Impact shock frequency components and attenuation in rearfoot and forefoot running

Background:The forefoot running footfall pattern has been suggested to reduce the risk of developing running related overuse injuries due to a reduction of impact related variables compared with the rearfoot running footfall pattern.However,only time-domain impact variables have been compared between footfall patterns.The frequency content of the impact shock and the degree to which it is attenuated may be of greater importance for injury risk and prevention than time-domain variables.Therefore,the purpose of this study was to determine the differences in head and tibial acceleration signal power and shock attenuation between rearfoot and forefoot running.Methods:Nineteen habitual rearfoot runners and 19 habitual forefoot runners ran on a treadmill at 3.5 m/s using their preferred footfall patterns while tibial and head acceleration data were collected.The magnitude of the first and second head acceleration peaks,and peak positive tibial acceleration were calculated.The power spectral density of each signal was calculated to transform the head and tibial accelerations in the frequency domain.Shock attenuation was calculated by a transfer function of the head signal relative to the tibia.Results:Peak positive tibial acceleration and signal power in the lower and higher ranges were significantly greater during rearfoot than forefoot running(/】 【 0.05).The first and second head acceleration peaks and head signal power were not statistically different between patterns(p 】 0.05).Rearfoot running resulted in significantly greater shock attenuation for the lower and higher frequency ranges as a result of greater tibial acceleration(p 【 0.05).Conclusion:The difference in impact shock frequency content between footfall patterns suggests that the primary mechanisms for attenuation may differ.The relationship between shock attenuation mechanisms and injury is not clear but given the differences in impact frequency content,neither footfall pattern may be more beneficial for injury,rather the type of injury sustained may vary with footfall pattern preference.

Achieving an optimal shock-wave mitigation inside open channels with cavities for weak shock waves:A computational study

This paper deals with a numerical study of weak shock-waves propagation and their attenuation in channel flow having different heights and exhibiting a hollow circular cavities with different depths and diffraction angles inside.The effect of initial diffraction angle and cavity depth on the shock mitigation is investigated.A better shock attenuation is achieved with diffraction angle by a factor of approximately 17%in terms of shock-Mach number and 38%in terms of total energy.The obtained results show also,in addition to the initial diffraction angle and cavity depth,the importance of reducing the channel heights as well as the position of the reduced section in achieving an optimal shock-wave attenuation.The presence of a cavity inside the channel helps to attenuate faster the shock wave.The underlying physics relies on the shock diffraction phenomenon that generates large amount of vortical structures capable of dissipating part of the shock energy by inducing a pressure loss behind it.A subtle arrangement of channel position/height and a cavity location leads to an efficient pressure attenuation by approximately a factor of 57%forMs=1.6 and 16%for Ms=1.1..

PARAMETRIC MATCHING SELECTION OF MULTI-MEDIUM COUPLING SHOCK ABSORBER

To achieve the dual demand of resisting violent impact and attenuating vibration in vibration-impact-safety of protection for precision equipment such as MEMS packaging system, a theo- retical mathematical model of multi-medium coupling shock absorber is presented. The coupling of quadratic damping, linear damping, Coulomb damping and nonlinear spring are considered in the model. The approximate theoretical calculating formulae are deduced by introducing transformation-tactics. The contrasts between the analytical results and numerical integration results are developed. The resisting impact characteristics of the model are also analyzed in progress. In the meantime, the optimum model of the parameters matching selection for design of the shock absorber is built. The example design is illustrated to confirm the validity of the modeling method and the theoretical solution.

Shock Propagation in Dual-Circulation Production Networks:Characteristics and Simulation

This article constructs a dual-circulation production network framework on the basis of integrating inter-country and China's multi-regional input-output tables,identifies the propagation and attenuation of sectoral shocks in dual-circulation production networks,and measures the effects of US-China trade frictions on the networks.The research finds that:(1)The asymmetry between domestic-and internationalcirculation production networks has increased,and with a few sectors becoming key sectors to dual-circulation production networks,sectoral shocks grow increasingly critical for aggregate volatility.(2)Based on the above analytical framework,the global extraction method(GEM)is adopted to simulate the GDP losses in scenarios of China-US industry-wide chain interruptions,certain sectoral frictions,and supplyside and demand-side chain interruptions.The simulation finds that increasing the domestic substitution rate will reduce the value losses caused by China-US chain interruptions,which is applied for both countries.However,even if full substitution can be achieved,the value losses cannot be avoided completely in the China-US decoupling.Whether it is the demand-side chain interruptions plus insufficient market substitution in China,or the supply-side chain interruptions plus insufficient supply substitution in the US,will cause great losses to their economy.