Abstract
One in three U.S. adults is obese, and in the Transportation, Warehousing, and Utilities (TWU) sector, two-thirds of workers fall into this category. Obesity is a major health concern and a key contributor to workplace musculoskeletal injuries. However, safety guidelines such as those from the National Institute for Occupational Safety and Health (NIOSH) remain based on individuals with normal weight. This dissertation addresses that gap by investigating how obesity impacts injury risk during manual material handling (MMH) tasks, with a focus on spinal loads and energy expenditure relative to the biomechanical, physiological, and psychophysical criteria of the Revised NIOSH Lifting Equation (RNLE).
To assess biomechanical stress, L5-S1 compression and shear forces were measured in 30 adults performing a NIOSH-guided lifting task. BMI significantly predicted spinal loads (p < 0.001), with strong positive correlations to compression (r² = 59.4%) and shear forces (r² = 61.3%). All obese participants exceeded NIOSH safety limits at a lifting index of 1.
Physiological stress was evaluated through energy expenditure rate (EER) during repetitive lifting and additional carrying and pushing/pulling tasks. Higher BMI was significantly associated with elevated EER (p < 0.001), and 80% of obese participants exceeded the 4.7 kcal/min safety threshold. BMI also significantly influenced EER during carrying (p = 0.003) and pushing/pulling (p = 0.013).
This dissertation further examined the connection between exceeding physiological safety limits and increased fall risk through balance and proprioception testing. Results revealed that higher BMI (p = 0.032) and elevated EER (p = 0.037) significantly impaired proprioception, while EER also negatively affected balance (p = 0.020).
These findings provide a foundation for future research aimed at developing targeted strategies to reduce injury risk among obese manual workers.