Search Results (364)

The bowling performance of cricket fast bowlers is highly dependent on lower limb power and stiffness. French Contrast Training (FCT) and Velocity-Based Training (VBT) are effective ways to improve rate of force development and peak power. The objective of this study was to investigate the effects of VBT-optimized FCT on the lower limb explosive power and bowling performance of cricket fast bowlers. Twenty adult male medium-fast bowlers volunteered for this study and were evenly divided into an experimental group (EG) and a control group (CG). The EG underwent an 8-week VBT-based FCT program, while the CG completed 8 weeks of traditional resistance training combined with traditional plyometric training. Before and after the intervention, subjects were tested on their Bulgarian split squat load–velocity profile, general lower limb power (countermovement jump height, squat jump height, Eccentric Utilization Ratio, and Reactive Strength Index), and bowling performance metrics (front foot contact time, peak force, impulse, front knee angle at ball release, and ball release speed). The results demonstrated that the EG showing significant advantage over the CG on movement velocity during the Bulgarian split squat at loads 20% 1RM, 40% 1RM, and 60% 1RM (p = 0.008, 0.011, 0.008, ${\eta }_p^2$ = 0.337, 0.313, 0.324). General lower limb power in the EG also improved significantly, with CMJ height, EUR, and RSI showing significant inter-group superiority compared to the CG (p < 0.001, = 0.019, 0.004, ${\eta }_p^2$ = 0.659, 0.281, 0.399). Regarding bowling performance, the EG demonstrated highly significant advantages in front foot contact impulse, front knee angle at ball release, and ball release speed (p < 0.001, ${\eta }_p^2$ = 0.572, 0.590, 0.704). In conclusion, the 8-week VBT-FCT program is more effective than the traditional resistance and plyometric training program of the same duration in enhancing lower limb power and bowling performance for medium-fast cricket bowlers. Full article

An artificial neural network (ANN) prediction model based on the Levenberg–Marquardt (LM) algorithm has been developed to predict the nonlinear heat and mass transfer characteristics of Cattaneo–Christov Carreau–Yasuda tri-hybrid nanofluid (CCHMF–THNF) flow over a porous stretching sheet. A mathematical model of the phenomenon was developed based on a number of elements, including the combined effect of magnetohydrodynamic forces, thermal and solutal relaxation and the influence of viscoelastic fluid behavior and is numerically analyzed utilizing MATLAB bvp4c software. A set of standard data was generated as a reference for developing the ANN-LM model with one hidden layer containing 10 neurons and log-sigmoid activation function, to achieve rapid predictions of velocity, temperature and concentration profiles from the identified data set. This study introduces a novel methodology to provide fast prediction capabilities for transport characteristics through integration of the ANN–LM model with the non-linear CCHMF-THNF model, producing computational savings by providing prediction accuracy of transport characteristics with MSE values on the order of $1.0\times {10}^{-10}$ using ANN–LM in place of repeated bvp4c solutions. Furthermore, the predictive capability of the developed ANN–LM framework may be beneficial in the areas of thermal management systems, polymer processing, energy transport applications, and magnetically controlled cooling technologies since they all share a need for fast access to transportation characteristic evaluation data. Full article

Controlling pollutant dispersion in high-rise buildings is crucial for public health. Vertical pollutant diffusion in stairwells occurs under thermal and wind effects. However, most existing studies rely on idealized boundary conditions. To address this, this study uses field-measured wall temperatures and a window wind velocity as boundary conditions for transient CFD simulations. We investigate the vertical diffusion characteristics of buoyant (CH₄) and dense (CO₂) pollutants under thermal pressure, window velocity, and wind–thermal coupling in a high-rise residential building in Taiyuan. Results show an asymmetric “fast-up, slow-down” diffusion under thermal pressure, a relatively symmetric profile under window velocity, and a hybrid pattern under coupling where the upper region is wind-dominated and the lower region resembles thermal-driven diffusion. Wind–thermal coupling most significantly enhances upward diffusion. Using the arrival time of CH₄ at the 28th floor (about 15 m above the source floor) as the benchmark, the diffusion rate under coupling is about 200% faster than under thermal pressure alone, and about 50% faster than under the window-velocity condition alone. Differences in density lead to variations in dispersion, with CH₄ exhibiting higher rates, concentrations (2–4 orders greater), and a broader influence range than CO₂. This work interprets the synergistic regulatory mechanism between driving forces and pollutant density, providing a theoretical basis for ventilation optimization and pollution control in high-rise buildings. Full article

