Search Results (78)

Background: Anterior cruciate ligament reconstruction (ACLr) often leads to asymmetries between limbs, with variable return-to-performance rates in athletes. The single-leg countermovement jump (SLCMJ) is commonly used to assess postoperative knee function. However, limited research has explored deficits specifically during the unweighting phase of the jump. Methods: This study assessed 53 recreational athletes (11 females, 42 males) between 6 and 9 months post-ACLr using a dual force plate system (1000 Hz). Each participant performed three maximal-effort SLCMJs per limb. Outcome measures included jump height, negative peak velocity, minimum force, and center of mass (COM) displacement. Paired t-tests and Wilcoxon tests were used to compare the ACLr limb with the contralateral limb. Results: Compared to the healthy limb, the ACLr limb showed significantly lower negative peak velocity (−0.80 ± 0.40 m/s vs. −0.94 ± 0.40 m/s, p < 0.001), higher minimum force (36.75 ± 17.88 kg vs. 32.05 ± 17.25 kg, p < 0.001), and reduced COM displacement (−17.62 ± 6.25 cm vs. −19.73 ± 5.34 cm, p = 0.014). Eccentric phase duration did not differ significantly. Conclusions: Athletes post-ACLr demonstrate altered neuromuscular control during the early SLCMJ phase. These findings highlight the importance of rehabilitation strategies targeting eccentric strength and symmetry restoration. Full article

This study examined the effects of a short-term ballistic training program on neuromuscular performance and strength-deficit (SDef) in elite youth female soccer players. Twenty-two under-20 athletes completed a 4-week intervention during the pre-season phase, comprising 12 loaded and 8 unloaded ballistic training sessions performed at maximal intended velocity. Pre- and post-intervention assessments included vertical jumps (squat jump [SJ], countermovement jump [CMJ]), sprinting speed (5, 10, and 20 m), one-repetition maximum (1RM) and peak force (PF) in the half-squat (HS), and peak power and velocity during jump squats (JS) at 30% of 1RM. SDef was calculated as the percentage difference in PF between 1RM in the HS and 30% 1RM. Significant improvements were observed in SJ, CMJ, sprint speed, 1RM-strength, and bar-derived mechanical outputs (ES = 1.18–1.66; p < 0.05), with no significant changes in SDef. These results indicate that elite youth female soccer players can improve strength-, power-, and speed-related capacities without compromising force production at higher movement velocities (thus maintaining their SDef). The improvements observed likely reflect the combined effect of a high-frequency, velocity-oriented training approach and a concurrent reduction in traditional technical–tactical (i.e., soccer-specific) training volume. This is the first study to demonstrate that ballistic exercises alone—when properly structured—can enhance neuromuscular performance in female soccer players without increasing SDef. These findings provide practical guidance for practitioners aiming to optimize physical development in team-sport athletes without relying on heavier training loads or extended resistance training sessions—and, especially, without compromising their ability to apply force at higher velocities. Full article

