## 5 Discussion  
The data on upper arm angular displacements are indispensable in the determination of the range of harvesting movements of the three main arm joints. However, very few studies have reported on the significance of angular displacements of all three arm joints during the push-pull-cutting technique used by oil palm harvesters. Thus, this study objectively investigated the angular displacements and range of harvesting movements, as well as the active range of harvesting movements of the arm joints. Moreover, the effects of age and initial shoulder posture on the harvesting movements on the arm joints were analysed. This study provided fundamental evidence on the movement patterns associated with the three phases of the push-pull-cutting technique, namely pushing, pulling, and end phases. During the preparation phase, the participants tended to push the harvesting tool to create a gap in the pulling range before executing the pulling technique. At the same time, there was a slight change in the angle at the end of the phase due to the forceful reaction from the FFB. Such shifts may imply a change in the force and muscle fibre length throughout these dynamic stages, subsequently influencing the underlying muscle activities [29]. The largest change in the angular displacement occurred at the execution phase. Based on the investigation performed by [30] on the muscle activity of the medial and posterior deltoid muscles all the infraspinatus, trapezius, and supraspinatus muscles exerted a 35% increase in electromyography activity when the arm was in flexion [30]. This study showed that the harvester tends to experience greater electromyography activity at the infraspinatus, trapezius, and supraspinatus muscles during the execution phase. This study provided the initial and maximum posture data in terms of the range of harvesting movement, as well as the performance data of pushing and pulling movement through the three phases. Compared with the previous study, [24] did not consider the phases that exist in the harvesting movement. However, [24] considered the movement directions such as flexion and extension of shoulder joint in terms of ROM. In this study, pushing and pulling were studied in terms of the active range of movement. The active range of movement was measured by phases which were preparation, execution and end phase. At the preparation phase, the active range of movement was measured through the determination of the angle difference between the angular displacements produced during placing the harvesting tool and the maximum posture of the three joints. Next, at the execution phase, the active range of movement was measured through the determination of angle difference between the angular displacements produced during maximum posture and after the pulling movement. Last, at the end phase the active range of movement was measured through the determination of angle difference between the angular displacements produced after the pulling movement and the final posture caused by the forceful reaction from the FFB. In this study, the range of harvesting movement and active range of harvesting movement were used to the study the effects that affect the harvesting movement. In many researches, RULA has been extensively utilised to evaluate the exposure of individual workers to the ergonomic risk factors associated with upper extremity MSDs. The RULA worksheet is used to evaluate the required body posture, force, and repetition to complete an action. Section A of RULA is used for the evaluation of the arm and wrist. Elevation of the shoulder at an angle of 90\({}^{\circ}\) and above results in a score of four that indicates a higher risk of MSD. Elevation of the shoulder at an angle of 90\({}^{\circ}\ \geq\ \theta\ \geq\ 45^{\circ}\) provides a score of three, followed by 45\({}^{\circ}\ >\ \theta\ \geq\ 20^{\circ}\) that provides a score of two and 20\({}^{\circ}\ \geq\ \theta\ \geq\ 0\) that provides a score of one.