Objective: To evaluate the capacity of the Upper Limb Performance Analysis: Comparative Analysis of Performance-Motor (CAP-M) to quantify change in adults with focal spasticity following injection of Botulinum Toxin-A (BTX-A) as a focal treatment for positive Upper Motor Neuron (UMN) features. Methods: Twenty-three adults with moderate-to-severe spasticity were assessed pre- and post-BTX-A injection using CAP-M. Post-hoc video analysis of three sub-tests from the Action Research Arm Test were analysed against expected movements for each task.Results: Post-injection, spasticity as measured by Modified Ashworth and Tardieu Composite scores decreased significantly (p < 0.001). Grouped CAP-M data showed a significant reduction (z = 2.1–2.7, ES = 0.51–0.56) in positive UMN features, with 145 fewer Excessive movements recorded. In addition, 31 more Expected movements were demonstrated (z = 2.9, ES = 0.60), consistent with ‘unmasking’ of movements.Conclusion: CAP-M analysis revealed that BTX-A injection decreased unwanted movement almost 5-times more frequently than ‘unmasking’ hidden voluntary muscle activity during active simulated tasks. In this way, CAP-M was able to simultaneously assess positive and negative UMN features. This quantitative framework may have greater functional relevance than traditional uni-dimensional, passive spasticity measures such as MAS and Tardieu Scale.