I know a lot of people seem to be using Deshaker for those kind of videos, but it's not really designed to handle videos where the camera "moves around", at least not where it moves very fast. Deshaker can only handle panning, rotation and zoom. That said, I've seen some very good deshaked videos of that kind.
As always, make sure you're using a high enough shutter speed, if possible. There shouldn't be any motion blur in each frame.
Also, you would probably get *a lot* better results if the camera didn't have a rolling shutter. But I believe most helmet mounted cameras today have a rolling shutter. Deshaker can remove rolling shutter effects but only if the shaking isn't extreme.
I would also recommend trying to stabilize only on the most distant parts in the frames, since the "moving inwards"-effect is less there. You can do that by ignoring the other areas.
And turn off zoom smoothing by settings zoom smoothness to 0. You will also need to change the edge compensation type if you do that. Start with "None", maybe.
Finally, you should probably increase the value for "discard motion of blocks that move > X pixels in wrong direction". That's to allow the blocks to move "freely" a little, since Deshaker can't handle the "moving inwards"-effect.
But maybe you should ask someone who's actually stabilized these kind of videos. I haven't.
