# Gender-Based Differences in Actual Thumb Force Exertions at Various Target Force Levels
## 4 Discussion  
This study was conducted to investigate the relationship between actual thumb force exertion and perceived thumb force exertion using the [PERSON]'s CR-10 scale. The relationship between actual and perceived thumb force exertions shows a non-linear S-shape curve. Most participants exerted their actual thumb force at 50% MTF accurately and with high accuracy. Based on the 50% MTF level, over-exertion was observed at 50% MTF or below, and under-exertion was found at 50% MTF level or above, and therefore, designated as the '50% phenomenon'. Several previous studies reported that the maximum force exerted by males was greater than that of females in pinching, grasping, and lifting tasks [21; 22]. In studies of elbow flexion and grip strength, females exerted 39.5-45.0% [23; 24] and 52.9-62.3% [25; 26; 27; 28] of male strength, respectively. The thumb force exertion studies [29; 30; 31] also showed that females exerted lower thumb forces (64.1-97.1%) than  
Figure 4: Interaction effect of gender and perceived exertion levels (%MTF). males. The current study was similar to that of previous studies involving thumb force exertions (female MTF was about 73.6% that of males). The difference between males and females in terms of maximum muscle exertions might be attributed to the size of physiological cross-sectional areas (PCSA) of muscle groups [32; 33]. The results of this study demonstrated that males exerted significantly greater thumb force (absolute magnitude) than females across all perceived exertion levels. However, when normalized to % MTF for each participant's MTF, there was no difference between male and female exertion as a function of the perceived exertion level (Figure 3). [PERSON] et al. [17; 34] also compared the perceived exertion of quadriceps femoris muscles with target forces at 10-90% MVCs. They found no significant difference between genders, although males generally lift or exert masses or forces of absolutely greater magnitude than females. The differences in actual exertion of different levels of perceived exertion were also investigated in this study. Results showed that the exertion force of % MTF differed significantly (\(p<0.05\)) at the perceived exertion levels of 10, 30, 70, and 90% MTFs, except at 50% MTF. The actual exertions of 10% and 30% MTFs were greater (over-exertion) than the perceived exertion levels, whereas the exertions for 70% and 90% MTFs were less (under-exertion) than that of the perceived exertion. Although the interaction between gender and perceived exertion on each % MTF was not statistically significant, females generally showed over-exertion at 10-30% MTF and under-exertion at 70-90% levels, when compared with males. Notably, they accurately exerted thumb forces at 50% MTF level in both genders (around 1.2% difference, Figure 3). Thus, the relationship between perceived thumb force exertion (% MTF) and actual thumb force (% MTF) showed an S-shaped pattern (Figure 4). It suggested a tendency to exert higher and lower thumb forces than the perceived levels of exertion at lower and higher than 50% MTF levels, respectively, as shown in Figure 4. Therefore, 50% MTF is an inflection point where curves change from concave to convex, suggesting that the participants were biased toward over-exertion under the 50% MTF level, and under-exertion above the 50% MTF level, respectively. It represents a \"50%-phenomenon\". This finding was also similar to that of previous studies, which reported that the actual forces of exertion trended toward over-exertion at low levels of perceived exertion, whereas the actual forces of exertion presented a trend toward under-exertion at high levels of perceived exertion involving pinching, gripping, lifting, and leg extension tasks among both genders [35; 36; 37; 38]. The findings of this study may be useful in assessing the workload of workers using thumb exertion forces in the manufacturing process.