Velocity-Load Jump Testing Predicts Acceleration Performance in Elite Speed Skaters: But Does Movement Specificity Matter?

PURPOSE: In this study, we compared the influence of movement specificity during velocity-load jump testing to predict on-ice acceleration performance in elite speed skaters. METHODS: Elite long-track speed skaters (N = 27) performed velocity-load testing with 3 external loads during unilateral horizontal jumping, lateral jumping, and bilateral vertical countermovement jumping. For the unilateral tests, external load conditions were set to 10 N, 7.5% and 15% of external load relative to body weight. For the countermovement jumping, load conditions were body weight and 30% and 60% of external load relative to body weight. On-ice performance measures were obtained during maximal 50-m accelerations from a standing start, including maximal skating speed, maximal acceleration capacity, and maximum horizontal power. The 100-m split time from a 500-m race was also obtained. Regularized regression models were used to identify the most important predictors of on-ice acceleration performance. In addition to regularized regression coefficients, Pearson correlation coefficients (r) were calculated for all variables retained by the model to assess interrelationships between single predictors and on-ice performance measures. RESULTS: The countermovement jump with 30% of body mass demonstrated the strongest association with maximal skating speed, maximum horizontal power, and 100-m time (regularized regression coefficient = .16-.49, r = .84-.97, P < .001). Horizontal jump with 15% of body mass was the strongest predictor of maximal acceleration capacity performance (regularized regression coefficient = .08, r = .83, P < .001). CONCLUSIONS: The findings of this study suggest that mechanical specificity rather than movement specificity was more relevant for predicting on-ice acceleration performance.

Lower-Body Power, Body Composition, Speed, and Agility Performance among Youth Soccer Players.

Speed and agility have been described as crucial abilities for soccer players. The purpose of this study was to analyze, in detail, the variance in speed and agility tasks explained by lower-body power after controlling for age and body composition. The participants were 96 male soccer players aged 16.1 ± 1.6 years. Body composition (stature, body fat percentage-BF%, body mass, and fat-free mass-FFM), lower-body power (countermovement jump-CMJ, and squat jump-SJ), speed (5-, 10-, and 35 m sprints), and agility (t-test) were assessed. Among body composition parameters, BF% presented the highest number of significant relationships with speed and agility, with the strength of correlations ranging from small (5 m sprint, r = 0.25) to large (35 m sprint, r = 0.52). The strongest correlation coefficient emerged between FFM and the 35 m sprint (r = -0.65). Significant correlations were found between vertical jump performance and the 35 m sprint (CMJ: r = -0.68; SJ: r = -0.69), followed by the t-test (CMJ: r = -0.35; SJ: r = -0.47). The hierarchical multiple regression model could explain 22% to 67% of the variance observed in agility scores and speed. BF% remained the most statistically significant negative predictor of all regression models. The CMJ remained a statistically significant positive predictor of the 35 m sprint (ß = -0.581, p ≤ 0.01) after controlling for age and body composition. Integrating programs targeting lower-body power might be important to enhance speed and agility performance in youth soccer. On the other hand, future research based on multidisciplinary approaches to investigate the effects of nutritional strategies in reducing or preventing gains in BF% is still needed, which remained a significant predictor of sprint and agility performance in the final models.

Input-to-state stability of stochastic nonlinear system with delayed impulses.

Stochastic input-to-state stability (SISS) of the stochastic nonlinear system has received extensive research. This paper aimed to investigate SISS of the stochastic nonlinear system with delayed impulses. First, when all subsystems were stable, using the average impulsive interval method and Lyapunov approach, some theoretical conditions ensuring SISS of the considered system were established. The SISS characteristic of the argumented system with both stable and unstable subsystems was also discussed, then the stochastic nonlinear system with multiple delayed impulse jumps was considered and SISS property was explored. Additionally, it should be noted that the Lyapunov rate coefficient considered in this paper is positively time-varying. Finally, several numerical examples confirmed validity of theoretical results.

Musculoskeletal Morphology and Joint Flexibility-Associated Functional Characteristics across Three Time Points during the Menstrual Cycle in Female Contemporary Dancers.

