Numerical calculation and study of differential equations of muscle movement velocity based on martial articulation body ligament tension

The paper analyses the impact of ligament stretch and tension on the speed of movement in martial arts from the perspective of sports physiology. It establishes the numerical relationship between the peak impact value of the ligament speed and the differential equation of the flexibility of the joints in the initial stage of tension (impact peak). It was found that the differential equation of the ligament tension of the movement is formed after the movement is stable, which cannot reflect the flexibility of the ligament and the mastery of the movement. In this paper, a tension calculation model for ligament equilibrium is established by using a kinetic method of motion. Although it is a static equation, continuous use can obtain dynamic effects. The simulation proves that the initial tension change is more realistic.

Relevance of Frequency-Domain Analyses to Relate Shoe Cushioning, Ground Impact Forces and Running Injury Risk: A Secondary Analysis of a Randomized Trial With 800+ Recreational Runners

Cushioning systems in running shoes are used assuming that ground impact forces relate to injury risk and that cushioning materials reduce these impact forces. In our recent trial, the more cushioned shoe version was associated with lower injury risk. However, vertical impact peak force was higher in participants with the Soft shoe version. The primary objective of this study was to investigate the effect of shoe cushioning on the time, magnitude and frequency characteristics of peak forces using frequency-domain analysis by comparing the two study groups from our recent trial (Hard and Soft shoe group, respectively). The secondary objective was to investigate if force characteristics are prospectively associated with the risk of running-related injury. This is a secondary analysis of a double-blinded randomized trial on shoe cushioning with a biomechanical running analysis at baseline and a 6-month follow-up on running exposure and injury. Participants (n = 848) were tested on an instrumented treadmill at their preferred running speed in their randomly allocated shoe condition. The vertical ground reaction force signal for each stance phase was decomposed into the frequency domain using the discrete Fourier transform. Both components were recomposed into the time domain using the inverse Fourier transform. An analysis of variance was used to compare force characteristics between the two study groups. Cox regression analysis was used to investigate the association between force characteristics and injury risk. Participants using the Soft shoes displayed lower impact peak force (p < 0.001, d = 0.23), longer time to peak force (p < 0.001, d = 0.25), and lower average loading rate (p < 0.001, d = 0.18) of the high frequency signal compared to those using the Hard shoes. Participants with low average and instantaneous loading rate of the high frequency signal had lower injury risk [Sub hazard rate ratio (SHR) = 0.49 and 0.55; 95% Confidence Interval (CI) = 0.25–0.97 and 0.30–0.99, respectively], and those with early occurrence of impact peak force (high frequency signal) had greater injury risk (SHR = 1.60; 95% CI = 1.05–2.53). Our findings may explain the protective effect of the Soft shoe version previously observed. The present study also demonstrates that frequency-domain analyses may provide clinically relevant impact force characteristics.Clinical Trial Registration:https://clinicaltrials.gov/, identifier: 9NCT03115437.

Can We Decrease Floor Impact Noise by Changing Walking Patterns? - a Preliminary Report

Floor impact noise from the footsteps of neighbors is one of the major social problems among people living in apartment buildings. In this laboratory environment, walking patterns and impact force on the floor were quantified from seventeen young adults while they were walking normally and quietly to investigate how the voluntary quiet walking to reduce the footstep noise would be different from the normal walking. Eight out of the 17 participants walked with a rearfoot strike pattern, and the rest (9 participants) changed their gait pattern to a non-rearfoot foot strike pattern when asked to walk quietly. Both groups showed decreases in impact peak and vertical loading rate, but the magnitude of the decrements was greater for the participants who walked with the non-rearfoot strike pattern. The preliminary result of this ongoing study suggests that people may not walk quietly even they believe to do so, and it warrants further studies to investigate more effective and easy-to-conduct walking strategies to address the floor impact noise issue of apartment buildings.

