# Stress Analysis on the Ankle Joint during Incline and Decline Standing
## 4 Discussion  
The FE model developed in the present study was analysed based on von Mises stress responses at the ankle for slope standing. The analysis was performed under static linear elastic and the stresses obtained at the ankle part was assumed to not exceed the yield limit of the materials. Von Mises stress was used to evaluate the failure risk for the ankle joint because it considered the combined effect of normal and shear stresses. Based on the results, there are a few potential reasons that contribute to the increment of stress at the ankle joint component during incline and decline standing compared to flat standing. Firstly, incline standing that involves a steeper slope requires the foot to be dorsiflexed, and similarly, declined standing requires the foot to be dorsiflexed to accommodate the slope [6]. Dorsiflexion is where the foot bends towards the shin. Inclined and declined standing changes the range of motion (ROM) at which joints operate [16]. The ankle joint experiences different angles of dorsiflexion and plantarflexion during slope standing compared to flat standing, impacting the distribution of forces and stress on the bones of the ankle. The decreased ROM of ankle dorsiflexion may lead to an increase in ground reaction force (GRF) and loading [17], which leads to an increment of stress on the ankle joint. Furthermore, the higher force generated during incline standing to move against gravity and the higher impact force absorbed and distributed during declined standing [18] lead to a higher stress on the bones of the ankle during slope standing compared to flat standing. This higher stress due to the impact forces and joint loading may contribute to the risk of injury related to signs of fatigue, fractures, and pain at the patellofemoral [19]. In addition, inclined standing requires more effort from the muscles that plantarflex the ankle (push the foot down), including the calf muscles. This increased activity puts an additional load on the talus bone. As for declined standing, it requires the activation of eccentric muscles [16; 19], especially in the lower leg, in order to control the descent. Eccentric muscle contractions involve lengthening of the muscle while producing force, and this can contribute to higher stress on the talus. As reported previously, the activation of the tibial muscle is changing due to the ankle response to the inclined surface during slope standing [20], and the magnitude and duration of activity in the gluteus maximus and hamstring are increased during incline standing [21; 22]. Therefore, another possible reason that leads to stress increment on the bones of ankle joints is muscle engagement [16; 23]. The combination of these factors results in an increased demand on the bones of the ankle during slope standing, leading to higher stress compared to standing on a flat surface. It is important to note that individuals with certain biomechanical issues, musculoskeletal  
Figure 8: Factor of safety on ankle joint bones. conditions, or improper footwear may be more susceptible to increased stress and potential injury during slope standing. While slope standing can increase stress on the bones of the ankle joint, proper gait mechanics, muscle strength, and joint stability play crucial roles in mitigating excessive stress and preventing injuries. In comparison to the maximum von Mises stress distribution view, the highest stress distribution was observed in ligaments compared to bones and cartilage. Ligaments, bones, and cartilage all undergo mechanical stresses during slope standing or any weight-bearing activity; but, because of their particular biomechanical characteristics and functions inside the body, the distribution and magnitude of these stresses might differ. The possible explanation for these differences is due to the material properties of the component itself. Ligaments are fibrous connective tissues that can resist tensile forces. The tensile strength of ligaments is high but the ability to withstand compressive forces is restricted [24].