Comparison of stoop versus prone postures for a simulated agricultural harvesting task.

Physical and psychophysical differences between working in the stooped and prone postures were compared while performing a simulated agricultural harvesting task for 30 min. Fifteen male subjects participated. The measures used to compare the two postures included perceived discomfort, electromyography (EMG), and heart rate (HR). Average hamstrings localized discomfort (0-10 scale) was 6.17 (SD=2.9) for the stoop posture and 0.67 (SD=1.29) for the prone posture. Erector spinae and hamstring EMG RMS increased 68% and 18%, respectively, while mean power frequency for the hamstrings decreased 13% for the stoop task. Mean power frequency for the middle trapezius muscle decreased in both postures (stoop 4.13%, prone 3.79%). Average heart rate during the last work cycle was 35% greater than the resting heart rate for the stoop posture while average heart rate was 17% greater for the prone posture. Subjects worked on the prone workstation without rest during the 15 min work simulations with less discomfort, no localized fatigue in the back or leg muscles tested, and lower working heart rates than subjects working in the stoop posture.