Your body is a surprisingly good shock absorber and the people that have suggested helmet mounting are on the right track. But you need a relatively light camera or it may cause issues is you mount it to the side of your helmet rather than on top. One other issue with helmet mounting is that it does require a bit more discipline in how you hold your head, you have to hold a pretty steady position with regard to level and that is harder than you might realize especially on longer rides or rides with short stretches of intense effort where their may be a tendency to lower your head position. Skewer mounts are used a lot with MTBers.