Guideline threshold limit values (TLVs) for discomfort in repetitive assembly work

This study focussed on two of the main occupational risk factors associated with WMSDs in light repetitive electronic assembly work, namely repetition and force. Present day evaluation techniques are primarily posture based and show low sensitivity with regard to rating repetition and force. Guidelines for acceptable workload are partly quantitative in the form of Threshold Limit Values (TLVs) for acceptable exposures. However, little experimental data about these risk factors have been generated. A simulated assembly task was conducted to investigate the interactions of risk factors and the suitability of Hand Activity Level (HAL) and TLV values for electronics assembly work. Subjects completed the assembly task for three levels of repetition and force. Movement velocities and joint angles were recorded using electrogoniometers. For each treatment a subjective rating of discomfort was recorded. Repeated measures ANOVA identified repetition and force as highly significant factors in light electronic assembly work (p<0.001, p<0.05, respectively). The two-way interaction between the factors was not significant (p>0.05). However, through regression analysis posture was also found to be a significant predictor of discomfort (p<0.05). The task was also rated using HAL and Normalised Peak Forces (NPF). This study questioned the ability of TLVs in rating discomfort and amendments to the TLVs are suggested.