Standardizing upper arm movement definitions across observational and sensor-based methods: A Delphi consensus study among European ergonomics experts

OBJECTIVES: Musculoskeletal disorders from repetitive upper arm movements contribute substantially to sickness absence and productivity loss. Despite widespread use of observational and sensor-based assessments, inconsistent definitions hinder comparison across studies and translation to practice. This study explored threshold criteria for defining upper arm movements and static postures across observational and sensor-based approaches and examined conceptual differences between practical observability and biomechanical measurability. METHODS: We conducted a two-round Delphi study following the ACCORD guidelines. We invited 35 European experts to rate agreement on proposed definitions. A consensus criterion was set to ≥75% agreement. A thematic analysis of free-text responses guided definition revisions between rounds. RESULTS: Fifteen (43%) and fourteen (93% retention) completed rounds 1 and 2, respectively. Consensus defined a fast-paced movement as ≤1 second (80% agreement) and static posture as ≥4 seconds with ±5° movements (87% agreement). No agreement emerged regarding the minimum amplitude threshold for defining an arm movement (eg, 10° versus 20°; 53% agreement). Experts' comments reflected a tension between observability, favoring higher amplitude thresholds, and biomechanical relevance, favoring lower thresholds, while highlighting velocity's importance. CONCLUSIONS: Expert consensus on time-based thresholds for fast-paced movements and static postures provides a starting point for standardized ergonomic assessment. The absence of consensus on amplitude thresholds highlights the need for field validation studies examining which thresholds capture measurement reliability and prediction of musculoskeletal health outcomes. These findings support efforts toward transparency and alignment in upper arm exposure definitions across research and practice, while acknowledging remaining conceptual and methodological challenges.