## 4 Discussion  
In the experiment, the participant grasped the handle and pulled. The muscles on the forearm were recruited to resist the back-swing force, followed by the muscles on the upper arm, shoulder, and legs. The CR-10 scores on the forearm were the highest, followed by those on the upper arm, and then the leg. This implies that the forearm was the body part with earliest onset of muscular fatigue. The time period of one pause of the 9-3 condition was 1.5 min, and the CR-10 score of the forearm changed slightly over time. The time period of one pause of the other test conditions were more than 2 min and the CR-10 score of the forearm changed significantly over time, which alluded that the accumulation of muscular fatigue was significant. The time periods of one pause of the 9-2 and 9-3 conditions were 2 and 1.5 min, respectively. The CR-10 scores of upper arm of these conditions changed slightly over time. The time periods of one pause of all other conditions were more than 2.25 min, the CR-10 score of the upper arm changed over time, which implied that the accumulation of muscular fatigue was significant. During the pulling tasks, participants reported little muscular fatigue on the lower back (less than 2). Therefore, the CR-10 score on lower back was excluded. This was inconsistent with that in the literature [3,14,27,28]. This might be attributed to the pause arrangement in our study. The mean CR-10 score of the forearm was less than 7 (very strong). The mean CR-10 score of the upper arm was less than 5 (strong) except for in condition 12-1. The mean CR-10 score of the leg was less than 3 (median). A significant (\(p<0.05\)) difference was found on the CR-10 score of the upper arm between the 12 and 9 min trials. For the forearm and leg, the difference between the 9 and 12 min trails was insignificant. This might be attributed to the gap of trials of 12 and 9 min, which was not long enough to lead to different fatigue accumulation. For test condition 12-1, the CR-10 score of the forearm was 5.27 after a 4.5 min pulling. After a rest of 3 min and then pulling for 4.5 min, the CR-10 became 6.55. It might be deduced that the CR-10 score would exceed 7 after having another rest of 3 min and then pulling for 4.5 min. Therefore, work schedules, such as 12-1 are not recommended because they could lead to significant muscular fatigue. For other test conditions, muscular fatigue progressing was relatively slow. In one of our previous studies [21], the scores of CR-10 on the hand/wrist, elbow, low back, leg/ankle, and shoulder were 6.9, 6.45, 5.68, 4.90, and 4.40, respectively, at the end of pulling tasks. In current study, the CR-10 score on the forearm was the highest. The CR-10 scores on the forearm for test conditions 12-1, 12-2, 12-3, 9-1, 9-2, and 9-3 were 6.55, 6.09, 6.18, 5.55, 5.82, and 5.73, respectively. The CR-10 scores on the upper arm were below 5 except in the 12-1 test condition. The CR-10 scores on the leg were below 3. The CR-10 scores on the forearm, upper arm, and leg for our pulling tasks with embedded pauses were lower than for those without pause arrangements [21]. It is apparent that pulling tasks  
Figure 5: The predicted and measured pull strength for six test conditions. (**a**) 9-1 condition, (**b**) 12-1 condition, (**c**) 9-2 condition, (**d**) 12-2 condition, (**e**) 9-3 condition, and (**f**) 12-3 condition. with pause(s) allow better blood circulation and, hence, lead to lower perceived muscle fatigue [15; 29]. There are limitations in this study. The pulling tasks in the current study were static without movement, while pulling tasks in practice are commonly performed while walking. When pulling and walking, the gait pattern and walking speed might affect the development of muscular fatigue. Future research may be performed to explore the effects of gait on the developing of muscle fatigue due to pulling. In addition, the time period of a single pull and a pause may be too short as compared to those that actually occur at workplaces.