Reactive Strength Index Research Articles

Association of multi-phase rates of force development during an isometric leg press with vertical jump performances.

This study aimed to elucidate characteristics of explosive force-production capabilities represented by multi-phase rate of force developments (IRFDs) during isometric single-leg press (ISLP) through investigating relationships with countermovement (CMJ) and rebound continuous jump (RJ) performances. Two-hundred-and-thirty male athletes performed ISLP, CMJ with an arm swing (CMJAS), and RJ with an arm swing (RJAS). IRFDs were measured during ISLP using a custom-built dynamometer, while CMJAS and RJAS were measured on force platforms. The IRFDs were obtained as rates of increase in force across 50 ms in the interval from the onset to 250 ms. Jump height (JH) was obtained from CMJAS, while RJAS provided JH, contact time (CT), and reactive strength index (RSI) values. All IRFDs were correlated with CMJAS-JH (ρ = 0.20-0.45, p ≤ 0.003), RJAS-JH (ρ = 0.22-0.46, p ≤ 0.001), RJAS-RSI (ρ = 0.29-0.48, p < 0.001) and RJAS-CT (ρ = -0.29 to -0.25, p ≤ 0.025). When an influence of peak force was considered using partial rank correlation analysis, IRFDs during onset to 150 ms were correlated with CMJAS-JH (ρxy/z = 0.19-0.36, p ≤ 0.004), IRFDs during onset to 100 ms were correlated with RJAS-JH and RJAS-RSI (ρxy/z = 0.33-0.36, p < 0.001), and IRFD during onset to 50 ms was only correlated with RJAS-CT (ρxy/z = -0.23, p < 0.001). The early phase (onset to 150 ms) IRFDs measured using ISLP enabled the assessment of multiple aspects of leg-extension strength characteristics that differ from maximal strength; these insights might be useful in the assessment of the athletes' leg-extension strength capabilities.

Twelve Weeks of Progressive Resistance Training Positively Improves Physical Fitness and Golf Swing Performance in Talented Youth Golfers.

Shaw, J, Gould, ZI, Oliver, JL, and Lloyd, RS. Twelve weeks of progressive resistance training positively improves physical fitness and golf swing performance in talented youth golfers. J Strength Cond Res 38(6): 1103-1110, 2024-This aim of this study was to investigate the effects of a 12-week resistance training program in talented junior golfers. Eighteen talented youth golfers were pair matched by maturity status and handicap, and subsequently allocated to an experimental (EXP) or control group. During the 12-week intervention, both groups continued with their normal golf practice while the EXP group also completed a progressive twice-weekly resistance training program. At baseline, subjects performed multiple trials of an isometric midthigh pull (IMTP), countermovement jump (CMJ), standing long jump, golf movement screen (GMS), and isometric plank hold. Club head speed (CHS) and carry distance for a 6-iron and driver were also measured using a commercial launch monitor. When controlled for maturity offset, there were significant ( p < 0.05) interaction effects in favor of the EXP group for absolute ( g = 1.29) and relative ( g = 2.06) peak force for the IMTP, CMJ absolute ( g = 0.73) and relative ( g = 0.66) peak power, jump height ( g = 1.05), modified reactive strength index ( g = 1.30), lateral ( g = 0.48-0.88) and horizontal jump distance ( g = 1.20), and GMS total score ( g = 1.07). Significant interaction effects were also reported in 6-iron and driver CHS and carry distance in favor of the EXP group ( p < 0.05; g = 0.41-1.64). These findings indicate that twice-weekly resistance training in combination with regular golf practice can stimulate increases in measures of strength, power, and movement competency in youth golfers, which should contribute to enhanced golf swing performance.

The effect of plyometric training and moderating variables on stretch-shortening cycle function and physical qualities in female post peak height velocity volleyball players.

