Skateboarding is an Olympic event with frequent jumping and landing, where the cushioning effect by the foot structure (from the arch, metatarsals, etc.) and damping performance by sports equipment (shoes, insoles, etc.) can greatly affect an athlete\'s sports performance and lower the risk of limb injury. Skateboarding is characterized by the formation of a \"man-shoe-skateboard system,\" which makes its foot cushioning mechanism different from those of other sports maneuvers, such as basketball vertical jump and gymnastics broad jump. Therefore, it is necessary to clarify the cushioning mechanism of the foot structure upon landing on a skateboard. To achieve this, a multibody finite element model of the right foot, shoe, and skateboard was created using Mimics, Geomagic, and ANSYS. Kinetic data from the ollie maneuver were used to determine the plantar pressure and Achilles tendon force at three characteristics (T1, T2, and T3). The stress and strain on the foot and metatarsals (MT1-5) were then simulated. The simulation results had an error of 6.98% compared to actual measurements. During landing, the force exerted on the internal soft tissues tends to increase. The stress and strain variations were highest on MT2, MT3, and MT4. Moreover, the torsion angle of MT1 was greater than those of the other metatarsals. Additionally, the displacements of MT2, MT3, and MT4 were higher than those of the other parts. This research shows that skateboarders need to absorb the ground reaction force through the movements of the MTs for ollie landing. The soft tissues, bones, and ligaments in the front foot may have high risks of injury. The developed model serves as a valuable tool for analyzing the foot mechanisms in skateboarding; furthermore, it is crucial to enhance cushioning for the front foot during the design of skateboard shoes to reduce potential injuries.

The purpose of this study was to determine the biomechanical mechanisms driving passengers\' lower-limb postural shifts during seated sleep on a flight to prevent negative effects on passengers\' physical health. Twenty subjects participated in an observational study and a subsequent experiment on fatigue development and tissue oxygenation changes during seated sleep in an economy-class aircraft seat. Three of the most frequently used postures, which involved four targeted muscles of the legs and the thigh-buttock region, were selected and examined in the experiment with the following measures: muscle electromyogram, tissue oxygenation, and body contact pressure distribution. The results showed that the fatigue of the tibialis anterior and gastrocnemius and the compression of the region under the medial tuberosities were relieved by alternations among the three positions-position 1 (placing the shanks forwards), position 2 (placing the shanks neutrally), and position 3 (placing the shanks backwards). This research reveals the mechanical properties of the biomechanical factors functioning in lower-limb postural shifts during seated sleep and provides design optimization strategies for economy-class aircraft seats to reduce the negative effects on passenger health.