Hadronic Equipartition of Quark and Glue Momenta
  If the ``glue'' which binds quarks within hadrons takes the form of strings, then a virial theorem may be derived which shows how the total hadron four momentum splits up into a quark contribution plus a glue contribution. The hadrons made up of light quarks exhibit an equipartion of four momentum into equal parts quarks and glue. The agreement with the experimental ``parton'' distribution four momentum sum rule is quite satisfactory as is the string fragmentation model. 
Y.N. Srivastava, A. Widom