This paper addresses a conceptual and formal limitation in the International Classification of Functioning, Disability and Health (ICF), where activity and participation are treated as a unified construct, creating ambiguity in rehabilitation contexts. We propose an ontology keeping the ICF structure but formally separating these concepts, enabling more precise participation assessment. A case-based query analysis demonstrates how the unified ICF model may yield false positives in participation documentation, while the refined ontology supports nuanced evaluation. Implementation details and future evaluation are discussed.