The purpose of this paper is to investigate what kinds of effects the multi-segmental body with actively controlled body part have on balancing. As part of the research, a biped mechanism is simplified to multi-segmental legged model in sagittal plane where the model is comprised of a stance leg, foot and actively controlled body part. Not only the system parameters are in place but also necessary and sufficient conditions for balancing have been implemented as constraints. The algorithm that we proposed iteratively solves nonlinear constrained optimization problems. The balanced state domain is constructed by connecting velocity extrema. The proposed algorithm is used to identify the balanced state domain in a deterministic scheme using numerical optimization.