Change Of Direction Research Articles

Anomalous diffusion of self-propelled particles

Abstract The transport equation of active motion is generalised to consider time-fractional dynamics to describe the anomalous diffusion of self-propelled particles. In the present study, we consider an arbitrary active motion pattern modelled by a scattering function that defines the dynamics of the change of the self-propulsion direction. The exact probability density of the particle positions at a given time is obtained. From it, the time dependence of the firsts moments, i.e. the mean square displacement and the kurtosis for an arbitrary scattering function, are derived and analysed. Anomalous diffusion is found with a crossover of the scaling exponent from 2α in the short-time regime to α in the long-time one, 0 < α < 1 being the order of the fractional derivative considered. It is shown that the exact solution found satisfies a fractional diffusion equation that accounts for the non-local and retarded effects of the Laplacian of the probability density function through a coupled temporal and spatial memory function. Such a memory function holds the complete information of the active-motion pattern. In the long-time regime, space and time are decoupled in the memory function, and the time fractional telegrapher’s equation is recovered. The theoretical framework presented here can be applied as model of active motion that exhibits anomalous diffusion.

Force–velocity–power profiling in flywheel squats: Differences between sports and association with countermovement jump and change of direction performance

ABSTRACT The objectives of our study were 1) to examine whether the force-velocity-power (FvP) outcomes in the concentric and eccentric phases of flywheel (FW) squats differ among sports disciplines and 2) to investigate the association between FvP outcome variables and two key sport-performance indicators: countermovement jump height (CMJ) and change of direction (CoD) time involving 90° or 180° turns. Tests were performed by 469 athletes from five different sport disciplines and physical education students. Our results showed that FvP outcomes, when measured during the eccentric phase of the FW squat, effectively differed between athletes from different sports. However, during the concentric phase of the squat, only for the slope variable differences between sports were found. Contrary to our hypothesis, there were no statistically significant correlations between FW squat FvP outcomes and CMJ or CoD test results. These results suggest that FvP outcomes derived from FW squats may lack external validity and cannot be reliably used as a predictor of athletes’ jumping and agility performance. The paper discusses possible reasons for the larger differences between sports in eccentric FvP outcomes, as well as the absence of correlations between FvP outcomes and functional tests.

A study on the uniformity of hot air drying quality for stacked flake materials based on multi-physical coupling fields

To improve the uniformity of the hot air drying quality for stacked flake materials, a heat and mass transfer study of stacked flake materials drying process based on multi-physical field coupling is carried out. A numerical simulation model of the stacked flake materials is developed based on the multi-physical field coupling theory, and the accuracy of the numerical simulation model is verified by the bidirectional alternating hot air drying test bed. The segmented hot air drying method is used to analyze the influence mechanism of single airflow direction and alternate airflow direction on the heat and mass transfer for stacked flake materials, and the optimization of drying parameters is studied. The results indicate that a single airflow direction may cause excessive drying, and the uneven stacking density significantly affects the drying quality. The increase of air flow direction change number will lead to the improvement of drying uniformity and moisture content of drying results, and at the same time, the flake material absorbs moisture significantly after changing the air flow direction. By adopting the down-down-up-up airflow direction and optimizing the parameters, the moisture content uniformity of the drying results is improved by 19%, while energy consumption is reduced.

Ruthenium-doped ZnO nanostructures: Growth, characterization, and applications in waveguides and light-emitting devices

ZnO based materials are gaining importance due to its potential applications. In many of these applications, the size, shape and dopability of the structures grown play a determinant role. In the present work, ZnO nano- and microstructures doped with Ru have been grown using the Vapour-Solid (VS) method. Among the different growth parameters, gas flux and initial dopant content seem to play the major role to determine both shape and size of the structures. The main morphologies obtained are self-arranged triangular grids and elongated structures. Based on microscopic observations a simplified growth model is proposed for the grids. An exhaustive characterization has been performed. X-Ray diffraction (XRD) investigations demonstrate good crystallinity and texturing related to preferential growth direction changes due to doping. Luminescence characterization through photo- and cathodoluminescence (PL and CL) techniques reveals typical ZnO near band edge and deep level emission bands at 3.2 and 2.3 eV, respectively. The potential use of elongated structures as waveguides and optical cavities, Fabry-Pèrot resonators, is explored.