Background: Bicycle Motocross (BMX) performance is strongly influenced by the start phase, which requires rapid force and power production to achieve optimal race posi-tioning; however, the relationship between lower-body power and sport-specific start performance remains insufficiently investigated. Objectives: The aim of this cross-sectional study was to assess lower-body muscular performance and analyze its relationship with start performance in international BMX riders. Methods: Ten international-level BMX riders (n = 10) completed a testing battery including squat jump and countermovement jump, force–velocity profile assessment, and a Wingate test preceded by 5 s maximal sprints to determine peak power (PP1, PP2), peak power during the 30 s Wingate test, and mean power. A sport-specific start test was performed on a BMX ramp, with time over the first 15 m recorded using photocell timing gates. Results: StartGate 15 m time showed a large negative correlation with PP2 (r = −0.800, 95% CI: −0.95 to −0.33, p = 0.05), whereas no significant correlations were observed with vertical jump performance or Power Mean Wingate. Strong correlations were observed among laboratory-based power variables. Conclusions: These findings suggest that short-duration peak cycling power may be associated with BMX start performance. However, given the small sample size and the borderline p-value, this relationship should be interpreted with caution. Sport-specific start testing may provide relevant information for performance assessment and training monitoring in international BMX riders. Full article

During the operation of a curved stepped spillway, a significant bias flow phenomenon may occur due to centrifugal force, potentially leading to an exposed bed of the inner bank and excessive water depth on the outer bank in severe cases. In order to address the uneven lateral water flow distribution, the transverse slope, where the bottom bed elevation of steps along the outer bank is higher than that along the inner bank, was designed to optimize the hydraulic characteristics of the curved step spillway. Through physical model experiments and three-dimensional numerical simulations, the hydraulic characteristics, including the water surface profiles, flow velocity, pressure on the spillway bed and energy dissipation, were obtained under different discharges and transverse slope angles. The results show that the transverse slope can reduce the bias flow and enhance the uniformity of flow velocity and pressure distribution by balancing centrifugal force. The rational matching of transverse slope angle and discharge is critical for optimizing the hydraulic characteristics of the curved stepped spillway. An appropriate transverse slope angle can effectively alleviate the excessive bias flow phenomenon and ensure uniform distribution of flow velocity, thereby improving the operational stability of the spillway. Full article

Building upon our previous aerodynamic characterizations of skewed jets, this study extends the investigation to systematically evaluate their thermal performance. Turbulent air jets are produced by unilaterally supplying coolant and forcing it through a series of concave perforated blockages having varying relative inner diameters (D_in/D_j = 3.0, 4.0 and 5.0) or relative thicknesses (t/D_j = 0.5, 2.0, 4.0, 6.0 and 8.0), with the jet diameter and Reynolds number fixed at D_j = 21 mm and Re_j = 20,000, respectively. The results demonstrate that the skewed jets exhibit pronounced asymmetric velocity profiles in both the x-z and y-z planes. Unlike the Gaussian distributions characteristic of conventional axisymmetric jets, these profiles manifest as distinctly skewed or saddle-shaped topologies. This topological distortion is exacerbated by reducing either D_in/D_j or t/D_j, albeit through fundamentally different mechanisms: the former only leads to jet deflection from the geometric axis, with the deflection angle increasing non-linearly from α = 4°, 5° to 12°; whilst the latter induces asymmetric internal flow development and exit momentum redistribution. The thermal performance of these jets on an iso-flux target flat plate, characterized by Nusselt number distributions at different jet-to-target spacings (H/D_j = 0 to 8.0), is shown to significantly differ from conventional axisymmetric jets. Full article

Asymptotic solutions are derived to model the development of atmospheric internal gravity waves generated by latent heating in a two-dimensional configuration involving a vertically-sheared background flow. The mathematical model comprises nonlinear partial differential equations derived from the conservation laws of fluid dynamics under the anelastic approximation where the background density and temperature vary with altitude. The latent heating is represented by a horizontally-periodic but vertically-localized nonhomogeneous forcing term in the energy conservation equation. This generates gravity waves that are considered as perturbations to the background flow and are expressed as perturbation series, with the leading-order contributions being the solutions of linearized equations. Taking into account the nonlinear terms at the next order gives expressions for the effects of the waves on the background mean flow. Due to the vertical shear, there is a critical level where momentum and energy are transferred from the wave modes to the mean flow. The asymptotic solutions show that the wave–mean-flow interaction is nonlocal and occurs over the range of altitudes from the thermal forcing level up the critical level. This is in contrast to what occurs in the case of waves forced by an oscillatory lower boundary, where the interaction is typically localized around the critical level. It is found that the wave drag is negative above the thermal forcing level, making the mean flow velocity more negative, but it becomes positive as the waves approach the critical level, indicating wave absorption in this region. There is wave transmission through the critical level, as well as absorption, and the extent of transmission depends on the depth of the latent heating profile. The mean potential temperature is reduced above the thermal forcing level and enhanced at the critical level, a situation that could ultimately lead to the development of convective instabilities. Full article

