Objective: The aim of this study is to evaluate a novel composite measure of active range of motion (XA) and determine whether this measure correlates with active function. Design: Post hoc analysis of two randomized, placebo-controlled, double-blind studies with open-label extensions exploring changes in active function with abobotulinumtoxinA. Setting: Tertiary rehabilitation centers in Australia, Europe, and the United States. Subjects: Adults with upper (n = 254) or lower (n = 345) limb spastic paresis following stroke or brain trauma. Interventions: AbobotulinumtoxinA (⩽5 treatment cycles) in the upper or lower limb. Main measures: XA was used to calculate a novel composite measure (CXA), defined as the sum of XA against elbow, wrist, and extrinsic finger flexors (upper limb) or soleus and gastrocnemius muscles (lower limb). Active function was assessed by the Modified Frenchay Scale and 10-m comfortable barefoot walking speed in the upper limb and lower limb, respectively. Correlations between CXA and active function at Weeks 4 and 12 of open-label cycles were explored. Results: CXA and active function were moderately correlated in the upper limb (P < 0.0001–0.0004, r = 0.476–0.636) and weakly correlated in the lower limb (P < 0.0001–0.0284, r = 0.186–0.285) at Weeks 4 and 12 of each open-label cycle. Changes in CXA and active function were weakly correlated only in the upper limb (Cycle 2 Week 12, P = 0.0160, r = 0.213; Cycle 3 Week 4, P = 0.0031, r = 0.296). Across cycles, CXA improvements peaked at Week 4, while functional improvements peaked at Week 12. Conclusion: CXA is a valid measure for functional impairments in spastic paresis. CXA improvements following abobotulinumtoxinA injection correlated with and preceded active functional improvements. [ABSTRACT FROM AUTHOR]