Purpose: Although several studies investigated the effect of plyometric training on physical performance, there is a lack of clarity regarding the effectiveness of plyometric training or its moderator variables in youth female volleyball players. The primary aim of this study was to explore the effect of horizontal plyometric training on explosive stretch-shortening cycle hops and jumps in the vertical and horizontal directions in female post peak height velocity (PHV) volleyball players. The secondary aim was to assess the influence of participant and training related moderators on horizontal plyometric training in post-PHV volleyball players. Methods: A total of 23 post-PHV volleyball players participated in this 8-week intervention with horizontal plyometric exercises, twice a week. Pre-testing and post-testing included bilateral and unilateral vertical sub-maximal hopping, horizontal jumping and hopping, and a drop jump test. The effectiveness of the intervention was assessed using a paired t-test. The influence of internal moderators such as age, maturity and body mass and external moderators such as training volume were assessed using regression and correlation analysis. Results: An 8-week plyometric training improved sub-maximal hopping at 2.5Hz left by 4.4%, bilateral sub-maximal hopping at 2.0Hz by 9.5% and bilateral sub-maximal hopping at 2.2Hz by 6.8% in post-PHV female volleyball players. Horizontal jumping and hopping, reactive strength index and other sub-maximal hopping conditions did not improve significantly. Body mass had a large moderating effect on vertical unilateral sub-maximal hopping at 2.5Hz right (p = 0.010, η 2 = 0.314), vertical unilateral hopping at 3.0Hz right (p = 0.035, η 2 = 0.170), and vertical unilateral hopping at 3.0Hz left (p = 0.043, η 2 = 0.203). Training volume together with generalized joint hypermobility moderated right leg triple broad hop performance, whereas maturity and age did not moderate any variables. Conclusion: This study determined that 8weeks of horizontal plyometric training can improve unilateral absolute leg stiffness in post-PHV female volleyball players, and this training effect can be moderated by body mass. Furthermore, the training effect on triple hopping performance on the right leg can be moderated by combined training volume with generalized joint hypermobility.

A holistic approach to performance prediction in collegiate athletics: player, team, and conference perspectives

Predictive sports data analytics can be revolutionary for sports performance. Existing literature discusses players' or teams' performance, independently or in tandem. Using Machine Learning (ML), this paper aims to holistically evaluate player-, team-, and conference (season)-level performances in Division-1 Women's basketball. The players were monitored and tested through a full competitive year. The performance was quantified at the player level using the reactive strength index modified (RSImod), at the team level by the game score (GS) metric, and finally at the conference level through Player Efficiency Rating (PER). The data includes parameters from training, subjective stress, sleep, and recovery (WHOOP straps), in-game statistics (Polar monitors), and countermovement jumps. We used data balancing techniques and an Extreme Gradient Boosting (XGB) classifier to predict RSI and GS with greater than 90% accuracy and a 0.9 F1 score. The XGB regressor predicted PER with an MSE of 0.026 and an R2 of 0.680. Ensemble of Random Forest, XGB, and correlation finds feature importance at all levels. We used Partial Dependence Plots to understand the impact of each feature on the target variable. Quantifying and predicting performance at all levels will allow coaches to monitor athlete readiness and help improve training.

Intra-Day and Inter-Day Reliability and Usefulness of Performance, Kinetic and Kinematic Variables during Drop Jumping in Hurling Players