Muscle size and architecture’s contribution to force and power production in young female acrobatic gymnasts (ACROs) remains unclear. This cross-sectional study examined the associations between quadriceps muscle size and architecture and strength–power performance in young elite female ACROs. Twenty base athletes (12–18 years) underwent ultrasound assessment of rectus femoris (RF) and vastus lateralis (VL) cross-sectional area (CSA), VL muscle volume, VL fascicle length, and VL pennation angle. Participants were additionally classified as pre/mid-pubertal (Tanner stages 1–3) and post-pubertal (Tanner stages 4–5) for descriptive analyses. Performance testing included one-repetition maximum (1RM) squat and hang power clean (HHPC), squat power (Pmax), and countermovement jump (CMJ). In adjusted (Tanner stage and height) linear regression models, VL CSA at 35% and 50% of femur length was positively associated with 1RM squat (β = 2.38–2.31 kg·cm⁻²; p = 0.031–0.011) and Pmax (β = 45.75–38.43 W·cm⁻²; p < 0.001). No associations were observed for CMJ, HHPC, or RF variables. Mid-thigh VL size appears to be an independent predictor of squat strength and power in ACRO. Full article

Background: This study examined the associations between dynamic maximum strength (front squat [FS] and clean [CL]), lower-limb vertical force–velocity (F–V) profile characteristics, and both absolute and scaled measures of competitive weightlifting performance in trained weightlifters. Methods: Fourteen competitive male weightlifters (age: 27.6 ± 4.2 years; height: 1.74 ± 0.05 m; body mass: 85.1 ± 6.7 kg; body fat: 11.7 ± 2.8%) completed three testing sessions separated by 48–72 h, including 1-RM assessment in the FS and CL, as well as vertical countermovement jump trials to determine individual force–velocity profile parameters (F₀, V₀, and Pmax). Official competition results obtained within the same competitive season were recorded for the snatch (SN), clean and jerk (C&J), total (TOT), and Sinclair score. Participants were additionally divided into higher and moderate jump performance groups using a median split of unloaded countermovement jump height. Results: Very strong correlations were found between 1-RM strength (FS and CL) and weightlifting performance, with CL showing the strongest associations with SN (r = 0.82), C&J (r = 0.93), and TOT (r = 0.94). Among F–V parameters, V₀ and Pmax were significantly associated with competitive outcomes (r = 0.63–0.70), whereas F₀ was not. V₀ was significantly associated with SN (r = 0.69), C&J (r = 0.63), and TOT (r = 0.70), while F₀ showed trivial-to-small associations (r = 0.08–0.28). When participants were divided using a median split of CMJ height, higher jumpers exhibited greater V₀ (3.02 ± 0.30 vs. 2.61 ± 0.23 m·s⁻¹, p = 0.014, g = 1.4) and relative Pmax (32.44 ± 2.65 vs. 27.28 ± 1.06 W·kg⁻¹, p = 0.001, g = 2.4), despite similar F₀ (p = 0.67). Higher jumpers also demonstrated superior SN (p = 0.016, g = 1.4), C&J (p = 0.041, g = 1.1), TOT (p = 0.018, g = 1.4), and Sinclair scores (p = 0.001, g = 2.1). Conclusions: In trained weightlifters, performance was strongly associated with maximal strength, while velocity- and power-oriented characteristics (V₀ and Pmax) were also associated with performance outcomes. In contrast, F₀ showed no meaningful associations with performance within this sample. These findings suggest that, among already strength-trained athletes, the ability to express force at higher contraction velocities may be associated with differences in competitive performance. Full article

