And... There is an important perspective with this possibility. When they zip off and defy inertial and G forces they are not physically moving that fast. It only appears so to us the observer. They are moving at a safe speed to themselves but accelerating space time instead. So they are moving at a comfortable clip themselves physically but their space time has accelerated in comparison to our own time frame as the observers. Their time is passing faster than ours is as we observe them. And they can speed theirs up or slow it down at will. Which appears to us to be physically moving faster or slower. I think we are looking at it from the wrong perspective and speed is actually an illusion of variable time difference.
And this would explain why they do not get squashed like bugs inside their craft when they make such drastic immediate high speed direction changes.