A damping method of grid strapdown inertial navigation system for polar region

Abstract The conventional north-pointing inertial navigation system (INS) always points to the geographic north. However, when the system crosses the pole in the polar region, the geographic north quickly changes with 180 degrees, and the rate of change of the geographic north direction will be infinite. Secondly, when the latitude approaches to 90 degrees, which will lead to singularities in math for the angular velocity caused by vehicle motion. With its special definition and mechanization, the grid coordinate system can solve the above problems. Nevertheless, the error analysis of the grid strapdown INS shows that there are Schuler periodic and Foucault periodic oscillations, which badly degrade the accuracy of the strap-down INS. To address the problem, the external horizontal damping technology is adopted in this paper, wherein the external velocity is provided by the Doppler velocity log (DVL). Finally, the feasibility and the effectiveness of the external damping technology were verified by simulation.

Interactions between Stress Levels and Hormonal Responses Related to Sports Performance in Pro Women's Basketball Team.

The testosterone to cortisol ratio (T:C ratio) is a measure of whether elite athletes are recovering from their training. This study described this hormone balance stress in elite women's basketball. (1) Objectives: to analyse the fluctuation of T:C ratio over a 16-week period and explore itis relation to their athletic performance. The participants characteristics were: (height: 177.6 ± 6.4 cm; body mass: 77.808 ± 12.396 kg age: 26.0 ± 5.9 years; and a playing experience of 14.7 ± 2.9 years with 5.0 ± 1.2 years at the elite level. The T:C ratio at Time 1 is: 4.0 ± 2.4 (n = 12); and at Time 2 is: 5.1 ± 4.3 (n = 12). (2) Methods: during 16 weeks of competition, participants underwent analysis of blood samples to assess various biochemical parameters including hormone levels. In addition, their athletic performance was assessed with the following tests: jumping (SJ, CMJ, ABK, DJ); throwing test with a medicine ball (3 kg); Illinois COD agility test; sprint repeatability with change of direction; 20-m speed test without change of direction; and Yo-yo intermittent endurance test IET (II). (3) Results: The main alterations observed were an increase in T levels (1.687%) and a decrease in C levels (-7.634%) between moments, with an improvement (26.366%) in the T:C ratio. Improvements were also observed in some of the tests developed, such as jumping (SJ: 11.5%, p = 0.029; CMJ: 10.5%, p = 0.03; DJ: 13.0%, p = 0.01), upper body strength (MBT: 5.4%, p = 0.03), translation ability (20 m: -1.7%), repeated sprint ability (RSA: -2.2%), as well as intermittent endurance test (Yy (IET): 63.5%, p = 0.01), with significant changes in some of the performance tests. (4) Conclusions: T:C ratio may differ in a manner unrelated to training volume, showing some variation. These results may be attributed to the accumulation of psychophysiological stress during the season.

Methodology and Uncertainty Analysis of Methane Flux Measurement for Small Sources Based on Unmanned Aerial Vehicles

The top–down emission rate retrieval algorithm (TERRA) method for calculating the net flux out of a box has been employed by other researchers to assess large sources of methane release. This usually requires a manned aircraft drone with powerful performance to fly over the boundary layer. Few studies have focused on low-altitude box sampling mass balance methods for small sources of methane release, such as at maximum flight altitudes of less than 100 m. The accuracy and sources of uncertainty in such a method still need to be determined as they differ from the conditions of large sources. Nineteen flights were conducted to detect methane emissions from Chinese oil field well sites using a measurement system consisting of a quadcopter and methane, wind speed, wind direction, air pressure, and temperature sensors. The accuracy and uncertainty of the method are discussed. The average absolute relative error of the measurement is 18.5%, with an average uncertainty of 55.75%. The uncertainty is mainly caused by the wind speed and direction, and the background CH4 concentration. The main paths to reduce uncertainty and improve accuracy for low-altitude box sampling include subtracting the background concentration during flux retrieval, enhancing the accuracy of methane measurements, selecting a period of downwind dominant or wind direction change of less than 30 degrees, and ensuring a maximum flight height greater than 50 m with a horizontal distance from the pollution source center of less than 75 m. The results show that TERRA-based low-altitude box sampling is suitable for quantifying methane release rates from small sources.

Relationship between Interlimb Asymmetries and Performance Variables in Adolescent Tennis Players.