Findings are inconsistent with regards to whether menstrual cycle phase-associated changes in physical functioning exist. It is possible that such discrepancies are due to varying rigour in experimental approaches. The current study aimed to systematically evaluate any effect of carefully tracked menstrual cycle phase on precisely measured muscle structure and function in a physically active group (contemporary dancers). Eleven women aged (M [SD]) 23.5 [2.94] years, undergoing 10.5 [1.73] hours of contemporary dance practice and 6.12 [2.36] hours of other physical activity per week, were recruited. Sex hormone level (enzyme-linked immunosorbent assays (ELISA), skin temperature and ovulation kits), physical pain assessments (Ice Water Test, Visual Analogue Scale, The Physical Activity Readiness Questionnaire, Self-Estimated Functional Inability Because of Pain Questionnaire, and Pain Anxiety Symptoms Scale), muscle architecture measurement (B-mode ultrasonography), and physical functioning (dynamometry, force-platform and electromyography) on both lower limbs were measured at three time points during one cycle, following three months of menstrual cycle monitoring. There was no difference in musculoskeletal flexibility variables between follicular, ovulatory, or luteal phases. Nonetheless, oestrogen change was associated with variability in 11 musculoskeletal variables, progesterone change was associated with variability in 7, and relaxin change was associated with variability in 15. Negative correlations existed between progesterone and flexibility and between oestrogen and jump variables. Moreover, oestrogen and relaxin were associated with increased musculoskeletal compliance, whilst progesterone was associated with increased muscle stiffness. In short, in absolute sex hormone levels, 'inter-individual' variances appear more impactful than 'intra-individual' variances. Not only are oestrogen and progesterone associated with differing musculoskeletal outcomes, but relaxin is also associated with musculoskeletal compliance changes. These effects are anticipated to impact jump height and flexibility, and hence, they could be expected to affect overall physical performance, including dance.

Comparison of Reported Fatalities, Falls and Injuries in Thoroughbred Horse Jumps and Flat Races in the 2022 and 2023 Jumps Race Seasons in Victoria, Australia.

Jumps racing is a form of Thoroughbred horse racing that involves hurdles and steeples and typically longer distances, and heavier weights compared with flat racing, which does not incorporate obstacles. In Australia, jumps racing is carried out only in Victoria, one of eight states and territories. The continuation of jumps racing is contentious due to the higher risk of fatalities, falls and injuries for horses, compared with flat racing. While measures have been introduced by the industry to improve the safety of riders and horses, the rates of fatalities, falls and injuries in horses participating in jumps races have not been collectively reported in Australia since the 2012 to 2014 race seasons. Although information on individual horse fatalities, falls and injuries is published by Racing Victoria in Stewards' Reports, the data are not aggregated, and so cannot readily be used to assess trends or evaluate the efficacy of safety measures introduced by the industry. The aim of this study was to determine the fatality, fall and injury rates for horses participating in hurdle and steeplechase races in Victoria in the 2022 and 2023 Thoroughbred horse jumps racing seasons compared with horses participating in flat races at the same race meets. Data on horse fatalities, falls and injuries were extracted from the published Racing Victoria race results and Stewards' Reports for the jumps races (n = 150) and corresponding flat races (n = 157) held at the 38 jumps race meets in Victoria in 2022 and 2023. Overall, horse fatalities, falls and injuries occurred at higher rates in jumps races compared with flat races during the study period. The rate of horse fatalities in jumps races was 3.3 per 1000 starts, with no fatalities in flat races. The rate of horse falls in hurdle races was 24 per 1000 starts and 41.6 per 1000 starts in steeplechase races, comparable with rates previously reported in the 2012 to 2014 seasons. There were no falls in flat races. Horse injuries occurred at a rate of 68.9 per 1000 starts in jumps races compared with 18.8 per 1000 starts in flat races. In hurdle and steeplechase races, veterinary clearance being required following horse injury was 5.4 times (OR 5.4, 95% CI 2.8-10.2) and 7.2 times (OR 7.2, 95% CI 3.3-15.6) more likely, respectively, compared with flat races. The risk of trauma was 4 times more likely in hurdle and steeplechase races (OR 4.8, 95% CI 1.7-13.3 and OR 4.1, 95% CI 1.2-13.4, respectively) and the risk of lameness was increased by 2.5 times in hurdles (OR 2.5, 95% CI 1.2-5.2) and 5.1 times in steeplechase races (OR 5.1, 95% CI 2.3-11.5), compared with flat races. These findings support concerns about the welfare of horses involved in jumps racing and of the need for further safety measures to reduce these risks.

