Validation Of A Predictive Equation For Recovery Time And Cumulative Fatigue

Musculoskeletal disorders remain a leading concern in physically demanding industries, driven by repetitive tasks and high physical loads. Although existing ergonomic models help quantify risk for singular, repetitive tasks, industrial workplaces often involve different physical tasks that such models do not adequately address. This study validates a reformulated version of our previously published duty‑cycle/maximum‑acceptable‑effort equation for back‑involved tasks: by substituting a duty‑cycle definition that includes both execution time and recovery time, we algebraically isolate the required recovery time and test whether the resulting break schedule prevents fatigue when four subtasks are interleaved over a one‑hour protocol. Three participants completed lifting and lowering tasks of varying intensity and frequency, with recovery times calculated using a modified predictive equation. Objective indicators, including heart rate and endurance time, along with subjective ratings of exertion and task perception, were used to assess the validity of the model. Results showed minimal fatigue accumulation and consistent heart rate levels during the experiment, with only a 5% decline in endurance time. Participants perceived physical demand and effort to be moderate and recovery times adequate. These findings support the equation’s application in multi-task contexts while highlighting the need for variation to mitigate task-related frustration in extended shifts. Additionally, how the equation can be used with exoskeletons is discussed.