Tennis is an individual sport characterised by high-intensity action, including sprints and changes of direction (COD). However, there is a gap in the knowledge of limb asymmetries in adolescent tennis players and their association with performance. The aim of this study was to investigate the relationship between asymmetry in vertical and horizontal jump tests (CMJ and HJ) and COD with lower limb performance variables in adolescent tennis players. Forty-five adolescent tennis players (age: 13.81 ± 1.08 years; height: 167.64 ± 9.9 cm; body mass: 57.48 ± 10.94 kg; body mass index: 20.27 ± 2.18 kg/m2) performed the CMJ test (unilateral and bilateral), horizontal jumps (unilateral and bilateral), 25 m sprint, and 180° COD test. The single-leg countermovement jump showed the greatest asymmetries among the different tests (6.62 ± 9.35%). Notable negative relationships were found between CMJ asymmetry and COD asymmetry with unilateral horizontal jump variables (r = -0.30 to -0.53). In addition, CMJ asymmetry showed notable relationships with CMJR (r = 0.49) and COD180R (r = 0.29), whereas COD asymmetry showed a notable relationship with COD180L (r = 0.40). On the other hand, HJ asymmetry showed no notable relationships with any variable. The main findings of this study indicate that greater imbalances in the CMJ and COD tests are associated with a reduced capacity to perform unilateral horizontal jumps. These results suggest the incorporation of training protocols to reduce interlimb asymmetries in growing athletes to improve their performance. This practical application is important for coaches and physical trainers who aim to improve the physical performance of adolescent tennis players. Greater asymmetry results in a reduced ability to produce unilateral horizontal force.

Reliability and Relationship between Hip Muscle Strength and Change of Direction Performance among Basketball Players

Background: Basketball change of direction (COD) tests are not specific to the defensive lateral shuffling movement, and no COD tests assesses the relationship between hip muscle strength and basketball specific lateral movements. Objective: We assessed the reliability of a COD test (2-2 shuffle test) performance and investigated its relationship to hip muscle strength. Methods: Using a prospective observational cohort design, data were collected from competitive male basketball players (n = 21; age 20.0 ± 3.5 years; height 194.7 ± 7.0 cm; weight 93.9 ± 14.7 kg). Participants performed two trials of the hip abductors/adductors isometric muscle strength assessment and the 2-2 shuffle test. Intraday reliability of the 2-2 shuffle test was computed using Bland-Altman plots, intraclass correlations (ICCs) with 95% confidence intervals (CI), and coefficient of variations (CVs). Pearson correlations with 95% CIs determined the relationship between shuffle test time and hip muscle’s isometric strength. Results: The 2-2 shuffle test time for left (ICC = 0.91, CV = 7.7%) and right (ICC = 0.86, CV = 8.4%) directions met acceptable reliability thresholds (ICC 0.8, CV 10%). The relationships observed between 2-2 shuffle test time and hip abductors/adductors were non-significant and unclear across parameters (p = 0.05, r = ≤ -0.26). Conclusion: Physical performance coaches may use the 2-2 shuffle test as the test time is a reliable metric. The hip abductors/adductors maximal isometric strength accounts for a trivial proportion of explained variance in the 2-2 shuffle test, suggesting other technical and physical abilities account for test performance.

Modulation on the twinning microstructure of Cu nanowires and its effect on oxidation behaviour

In this study, nanotwinned Cu nanowires (nt-Cu NWs) with varying twin characteristics were fabricated via pulse electrodeposition using a novel H3BO3 based electrolyte, and their impact on the oxidation process was investigated. The density and direction of twin lamellas within nt-Cu NW were adjusted by modifying the concentration of H3BO3 and the current density. Specifically, the average twinning thickness of Cu NWs increases from 26.7 nm to 424.5 nm as the concentration of H3BO3 increases from 0 g/L to 6 g/L. Moreover, three types of nt-Cu NWs with distinct twinning directions, namely waterfall type, bevel type, and ladder type were fabricated by changing the current density from −0.16 ASD to -1.6 ASD (vs Ag/AgCl). A nanowire Winand (NWW) diagram was established to describe the change of twin density and direction based on the difference between the growth behaviour of thin films and nanowires. The thermogravimetric analysis (TGA) and transmission electron microscopy (TEM) were further used to characterize the oxidation process of nt-Cu NWs. It revealed that the oxide thickness was closely related to the thickness of twin lamellas for the ladder type nt-Cu NWs. Also, the waterfall type Cu NWs exhibited a unique bead-chain like oxide morphology and a slower oxidation rate through the impact on the nanoscale Kirkendall effect (NKE). This study provides valuable insights into the controllable fabrication of nt-Cu NWs and Cu oxide NWs.