Jumping Motor Skills in Typically Developing Preschool Children Assessed Using a Battery of Tests.

The preschool period is characterised by the improvement in motor skills. One of the developmental tasks in children is the ability to jump. Jumping plays an important role in the development of leg strength and balance. It is the gateway to more complex movements. In the physiotherapy clinic, we see a lot of difficulties in jumping performance in 5-7-year-old children. The aim of this study is to present the jumping ability, assessed by the Motor Proficiency Test (MOT) and the G-sensor examination of the vertical countermovement jump (CMJ) and countermovement jump with arms thrust (CMJAT) parameters. A total of 47 children (14 boys and 33 girls) were randomly recruited. The mean age was 5.5 years. The mean height was 113 cm and the mean weight was 19.7 kg. The children were divided into two groups according to their results. Children with low basic motor skills have the greatest difficulty with jumping tasks. In the CMJ jump, the take-off force was lower than in the CMJAT (p = 0.04). Most CMJAT parameters correlate with age, weight, and height. Height correlates most with children's jumping performance. This study may be useful for sport educators and developmental researchers. The topic should be further explored and the CMJ and CMJAT parameters may be established as a basis.

Dynamics of a stochastic hybrid delay food chain model with jumps in an impulsive polluted environment.

In this paper, a stochastic hybrid delay food chain model with jumps in an impulsive polluted environment is investigated. We obtain the sufficient and necessary conditions for persistence in mean and extinction of each species. The results show that the stochastic dynamics of the system are closely correlated with both time delays and environmental noises. Some numerical examples are introduced to illustrate the main results.

The influence of jump-landing direction on dynamic postural stability following anterior cruciate ligament reconstruction.

BACKGROUND: Traditional testing prior to return to sport following anterior cruciate ligament reconstruction typically involves jump-landing tasks in the forward direction. As injury is most likely the result of multiplanar neuromuscular control deficits, assessment of dynamic postural stability using landing tasks that require multiplanar stabilization may be more appropriate. The purpose of this study was to examine how dynamic postural stability is affected when performing jump-landing tasks in three different directions. METHODS: Fifteen athletes [11 females (18.0 ± 3.0 years) and 4 males (18.5 ± 3.1 years)] following anterior cruciate ligament reconstruction performed a series of single-limb jump-landing tasks in 3 directions. Individual directional stability indices and a composite dynamic postural stability index were calculated using ground reaction force data and were compared using separate one-way repeated measures ANOVAs. FINDINGS: All directional stability indices demonstrated a significant main effect for jump-landing direction (medial-lateral P < 0.001, η2p = 0.95; anterior-posterior P < 0.001, η2p = 0.97; vertical P = 0.021, η2p = 0.24). The diagonal jump-landing direction produced increased medial-lateral stability and vertical stability scores, while the forward and diagonal jump-landing directions produced increased anterior-posterior stability scores. There was no significant effect for the composite dynamic stability index score. INTERPRETATION: Jump-landing direction affects dynamic postural stability in all 3 planes of movement in athletes following anterior cruciate ligament reconstruction. Results indicate the potential need to incorporate multiple jump-landing directions to better assess dynamic postural stability prior to return to sport.

Predicting repeat power ability through common field assessments: is repeat power ability a unique physical quality?