Collision simulation of potato on rod separator

To obtain the collision characteristics of potatoes colliding with steel rods of different parameters, the finite element analysis (FEA) method was used to study the impact contact stress, collision displacement, acceleration and impact force. The results showed that with increasing rod diameter, the maximum collision displacement of the potato in the Y direction decreased, and the maximum collision acceleration and impact peak force increased. With increasing rod tilt angle and rod spacing, the maximum collision displacement increased linearly, but the maximum collision acceleration and impact peak force decreased linearly. Within the range of analysis factors, the fluctuation of the maximum collision displacement, acceleration and impact peak force caused by the change in rod diameters were the smallest, which were 0.34 mm, 38 m/s2 and 9 N, respectively. When potatoes collided with single and double rods, all the collision characteristics increased with the increase in potato drop height, and the results for double rods were significantly smaller than those for single rod collision. When the potato mass was 250 g, the drop height was 200 mm for single rod collision or 250 mm for double rod collision, the impact contact stress reached the yield stress, and the potato was damaged. This article provides a data basis and a referenced method for the optimized design of the structural parameters and working parameters of the rod separator in the process of potato mechanized harvesting.

Principal Component Analysis of the Running Ground Reaction Forces With Different Speeds

Ground reaction force (GRF) is a key metric in biomechanical research, including parameters of loading rate (LR), first impact peak, second impact peak, and transient between first and second impact peaks in heel strike runners. The GRFs vary over time during stance. This study was aimed to investigate the variances of GRFs in rearfoot striking runners across incremental speeds. Thirty female and male runners joined the running tests on the instrumented treadmill with speeds of 2.7, 3.0, 3.3, and 3.7 m/s. The discrete parameters of vertical average loading rate in the current study are consistent with the literature findings. The principal component analysis was modeled to investigate the main variances (95%) in the GRFs over stance. The females varied in the magnitude of braking and propulsive forces (PC1, 84.93%), whereas the male runners varied in the timing of propulsion (PC1, 53.38%). The female runners dominantly varied in the transient between the first and second peaks of vertical GRF (PC1, 36.52%) and LR (PC2, 33.76%), whereas the males variated in the LR and second peak of vertical GRF (PC1, 78.69%). Knowledge reported in the current study suggested the difference of the magnitude and patterns of GRF between male and female runners across different speeds. These findings may have implications for the prevention of sex-specific running-related injuries and could be integrated with wearable signals for the in-field prediction and estimation of impact loadings and GRFs.

Leg Stiffness and Vertical Stiffness of Habitual Forefoot and Rearfoot Strikers during Running

Foot strike patterns influence the running efficiency and may be an injury risk. However, differences in the leg stiffness between runners with habitual forefoot (hFFS) and habitual rearfoot (hRFS) strike patterns remain unclear. This study aimed at determining the differences in the stiffness, associated loading rate, and kinematic performance between runners with hFFS and hRFS during running. Kinematic and kinetic data were collected amongst 39 runners with hFFS and 39 runners with hRFS running at speed of 3.3 m/s, leg stiffness (Kleg), and vertical stiffness (Kvert), and impact loads were calculated. Results found that runners with hFFS had greater Kleg ( P = 0.010 , Cohe n ’ s d = 0.60 ), greater peak vertical ground reaction force (vGRF) ( P = 0.040 , Cohe n ’ s d = 0.47 ), shorter contact time( t c ) ( P < 0.001 , Cohe n ’ s d = 0.85 ), and smaller maximum leg compression ( Δ L ) ( P = 0.002 , Cohe n ’ s d = 0.72 ) compared with their hRFS counterparts. Runners with hFFS had lower impact peak (IP) ( P < 0.001 , Cohe n ’ s d = 1.65 ), vertical average loading rate (VALR) ( P < 0.001 , Cohe n ’ s d = 1.20 ), and vertical instantaneous loading rate (VILR) ( P < 0.001 , Cohe n ’ s d = 1.14 ) compared with runners with hRFS. Runners with hFFS landed with a plantar flexed ankle, whereas runners with hRFS landed with a dorsiflexed ankle ( P < 0.001 , Cohe n ’ s d = 3.35 ). Runners with hFFS also exhibited more flexed hip ( P = 0.020 , Cohe n ’ s d = 0.61 ) and knee ( P < 0.001 , Cohe n ’ s d = 1.15 ) than runners with hRFS at initial contact. These results might indicate that runners with hFFS were associated with better running economy through the transmission of elastic energy.

