In this paper, we propose an approach which ensures the dynamicstability of a biped robot called “BIPMAN”. It is based on the correction of thetrunk center of mass acceleration and on the distribution of the forces exertedby the limbs on the trunk. This latter is performed by means of a linearprogramming method (the simplex method). The retained criterion allows tooptimize force distribution as well as trunk roll and pitch angles. Weightingfactors are introduced into this criterion in order to define criteria adaptedto specific tasks. Modifying these factors is a solution to the task transitionproblem. Many simulation results are presented to demonstrate criteria andconstraints influences on dynamic stability. They lead us to introduce a newapproach called RTCA (Real Time Criteria andConstraints Adaptation). This relies on the analysis ofposition, velocity and acceleration vectors for criterion real time adaptationand on forces analysis for constraints real time adaptation. The RTCA approach is finally validated through simulations results for a specifictask.