What physics could be applied to accelerate a person from zero to 8000 m/s if you want to: a) Minimize the time, and b) Not kill or hospitalize them? My thoughts on this are that you would:

*

*Immerse the person facing forwards in a neutral buoyancy fluid,

*Slew the acceleration up and down just enough to avoid shock waves in their body,

*Increase air pressure in their lungs during acceleration to prevent their lungs from collapsing,

*Train and/or prepare the person in some way to better survive the high gees.

*Directly support their bones, which are denser, with many temporarily implanted "cradles" of thin high-strength fiber. These fibers would be detached and pulled out after launch, like stitches.

Let's assume that some bruising, small punctures that will heal, and passing out would be considered acceptable. Slow recovery, hospitalization, organ damage, or adverse long-term health effects would not be ok.
What kind of acceleration times might be possible?
(Note: $t=8000/a$, and $d=0.5at^2$. For example, if $a=400m/s^2, t=20s$ and $d=80km$)
Any thoughts on where laws of physics and limits human physiology place a hard limit on what is possible? Are there any specific hard-to-avoid ways that brief-but-intense acceleration will damage the human body?
 A: The pseudonymous James S.A.Corey addresses this pretty well:  To survive the accelerations possible with the Epstein Drive,  the characters have to inject special fluids to pressure-balance.
Yes, I know that's SciFi.  My point is that you cannot exceed certain accelerations regardless of the external (to the human body) conditions.  You have to do what is essentially SciFi "magic" to keep the various internal organs at a matching pressure to that created by the acceleration.  Scuba divers do this to some extent by breathing pressurized air; depressurization doesn't work perfectly.
I'm aware of the "G-suits" that fighter pilots and the like use, but those primarily ensure that blood doesn't pool in extremities, thus avoiding blackouts due to lack of blood in the cranium.  That's a different issue.
A: See this article. The human body is capable of withstanding several $G$'s of acceleration for a brief period, but prolonged high acceleration will be fatal. In fact, to be comfortable, $1G$ is about all you can do.
To get to $8000m/s$ at $1G$ acceleration, you need about $800$ seconds.