Background: The repeat power ability (RPA) assessment is used to test the ability to repeatedly produce maximal ballistic efforts with an external load. The underpinning physical qualities influencing RPA are undetermined. This study aimed to gain further insight into the physical qualities that determine RPA by analysing the association between physical qualities and an assessment of RPA. Materials and methods: Ten well-trained male field hockey players performed an RPA assessment consisting of 20 repetitions of loaded countermovement jumps (LCMJ20), with a percent decrement score of peak power output calculated. Over a two-week period, each participant performed the YoYo Intermittent Recovery Test 2 (IRT2), a repeated speed ability assessment incorporating a 180° change of direction (RSA180), a 40-meter linear speed test (40 mST), an isometric mid-thigh pull (IMTP), a countermovement jump (CMJ), and a 3-repetition maximum half squat (HS) assessment. Pearson's correlation analysis was used to determine the strength of relationships between each assessment variable and the LCMJ20. The assessment variables with the strongest relationships within each assessment were used in a stepwise multiple linear regression analysis to determine the best predictor model of LCMJ20. Results: RSA180percent decrement score (RSA180% had a very strong, significant relationship with LCMJ20 (r = 0.736: p < 0.05). HS relative strength (HSrel) was found to have a significant and very strong, negative relationship with LCMJ20 (r =  - 0.728: p < 0.05). Stepwise multiple linear regression analysis showed RSA180 to explain 48.4% of LCMJ20 variance (Adjusted R2 = 0.484) as the only covariate included in the model. Conclusion: The findings indicate that RSA180 as a repeated high intensity effort (RHIE) task is strongly related to LCMJ20 and is also the best predictor of LCMJ20. This may suggest that RPA can provide practitioners with information on RHIE performance. The variance between assessment methods indicates that RPA may be a distinct physical quality, future research should assess other physical capacities to better understand the factors contributing to RPA.

Validation of a Portable Wireless Force Platform System To Measure Ground Reaction Forces During Various Tasks.

Background: Force platforms are widely used in biomechanics to measure ground reaction forces (GRF) during various human movements. However, traditional force plates are not easily used outside a research lab. To overcome this issue, researchers and manufacturers are developing low-cost portable force platforms that can be used in a variety of settings, including outdoors. Purpose: To validate the kinetic data obtained from a pair of portable K-Deltas force platforms compared to gold standard platforms fixed in the lab and to examine the measurement reliability between this pair of portable force platforms. Methods: Force-time curves from known masses, countermovement vertical jumps, and balance tests were used to assess validity of K-Deltas using a pair of Bertec force plates as a gold standard and between the K-Deltas pair of plates. Bland-Altman plots were used to evaluate the differences between K-Deltas and Bertec force plates. For the assessment of countermovement vertical jumps, impulse, peak rate of force development and peak force were calculated for both instruments and checked for agreement between instruments. Three young adults (2 male, 1 female, 25.4±0.83 years) participated in the study. Results: The percentage of Bland-Altman plot point within the limits of agreement was 94.59 % for the comparison between K-Deltas and Bertec and 94.83% between the pair of K-Deltas. Conclusion: The results show that the portable force platforms could be utilized successfully for assessing pertinent parameters in clinical and sports biomechanics. The findings suggest that portable force platforms can be used as an alternative to traditional laboratory equipment for field assessment, providing significant improvements compared to the past. Level of Evidence: Level 3.

Asimetrías en jugadores alevines de fútbol de una cantera de élite: diferencias entre sexos / Assymetries in junior football players from an elite youth academy: differences between sexes

El objetivo de este estudio fue detectar las asimetrías en jugadores/as de fútbol a través de una batería de test, analizar las asimetrías del lado dominante y no dominante, y comparar la correlación entre ambos sexos. 25 jugadores de fútbol del Real Racing Club de Santander, pertenecientes a la categoría Alevín, 13 jugadoras femeninas y 12 masculinos, fueron evaluados en diferentes test neuromusculares para detectar las asimetrías del miembro inferior: Single Hop Test (SHT), Triple Hop Test (THT), Salto de contramovimiento unilateral (SLCMJ), y test de cambio de dirección (505 COD). Con el fin de identificar el índice de asimetrías (ASI) neuromusculares entre los miembros inferiores se comparó la pierna dominante (PD) con la no dominante (PND) a través de la siguiente fórmula: ASI = ((PD-PND)/PD)x100. En los hallazgos se encontraron diferencias significativas (p <0.05) al comparar las asimetrías neuromusculares entre ambos sexos en los diferentes test. En cambio, no se encontraron diferencias entre pierna dominante y no dominante. Además, se observó que un 36% de la muestra de jugadores/as obtuvo un ASI >10%, considerado un factor de mayor probabilidad de sufrir una lesión en el miembro inferior. En conclusión, se ha podido comprobar a través de este estudio que se han encontrado diferencias significativas en las asimetrías del miembro inferior en función del sexo, pero no entre la pierna dominante y no dominante. En definitiva, son necesarios más estudios donde analicen las asimetrías en diferentes sexos con el fin de obtener un mayor análisis de los resultados. (AU)

