The Changing Workforce: Optimizing the Work-Rest Cycle

The U.S. Department of Health and Human Services estimates that more than two-thirds of adults in the United States are obese or overweight. Over the last decade there has been a surge in the number of obese employees and female employees in manufacturing industries. Many jobs performed by obese workers in the manufacturing industry consist of highly repetitive upper limb tasks that often require excessive force exertions. The development of fatigue-related musculoskeletal disorders is magnified with the prevalence of high obesity levels. In this study, fatigue recovery rate after performing tasks of varying force and repetition levels among obese and normal body mass index (BMI) participants was evaluated. A total of 60 participants were recruited (30 males, and 30 females) and grouped in three body mass index categories (BMI less than 25 kg/m2, BMI between 25-30 kg/m2, and BMI greater than 30 kg/m2). Each participant performed four tasks (high force / high repetition, low force / high repetition, high force / low repetition, and low force / low repetition), simulated by exerting a grip force of a predetermined level on a hand grip dynamometer. Fatigue recovery rate was measured by comparing the maximal voluntary grip strength of a participant before performing a task and at one-minute, two-minute, five-minute, and ten-minute rest intervals after performing a task. Preliminary results have indicated that as obesity levels increase, a longer rest interval is needed for muscles to recover after performing a task. Initial analysis also indicated that fatigue effects are magnified when the tasks a performed require high forces and in females. Results of this study can be used to incorporate factors such as obesity levels and gender in the design of work-rest cycles to reduce the risk of fatigue related musculoskeletal disorders.