Comparison and Association of Neck Extensor Muscles’ Endurance and Postural Function in Subjects with and without Chronic Neck Pain – A Cross-Sectional Study

Purpose Neck extensor endurance (NEE) and position sense are vital for maintaining cervical spine function and defects in these processes may be associated with impaired postural control in chronic neck pain (CNP) subjects. The study’s objectives are 1) to compare the cervical extensor endurance capability and postural control of CNP subjects with those of asymptomatic controls; 2) to investigate the association between NEE and postural control. Materials and Methods Sixty-four participants (38 asymptomatic, 38 with CNP) participated in this cross-sectional study. NEE was assessed using a clinical extensor endurance test. Under open and closed eyes conditions, postural control measures were tested with the Good Balance system. The postural control parameters were AP-velocity (mm/s), ML-velocity (mm/s) and Velocity moment (mm2). NEE capacity and postural control parameters were compared and correlated between asymptomatic and CNP subjects. Results and Discussion CNP subjects showed lower NEE capacity (p<0.001) and significantly larger AP-velocity (p<0.001), ML-velocity (p<0.001) and Velocity moment (p<0.001) than asymptomatic participants. NEE negatively correlated with AP-velocity (r=−0.51, p=0.001), ML-velocity (r=0.46, p=0.003) and velocity moment (r=0.38, p=0.020) in asymptomatic subjects in eyes open condition and no correlations in subjects with CNP. CNP subjects showed increased postural sway velocities and lowered extensor endurance capacity compared to asymptomatic participants. No correlations existed between NEE and postural control parameters in CNP subjects.

A comprehensive biomechanical analysis of the barbell hip thrust

Barbell hip thrust exercises have risen in popularity within the biomechanics and strength and conditioning literature over recent years, as a method of developing the hip extensor musculature. Biomechanical analysis of the hip thrust beyond electromyography is yet to be conducted. The aim of this study was therefore to perform the first comprehensive biomechanical analysis the barbell hip thrust. Nineteen resistance trained males performed three repetitions of the barbell hip thrust at 70% one-repetition maximum. Kinematic (250 Hz) and kinetic (1000 Hz) data were used to calculate angle, angular velocity, moment and power data at the ankle, knee, hip and pelvic-trunk joint during the lifting phase. Results highlighted that the hip thrust elicits significantly (p < 0.05) greater bilateral extensor demand at the hip joint in comparison with the knee and pelvic-trunk joints, whilst ankle joint kinetics were found to be negligible. Against contemporary belief, hip extensor moments were not found to be consistent throughout the repetition and instead diminished throughout the lifting phase. The current study provides unique insight to joint kinematics and kinetics of the barbell hip thrust, based on a novel approach, that offers a robust evidence base for practitioners to guide exercise selection.

Investigation on the Horn-Like Vortices in Stator Corner Separation Flow in an Axial Flow Pump

Stator corner separation flow existing in the guide-vane domain has significant effects on the characteristics of an axial-flow pump. The objective of this paper is to investigate the vortical structures in stator corner separation flow. Transient numerical simulation with a proof experiment was conducted for an axial-flow pump. Structural features of the vortices and their effects on velocity moment attenuation and pressure fluctuations in the guide-vane domain were analyzed. Horn-like vortices are found in the stator corner separation flow. A full cycle of the horn-like vortex evolution, “inception-growth-development-decay,” is presented. During this transit process, the vortex tube is gradually elongated and deformed, which forms an oblique separation line on the vane suction surface. High velocity moment always exists in the flow passages of the guide-vane domain, and the uniformity of main flows is gradually reduced. Meanwhile, periodic pressure fluctuations arise. The maximum amplitude of pressure fluctuations in the flow passages occurs in the region where the horn-like vortex cores at the “growth” stage lie in, which is approximately 3.39 times higher than that in the vaneless region between the impeller and guide-vane. The dominant frequency of pressure fluctuations in the flow passages is approximately 0.75 times the rotating frequency, which is close to the frequency of the full cycle of the horn-like vortex evolution. Horn-like vortices have remarkable effects on the flow fields, and more attention should be paid to them.

Controllable velocity moment and prediction model for inlet guide vanes of a centrifugal pump

Purpose This paper aims to investigate the effect of three-dimensional (3D) inlet guide vanes (IGVs) on performance of a centrifugal pump. Design/methodology/approach A design method for 3D IGVs is proposed based on the controllable velocity moment, which is determined by a fourth-order dimensionless function. Numerical simulation of the centrifugal pump with IGVs is carried out by solving the Reynolds-averaged Navier–Stokes equations. The method of frozen rotor is applied to couple the stationary and rotational domain. Findings The efficiency of pump with 3D IGVs is higher than that with 2D IGVs for most prewhirl angles, which validate the advancement of 3D IGVs on prewhirl regulation. The effect of prewhirl regulation at small flow rate is more significant than that at large flow rate. Originality/value A prediction model of velocity moment based on the Oseen vortex is proposed to describe the flow pattern downstream the IGVs.

The effect of a localized fault in the planet bearing on vibrations of a planetary gear set

Dynamic characteristics of a planetary gear set can be greatly affected by a localized fault in the planet bearing. To understand the relationship between the dynamic characteristic of the planetary gear set and the localized fault sizes, a dynamic finite element model for a planetary gear set is developed. A localized fault is assumed to be located in the outer race of the planet bearing. The fault profile is defined as a rectangular one. To formulate the elastic deformations of the components and elastic contact deformations between the mating components, all components of the planetary gear set are considered as elastic bodies in the finite element model. A standard gravity is also considered in the finite element model. A Coulomb frictional model is used to formulate the frictional forces in the planetary gear set. Influences of the rotational velocity, moment, and fault width on the dynamic characteristics of the planetary gear set are discussed. The simulation results are compared with those from the previous method to validate the finite element model. It seems that the presented finite element model can be applied to simulate the dynamic characteristics of a planetary gear set caused by a localized fault in the outer race of the planet bearing.