Characteristics and Driving Mechanisms of Coastal Wind Speed during the Typhoon Season: A Case Study of Typhoon Lekima

The development and utilization of wind energy is of great significance to the sustainable development of China’s economy and the realization of the “dual carbon” goal. Under typhoon conditions, the randomness and volatility of wind speed significantly impact the energy efficiency and design of wind turbines. This paper analyzed the changes in wind speed and direction using the BFAST method and Hurst index based on data collected at 10 m, 30 m, 50 m, and 70 m heights from a wind power tower in Yancheng, Jiangsu Province. Furthermore, the paper examined the causes of wind speed and direction changes using wind speed near the typhoon center, distance from the typhoon center to the wind tower, topographic data, and mesoscale system wind direction data. The conclusions drawn are as follows: (i) Using the BEAST method, change points were identified at 10 m, 30 m, 50 m, and 70 m heights, with 5, 5, 6, and 6 change points respectively. The change points at 10 m, 30 m, and 50 m occurred around node 325, while the change time at 70 m was inconsistent with other heights. Hurst index results indicated stronger inconsistency at 70 m altitude compared to other altitudes. (ii) By analyzing the wind direction sequence at 10 m, 30 m, 50 m, and 70 m, it was found that the wind direction changes follow the sequence Southeast (SE)—East (E)—Southeast (SE)—Southwest (SW)—West (W)—Northwest (NW). Notably, the trend of wind direction at 70 m significantly differed from other altitudes during the wind speed strengthening and weakening stages. (iii) Wind speed at 10 m and 70 m altitudes responded differently to the distance from the typhoon center and the wind near the typhoon center. The correlation between wind speed and the distance to the typhoon center was stronger at 10 m than at 70 m. The surface type and the mesoscale system’s wind direction also influenced the wind speed and direction. This study provides methods and theoretical support for analyzing short-term wind speed changes during typhoons, offering reliable support for selecting wind power forecast indicators and designing wind turbines under extreme gale weather conditions.

Contribution of Physical Characteristics to Game Performance in Male Wheelchair Basketball Athletes at the Tokyo Paralympic Games.

Snyder, L, Goods, PSR, Peeling, P, Balloch, A, Peiffer, JJ, Binnie, MJ, and Scott, BR. Contribution of physical characteristics to game performance in male wheelchair basketball athletes at the Tokyo Paralympic Games. J Strength Cond Res XX(X): 000-000, 2024-This investigation explored the physical characteristics of elite male wheelchair basketball (WCB) athletes and their association with game performance during the Tokyo 2020 Paralympic Games. Sixteen male athletes from the Australian national WCB squad were assessed for anthropometrics, speed, change of direction, aerobic power, and upper-body power during a training camp before the 2020 Paralympic Games. Athletes were grouped according to the International Wheelchair Basketball Federation disability classification system (1.0-4.5) as low- (≤2.5, more severe impairments) or high-point (≥3.0, less severe impairments) athletes. Physical and performance characteristics between groups were compared using independent-samples t-tests, and their relationship to game statistics (points, rebounds, assists, and steals) per minute played was explored through stepwise regression. High-point athletes were 13% taller (p = 0.001), 4-9% faster (p < 0.001-0.017), and demonstrated superior change of direction ability (15%, p < 0.001) compared with low-point athletes. Approximately 74% of the variance in points scored per minute was accounted for by athlete classification, whereas the most important modifiable physical characteristic was speed, which contributed significantly to steals (54% of variance) and assists (96% of variance when arm span and sitting reach height were also considered). Low-point athletes with spinal cord injuries generally have impaired trunk control, which is a likely explanation for performance differences between groups. A range of nonmodifiable (classification, sitting reach height, and arm span) and modifiable (speed) physical characteristics contribute to game performance outcomes and should therefore be considered when identifying, developing, and selecting WCB athletes for elite competition.

The Effects of Volume-Matched 1- and 2-Day Repeated Backward Sprint Training Formats on Physical Performance in Youth Male Soccer Players.