This study aims to advance the understanding of laminar magnetohydrodynamic (MHD) fluid flow between two parallel plates subjected to a uniform transverse magnetic field, motivated by its significant applications in engineering and industrial systems such as nuclear reactor cooling, MHD generators, and electromagnetic pumping devices. The governing equations are simplified using a one-parameter Lie group symmetry transformation, which exploits the inherent symmetry properties of the system to reduce the original unsteady partial differential equations to a system of ordinary differential equations. The reduced equations are solved exactly under appropriate boundary and initial conditions, ensuring mathematically consistent and physically realistic solutions. A comprehensive analysis is conducted to examine the influence of key physical parameters, along with the applied magnetic field, on the velocity, temperature, and concentration profiles. The selected parameter ranges encompass a broad spectrum of physically relevant cases, enabling a detailed assessment of their effects. The results indicate that the transverse magnetic field exerts a damping effect on the flow, reducing the velocity profile due to the Lorentz force. Moreover, an increase in the Schmidt number accelerates the achievement of a steady-state concentration, while higher Prandtl numbers reduce the temperature profile. In contrast, the radiation parameter enhances the temperature distribution. In addition, the skin-friction coefficient is presented graphically, and the Nusselt number is evaluated to characterize the heat transfer performance. Overall, the findings provide valuable insight into the effects of magnetic, thermal, and solutal parameters on laminar MHD flow between parallel plates. Full article

Propagating easterly waves (EW) are analyzed here, within the dynamical environment of the Caribbean Low-Level Jet (CLLJ) using radiosondes from the Organization of Tropical East Pacific Convection (OTREC) field campaign, ERA5 reanalysis, and lightning from the World Wide Lightning Location Network (WWLLN) over $5^{\circ }$–${20}^{\circ }$ N, ${60}^{\circ }$–${100}^{\circ }$ W during 21 August–30 September 2019. Radiosondes resolve the vertical structure of the waves at San Andrés (Colombia), Limón and Santa Cruz–Guanacaste (Costa Rica), while ERA5 provides spatial–temporal continuity and vertically integrated diagnostics—namely, the vertically integrated moisture flux divergence (VIMFD) and the vertically integrated geopotential flux divergence (VIGFD). Lightning from WWLLN and precipitation from ERA5 and the Integrated Multi-satellite Retrievals for the Global Precipitation Measurement mission (GPM IMERG) offer independent convective proxies to track disturbances. Mean profiles from radiosondes and ERA5 show strong agreement at Limón and Guanacaste and some differences at San Andrés, yet all datasets capture coherent, phase-locked anomalies in zonal wind, meridional wind, temperature, humidity, vertical velocity and vorticity used to diagnose EW–CLLJ interactions. VIMFD, VIGFD, lightning and precipitation exhibit westward-propagating cores that align with the above anomalies, indicating that organized convection is coupled to the disturbances, whereas the mean state preconditions the environment to enable wave-induced upward motion. A robust vertical adjustment of the CLLJ is documented: the core shifts from near 925 hPa over the Caribbean Sea to about 700 hPa over the Eastern Tropical Pacific ($\Delta p\sim 150$ hPa). This feature is reproduced by a 30-year ERA5 climatology, consistent with jet-exit forcing and enhanced boundary-layer coupling over land. Conditions favorable for barotropic instability using the Rayleigh–Kuo criterion, were present over most of the period. A qualitative barotropic conversion proxy, computed from the eddy momentum covariance $⟨u^{\prime }{v}^{\prime }⟩$, shows positive values in the lower troposphere at Guanacaste and in the layer 850–700 hPa at San Andrés, suggesting mean-to-eddy momentum transfer, whereas the signal at Limón is weaker. Together, these results provide a physically consistent view of EW–CLLJ interactions across the IAS; therefore, a schematic of those mechanisms is proposed here. The results highlight the need for high-resolution modeling and full energy-budget analyses. Full article

Objectives: This study compares linear sprint force–velocity (F–v) mechanical variables between elite Under-19 (U19) academy players and senior professional players. Methods: Thirty-eight senior players (SP; mean age 24.5 ± 4.3 y) and 214 U19 academy players (YP; mean age 17.4 ± 0.5 y) from 14 first-division club academies were tested during October 2023 using a motorized resistance device (1080 Motion). The following F–v variables were assessed: maximal theoretical force (F₀, N·kg⁻¹), maximal theoretical velocity (v₀, m·s⁻¹), maximal ratio of horizontal-to-resultant force (RF_max, %), and decrease in the ratio of forces (DRF, %). Between-group comparisons were performed using the t-test, and Cohen’s d effect sizes were reported. Results: Senior players outperformed U19 players across all F–v variables. F₀ exhibited a mean difference = 0.220 N·kg⁻¹, with a 95% confidence interval (CI) [0.056, 0.384], p = 0.0166, and d = 0.46. v₀ exhibited a mean difference = 0.560 m·s⁻¹, with a 95% CI [0.410, 0.710], p < 0.0001, and d = 1.07. RF_max exhibited a mean difference = 1.470%, with 95% CI [0.830, 2.110], p = 0.0003, and d = 0.69. DRF exhibited a mean difference = 0.260%, with a 95% CI [0.103, 0.417], p = 0.0013, and d = 0.53. Conclusions: U19 players demonstrated lower F₀, lower v₀, and reduced mechanical effectiveness compared with senior players. Regular monitoring of F–v profiles and individualized training interventions (force- or velocity-targeted) may be useful for training and monitoring strategies aimed at supporting physical preparation during the transition to senior soccer. Full article

