Just for interest, I'll post the iron palm training that was taught to me -- it's a series of hand positions with the bag on a flat surface in front of me, dropping the body, not the arm, so the hand will strike the bag as I drop. we are to train each bag filling for two years, I think -- nine months on, three off -- winter and summer -- this for healing time. we are to apply the ointment after training, for healing as well - dit ja (sp?) and the series is mung beans, sand, gravel, ball bearings.
I stopped at sand for musical purposes -- probably not necessary but my preference.
Hard body chi gong is discussed by yang in his book called "the roots of chi gong." breath is emphasized in all hard body training, including iron palm, in my school.