The constraint performance analysis in the limited kinetostatic subspace of parallel manipulators is a significant but ignored issue. The motion/force constrainability analysis, with focus on lower-mobility parallel manipulators, is the subject of this study. Via the theory of screws, three generalized frame-invariant constraint indices are proposed based on the concept of the power coefficient. The introduced indices can not only identify the singularity and the fully constrained property but also measure the closeness between a particular pose and an unconstrained configuration (or fully constrained configuration). In order to demonstrate the feasibility and the validity of the analysis methods and indices, the detailed evaluation of two typical industrial parallel manipulators are presented, the Sprint Z3 head and the Tricept mechanism.