The present study uses a cross-sectional design of independent and related samples whose objectives were: to detect asymmetries in football players through a battery of tests, to analyse the asymmetries of the dominant and non-dominant side, and to compare the correlation between both sexes. A total of 25 football players from Real Racing Club de Santander belonging to the Alevín category, 13 female players and 12 male players were evaluated in different neuromuscular tests to detect lower limb asymmetries: Single Hop Test (SHT), Triple Hop Test (THT), Unilateral Countermovement Jumping (SLCMJ), and Change of Direction Test (505 COD). In order to identify the neuromuscular asymmetry index (ASI) between the lower limbs, the dominant leg (PD) was compared to the non-dominant leg (PND) using the following formula: ASI = ((PD-PND)/PD)x100. Significant differences (p<0.05) were found in the findings when comparing the neuromuscular asymmetries between both sexes in the different tests. In contrast, there is no difference between dominant and non-dominant leg. In addition, it was observed that 36% of the sample of players had an ASI >10%, which is considered to be a factor of increased likelihood of lower limb injury. The highest asymmetry was detected at 20% in the SLCMJ test, which may be the most suitable jump test for identifying asymmetries. In conclusion, this study has shown that significant differences were found in lower limb asymmetries according to sex, but not between the dominant and non-dominant leg. (AU)

Risk Factors for Horse Fatality in Thoroughbred Jumps Racing in New Zealand.

The aim of this study was to examine the race-, horse- and jockey-level risk factors for race day fatality in New Zealand Thoroughbred jumps racing using retrospective race day data from the 2011/12 to 2021/22 seasons (n = 8,970 starts). There were 51 race day fatalities resulting in an incidence rate of 5.7 per 1,000 starts (95% C.I. 4.3-7.5). The majority of fatalities were the result of fractures (44/51, 4.9 per 1,000 starts, 95% C.I. 3.7-6.6). Steeplechase and hurdle races had the same incidence of fatal fractures of 4.9 per 1,000 starts (95% C.I. 3.7-6.6, P > .05). Most (70.5%) of the fatal fractures were due to a horse falling during the race. In steeplechase races, horses running in races over 4,201 m were 5.0 times (95% C.I. 1.2-33.0) more likely to sustain a fatal fracture than horses in racing over shorter distances. In hurdle races, horses racing during spring were 2.2 times (95% C.I. 1.0-4.8) more likely to sustain a fatal fracture compared to winter. Due to the low number of suspected cardiac failures and fatal soft tissue injuries, risk factors for these fatalities could not be identified. These data provide a baseline to enable evidence-based regulatory changes and prospectively monitor the effectiveness of changes made.

The Cauchy Process on Phylogenies: A Tractable Model for Pulsed Evolution.