Objectives: This study examined physiological, biochemical, and performance adaptations in 18 semi-professional male soccer players across three seasonal phases: pre-season initiation (PS), pre-competition (PC), and mid-season (MS). Methods: Assessments included physical/performance/hormonal/biochemical markers. Results: From PS to PC, body fat (Cohen’s d = −0.88; p ≤ 0.01) and speed drop rate (Cohen’s d = −1.52; p ≤ 0.01) significantly decreased, while V̇O₂max (Cohen’s d = 0.80; p ≤ 0.01), velocity at V̇O₂max (Cohen’s d = 1.86; p ≤ 0.01), and velocity at the second ventilatory threshold (Cohen’s d = 1.54; p ≤ 0.01) significantly increased. Significant fluctuations were observed in creatine kinase (Cohen’s d = 4.34; p ≤ 0.01), myoglobin (Cohen’s d = 0.66; p ≤ 0.01), and cortisol (Cohen’s d = −1.14; p ≤ 0.01) levels. From PS to MS, further reductions in body fat (Cohen’s d = −0.81; p ≤ 0.01) and speed drop rate (Cohen’s d = −1.12; p ≤ 0.01) were observed, along with significant improvements in countermovement jump performance (Cohen’s d = 1.08; p ≤ 0.01) and cardiorespiratory fitness (Cohen’s d ≥ 0.83; p ≤ 0.01). Creatine kinase (Cohen’s d = 3.82; p ≤ 0.01), myoglobin (Cohen’s d = 1.50; p ≤ 0.01), interleukin-6 (Cohen’s d = 1.24; p ≤ 0.01), and testosterone (Cohen’s d = 0.92; p ≤ 0.01) significantly increased. Stability in lower limb strength, flexibility, triglycerides, C-reactive protein, ferritin, liver enzymes, and most hematological parameters suggest resilience to seasonal demands. Conclusions: Seasonal training enhanced fitness and hormonal balance while maintaining physiological stability. These findings underscore the importance of periodized training to manage muscle damage and sustain an anabolic hormonal profile for peak performance. Consistent diet and training support metabolic health, while tailored recovery strategies and season-specific interventions are essential for optimizing performance and minimizing injury risk. Full article

Coaches manipulate training variables to optimize and improve them, with intensity being crucial. Velocity-based training, measuring intensity by the movement speed, is advantageous over traditional methods. Flywheel training, offering concentric and eccentric loads, allows for supramaximal loading during the eccentric phase, enhancing muscle hypertrophy and performance and reducing injury risk. This study examines the specific effects of flywheel training on post-activation potentiation (PAP). Forty-one high-level male athletes performed flywheel half squats at fast (0.95–1.05 m/s), medium (0.65–0.75 m/s), and slow (0.35–0.45 m/s) speeds. Their drop jump performance was assessed at 30 s and 4, 8, and 12 min post-induction. Lower-limb kinematic data and ground reaction forces were recorded using infrared motion capture and force plates. Measures included peak collision force, peak extension force, knee joint extension moment, knee joint power, average power output, and vertical jump height. High-speed intensity significantly increased peak impact force, peak vertical ground reaction force, knee joint eccentric power, concentric power, and extension torque at 4, 8, and 12 min post-induction (p < 0.05). Fast- (0.95–1.05 m/s) and medium-speed (0.65–0.75 m/s) flywheel squats acutely improved lower-limb performance, especially vertical jump height, within 4–12 min post-stimulation. Fast-speed loading showed greater benefits for reactive strength and power output, while a medium speed also yielded meaningful gains. These findings support using movement velocity to guide flywheel training intensity. Full article

