A comparison of work-rest models using a “breakpoint” analysis raises questions

TECHNICAL ABSTRACT Rationale: There is a need for tools to help design sustainable work in which muscular capacity and other human resources can recover at least as quickly as they are used. Purpose: In this brief report, three different approaches presented in the literature to determining work-rest schedules in cyclic work are compared. Methods: First, a set of five different muscular endurance models coupled with a recovery time model were considered, both with and without a dynamic work correction factor. Second, we examined a model of "resumption time", and third a psychophysically-based model of maximum duty cycle was included. These models were compared using the concept of a "breakpoint" in fatigue accumulation - the point at which a given load amplitude and duty cycle combination begins to cause accumulation of fatigue in each cycle and from which there is inadequate time to recover. Results: While the five endurance time models all behaved similarly, both with and without the static-to-dynamic correction factor applied, the three different types of modelling approaches provided substantially different response patterns. The psychophysically based model provided the most protective guideline among the models compared. Conclusion: These models should be applied with caution to particular work scenarios. Further research is needed to test accuracy and effectiveness when applying such models to a range of task scenarios to establish safe workloads and loading times in the design of repetitive work.