Nuclear muon-capture sum rules and mean nuclear excitation energies

A discussion is given of non-energy-weighted and of energy-weighted sum rules in nuclear muon capture. It is argued that the mean nuclear excitation energy in muon capture does not vary appreciably as $A$ and $Z$ vary. A combined non-energy-weighted and energy-weighted sum rule which constitutes a three-parameter fit to the experimental data on total muon-capture rates is presented.