Bouguezzi, R, Negra, Y, Sammoud, S, Uthoff, A, Moran, J, Behrens, M, and Chaabene, H. The effects of volume-matched 1- and 2-day repeated backward sprint training formats on physical performance in youth male soccer players. J Strength Cond Res XX(X): 000-000, 2024-This study examined the effects of a 6-week, 1 vs. 2 sessions of volume-matched weekly repeated backward sprint training (RBST) on measures of physical fitness in youth male soccer players. Thirty male youth soccer players from a regional soccer team were randomly assigned to a 2-day group (n = 15; age = 16.40 ± 0.64 years; Maturity-offset = 2.19 ± 0.65 years) or a 1-day group (n = 15; age = 16.27 ± 0.51 years; Maturity-offset = 1.91 ± 0.40 years). Measures of jumping ability, linear sprint speed, change-of-direction (CoD) speed, aerobic endurance (AE), and repeated sprint ability (RSA) were measured before and after 6 weeks of training. The training interventions involved 1 to 2 sets, each comprising 7 repetitions over a 20-m distance of RBST in the 2-day group, and 2 to 4 sets, also with 7 repetitions each over the same distance, in the 1-day group. Statistical analyses were conducted using the analysis of covariance model with baseline measurements entered as covariates. Results indicated that RBST over 2 days generated greater benefits compared with a single day for improving CoD speed (∆4.91 vs. 0.04%; effect size [d] = 0.78 vs. 0.00, respectively), linear sprint speed (10-m: ∆4.74 vs. 0.36%; d = 0.96 vs. 0.00, respectively; 20 m: ∆3.34 vs. 0.82%; d = 1.00 vs. 0.49, respectively), and RSA performances (RSAbest: ∆2.61 vs. 0.29%; d = 0.71 vs. 0.16, respectively; RSAmean: ∆2.86 vs. 0.89%; d = 0.59 vs. 0.16, respectively; RSAtotal: ∆2.86 vs. 0.89%; d = 0.62 vs. 0.41, respectively). However, similar improvements in the 2 RBST formats were observed on jumping (2-day group: ∆6.9%; d = 0.75; 1-day group: ∆10.6%, d = 1.26) and AE performance (2-day group: ∆17.24%, d = 1.04; 1-day group: ∆27.25%, d = 2.25). In summary, the findings suggest that, when volume is matched, spreading the RBST regimen over 2 days may result in greater improvements compared with a single-day approach for enhancing CoD speed, linear sprint speed, and RSA performance.

Supporter-Type Anterior Cruciate Ligament Prevention System Based on Estimation of Knee Joint Valgus Angle Using Stretch Sensors

Anterior cruciate ligament (ACL) injuries are common in sports involving jumping and rapid direction changes, often occurring in non-contact situations. The risk of ACL injury is evaluated by knee flexion and valgus angles; a small knee flexion angle combined with a large valgus angle increases the risk. Monitoring these angles during activities can help athletes recognize their ACL injury risk and adjust their movements. Traditional 3D motion analysis, used for measuring knee angles, is costly and impractical for daily practice. This study proposes a knee supporter with stretch sensors to estimate knee flexion and valgus angles in practice settings, evaluating ACL injury risk and notifying athletes of high-risk movements. The proposed device wirelessly transmits data from three stretch sensors placed on the device to a PC and uses machine learning to estimate the knee angles. The results of the evaluation experiments, conducted with data from five healthy male and female participants in their twenties, indicate that the estimation accuracy for the knee flexion angle, achieved by a model trained using a Random Forest Regressor (RFR) with data from individuals other than the target user, resulted in a Mean Absolute Error (MAE) of 8.86 degrees. For the knee valgus angle, a model trained with the user’s own data using the RFR achieved a MAE of 0.81 degrees.

High-Intensity Running During International Male Field Hockey Involves Frequent Changes of Direction and Repeated Accelerations but Seldom Reaches Sprint Velocities.

