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Evaluating the Reliability of a Marker-Less, Digital Video Analysis Approach to Characterize Fire-fighter Trunk and Knee Postures During a Lift Task: A Proof-of-Concept Study

Kathryn E Sinden, Joy C MacDermid, Thomas R Jenkyn, Sandra Moll and Robert D’Amico

Background: Valid and reliable postural assessment tools can better support injury prevention strategies. 3- dimensional movement analysis as the gold standard to assess human movement is often not feasible in applied, occupational settings. For example, heavy lifting associated with known injury risk factors is impacted when performed by fire-fighters wearing personal protective equipment (PPE). Task simulations including PPE complicate postural assessment methods. Consequently, the study purposes were: a) To establish proof-of-concept using Dartfish movement analysis software to measure fire-fighters’ trunk and knee postures during a fire-fighting lift task while wearing PPE and b) To establish the reliability of this approach. Methods: A sample of twelve active-duty fire-fighters lifted a high-rise pack from floor to shoulder level. Frontal and sagittal trunk and knee flexion angles and hip vertical displacement were measured using Dartfish. All measurements were repeated on a second day for reliability analysis. Descriptive statistics characterized fire-fighter lower extremity postures. Intra-class correlation coefficients, standard error of measurement and minimal detectable change determined reliability of trunk and knee angles and hip displacement measures. Results: Fire-fighters demonstrated 150° ± 12° of left knee flexion, 150° ± 13° of right knee flexion and 98° ± 17° of trunk flexion when lifting a high-rise pack from floor to shoulder level. Hip vertical displacement was 19% ± 8% when normalized to the individual’s height. Absolute reliability results indicated that fire-fighter knee postures could be assessed within 5° and trunk postures within 9° when using Dartfish. Conclusion: Although measurement reliability of trunk and knee angles was comparable to previous studies, accuracy limitations and methodological challenges were identified. Protocol recommendations to optimize reliability and interpretability include focusing on using positional coordinates to identify hip displacement; further research to validate this approach is suggested. Implications include measuring impacts of ergonomic designed to modify fire-fighter task performance strategies in response to known injury risk factors.