Effects of handle height and COF on maximal strength generation during push/pull activities



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Texas Tech University


Manual materials handling, or MMH, is the process of a human lifting, lowering, pushing, pulling, or conducting any similar task in which an object is moved through space solely by the power of that human. Historically, manual material handling is a known contributor to the number of accidents and/or injuries that occur in industry, especially injuries related to the low back. Employee well being and safety are precursors for a productive and fully operational employee. Therefore it is advantageous to prevent employee injuries by designing and implementing ergonomically designed equipment and safety procedures which reduce the risk of musculoskeletal injuries.

The following analysis studied the effects of handle height and coefficient of friction and whether or not there was an interaction between the two variables. An isometric strength testing fixture was used to measure the push/pull hand forces. The apparatus had a stationary bar, which was attached to a Bertec force plate, which was used by the subjects to input their force capabilities.

Alternative Hypothesis one validated results that for all push and pull trials, handle height was the significant factor that affected force generation. Subjects were able to produce a maximum force when the handle height was set at the 66cm level. Alternative Hypothesis two results indicate that COF was a significant factor in the pull trials, while not as important in the push trials. Alternative hypothesis three concluded that the interaction between the 66cm handle height and high COF produced the highest amount of force.