When the swelling in my neck finally subsided, my muscles had atrophied so badly that my chin was on my chest.

To rebuild the muscles, my PT had me do isometrics. It doesn't seem like much, little pushed under the chin, on the forehead, etc... but it does work.

I doubt any of that would help spare me from future concussions, but it did help with lessen the headaches and ease some neuro symptoms.