## 2 Methods
### Experimental Procedure  
The motion studied included the harvesting movements of the bilateral upper arm joints, namely the shoulder, elbow, and wrist joints. In total, the movements of the six joints were evaluated from the initial posture of the oil palm harvesters. Two high-speed cameras of 120 frames per second (SJCAM SJ5000X and YI action camera) were used as part of the Quintic Biomechanics system to capture the 1-D movements involved in harvesting FBBs at the sagittal plane.  
These cameras were placed perpendicular to the plane of movements, as portrayed in Figure 1. Hence, all the movements of push-pull-cutting (\(\geq\)3 m FFB height) that took place at the sagittal plane could be captured. The push-pull-cutting was performed with a commonly-used tool called an egrek, a sickle-shaped tool [24]. Figure 1a,b shows the front and side view of the camera positions to capture the harvesting of FFBs movement at the sagittal plane, respectively. The participants were informed about the motion-recording process. After obtaining informed consent, spherical markers were placed on the three anatomical landmarks on the participants' right and left arms: the shoulder (acromiodavicular), elbow (olecranon), and wrist (bar pinkie side) joints. The three anatomical landmarks were selected so that they would not impede harvester movement and would be easy to identify during the digitization process. Next, Figure 2a illustrates the Quintic Biomechanics system anatomical landmarks at the sagittal plane. As displayed in Figure 2b, the participants' arms were divided into two categories, namely the dominant arm or support arm for analysis purpose. The support arm was the arm placed above the dominant arm on the tool while the dominant arm served as the main arm that drove the pulling action during the harvesting movements. Each participant was asked to perform his normal push-pull-cutting routine for the FFB harvesting activity up to five trials (n = 100). Next, Figure 3 shows one cycle of push-pull-cutting movement of an oil palm harvester. In each cycle of push-pull-cutting, the participant began in a posture corresponding to the placement of the harvesting tool on the targeted FFB. This was followed by the pushing movement, the pulling movement, and lastly returning to the original resting position.  
Figure 1: (**a**) Front and (**b**) side view of the camera positions to capture the harvesting of FFBs movement at the sagittal plane.  
Figure 2: (**a**) The dominant and support arms. (**b**) The anatomical landmarks placed on the participants at their initial posture from the sagittal plane view.  
Next, Figure 4 exhibits the 1-D movements that were studied: flexion and extension of the shoulder and elbow joints, and radial-ulnar deviation of the wrist joint. The 1-D movements from Figure 4 were used to facilitate the determination of angular displacements of each joint in the Quintic Biomechanics system. The angular displacements were determined from the determination of the angle between two segments in the Quintic Biomechanics system. The angular displacement of the shoulder joint was determined from the determination of the angle between the vertical axis and the upper arm segment; while the angular displacement of the elbow joint was determined from the determination of the angle between the upper arm and lower arm segment. Last, the angular displacement of the wrist joint was determined from the determination of the angle between the lower arm segment and the horizontal axis. The horizontal axis was chosen because the lower arm and hand were parallel to the horizontal axis when holding the pole at 90\({}^{\circ}\) of the elbow joint. Next, Equation (1) was used as part of the determination of the angular displacement for both shoulder and wrist joints.  
\[\theta=180^{\circ}-q \tag{1}\]