Goods, PS, Appleby, B, Scott, BR, Peeling, P, and Galna, B. High-intensity running during international male field hockey involves frequent changes of direction and repeated accelerations but seldom reaches sprint velocities. J Strength Cond Res XX(X): 000-000, 2024-The aim of this investigation was to quantify the characteristics of high-intensity running in international male field hockey. Player movement data were collected through wearable player tracking devices across 3 tournaments (17 matches) from 27 members of the Australian male field hockey team (totaling 266 player matches). Active duration (minute), high-intensity efforts (>2.5 m·s-2 for >1 second), repeated high-intensity efforts (≥3 efforts with ≤45-second recovery between efforts), and sprints (>7 m·s-1) were extracted and aggregated for each player match. The duration, distance, mean and peak speed, mean change of direction and straightness for each high-intensity effort, and peak deceleration at the conclusion of each effort were calculated. Mixed-effects models were used to estimate the mean for each outcome (fixed effect), with random intercepts modeled for player and match. On average, players completed 42.2 high-intensity efforts and 2.1 sprints per match. High-intensity efforts were short (3.61 seconds, 12.9 m), failed to reach high velocities (average peak velocity: 4.8 m·s-1), and involved frequent changes of direction (56% of efforts were not straight). There were 4.7 bouts of repeated high-intensity efforts per player, per match (comprising 3.8 efforts, with 3.53 seconds per effort separated by 16.2-second recovery). Last, we also found that 29% of high-intensity efforts involved a high-speed deceleration (>3.5 m·s-2), and these occurred frequently when in conjunction with a >45° (86%) or >90° (89%) change of direction. We recommend practitioners focus on developing players' ability to repeatedly accelerate, decelerate, and change direction over short distances and adopt testing and monitoring programs that assess these qualities.

Seasonal Variations in Performance and Asymmetry Data for Jump and Change of Direction Abilities in Female Soccer Players.

Mainer-Pardos, E, Bishop, C, and Gonzalo-Skok, O. Seasonal variations in performance and asymmetry data for jump and change of direction abilities in female soccer players. J Strength Cond Res XX(X): 000-000, 2024-The study aimed to evaluate the progression of the percentage-based change of direction (COD) deficit (%CODD) over a competitive season, along with its correlation with performance tests and to examine the impact of the magnitude and direction of asymmetry at 4 stages of the season. Forty-seven (U-16, U-18, and U-20), highly trained, female soccer players performed unilateral vertical jumping (countermovement jump [CMJ]) and horizontal jumping (HJ), 10-m sprint, and 180° change of direction (COD180) tests. The %CODD was also calculated. Significant group and time effects (p < 0.05) were observed in CMJ, HJ, 10-m sprint, and COD180 tests, with U-20 players generally outperforming the U-18 and U-16 groups. Nonsignificant differences were reported in the %CODD between any time point or groups throughout the season. Moderate or large significant (r = 0.44-0.64; p < 0.05) relationships were found between %CODD and 10 m. The direction of asymmetry within and between tests at all time points was slight to moderate (k = -0.29 to 0.57). Notwithstanding, 51% of the players showed the best performance in the horizontal jump with the same leg throughout the season, whereas only 36% in %CODD. This study highlights the importance of developing strategies to improve %CODD depending on the player's position demands. Finally, individually monitoring the magnitude and direction of asymmetry can help practitioners monitor the effects of training and competition throughout the season.

Climate Disaster and Cognitive Ability: Evidence From Wildfire.

We investigate the impact of wildfire disasters on cognitive health (i.e., thinking and language skills) in individuals aged 10years and older using 2014 and 2018 wildfire and cognitive ability survey data from China. We distinguished wildfires in each county at different wind directions each day by exogenous wind direction changes, and analyzed the effects of wildfires on cognitive abilities through upwind and non-upwind wildfires. Our analysis shows that for every 10-unit increase in upwind wildfires compared to non-upwind wildfires, respondents' scores on word and math tests decrease by 0.235 and 0.236 standard deviations, respectively. Furthermore, we find that the impact of wildfire on cognitive ability is more pronounced in younger individuals, and those with lower defensive expenditures experience more severe impacts. Additionally, wildfires negatively affect individuals' cognitive abilities by generating air pollution. Wildfires significantly reduce individuals' cognitive abilities. Two recommendations are as follows: 1) governments should follow the principle of green development, introduce relevant regulations, and increase investment in adaptive technologies. 2) Individuals should raise awareness of climate hazards preparedness and strengthen defensive protection.

Moderate-dose caffeine enhances anaerobic performance without altering hydration status.

