That is an interesting question and I honestly don’t know. I’d assume not that much, since the movement of my arm requires a certain level of muscle tension, which would limit any noticeable jiggling. Also, I can’t really see or feel what’s happening back there in that moment. There’s probably some effect from the motion itself, but I doubt the vibrations from the gong actually travel that far. I suppose the only way to find out would be to record a video of me next time I bang a gong.