Running couplings for the simultaneous decoupling of heavy quarks
  Scale-invariant running couplings are constructed for several quarks being decoupled together, without reference to intermediate thresholds. Large-momentum scales can also be included. The result is a multi-scale generalization of the renormalization group applicable to any order. Inconsistencies in the usual decoupling procedure with a single running coupling can then be avoided, e.g. when cancelling anomalous corrections from t,b quarks to the axial charge of the proton. 
Steven D. Bass, R.J. Crewther, F.M. Steffens and A.W. Thomas