Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

First Advisor

Kwan S. Lee


The objective of this research was to study the effects of fatigue on lifting acceleration and posture caused by repetitive manual lifting. Electromyogram, oxygen consumption and heart rate were used as indices of a subject's physiological fatigue. Data were collected for a period of two hours of continuous lifting, at a rate of 4 lifts per minute using the free-style posture. A box of fixed dimensions (30cm x 30cm x 20cm) and fixed weight (15.9 Kg) was used as load. It was found that the average load acceleration increased with work duration. Peak acceleration was found to be maximum in the initial lifting period of zero to 0.3 seconds. Back compressive force was highest at the beginning of a lifting cycle. It was found that the shorter subjects' lifting technique was more stable than taller subjects'. It was also found that lifting posture changed from stoop to squat and then back to stoop during two hours of lifting. EMG analysis showed that arms were stressed most during the initial lifting phase (that is in the stoop position). EMG level of a leg was higher when the squat posture was used.