With the application and promotion of space geodesy, the popularization of remote sensing technology, and the development of artificial intelligence, a more accurate and stable Terrestrial Reference Frame (TRF) has become more urgent. For example, sea level change detection, crustal deformation monitoring, and driverless cars, among others, require the accuracy of the terrestrial reference frame to be better than 1 mm in positioning and 0.1 mm/a in velocity, respectively. However, the current frequently used ITRF2014 and ITRF2020 do not satisfy such requirements. Therefore, this paper analyzes the coordinate residual time series data of linear TRFs and finds there are still some unlabeled jumps and time-dependent periodic signals, especially in the GNSS coordinate residuals, which can lead to incorrect station epoch coordinates and velocities, further affecting the accuracy and stability of the TRF. The unlabeled jumps could be detected by the sequential t-test analysis of regime shifts (STARS) combined with the generalized extreme Studentized deviate (GESD) algorithms introduced in our earlier paper. These nonlinear time-dependent periodic signals could be modeled better by singular spectrum analysis (SSA) with respect to least squares fitting; the fitting period is no longer composed of semi-annual and annual items, as with ITRF2014. The periods of continuous coordinate residual time series data longer than 5 years are obtained by FFT. The results show that there are no period signals for individual SLR/VLBI sites, and there are still other period terms, such as 34 weeks, 20.8 weeks and 17.3 weeks, in addition to semi-annual and annual items for some GNSS sites. Moreover, after SSA corrections, the re-calculated TRF and the corresponding EOP could be obtained, based on data from the Chinese Earth Rotation and Reference System Service (CERS) TRF and the Earth Orientation Parameter (EOPs) multi-technique determination software package (CERS TRF&EOP V2.0) developed by the Shanghai Astronomical Observatory (SHAO). Their accuracy could be evaluated with respect to the ITRF2014 and the IERS 14 C04, respectively. The results show that the accuracy and stability of the newly established a nonlinear TRF and EOP based on SSA have been greatly improved and better than a linear TRF and EOP. SSA is better than least squares fitting, especially for those coordinate residual time series with varying amplitude and phase. For GPS, comparing with the ITRF2014, the station coordinate accuracy of 10.8% is better than 1 mm, and the station velocity accuracy of 4.4% is better than 0.1 mm/year. There are 3.1% VLBI stations, for which coordinate accuracy is better than 1 mm and velocity accuracy is better than 0.1 mm/year. However, there are no stations with coordinates and velocities better than 1 mm and 0.1 mm/year for the SLR and DORIS. The WRMS values of polar motion x, polar motion y, LOD, and UT1-UTC are reduced by 2.4%, 3.2%, 2.7%, and 0.96%, respectively. The EOP’s accuracy in SOL-B, in addition to LOD, is better than that of the JPL. Full article

Jump rope is a widely applied basic training technique in various sports, yet it is understudied biomechanically. This study investigates the impact of cycle-tempo-induced motor control changes in elite jump rope athletes, addressing the biomechanical gap of cyclic skill control. The hypothesis posited two accelerations per jump cycle—one in front of and one behind the body—and anticipated that increased cycle frequency would alter the distribution of acceleration time within a cycle. Using 3D motion capture technology, 12 young elite jump rope athletes were analyzed at 100, 140, and 180 revolutions per minute (rpm). The kinematic parameters obtained confirmed the presence of two distinct accelerations per cycle. As tempo increased, the percentage of rear acceleration time increased from 9.58% at 100 rpm to 17.42% at 180 rpm, while front acceleration time decreased from 39.03% at 100 rpm to 31.40% at 180 rpm, along with peak velocities increasing from 12.94 m/s at 100 rpm to 22.74 m/s at 180 rpm significantly (p < 0.01). Rope trajectory analysis indicated a consistent movement pattern across tempos, primarily in the sagittal plane. Variations in skill control revealed shorter contact phases, decreasing from 61.53% at 100 rpm to 48.25% at 180 rpm, as well as a reduced vertical range of motion for the center of gravity (from 0.15 body height at 100 rpm to 0.06 body height at 180 rpm) and feet (from 0.05 body height at 100 rpm to 0.03 body height at 180 rpm) (p < 0.05). Significant reductions were also observed in the flexion/extension range of motion for the hip (from 22.31° at 100 rpm to 3.47° at 180 rpm), knee (from 49.31° at 100 rpm to 9.35° at 180 rpm), and ankle (from 52.99° at 100 rpm to 21.41° at 180 rpm) (p < 0.01). These findings enhance the understanding of motor control adaptations to different tempos and have practical implications for developing coaching programs aimed at optimizing performance, stability, and efficiency in jump rope training. Full article

