agent in a specific
circumstance as proof for a universal decline in health. The
writer pointed out that the sex ratio of offspring among fighter
pilots is skewed toward girls, perhaps as a result of one parent
being subjected to higher than normal gravity forces
(i.e., G forces) during acceleration. If this hypothesis is
correct in this specific subpopulation, then logically there should
be a decline in the sex ratio for the whole United States. After all,
high-speed elevators, roller coasters, and airplane travel have
subjected most people to higher than normal G forces."
The study being cited is:
Little, B. B., C. H. Rigsby, and L. R. Little. Pilot and astronaut
offspring: possible G-force effects on human sex ratio. Aviation
Space and Environmental Medicine 58:707-709.
All of the above is from this page:
Here's the cited study:
"Ratio of male to female offspring in tactical pilots and astronauts
who experienced G forces was compared to that of pilots and
non-rated officers who were not exposed to such conditions.
In the analysis presented here we found 62 pilots and astronauts
exposed to higher G forces had a significantly lower ratio of
males to females in their offspring (.40) than did 220 pilots and
non-pilots who were not exposed to high G forces. Other studies
have also reported a decreased sex ratio in offspring of men
exposed to high G forces. Reduction in number of males
produced by fathers routinely exposed to comparatively high-G
stresses may be related to G-force effects on sperm. This study
suggests high-G exposure may affect the reproduction process."
Here's another study, by Goerres HP, Gerbert K. which
contradicts the previous one, saying:
"An old rumor - lately substantiated by statistical examinations
from England - to the effect that pilots of high-performance
military aircraft are "girl-fathers", could be reduced to absurdity
through a comprehensive questionnaire investigation in the
German Federal Armed Forces.Spermiogenesis does not
seem to be disturbed by professional-specific influences
(Radar radiation, G-forces etc.), as implied by the questionnaire
findings. In times of high flying and personal stress (first 1000
flying hours) military jet pilots are even "boy-fathers". As soon
as flying becomes a routine matter (after the 1000th flying hour)
and thus less stressful, jet and helicopter pilots even become
These, and over 12 million medical studies, can be found at:
"PubMed, a service of the National Library of Medicine, provides
access to over 12 million MEDLINE citations back to the mid-
1960's and additional life science journals. PubMed includes
links to many sites providing full text articles and other related
resources." From the PubMed homepage:
Searches done, via Google:
Pilot and astronaut offspring
g-force + sperm-count
"G force" + sperm
Please feel free to post a clarification if this answer is not
everything you hoped for...