Experimental Research on the Mechanical Performance of the Bolted Rock under Lateral Impact Load: Effect of Prestress, Body Material, and Anchorage Style

In order to reveal the impact mechanical properties and their key influencing factors of the bolted rock under the lateral impact load, through the lateral drop hammer impact test, the time-history curve of impact force, axial force of the bolt, and surface strain of the sample under different combination types of influencing factors is obtained, and the whole process of deformation and failure of the bolted rock is recorded. The test results show that the material of the bolt has a significant influence on the impact force and axial force of the bolt. There is a positive correlation between bolt strength and impact peak and impact attenuation slope and a negative correlation between bolt strength and impact action time. The effect of prestress on the impact resistance of the bolted rock was also evaluated by the test which suggested that prestress of the bolt can significantly reduce both impact time and bolt axial force of the bolted rock but has limited effect on the impact force. It was also found that the time-history curve of the impact force of anchoring rock mass had significant difference with full-length anchoring and nonanchoring. Compared with the nonanchoring bolt, the full-length anchored rock mass has a larger impact peak and shorter action time, which means that the impact resistance of the full-length bolted rock has a certain degree of weakening. Through scientific research, determining the reasonable bolt material, prestress value, and anchorage style can improve the impact resistance of the sample.

TEST RESEARCH ON THE IMPACT PEAK FORCE AND DAMAGE DEPTH OF POTATO

To analyse the influence factors of impact peak force (IPF) and damage depth (DD) on potatoes, the orthogonal test and single factor test were carried out on two potato varieties. The results showed that the IPF of Xiabodi was smaller and DD was greater than those of Gaoyuanhong. Potato mass had the greatest effect on IPF, and that of drop height on DD. The equations between IPF, DD and potato mass, drop height were obtained. Both IPF and DD impacting with steel were the largest, and the smallest with steel- rubber. With the increase of impact times, IPF decreased first and then increased, and DD increased gradually.

Effects of 12-week cadence retraining on impact peak, load rates and lower extremity biomechanics in running

Background Excessive impact peak forces and vertical load rates are associated with running injuries and have been targeted in gait retraining studies. This study aimed to determine the effects of 12-week cadence retraining on impact peak, vertical load rates and lower extremity biomechanics during running. Methods Twenty-four healthy male recreational runners were randomised into either a 12-week cadence retraining group (n = 12), which included those who ran with a 7.5% increase in preferred cadence, or a control group (n = 12), which included those who ran without any changes in cadence. Kinematics and ground reaction forces were recorded simultaneously to quantify impact force variables and lower extremity kinematics and kinetics. Results Significantly decreased impact peak (1.86 ± 0.30 BW vs. 1.67 ± 0.27 BW, P = 0.003), vertical average load rates (91.59 ± 18.91 BW/s vs. 77.31 ± 15.12 BW/s, P = 0.001) and vertical instantaneous load rates (108.8 ± 24.5 BW/s vs. 92.8 ± 18.5 BW/s, P = 0.001) were observed in the cadence retraining group, while no significant differences were observed in the control group. Foot angles (18.27° ± 5.59° vs. 13.74° ± 2.82°, P = 0.003) and vertical velocities of the centre of gravity (CoG) (0.706 ± 0.115 m/s vs. 0.652 ± 0.091 m/s, P = 0.002) significantly decreased in the cadence retraining group at initial contact, but not in the control group. In addition, vertical excursions of the CoG (0.077 ± 0.01 m vs. 0.069 ± 0.008 m, P = 0.002) and peak knee flexion angles (38.6° ± 5.0° vs. 36.5° ± 5.5°, P < 0.001) significantly decreased whilst lower extremity stiffness significantly increased (34.34 ± 7.08 kN/m vs. 38.61 ± 6.51 kN/m, P = 0.048) in the cadence retraining group. However, no significant differences were observed for those variables in the control group. Conclusion Twelve-week cadence retraining significantly increased the cadence of the cadence retraining group by 5.7%. This increased cadence effectively reduced impact peak and vertical average/instantaneous load rates. Given the close relationship between impact force variables and running injuries, increasing the cadence as a retraining method may potentially reduce the risk of impact-related running injuries.