The aim of this study was to estimate the intra-day and inter-day reliability and usefulness of performance (Jump height (JH), ground contact time (GCT) and reactive strength index (RSI)), kinetic (force, power, eccentric rate of force development [E-RFD] and leg stiffness [LS]) and kinematic (velocity) variables during drop jumping (DJ) in hurling players. Seventeen (n = 17; mean ± SD; age = 23.35 ± 5.78 years, height = 178.35 ± 6.30 cm, body mass = 78.62 ± 8.06 kg) male club-level hurling players completed two maximal DJs from 0.20, 0.30, 0.40, 0.50 and 0.60 m drop heights on three testing days separated by 5–9 days of rest. Reliability was assessed using the coefficient of variation percentage (CV% ≤ 15%) and intraclass correlation coefficient (ICC &gt; 0.70). For intra-day reliability, GCT (0.40 m, 0.50 m and 0.60 m), peak force (absolute and relative) (0.40 m and 0.50 m) and leg stiffness (0.40 m and 0.50 m) were found to be unreliable (ICC = 0.32–0.68 and CV% = 3.67–11.83%) from those specific drop heights. All other variables were found to be reliable (ICC = 0.72–0.98 and CV% = 1.07–14.02%) intra-day. All variables were found to be reliable (ICC = 0.72–0.96 and CV% = 2.57–14.68%) inter-day except for relative peak force and absolute and relative eccentric RFD (0.30 m and 0.40 m) (ICC = 0.68–0.90 and CV% = 7.76–16.47%). Practitioners have multiple reliable DJ performance, kinetic and kinematic variables for performance testing and training purposes.

Effect of Ball Inclusion in Drop Vertical Jump Test on Performance and Movement Variability in Basketball Players

The aim of this study was to assess and compare performance and movement variability (MV) in both bilateral and unilateral vertical drop jumps (DVJs) under conditions involving the incorporation or exclusion of ball catching. Twelve amateur basketball players were recruited for participation in the study (seven females and five males). Participants performed three jumps in each of the six conditions analyzed in randomized order: bilateral DVJ without (BNB) and with ball (BB); unilateral DVJ right leg without (RNB) and with ball (RB); and unilateral DVJ left leg without (LNB) and with ball (LB). MV and DVJ performance parameters were analyzed with an accelerometer and a force platform. MV was quantified using the sample entropy (sample entropy; SampEn) derived from the acceleration of the lower back. Differences between the different DVJ conditions were determined with the Wilcoxon test, with a significance level set at p &lt; 0.05. The comparisons were also assessed via standardized mean differences (Cohen’s d). No significant differences were observed in jump height, contact time and reactive strength index between conditions. However, the RB condition reported higher MV compared to RNB (effect size = 0.79; p = 0.016). Similarly, LNB showed greater MV compared to RNB (effect size = −0.62; p = 0.042). The inclusion of the ball in the DVJ increased the MV in the bilateral condition and in the right leg, but not in the unilateral condition with the left leg. The asymmetry between legs (right vs. left) in MV values in NOBALL conditions was higher (≈15%) compared to the BALL condition (≈5%).

Unimodal and bimodal curves of ground reaction force-time profiles identify the drop jump performance

ABSTRACT This study aimed to investigate the kinematics and kinetics differences in ground reaction force (GRF)-time profiles with uni- and bimodal curves (UNC and BIC) during the concentric phase of the drop jump (DJ). Twenty two male Physical Education college student who met UNC (N = 11) or BIC (N = 11) of the GRF-time profile of were recruited. Two force plates and eight infrared optical cameras were synchronised to collect the GRF and motion data during DJ from a 30-cm height. The Shapiro-Wilk test was used to assess the normality of data. The Wilcoxon test was used when data were not normally distributed. Otherwise, Independent t-tests were used to compare differences between the UNC and BIC groups for each dependent variable. The UNC group demonstrated shorter ground contact time, lower jump height, greater leg stiffness, greater peak power during the eccentric phase, less work during the eccentric and concentric phases, and greater hip and knee joint flexion and extension angle displacements (p < 0.05). No significant intergroup differences were found in reactive strength index (p > 0.05). The UNC and BIC of the GRF-time profiles can indicate whether athletes can practice DJ appropriately. UNC can be representative of a better DJ performance with an efficient stretch-shortening cycle function.

