[mftrhu]

> accelerate human body to the speed of light

Nothing with mass can have the same speed as light, but you can trivially accelerate a human body - or something similar - to a speed which is arbitrarily close to it, without risking anything from the G-forces involved.

You just need to do it very slowly.

That is, in any case, neither here nor there, since this is a thought experiment used in a discussion about the effects of moving at a speed close to c - people in thought experiments are stronk.