Recent research has found that workers in m anual materials handling jobs do not use the lift technique taught for proper lifting safety. However, little quantitative data exist on the lift technique used by experienced lifters. It was therefore, the purpose of this study to describe the freestyle lift of experienced manual material handlers by examining upper body kinematic and kinetic motion curves during the entire sagittal box lift.

Using a novel approach on the set of motion curves, namely a cluster analysis, similarities between the manual material handlers' lifting motions were determined. The clustering approach provided a means of assessing eleven lifting curve profiles together to determine similarities between subjects. The similarity in lifting curves resulted in three general groupings.

The first grouping, consisting of 29 subjects, began the lift from a knee flexed and straight back position similar to the squat lift technique. The second grouping, consisted of 33 workers who began the lift with little knee flexion and a flexed trunk, resembling a stoop lift posture. The third grouping of 46 subjects also flexed their trunk to pick up the box, but they differed from the second grouping by bending their knees as well. The workers from group one typically extended their back segments also at a significantly slower rate than workers from group two. The lift posture did not consistently dictate the rate of trunk extension as the members in the third group demonstrated. Results showed that lift posture did not provide enough detail on load handling and that both lift posture and trunk motion were required to describe technique.

The largest differences in trunk segment velocities and lumbosacral loading (moment, compression and shear forces) were observed in the first 20% of the lift. Lifting from a more squat-like position and extending the trunk slowly resulted in the lowest lumbosacral loads. Conversely, lifts performed by extending a flexed trunk quickly generated higher lumbosacral loads. The lifts were considered 'safe' on the grounds that the lifters were healthy, experienced workers w ithout incidence o f lower back pain and the average peak L5/S1 compressive forces were below the NIOSH maximum permissible limit.

The collection of data on a sample of 108 experienced manual material handlers has allowed for the development of a normative database of trunk kinematics and kinetics associated with lifting a moderately heavy load (15 kg).

The database is provided in this thesis and reports both measured and normalized values for 11 kinematic and 5 kinetic curve profiles. A database of this nature has direct value to the research community. The lift techniques described for the experienced lifters provide a start in understanding the lifting motions im portant for safe lifting. The database o f lifting kinematics and kinetics will allow for future comparisons of lift technique due to task and environmental changes. The normative data may also play a role in understanding differences in lift technique of workers suffering with lower back pain.