Background/Objectives: The underlying mechanisms of taekwondo-specific jumping ability among different competition levels are still unknown. This study aimed to compare vertical and horizontal stretch-shortening cycle (SSC) performance between athletes of different competitive levels and examine the relationships of force and power production abilities between those two directions in Taiwanese collegiate-level male taekwondo athletes. Methods: Seventeen male collegiate taekwondo athletes were divided into two groups: medalists (MG, n = 8) and non-medalists (NMG, n = 9); both groups performed countermovement jumps (CMJ) on a force platform and single-leg lateral hops (SLLHs) via an optoelectronic measurement system. Eccentric and concentric phase measures from CMJ and distant and temporal variables of SLLH were collected for further analysis. Results: The MG achieved statistically superior jump height (JH), concentric peak velocity, eccentric peak force, force at 0 velocity, and eccentric displacement than NMG (d = 1.05–1.36). Although non-significant differences showed in SLLH variables, MG had better results than NMG (d = 0.40–0.84). Moderate relationships were identified between SLLH step 1 and JH, reactive strength index modified, peak concentric power, and peak concentric velocity of CMJ (r = 0.50–0.57, p < 0.05). Furthermore, step 2 ground contact time and lateral reactive strength index from SLLH were associated with CMJ peak eccentric force, peak concentric force, and force at 0 velocity (r = 0.53–0.59, p < 0.05). Conclusions: Taekwondo MG achieved superior CMJ and SLLH performance. In addition, jumping abilities in vertical and lateral directions shared specific underlying mechanisms in collegiate male taekwondo athletes. Full article

Objective: The purpose of this study was to investigate differences in countermovement jump (CMJ) force–time metrics between male and female youth basketball players. Methods: Twenty-two female and seventeen male basketball players (ages 12–16) performed CMJs on a portable force plate system (VALD Performance). The data collected were analyzed for differences in force–time characteristics, specifically during the concentric and eccentric phases of the CMJ. Results: The results showed no statistically significant differences in anthropometric characteristics between the sexes. However, male athletes demonstrated better performance in several force–time metrics during the concentric phase of the CMJ, including concentric impulse, peak velocity, and mean power, ultimately leading to higher vertical jump heights. Sex-specific differences in the eccentric phase were less pronounced, though males exhibited greater relative eccentric mean power. Conclusions: The findings suggest that male players tend to display greater force and power-producing capabilities during the propulsive (concentric) phase of the CMJ. These differences highlight the importance of tailoring training programs to address specific needs, particularly focusing on enhancing concentric force and power production in female basketball players. Full article

The countermovement vertical jump (CMJ) is widely used in sports science and rehabilitation to assess lower body power. In controlled laboratory environments, a complex analysis of CMJ performance is usually carried out using motion capture or force plate systems, providing detailed insights into athlete’s movement mechanics. While these systems are highly accurate, they are often costly or limited to laboratory settings, making them impractical for widespread or field use. This study aimed to evaluate the accuracy of MMPose, a markerless 2D pose estimation framework, for CMJ analysis by comparing it with force plates. Twelve healthy participants performed five CMJs, with each jump trial simultaneously recorded using force plates and a smartphone camera. Vertical velocity profiles and key temporal variables, including jump phase durations, maximum jump height, vertical velocity, and take-off velocity, were analyzed and compared between the two systems. The statistical methods included a Bland–Altman analysis, correlation coefficients (r), and effect sizes, with consistency and systematic differences assessed using intraclass correlation coefficients (ICC) and paired samples t-tests. The results showed strong agreement (r = 0.992) between the markerless system and force plates, validating MMPose for CMJ analysis. The temporal variables also demonstrated high reliability (ICC > 0.9), with minimal systematic differences and negligible effect sizes for most variables. These findings suggest that the MMPose-based markerless system is a cost-effective and practical alternative for analyzing CMJ performance, particularly in field settings where force plates may be less accessible. This system holds potential for broader applications in sports performance and rehabilitation, enabling more scalable, data-driven movement assessments. Full article

This study investigates the impact of quadriceps fatigue on lower limb biomechanics during the landing phase of a single-leg vertical jump (SLJ) in 25 amateur male basketball players from Ningbo University. Fatigue was induced through single-leg knee flexion and extension exercises until task failure. Kinematic and dynamic data were collected pre-fatigue (PRF) and post-fatigue (POF) using the Vicon motion capture system and the AMTI force platform and analyzed using an OpenSim musculoskeletal model. Paired sample t-tests revealed significant changes in knee and hip biomechanics under different fatigue conditions, with knee joint angle (p < 0.001), velocity (p = 0.006), moment (p = 0.006), and power (p = 0.036) showing significant alterations. Hip joint angle (p = 0.002), moment (p = 0.033), and power (p < 0.001) also exhibited significant changes. Muscle activation and joint power were significantly higher in the POF condition, while joint stiffness was lower. These findings suggest that quadriceps fatigue leads to biomechanical adjustments in the knee and hip joints, which may increase the risk of injury despite aiding in landing stability. Full article

