Background <p>Construct validity and responsiveness of upper limb outcome measures are essential to interpret motor recovery poststroke. Evaluating the associations between clinical upper limb measures and sensor-based arm use (AU) fosters a coherent understanding of motor recovery. Defining sensor-based AU metrics for intentional upper limb movements could be crucial in mitigating bias from walking-related activities. Here, we investigate the measurement properties of a comprehensive set of clinical measures and sensor-based AU metrics when gait and non-functional upper limb movements are excluded.</p> Methods <p>In this prospective, longitudinal cohort study, individuals with motor impairment were measured at days 3 ± 2 (D3), 10 ± 2 (D10), 28 ± 4 (D28), 90 ± 7 (D90), and 365 ± 14 (D365) after their first stroke. Using clinical measures, upper limb motor function (Fugl-Meyer Assessment), capacity (Action Research Arm Test, Box &amp; Block Test), and perceived performance (14-item Motor Activity Log) were assessed. Additionally, individuals wore five movement sensors (trunk, wrists, and ankles) for three days. Thirteen AU metrics were computed based on functional movements during non-walking periods. Construct validity across clinical measures and AU metrics was determined by Spearman’s rank correlations for each time point. Criterion responsiveness was examined by correlating patient-reported Global Rating of Perceived Change (GRPC) scores and observed change in upper limb measures and AU metrics. Optimal cut-off values for minimal important change (MIC) were estimated by ROC curve analysis.</p> Results <p>Ninety-three individuals participated. At D3 and D10, correlations between clinical measures and AU metrics showed variability (range r_s: 0.44–0.90). All following time points showed moderate-to-high positive correlations between clinical measures and affected AU metrics (range r_s: 0.57–0.88). <i>Unilateral nonaffected</i> AU duration was negatively correlated with clinical measures (range r_s: -0.48 to -0.77). Responsiveness across outcomes was highest between D10-D28 within moderate to strong relations between GRPC and clinical measures (r_s: range 0.60–0.73), whereas relations were weaker for AU metrics (range r_s: 0.28–0.43) Eight MIC values were estimated for clinical measures and nine for AU metrics, showing moderate to good accuracy (66–87%).</p> Conclusions <p>We present reference data on the construct validity and responsiveness of clinical upper limb measures and specified sensor-based AU metrics within the first year after stroke. The MIC values can be used as a benchmark for clinical stroke rehabilitation.</p> Trial registration <p>This trial was registered on clinicaltrials.gov; registration number NCT03522519.</p>