Background: This systematic review critically examined how vertical force–velocity profiling has been used and interpreted in soccer research, with particular attention to methodological limitations and practical constraints. Methods: Following PRISMA guidelines, four databases were searched up to January 2025, and eleven studies met the inclusion criteria. Results: Several studies reported statistical associations between vertical F–V variables (particularly Pmax and V₀) and jump- and sprint-related outcomes; however, these associations were heterogeneous, task-dependent, and sensitive to modeling assumptions. Age- and maturity-related studies demonstrate progressive increases in F₀ and Pmax across developmental stages, explaining much of the inter-individual variability in youth populations. Positional and sex-based analyses reveal distinct neuromuscular profiles, with wide and attacking players displaying more velocity-oriented characteristics, and female players showing lower Pmax values. Indirect links with match-related demands, inferred from positional profiles and external load literature, suggest potential ecological relevance; however, direct evidence linking vertical F–V parameters to match-derived GPS metrics remains limited. Intervention studies show that individualized F–V-based training can modify selected vertical mechanical parameters, but improvements in sprint or match performance are not systematic. Conclusions: Vertical F–V profiling may provide descriptive information under tightly controlled conditions; however, evidence supporting its use for individualized or deficit-based training prescription in soccer remains limited and inconsistent. For this reason, vertical F–V profiling should not be interpreted as a mechanistic model of soccer performance, but rather as a context-dependent descriptive framework with restricted ecological validity. Full article

Background: Modern electromechanical technologies can be integrated into strength training machines to regulate the magnitude, direction, and point of application of resistance during exercise, either through preprogrammed settings or adaptively in response to real-time kinematic data. However, this potential remains largely unexplored. The objective of this study was to investigate how these new-generation devices may be managed to enable precise control of the mechanical load applied to specific joint structures during strengthening exercises. Methods: A foundational framework of biomechanical equations was developed to establish the functional relationships between joint reaction forces and key variables, including kinematic parameters (joint angle, angular velocity, and angular acceleration) and resistance characteristics (magnitude, direction, and point of application). The analysis focused on analytically determined single-joint exercises, which are commonly employed in early-stage rehabilitation and athletic conditioning programs. Results: Application of the model to single-joint knee extension exercises demonstrated that the anterior cruciate ligament (ACL)-loading shear tibiofemoral force can be entirely eliminated throughout the full range of knee motion, without increasing either the tibiofemoral compressive force or the posterior cruciate ligament (PCL)-loading shear component, while preserving the desired peak and profile of the resistance torque. Conclusion: The proposed analytical framework enables a comprehensive understanding of how to regulate resistance parameters through advanced electromechanical technologies to minimize joint stress during single-joint strengthening exercises. Precise control of joint reaction forces during exercise is critical for the design of therapeutic and safety-enhanced training protocols. Full article

As a critical component for motion control in heavy machinery, high-speed hydraulic actuators require effective buffering to mitigate end-impact. This paper proposes a compact buffering cylinder with a multi-orifice sleeve. A theoretical model was established to derive the throttling area profile for constant deceleration. A detailed numerical simulation model was then developed, and the key orifice parameters (diameter and spacing) were optimized using a Particle Swarm Optimization (PSO) algorithm to maximize buffering efficiency and smoothness. A prototype based on the optimal design was manufactured and tested dynamically. Experimental results demonstrate that the buffer smoothly arrested a piston with an initial velocity of 8 m/s and a moving mass of 80 kg within a 250 mm stroke. The optimized design achieved a 14% increase in buffering efficiency and reductions in peak force and pressure compared to the initial design, validating the proposed optimization methodology and providing a reliable solution for high-speed actuator protection. Full article