This study aimed to validate the automated temporal analysis of countermovement vertical jump (CMJ) using MMPose, a markerless pose estimation framework, by comparing it with the gold-standard 3D marker-based motion capture system. Twelve participants performed five CMJ trials, which were simultaneously recorded using the marker-based system and two smartphone cameras capturing both sides of the body. Key kinematic points, including center of mass (CoM) and toe trajectories, were analyzed to determine jump phases and temporal variables. The agreement between methods was assessed using Bland–Altman analysis, root mean square error (RMSE), and Pearson’s correlation coefficient (r), while consistency was evaluated via intraclass correlation coefficient (ICC 3,1) and two-way repeated-measures ANOVA. Cohen’s effect size (d) quantified the practical significance of differences. Results showed strong agreement (r > 0.98) with minimal bias and narrow limits of agreement for most variables. The markerless system slightly overestimated jump height and CoM vertical velocity, but ICC values (ICC > 0.91) confirmed strong reliability. Cohen’s d values were near zero, indicating trivial differences, and no variability due to recording side was observed. Overall, MMPose proved to be a reliable alternative for in-field CMJ analysis, supporting its broader application in sports and rehabilitation settings. Full article

Background/Objectives: The triple jump is included in the Paralympic Athletics competition. The aim of the research was to examine the relationship of the phase ratios and the inter-limb asymmetry in the spatiotemporal parameters of the approach run in Paralympic and international-level Class T46/T47 triple jumpers. Methods: Eleven Class T46/T47 male athletes were recorded during the examined competitions. Step length (SL), frequency (SF), and average velocity (ASV) for the late approach run as well as the length and the percentage distribution of each jumping phase (hop, step, jump) were measured using a panning video analysis method. The inter-limb asymmetry was estimated using the symmetry angle. Results: No significant inter-limb asymmetry was found (p > 0.05). In addition, SL, SF, and ASV were not different (p > 0.05) between the steps initiated from the ipsilateral and the contralateral leg regarding the impaired arm. However, the direction of asymmetry for SF was towards the ipsilateral leg to the impaired arm in the majority of the examined athletes. The maximum speed of the approach was correlated with the triple jump distance and the magnitude of asymmetry for AVS was correlated with the vertical take-off velocity and angle for the step. Conclusions: Since the distance of the triple jump related with the peak approach speed added the negative correlation of peak approach speed with the magnitude of the symmetry angle for SL, it is suggested to minimize the asymmetries in the step characteristics during the approach run to improve triple jump performance in Class T46/T47 jumpers. Full article

The hydraulic performance of pooled stepped spillways has received less recognition compared to the traditional stepped spillways. Regarding the effectiveness of pooled stepped spillways in managing flow dynamics, previous studies have focused on investigating how different step configurations and varying chute angles can enhance energy dissipation in gravity flow over the chute. However, the potential for optimal performance and the importance of proper design have not been thoroughly explored in the existing literature. This study aims to explore new configurations of pooled stepped spillways and compare them to traditional stepped spillway designs to enhance hydraulic efficiency and maximize energy dissipation. The study examines two types of configurations of stepped spillways—two flat and two pooled configurations, each with ten steps. Using the computational Fluid Dynamics (CFD) technique, such as Volume of Fluid Method (VOF) and the realizable k-ε turbulence model for two-phase flow analysis with a 26.6° chute slope. Initially, the model was validated with experimental data by comparing various hydraulic parameters. These parameters include water depth, roller length, jump length, ratio of critical depth, and sequent depth. The hydraulic performance of both stepped geometric configurations was evaluated through numerical simulations to examine how the geometries of flat and pooled stepped spillways influence flow characteristics, energy dissipation, velocity, pressure distribution, and the Froude number at the downstream. The study analyzed downstream flow characteristics, maximum energy dissipation rates, depth-averaged velocity, static pressure, and pressure contours at the lateral direction under six different flow rates in flat and pooled stepped spillways. The findings indicate that flat-step configurations exhibit lower energy dissipation compared to pooled configurations. The relative energy loss of flow on pooled steps dissipates more energy than on flat steps. Furthermore, it is observed that the pooled configurations performed better for energy dissipation and flow stability compared to the flat configurations. The energy dissipation increased in pooled stepped spillways by 34.68% and 25.81%, respectively. Additionally, the depth-averaged flow velocity and pressure distribution decreased in case 2 and case 4 compared to the flat-step configurations. Full article

