Physic problem


i have one issue that i cant fix , i will be very thankful if somebody can give help on this . I have exported character from 3ds max ,Rigged mesh with biped bones, then i import it in UE4 and i set up the physic and some animations all works fine.
But when i set up some fast animation like fast attack or run , the bones of the mesh start to detach if they move to fast … i record video to show how if i move the mesh fast the bones fly around in the air ,

Please if somebody know how i can fix this

video linck :

Thanks so much !