Phylogenetic comparative methods use random processes, such as the Brownian Motion, to model the evolution of continuous traits on phylogenetic trees. Growing evidence for non-gradual evolution motivated the development of complex models, often based on Lévy processes. However, their statistical inference is computationally intensive and currently relies on approximations, high-dimensional sampling, or numerical integration. We consider here the Cauchy Process (CP), a particular pure-jump Lévy process in which the trait increment along each branch follows a centered Cauchy distribution with a dispersion proportional to its length. In this work, we derive an exact algorithm to compute both the joint probability density of the tip trait values of a phylogeny under a CP and the ancestral trait values and branch increments posterior densities in quadratic time. A simulation study shows that the CP generates patterns in comparative data that are distinct from any Gaussian process, and that restricted maximum likelihood parameter estimates and root trait reconstruction are unbiased and accurate for trees with 200 tips or less. The CP has only two parameters but is rich enough to capture complex-pulsed evolution. It can reconstruct posterior ancestral trait distributions that are multimodal, reflecting the uncertainty associated with the inference of the evolutionary history of a trait from extant taxa only. Applied on empirical datasets taken from the Evolutionary Ecology and Virology literature, the CP suggests nuanced scenarios for the body size evolution of Greater Antilles Lizards and for the geographical spread of the West Nile Virus epidemics in North America, both consistent with previous studies using more complex models. The method is efficiently implemented in C with an R interface in package cauphy, which is open source and freely available online.

The effect of two sessions of combined jump and sprint training per week on fitness parameters in soccer players. A randomized controlled trial.

This study aimed to investigate the effect of a combined jump and sprint training program, two sessions a week for 6 weeks, on sprinting, change of directions (COD) and jumping performance in semi-professional soccer players. Twenty soccer players were enrolled in this randomized controlled trial (age 20 ± 2 years, body mass 74.3 ± 5.9 kg). Players were randomized into two groups such as training group (TG, n = 10 players) or control group (CG, n = 10 players). Physical tests were performed before and after 6 weeks of training such as sprint 10 m, sprint 30 m, 505-COD test and standing long jump (LJ). The two groups performed the same training except for the combined jump and sprint training performed twice a week by TG. After 6 weeks of training, between-group analysis reported statistical difference in favor of the TG in sprint 10 m (p = 0.015, η2 = 0.295, large), sprint 30 m (p < 0.001, η2 = 0.599, large), in 505-COD (p = 0.026, η2 = 0.154, large), and LJ (p = 0.025, η2 = 0.027, small). These data indicate that combined sprint and jump training, when performed twice a week, for the duration of 6 weeks, in addition to the regular team training, can improve specific physical performance in male soccer players. This study has shown that a volume increment of 10% after 3 weeks of training can be a suitable training dose progression and that a combination of 64-70 jumps and 675-738 m of sprinting training per session can yield benefits in sprint, COD and jump performance.

Spatiotemporal phase slip patterns for visual evoked potentials, covert object naming tasks, and insight moments extracted from 256 channel EEG recordings.

Phase slips arise from state transitions of the coordinated activity of cortical neurons which can be extracted from the EEG data. The phase slip rates (PSRs) were studied from the high-density (256 channel) EEG data, sampled at 16.384 kHz, of five adult subjects during covert visual object naming tasks. Artifact-free data from 29 trials were averaged for each subject. The analysis was performed to look for phase slips in the theta (4-7 Hz), alpha (7-12 Hz), beta (12-30 Hz), and low gamma (30-49 Hz) bands. The phase was calculated with the Hilbert transform, then unwrapped and detrended to look for phase slip rates in a 1.0 ms wide stepping window with a step size of 0.06 ms. The spatiotemporal plots of the PSRs were made by using a montage layout of 256 equidistant electrode positions. The spatiotemporal profiles of EEG and PSRs during the stimulus and the first second of the post-stimulus period were examined in detail to study the visual evoked potentials and different stages of visual object recognition in the visual, language, and memory areas. It was found that the activity areas of PSRs were different as compared with EEG activity areas during the stimulus and post-stimulus periods. Different stages of the insight moments during the covert object naming tasks were examined from PSRs and it was found to be about 512 ± 21 ms for the 'Eureka' moment. Overall, these results indicate that information about the cortical phase transitions can be derived from the measured EEG data and can be used in a complementary fashion to study the cognitive behavior of the brain.

Countermovement Jump Performance Is Related to Ankle Flexibility and Knee Extensors Torque in Female Adolescent Volleyball Athletes.