Objectives: The aim of this study was to assess the relationship between the countermovement jump (CMJ) and sprint performance of professional football players, and to determine which strength and speed elements assessed by the CMJ translate into effective running. Methods: The research sample comprised 87 male professional football players (age 23.7 ± 4.20 years; body mass 82.33 ± 6.56 kg; body height 1.86 ± 0.05 m) who performed the CMJ on a dual-force platform, as well as the 30 m sprint test. The time and velocity of the run were recorded by photocells at 0, 5, 10, and 30 m of the distance. Results: No significant differences were noted in the time or velocity of the sprint over the initial 5 m between the groups of football players with a higher and lower braking rate of force development (RFD) in the CMJ (p > 0.05). However, at subsequent intervals (5–10 m and 10–30 m), players with a higher braking RFD achieved significantly better time and velocity than those with a lower RFD. Significant correlations in the group with a lower braking RFD between the CMJ and sprint variables occurred in the propulsion phase of the CMJ and most of them were in the first interval (0–5 m). In the group with a higher braking RFD, significant relationships were visible in both the propulsion (concentric) and braking (eccentric) phases of the CMJ, mainly during the second and third intervals of the sprint test. Conclusions: The noted observations may suggest that the relationship between strength and running performance is more complex than previously indicated, and that higher strength in the CMJ does not fully correlate with better sprinting. Therefore, it has been hypothesized that training aimed at generally increasing strength may not always be fully beneficial for running performance in football players and hence specific training guidelines are suggested for targeted strengthening of the required muscle performance characteristics. This may possibly contribute to reducing the unnecessary muscle overload during both training and matches, thereby preventing sports-related injuries. Full article

The complex service environment of railway vehicles leads to changes in the wheel–rail adhesion coefficient, and the decrease in critical speed may lead to hunting instability. This paper aims to reveal the diversity of periodic hunting motion patterns and the internal correlation relationship with wheel–rail impact velocities after the hunting instability of a bogie system. A nonlinear, non-smooth lateral dynamic model of a bogie system with 7 degrees of freedom is constructed. The wheel–rail contact relations and the piecewise smooth flange forces are the main nonlinear, non-smooth factors in the system. Based on Poincaré mapping and the two-parameter co-simulation theory, hunting motion modes and existence regions are obtained in the parameter plane consisting of running speed v and the wheel–rail adhesion coefficient μ. Three-dimensional cloud maps of the maximum lateral wheel–rail impact velocity are obtained, and the correlation with the hunting motion pattern is analyzed. The coexistence of periodic hunting motions is further revealed based on combined bifurcation diagrams and multi-initial value phase diagrams. The results show that grazing bifurcation causes the number of wheel–rail impacts to increase at a low-speed range. Periodic hunting motion with period number n = 1 has smaller lateral wheel–rail impact velocities, whereas chaotic motion induces more severe wheel–rail impacts. Subharmonic periodic hunting motion windows within the speed range of chaotic motion, pitchfork bifurcation, and jump bifurcation are the primary forms that induce the coexistence of periodic motion. Full article