Manual materials handling has been examined as it relates to musculoskeletal injury; however, due to the complexity of handling tasks and individual characteristics in technique further analysis is required. Lifting tasks, specifically, show great variability between individuals despite task parameter restrictions and further variability was expected when fatigue or injury alters lifting method. In order to assess the effects of fatigue on lifting technique, individuals underwent several testing sessions which resulted in quantitative generalized fatigue, and localized shoulder and back fatigue which were compared to initial lifting in a non-fatigued condition and then across fatigue states. The kinematic and relative phase lifting waveform differences between fatigue states were analyzed using Principal Component Analysis (PCA) with further investigation of relative phase through frequency analysis. PCA enabled isolation of variability within the data and therefore provided an indication of area of greatest variability within the lifting waveform. Frequency analysis of relative phase waveforms allowed for a greater understanding of lifting coordination changes. The results of this study showed significant alterations in kinematic and relative phase lifting waveforms, which varied significantly depending on the fatigue state. The type of fatigue had a significant effect on the corresponding compensations and alterations to lifting technique and coordination even though task parameters remained constant. Altered lifting technique may result in an increased risk of injury particularly in the initiation and placement phases and further variability in coordination during transition of the load could also result in an increased risk of injury with fatigue.
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