Ankle flexibility and isokinetic knee torque/power generating capacity were previously suggested to contribute or to be correlated to the vertical countermovement jump (CMJ) performance. The aim of this study was to investigate the effect of the passive ankle joint dorsi flexion (θPDF) and the knee muscle's isokinetic torque and power on the CMJ in adolescent female volleyball players. The θPDF at a knee extension angle of 140 degrees were measured for 37 female post-pubertal volleyball players. Then, the players were assigned to either the flexible (n = 10) or inflexible (n = 14) groups according to earlier recommended criteria. Testing included the CMJ with and without an arm swing, and maximal knee extensions and flexions in 3 angular velocities on an isokinetic dynamometer. CMJ height performed with or without an arm swing (r(22) = 0.563, p = 0.040 and r(22) = 0.518, p = 0.009, respectively) and relative power (r(22) = 0.517, p = 0.010 and r(22) = 0.446, p = 0.030, respectively) were positively correlated with the extensors' torque at 180°/s and were negatively correlated with the flexibility level of the dominant side ankle (r(22) = -0.529, p = 0.008 and r(22) = -0.576, p = 0.030, respectively). A moderate positive correlation was also revealed between the CMJ height with and without an arm swing and the power of the non-dominant knee extensors (r(22) = 0.458, p = 0.024 and r(22) = 0.402, p = 0.049, respectively) and flexors (r(22) = 0.484, p = 0.016 and r(22) = 0.477, p = 0.018, respectively). Results of the 2 × 2 repeated ANOVA measurements revealed that flexible players jumped significantly (p < 0.05) higher during the CMJs, whilst there was a group effect only on the isokinetic knee extensor muscles' torque. In conclusion, a more flexible ankle joint and a higher isokinetic knee extensor's torque generating capacity resulted in higher CMJ performance. Therefore, ankle flexibility should be emphasized in training and is suggested to be included in preseason screening tests of youth female volleyball players.

Agreement between Force Platform and Smartphone Application-Derived Measures of Vertical Jump Height in Youth Grassroots Soccer Players.

Given the importance of vertical jump assessments as a performance benchmarking tool, the assessment of neuromuscular function and indicator of health status, accurate assessment is essential. This study compared countermovement jump (CMJ) height assessed using MyJump2 (JHMJ) to force-platform-derived jump height calculated from time in the air (JHTIA) and take-off velocity (JHTOV) in youth grassroots soccer players. Thirty participants (Age: 8.7 ± 0.42 yrs; 9 females) completed bilateral CMJs on force platforms whilst jump height was simultaneously evaluated using MyJump2. Intraclass correlation coefficients (ICC), Standard error of measurement (SEM), coefficient of variance (CV) and Bland-Altman analysis were used to compare performance of MyJump2 to force-platform-derived measures of CMJ height. The median jump height was 15.5 cm. Despite a high level of agreement between JHTIA and JHTOV (ICC = 0.955), CV (6.6%), mean bias (1.33 ± 1.62 cm) and 95% limits of agreement (LoA -1.85-4.51 cm) were greater than in other comparisons. JHMJ performed marginally better than JHTIA when compared to JHTOV (ICC = 0.971; 95% CI's = 0.956-0.981; SEM = 0.3 cm; CV = 5.7%; mean bias = 0.36 ± 1.61 cm; LoA = -3.52-2.80 cm). Irrespective of method, jump height did not differ between males and females (p > 0.381; r < 0.093), and the comparison between assessment tools was not affected by sex. Given low jump heights achieved in youth, JHTIA and JHMJ should be used with caution. JHTOV should be used to guarantee accuracy in the calculation of jump height.

The reliability and validity of repeat power ability assessments and measurement indices in loaded vertical jumps.

