This paper presents an approach using System Dynamics (SD) to model long-run effects of given workload levels on employee health and quality of the system output. The models integrate scientific evidence on injury and burnout risk factors, error making probabilities, and presenteeism phenomena to create two SD models – one for a manufacturing assembly line and the other for a hospital nursing unit – that can help users explore the ergonomics-system performance relationship. The manufacturing model results show an increase in injury rates and a decrease in yield as the operators are exposed to higher spinal loads. The nursing model results show an increase in nurse burnout and medical errors as nursing workload is increased. This demonstration reveals the feasibility of SD modeling to help managers and engineers explore the long-run consequences of the human factors in their operations system design and inform policy decisions in terms of both human health and system performance outcomes.