Structural Loading of the Lower Lumbar Area in Different Level of Rubber Tapping

Around half of professional rubber tappers are known to have low back pain. It is speculated that this is due to prolonged lateral and forward bending of the trunk. Yet assessment on compression and shear force on the back and the level of back muscle fatigue and the role of degree of bending have never been done. This study aimed to evaluate the effects of tapping level on structural loading of the lower lumbar area and evaluated the factors associated with fatigue after a day of routine rubber tapping work. 48 healthy rubber tappers volunteered to join in the study. Data collected includes onetime biomechanical modeling of the lower lumbar spine during varying levels of rubber tapping using the University of Michigan 3D Static Strength Prediction Program (3DSSPP) and before-and-after one-day work evaluation of low back muscle activity using electromyography (EMG) and perceived fatigue scale. The results show that the lower the tapping level was, the higher the values of compression and shear force at L5/S1 and L4/L5 would be (p-value=0.001). For EMG, the amplitude was increased with a spectrum shifted toward lower frequency. The percentage of maximal voluntary contraction (%MVC) was also increased by more than 20%. The degree of perceived fatigue after work was at moderate level. These parameters were more severe among those tapping at lower level both before work, and more importantly, after work. Other independent predictors for fatigue were number of trees tapped per day but not sex, age, weight, and height. Low level rubber tapping exerts harmful effects on trunk structural loading. Further research to prevent its consequence is needed. Relevance to Industry Rubber tapping potentially has many ergonomic problems and high prevalence of low back pain was confirmed. Prior to this research there has not been study to quantify the excessive stress imposed on the lower lumbar area during rubber tapping at different tapping levels.