To realize real-time monitoring and evaluation of muscle strength, this study designed and validated a wearable muscle strength monitoring system based on muscle perimeter changes.

Six healthy college students who are not sports majors wore the monitoring gear based on the change of muscle perimeter to perform the isokinetic muscle strength test, the real-time data of the change of muscle perimeter during the isokinetic exercise was obtained. After analyzing and processing the curve of muscle perimeter change over time, namely, the peak muscle perimeter change (PP), the peak velocity of muscle perimeter change (PVP) and the accumulation of muscle perimeter change (AP) over time in a single exercise, Pearson correlation analysis was conducted with the peak torque (PT), the peak torque to body weight ratio (PT/BW), the torque at 0.18 s (T0.18) and the endurance ratio (ER) obtained by the isokinetic muscle strength test. The reliability of wearable system for real-time muscle strength monitoring was verified. The muscle perimeter changes were sampled with the arm and leg wearable protectors, and the muscle perimeter monitoring positions corresponded to the largest muscle perimeter changes when the strength of biceps in the upper arm was applied, as well as the largest muscle perimeter changes when the strength of quadriceps above the knee was applied. The isokinetic muscle strength test was performed on elbow and knee joints using the Biodex System 4 pro device.

Dynamic muscle perimeter changes could be used to monitor the muscle strength level of the human body. There was a significant correlation between arm muscle perimeter and elbow muscle strength index (P≤0.01), and the maximum correlation coefficient was 0.91. Leg muscle perimeter was significantly correlated with knee muscle strength (P≤0.01), and the maximum correlation coefficient was 0.99.

The wearable muscle strength monitoring system has a high reliability and can be used for real-time monitoring of the elbow and knee muscle strength during isokinetic exercise.

To explore the correlation between single-leg standing posture control and ankle plantar flexor muscle stability, so as to provide a new theoretical basis for improving the ability of human posture control.

A total of 20 healthy male college students were randomly selected as the experimental subjects. The iBalance tester and training system was used to test the trajectory data of the center of pressure (COP) of the foot standing on one leg. The CON-TREX MJ multi-joint isokinetic test and training system was used to test the moment amplitude data during the contraction of ankle plantar flexor muscles. Univariate repeated measures variance analysis was used to analyze the standard deviation data of ankle plantar flexor moment amplitude between groups. The Pearson correlation coefficient was used to study the correlation.

The greater the intensity of the muscle stabilization task performed by the ankle plantar flexor muscle, the greater the standard deviation of the moment amplitude. The C90 area was positively correlated with the coefficient of variation (CV) of the 10% maximum voluntary contraction (MVC) moment of ankleplantar flexor muscle (r=0.761, P<0.05) during single-leg standing without interference. The C90 area was positively correlated with the CV (r=0.632, P<0.05) of the 30% MVC moment of ankle plantar flexor muscle during single-leg standing. When the proprioception was interfered during single-leg standing, the C90 area was positively correlated with the CV (r=0.583, P<0.05) of the 20% MVC moment amplitude of ankleplantar flexor muscle.

With the increasing difficulty of muscle strength stabilization performed by the ankle plantar flexor muscles, muscle stability decreases. There is a positive correlation between ankle plantar flexor strength stability and single-leg standing posture control. Compared with the case without interference, under visual and proprioceptive interference, an additional information input is reduced or disturbed, and it is more difficult to maintain body balance, and the ankle plantar flexor muscle needs a higher muscle stability in the force mode to participate in the posture control of the human body during single-leg standing.

By applying the long short-term memory (LSTM) neural network model and using lower body landmark coordinates obtained from a markerless motion capture system as inputs, to estimate ground reaction force (GRF) curves during running.

The video images and GRF data of 59 amateur runners during running were collected by the markerless motion capture system and three-dimensional (3D) force plates. The LSTM model was established, and the 3D coordinates of 11 lower body landmarks, obtained via the Theia3D markerless system, were used as inputs to estimate the 3D GRF curves during the stance of running. The estimation performance was evaluated using correlation coefficients r, root mean square error (RMSE), and normalized root mean square error (nRMSE) by comparing LSTM model estimation and force plate measurement. Statistical parametric mapping was used to analyze differences in GRF curves estimated by the LSTM model and measured by the force plate, while paired t-tests were used to assess differences in GRF characteristics between model estimation and actual measurement.

