This paper discusses findings from the introduction and integration of qualitative design research methods into the overall methodology for the design and evaluation of a ‘complex intervention’ through a set of pilot random control trials. A visualisation tool was co-designed and developed with stakeholders to enhance patient-therapist interaction in the context of stroke rehabilitation. The participative approach recognised the importance of mobilising lay knowledge and experience to drive innovation in the tool whose use helped reduce the ‘social distance’ between therapist, patient and clinical biomechanist to: i) aid understanding for patients; ii) enhance communication between patient and therapist; and iii) provide an objective tool for therapists to monitor progress and communicate it to patients. The implications for the use of design methods in rehabilitation service design innovation is also discussed.