Finally did it. It's still a wip, and need some work, but i have succed to switch between keyframe character animation and ragdoll physics. For realistic animation, I needed to find a solution to paste bones biped animation to my own bones skeleton. 3dsMax biped are too detailed to use with md5 and Physics. So I used my own bones sketeon (11 bones in red in the jpg). When I tried to link my bones to biped's bones, I had some weird issues when exporting animation
I found a solution to paste biped animation to my bones, and have a clean MD5 export . As I said, link bones to biped part doesn't work. So I use for each bone's position the controller 'Position Constraint' and for bone's rotation the controller Orientation Constraint ( .jpg attached file).