A strong correlation (r>0.85, P<0.001) and lower error (RMSE<0.3 body weight, nRMSE<15%) was found between the LSTM model estimation and actual measurements. No significant difference was found in GRF curve intervals between LSTM model estimation and actual measurements. There was no significant difference in GRF characteristics between LSTM model estimation and actual measurements (P>0.05).

Based on the LSTM model, the 3D GRF curves can be effectively estimated by lower body landmark coordinates obtained from the makerless motion capture system, thereby acquiring the highly accurate GRF characteristics. The LSTM model developed in this study can be used to monitor injury risks during running in outdoor environments.

To study the hemodynamic characteristics of autologous arteriovenous fistula (AVF) and provide a theoretical basis for reducing its stenosis rate.

Bidirectional fluid-structure interaction (FSI) simulations were conducted on a modified AVF model. Flow field and wall shear stress (WSS) distributions in the internal fistula at different periods and angles in a cardiac cycle were analyzed for retrograde flow (confluence) and anterograde flow (shunt) modes in models with varying anastomosis angles.

Under confluence modes, the WSS<1 Pa area in the 60° anastomosis angle model was the smallest (7.027 mm²), while the 45°, 60°, and 90° models showed no significant differences in eddy current size and intensity. Under shunt modes, the 45° anastomosis angle model had the smallest WSS<1 Pa area (9.079 mm²), but the 60° model exhibited the lowest eddy current intensity and distribution area. In addition, the difference in the WSS<1 Pa area between the 60° and 45° models was only 2.661 mm².

Under both confluence and shunt flow modes, establishing an AVF with 60° anastomosis angle is conducive to reducing the risk of vascular stenosis in arteriovenous fistula.

To investigate stress distributions of the knee joint at 0 and 15^th day after anterior cruciate ligament reconstruction (ACLR) under a compressive force through the axis of the femoral shaft onto the proximal femur.

A three-dimensional (3D) finite element model of the human knee joint incorporating viscoelastic material properties was developed. The one-dimensional (1D) Prony series viscoelastic constitutive model parameters for articular cartilage, menisci, ligaments, and anterior cruciate ligament (ACL) grafts were determined by fitting experimental creep curves. The viscoelastic parameters of ACL grafts at 15^th day after ACLR surgery were extrapolated. Finite element simulations were then performed to analyze the von Mises stress distributions in knee ligaments, ACL grafts, articular cartilage, and menisci under 1.5 kN vertical downward compressive load applied to the femur, with loading durations of 1 second and 600 seconds.

At 15^th day after ACLR surgery, the initial relaxation modulus and equilibrium modulus of human ACL grafts remained elevated compared to native ACL tissues, resulting in a significantly higher stress concentration within the grafts relative to healthy ACL. Despite the compromised mechanical properties of the grafts after ACLR surgery, the vertical downward compressive force applied to the femur under both short-term (1 s) and prolonged (600 s) loading durations, exhibited a minimal biomechanical impact on articular cartilage and meniscal structures.

Following ACLR, vertical compressive loads during weight-bearing rehabilitation exercises such as standing demonstrate minimal impact on articular cartilage and meniscus, while promoting fibrous regeneration of the graft. This renders such exercises a prudent early-stage rehabilitation strategy. Graft preparation requires balanced consideration of elastic and viscous properties, with grafts exhibiting higher relaxation modulus and viscosity coefficient than healthy ACL proving more effective in maintaining early postoperative knee stability.

To investigate the risk of thoracoabdominal injuries in six-year-old child occupants in a reclined seating posture during frontal collisions, and provide a reference for developing child restraint systems (CRS).

Three validated biomechanical models of six-year-old child occupants in different seating postures with detailed anatomical structures were used. The acceleration curve from a sport utility vehicle crash test was applied to analyze the effects of seating posture on thoracic motion trajectory, chest acceleration, thoracoabdominal compression, viscous criterion (VC) of the chest and abdomen, internal organ strain, and spinal stress.

Thoracic motion trajectories varied in the Z-direction under three seating postures. As the upper torso angle increased, thoracoabdominal kinematic injury parameters showed an upward trend. The thoracic and abdominal VC under 120° and 135° posture increased by 67% and 113%, 10.7% and 25% compared with that under 105° standard sitting posture. The risk of thoracic internal organ injury was inversely related to the seating angle, while the risk of abdominal internal organ injury was positively related to the seating angle. The primary spinal injury mechanism was compression-flexion.

CRS protection evaluation should comprehensively consider thoracoabdominal kinematic parameters, internal organ biomechanics, and spinal injury risk. These findings have important implications for CRS development in intelligent driving systems and occupant protection strategy formulation.