The effect of clinically elevated body mass index on physiological stress during manual lifting activities

Individuals with a body mass index (BMI) classified as obesity constitute 27.7% of U.S. workers. These individuals are more likely to experience work-related injuries. However, ergonomists still design work tasks based on the general population and normal body weight. This is particularly true for manual lifting tasks and the calculation of recommended weight limits (RWL) as per National Institute of Occupational Safety & Health (NIOSH) guidelines. This study investigates the effects of BMI on indicators of physiological stress. It was hypothesized that, for clinically elevated BMI individuals, repeated manual lifting at RWL would produce physiological stress above safety limits. A repetitive box lifting task was designed to measure metabolic parameters: volume of carbon dioxide (VCO2) and oxygen (VO2), respiratory exchange ratio (RER), heart rate (HR), and energy expenditure rate (EER). A two-way ANOVA compared metabolic variables with BMI classification and gender, and linear regressions investigated BMI correlations. Results showed that BMI classification represented a significant effect for four parameters: VCO2 (p < 0.001), VO2 (p < 0.001), HR (p = 0.012), and EER (p < 0.001). In contrast, gender only had a significant effect on VO2 (p = 0.014) and EER (p = 0.017). Furthermore, significant positive relationships were found between BMI and VCO2 (R-2 = 59.65%, p < 0.001), VO2 (R-2 = 45.01%, p < 0.001), HR (R-2 = 21.86%, p = 0.009), and EER (R-2 = 50.83%, p < 0.001). Importantly, 80% of obese subjects exceeded the EER safety limit of 4.7 kcal/min indicated by NIOSH. Indicators of physiological stress are increased in clinically elevated BMI groups and appear capable of putting these individuals at increased risk for workplace injury.

Automated summary

Individuals classified as obese based on body mass index (BMI) make up 27.7% of U.S. workers. These individuals are more prone to work-related injuries. However, work tasks are still designed with the assumption of a general population and normal body weight. This study explores the impact of BMI on physiological stress indicators and finds that clinically elevated BMI individuals experience increased physiological stress levels when performing repetitive manual lifting tasks at recommended weight limits (RWL). Notably, 80% of obese subjects exceeded the safety limit for energy expenditure rate (EER) indicated by the National Institute of Occupational Safety & Health (NIOSH).