The effects of direct nutritional supplements on athletic performance are still being investigated and arouse curiosity. Only one study in the literature was found that investigated the kicking speed performance of futsal players following low-dose caffeine supplementation (3 mg/kg); thus, the question of whether caffeine supplementation improves kicking speed as well as essential physical parameters in soccer players is still controversial. Therefore, the aim of this study was to determine the effect of caffeine supplementation on vertical jump (VJ), sprint, reaction time, balance, change of direction (COD), and ball-kicking speed in soccer players. In a double-blind, cross-over design, nine moderately trained male soccer players (21.11 ± 2.02 years, 171.22 ± 6.14 cm, 71.78 ± 10.02 kg) consumed caffeine (6 mg/kg) or a placebo 60 min before completing balance, reaction time, vertical jump, agility, 30 m sprint, and ball-kicking speed tests. Greater VJ height (p = 0.01) and power (p = 0.08), and faster completion time according to the Illinois Agility Test (p = 0.08) were found following caffeine supplementation compared to placebo. Elapsed time (p = 0.01), average (p = 0.01) time, and the slowest reaction times (p = 0.016) were significantly reduced after caffeine consumption compared to placebo supplementation. Caffeine intake significantly improved VJ, agility, and reaction time (p < 0.05) but did not affect 30 m sprint, ball-kicking speed, balance, and RPE values in soccer players (p > 0.05). Although non-significant, caffeine intake also improved sprint (0.67%) and ball kicking (2.7%) performance percentages. Also, caffeine consumption did not induce dehydration, and the athletes' body hydration levels were normal. These findings support the use of caffeine supplementation as an effective nutritional ergogenic aid to enhance anaerobic performance, at least for vertical jumps, COD speed, and reaction time, in trained male soccer players.

Inclusion of Game-Based Stimulus During Flywheel Resistance Training Positively Influences Physical Performance in Handball Players

ABSTRACT Handball is a body-contact Olympic ball sport that is characterized by fast-paced defensive and offensive actions. Players must coordinate explosive movements (e.g. changing of direction) and handball-specific skills (e.g. passing). Maximizing performance requires a systematic approach to training that includes physical, psychological, technical, and tactical preparation. Purpose: The aim of this study is to determine the effects of movement-based (MOV; unspecific sport stimulus) or game-based (GAM; sport-specific stimulus) flywheel resistance training intervention in highly trained youth handball players. Method:Twenty-five highly trained youth male handball players completed two sessions per week of flywheel resistance training (MOV, n = 12; GAM, n = 13) over the 7-week intervention period. Change-of-direction tests (180º change-of-direction speed test of both legs and test) and handball-throwing test were conducted before and after the intervention. Results: Both groups significantly improved V-cut, and 180º Change-of-direction speed test performance (p < .05; d = 0.79–2.05). Notwithstanding, the GAM group demonstrated greater improvements in V-cut and COD180ASY compared with the MOV group (p < .05) with small effect. Handball throwing speed performance remained unchanged independently of training condition (p > .05). Conclusions: These findings provide further support for the training principle of “specificity” and highlight the importance of including a game-based training stimulus during resistance training. This is a key consideration for coaches wanting to enhance physical performance in youth handball players.

Size effect and underlying microstructural mechanism in cyclic deformation behavior of nickel-based superalloy sheet

The nickel-based GH4169 superalloy is widely used in the aerospace field, which has desirable oxidation resistance and strength in extreme environments. However, the size effect and underlying microstructural mechanism in the cyclic deformation of the GH4169 sheet are still not fully elucidated, which affects the forming accuracy precision of thin-walled components. To this end, the cyclic mechanical properties and microstructural evolution of the GH4169 sheets with different thicknesses and grain sizes were systematically investigated via cyclic shearing tests. The superalloy sheet exhibits obvious early re-yielding, instantaneous softening and permanent softening during the cyclic deformation and these cyclic deformation behaviors are obviously affected by size effect. To rationalize the cyclic mechanical responses and size effect, transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) tests were conducted. The results indicated that the dislocation slip patterns are principally planar array slip and cross slip in the cyclic shearing deformation. Meanwhile, the annihilation of unstable dislocation and the presence of carbides led to the instantaneous softening. Moreover, the change of loading direction, the reduction of texture strength, the proportion of low-angle grain boundary (LAGB), and geometrically necessary dislocation (GND) density together result in the occurrence of permanent softening. Based on the comparative analysis of the microstructure evolution of superalloy sheets with different size factors, the underlying mechanism of size effect on cyclic deformation was clarified. The findings in the research combine the cyclic mechanical response and microstructure evolution closely in the cyclic deformation of superalloy sheets and deepen the understanding of size effect under complex loading paths.