Integrating energy expenditure into MTM-UAS: the Motion Energy Measurement (MEM) system for ergonomic assessment in...

Production engineers increasingly integrate ergonomics intoassembly line design, given the long-term adverse effects on operator health. This paper proposes the Motion Energy Measurement (MEM) system, an extension of the MTM-UAS method for assessing manual tasks. While MTM-UAS standardises task timing through basic motion units, it does not account for physiological workload.MEM addresses this gap by integrating metabolic energy expenditure models into each MTM-UAS motion element, enabling quantifiable assessment of physiological workload. A case study conducted at Bosch Thermotechnology in Portugal, involving a hot water boiler assembly line, revealed a disparity between task duration uniformity (CV $\approx$ 0.5%) and energy variability (CV $\approx$ 11.7%) across operators. These results expose critical ergonomic blind spots in time-based balancing strategies and underline the potential of MEM for real-time identification of high-strain tasks. This work advances ergonomic diagnostics by introducing a scalable, physiology-informed layer to traditional time-motion analysis.