Mapping the longitudinal trajectories of postural control and functional activity after stroke using clinical and sensor-based assessments: protocol of the FOSTER prospective cohort study.

introductionStroke is a leading cause of long-term disability, yet recovery trajectories are highly heterogeneous and difficult to predict at the individual level. Standardised clinical assessments primarily capture task accomplishment under controlled conditions but may overlook changes in movement quality, including the distinction between compensatory strategies and behavioural restitution. Additionally, they provide limited insight into the postural control processes that underlie functional task performance. Recent consensus initiatives emphasised the need for sensitive, functionally relevant measures of balance and mobility after stroke. Integrating routine clinical assessments with a sensor-based approach during functional tasks offers new opportunities to characterise recovery more precisely and to map longitudinal trajectories of poststroke change. Within the European Union-funded TARGET project, the FOSTER study aims to generate multimodal data to support data-driven, individualised prognostic models, so-called virtual twins, for personalised rehabilitation. METHODS AND ANALYSIS: FOSTER is a prospective, single-centre observational cohort study at Rehabilitation Hospital Inkendaal (Belgium). We aim to include 100 adults within 8 weeks poststroke, assessed at three to five time points, including an entry assessment after admission and follow-up assessments within predefined windows at approximately 5, 8, 12 and 24 weeks poststroke. The protocol combines synchronised sensor-based measurements during functional tasks (seated reaching, standing reaching and gait initiation) obtained during an exergame, with standardised clinical tests and patient-reported outcome measures (PROMs). Sensors include surface electromyography, inertial measurement units, force plates and markerless motion capture. Sensor-based measurements target movement quality, and anticipatory and reactive postural control during self-initiated functional tasks. Derived outcomes will capture kinetic, kinematic and neuromuscular features of movement strategies, including temporal and asymmetry characteristics. In addition, in-task performance metrics, real-world activity monitoring through accelerometry, standardised clinical assessments and PROMs will be collected to provide a comprehensive, multimodal characterisation of recovery. Linear mixed-effects models will characterise longitudinal trajectories and relationships between clinical and sensor-derived measures. ETHICS AND DISSEMINATION: The FOSTER study was approved by the Ethics Committee of Rehabilitation Hospital Inkendaal (B.U.N. 2024-TEE-002). Participants will be included after providing informed consent. Data are pseudonymised and stored on a General Data Protection Regulation-compliant platform. Findings will be disseminated through peer-reviewed publications, conferences and within the TARGET consortium. TRIAL REGISTRATION NUMBER: NCT06806761.