Background: Repeat power ability (RPA) assessments are a valuable evaluation of an athlete's ability to repeatedly perform high intensity movements. Establishing the most reliable and valid loaded jump RPA assessment and method to quantify RPA has yet to be determined. This study aimed to compare the reliability and validity of an RPA assessment performed with loaded squat jumps (SJ) or countermovement jumps (CMJ) using force-time derived mean and peak power output. Materials and Methods: RPA was quantified using calculations of average power output, a fatigue index and a percent decrement score for all repetitions and with the first and last repetitions removed. Validity was established by comparing to a 30 second Bosco repeated jump test (30BJT). Eleven well-trained male field hockey players performed one set of 20 repetitions of both SJs (20SJ) and CMJs (20CMJ) on separate occasions using a 30% one repetition maximum half squat load. These assessments were repeated 7 days apart to establish inter-test reliability. On a separate occasion, each participant performed the 30BJT. Results: The reliability of average peak power for 20SJ and 20CMJ was acceptable (CV < 5%; ICC > 0.9), while average mean power reliability for 20CMJ (CV < 5%; ICC > 0.9) was better than 20SJ (CV > 5%; ICC > 0.8). Percent decrement of 20CMJ peak power, with the first and final jump removed from the percent decrement calculation (PD%CMJpeak18), was the most reliable measurement of power output decline (CV < 5 %; ICC > 0.8). Average mean and peak power for both RPA protocols had moderate to strong correlations with 30BJT average mean and peak power (r = 0.5-0.8; p< 0.05-0.01). No RPA measurements of power decline were significantly related to BJT measurements of power decline. Conclusions: These findings indicate that PD%CMJpeak18 is the most reliable measure of RPA power decline. The lack of relationship between power decline in the loaded RPA and the 30BJT assessment suggest that each assessment may be measuring a different physical quality. These results provide sport science practitioners with additional methods to assess RPA and provide useful information on the reliability and validity of these outcome measures. Additional research needs to be performed to examine the reliability and validity of the novel RPA assessments in other athletic populations and to determine the sensitivity of these measurements to training and injury.

Single and Combined Effects of Preferred Music and Endpoint Knowledge on Jump Performance in Basketball Players.

Both music and endpoint knowledge of exercise have been shown to independently influence exercise performance. However, whether these factors work as synergists or counteract one another during exercise is unknown. The purpose of this study was to determine the single and combined effect of listening to preferred music and types of endpoint knowledge on repeated countermovement jump (CMJ) test performance. Twenty-four (n = 24) current or previously competitive basketball players underwent CMJ testing under the following endpoint knowledge conditions: (1) unknown/no knowledge, (2) knowledge of the number of jumps, and (3) knowledge of exercise duration. For each of these, participants listened to either their preferred music or no music during the duration of testing. For the exercise portion, participants completed repeated CMJs where participants were encouraged to jump as high as possible with jump height, contact time, and flight time as outcomes. Rate of perceived exertion (RPE) and feeling scale were measured before and after exercise. The results showed that, regardless of knowledge type, preferred music resulted in a significant decrease in both contact time and flight time (F ≥ 10.4, p ≤ 0.004, and ηp2 ≥ 0.35), and a significant improvement of jump height (F = 11.36, p = 0.001, and ηp2 = 0.09) and feeling scale ratings (F = 36.9, p < 0.001, and ηp2 = 0.66) compared to no-music condition, while RPE was not significantly affected. Regardless of the presence of music, knowledge of the number of jumps and duration resulted in lower contact time (p < 0.001, 0.9 < d < 1.56) versus unknown condition during CMJs. Moreover, a significant decrease in RPE values was found during prior endpoint knowledge of number (p = 0.005; d = 0.72) and duration (p = 0.045; d = 0.63) compared to unknown condition. However, feeling scale ratings were not significantly affected. Moreover, no interactions with significance findings were found for any parameters. Overall, data suggest that listening to music and endpoint knowledge alter exercise responses in basketball players, but they do not interact with one another.

Upside and downside correlated jump risk premia of currency options and expected returns.

This research explores upside and downside jumps in the dynamic processes of three rates: domestic interest rates, foreign interest rates, and exchange rates. To fill the gap between the asymmetric jump in the currency market and the current models, a correlated asymmetric jump model is proposed to capture the co-movement of the correlated jump risks for the three rates and identify the correlated jump risk premia. The likelihood ratio test results show that the new model performs best in 1-, 3-, 6-, and 12-month maturities. The in- and out-of-sample test results indicate that the new model can capture more risk factors with relatively small pricing errors. Finally, the risk factors captured by the new model can explain the exchange rate fluctuations for various economic events.