[Biomechanical analysis of ankle-foot complex during a typical Tai Chi movement-Brush Knee and Twist Step]

Cushioning mechanism of the metatarsals during landing for the skateboarding ollie maneuver

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.

Study on Two Typical Progressive Motions in Tai Chi (Bafa Wubu) Promoting Lower Extremity Exercise

BACKGROUND

By comparatively investigating the joints, muscles and bones of the lower extremity during two progressive motions in Bafa Wubu and normal walking, this paper aims to enrich the diversity of walking exercise and scientifically provide theoretical guidance for primary practitioners. The scientific training methods and technical characteristics of Bafa Wubu, as well as its contribution to comprehensive exercise of the lower extremities, are further explored.

METHODS

A total of eight professional athletes of Tai Chi at the national level were recruited. The kinetic parameters of the lower extremity were calculated using AnyBody 7.2 musculoskeletal modeling. Stress analysis of the iliac bone was performed using an ANSYS 19.2 workbench.

RESULTS

In Bafa Wubu, the ground reaction force during two progressive motions was significantly smaller than that noted during normal walking. During warding off with steps forward and laying with steps forward, the load at the three joints of the lower extremity was significantly smaller than that during normal walking in the frontal plane, but significantly greater than that noted during normal walking in the vertical axis. In addition, the lower limb joint torque was higher than that of normal walking in both progressive movements, and lower limb muscle activation was higher. The iliac bone loads during the two progressive motions were larger than those during normal walking, and the maximum loading point differed.

CONCLUSIONS

This is the first study to demonstrate the biomechanical performance of Bafa Wubu in professional athletes of Tai Chi. Two progressive motions of Bafa Wubu require the lower extremity to be slowly controlled, thereby resulting in a smaller ground reaction force. In addition, the loads of the three joints at the lower extremity all increase in the vertical direction and decrease in the lateral direction, reducing the possibility of lateral injury to the joints. In addition, the two progressive motions significantly enhance the muscle strength of the plantar flexion muscles, dorsiflexor, and muscles around the thigh, and effectively stimulate the bones of the lower extremity. Therefore, progressive motion training contributes to improving the controlling and supporting capabilities of the lower extremities during normal walking.

Biomechanical Analysis of the Human Knee Joint

Exercise is an indispensable part of human daily life. The knee joint is inseparable from human movement. The knee is relatively fragile and easy to get injuries. Therefore, the biomechanical properties of knee joints were studied. The VICON T40S 3D motion acquisition and analysis system and the AMTI 3D force measurement platform were used to collect the lower limb kinematics and dynamics data of five male volunteers. Then the knee angle and moment of the human body are analyzed, the foot pressure was obtained by force plate, and the ground reaction force was obtained. The results show that: (1) in terms of knee flexion and extension torques, the peak stretching torques occurred in about 25% and 65% of the gait cycles. At the beginning of the gait, which is the flexion moment, the knee joint produces a moment of -24.65 Nmm, 25% of gait cycles reached the maximum peak value of 896.89 Nmm, 65% of gait cycles reached the second peak value of 315.81 Nmm; (2) The change of reaction force in a gait cycle is: when the ground starts to react, the ground reaction reaches 600 N. At normal times, the ground reaction force rapidly rises to the maximum value of 890 N; when the gait is in the middle of a single support phase, the ground reaction force is 462 N; when the ankle joint moves in plantar flexion, the ground reaction force increases to 830 N again; finally, when the toe is lifted off the ground, the ground reaction force quickly drops to zero; (3) in the course of a gait cycle, the spatial and temporal parameter curve distribution of the subjects was consistent, and the difference was not significant (P > 0.05).

[Structural design and performance analysis of an auxiliary dining robot]

An auxiliary dining robot is designed in this paper, which implements the humanoid feeding function with theory of inventive problem solving (TRIZ) theory and aims at the demand of special auxiliary nursing equipment. Firstly, this robot simulated the motion function of human arm by using the tandem joints of the manipulator. The end-effector used a motor-driven spoon to simulate the feeding actions of human hand. Meanwhile, the eye in hand installation style was adopted to instead the human vision to realize its automatic feeding action. Moreover, the feeding and drinking actions of the dining robot were considered comprehensively with the flexibility of spatial movement under the lowest degree of freedom (DOF) configuration. The structure of the dining robot was confirmed by analyzing its stresses and discussing the specific application scenarios under this condition. Finally, the simulation results demonstrate high-flexibility of the dining robot in the workspace with lowest DOF configuration.