Changes in eccentric utilization ratio, reactive strength index and leg stiffness in highly trained sprinters between training phases

Purpose: To determine changes in eccentric utilization ratio (EUR), reactive strength index (RSI), squat jump (SJ) and countermovement jump (CMJ) parameters in elite sprinters from the preparation phase to the competition (indoor) phase.Methods:Ten elite-level sprinters (n=10) were examined. All sprinters performed the SJ, CMJ and 10/5 rebound jump (RJ) tests. Body composition analysis was assessed using dual X-ray absorptiometry (DXA) method. A paired t-test was performed to determine statistical significance.Results:SJ height and relative peak power increased significantly from 43.10 ± 6.1 cm to 46.30 ± 5.7 cm (P= .013, Cohen’s d= .98) and from 52.62 ± 4.5 W·kg BM-1 to 55.55 ± 4.5 W·kg BM-1 (P= .017, d= .92) respectively. CMJ height and relative peak power increased significantly from 46.78 ± 6.1 cm to 49.18 ± 5.5 cm (P= .039, d= .76) and from 55.53 ± 4.1 W·kg BM-1 to 57.92 ± 4.0 W·kg BM-1 (P= .024, d= .86) respectively. No significant differences were observed in RJ performance parameters.Conclusions:SJ and CMJ height, flight time and peak power output per body mass increased in elite sprinters from the preparation to the competition phase while RSI, EUR and leg stiffness (LS) values did not. SJ and CMJ performance can be used as markers of training phase changes in elite sprinters. EUR should be used cautiously to determine training status in elite sprinters since sprint training encompasses reactive strength training all year round. Reactive strength levels via RSI and stiffness levels should be assessed individually in each training phase to determine whether the measured value of these parameters is satisfactory to optimize competition readiness. LS levels should not be compared to general guidelines but rather individually to the athletes’ sprint performance and then training should be adjusted accordingly.

Test-Retest Reliability and Usefulness of aFoot-Ankle Rebound-Jump Test for Measuring Foot-Ankle Reactive Strength in Athletes.

This study investigated the test-retest reliability and usefulness of the foot-ankle rebound-jump test (FARJT) for measuring foot-ankle reactive strength metrics in athletes. Thirty-six highly trained, healthy athletes (5 female; 21.5 [3.9]y; 1.80 [0.10]m; 72.7 [10.4]kg) performed 8 repeated bilateral vertical foot-ankle rebound jumps on 2 testing days. Testing days were 1week apart, and these sessions were preceded by a familiarization session. Reactive strength metrics were calculated by dividing jump height (in meters) by contact time (in seconds) for the reactive strength index (RSI) and flight time (in seconds) by contact time (in seconds) for the reactive strength ratio (RSR). The mean of 4 jumps (excluding the first and last 2 jumps) on each testing session were considered for RSI and RSR reliability and usefulness analysis. We found a high reliability of the FARJT for RSI (intraclass correlation coefficient [ICC]> .90 and coefficient of variation [CV] = 12%) and RSR (ICC ≥ .90 and CV = 8%). Regarding their usefulness, both RSI and RSR were rated as "marginal" in detecting the smallest worthwhile change (typical error > smallest worthwhile change) and "good" in detecting a moderate change in performance. The results showed that a FARJT is a highly reliable test for measuring foot-ankle reactive strength in athletes and useful for quantifying changes, for example, following a training block. However, its usefulness as an accurate daily or weekly monitoring tool in practice is questionable.

Fast and Slow Jump Training Methods Induced Similar Improvements in Measures of Physical Fitness in Young Females

This study aimed to contrast the impacts of an exercise intervention using either bounce drop jump (DJ; fast stretch-shortening cycle exercise) or countermovement jump (CMJ; slow stretch-shortening cycle exercise) on measures of physical fitness in young females. A total of 23 young females (age: 19.7 ± 1.0 years, height: 159.8 ± 4.2 cm, body mass: 54.3 ± 14.3 kg) were randomly assigned to either DJ (n = 12) or CMJ (n = 11) training, which spanned 6 weeks. Pre- and posttraining assessments were conducted for 10 m and 30 m linear sprints, change-of-direction speed, CMJ, DJ (jump height, contact time, and reactive strength index), standing long jump, triple-hop distance, and isometric strength. Apart from the variance in jump technique, both interventions were standardized in terms of total repetitions, intensity, and surface type. No significant Group × Time effect was observed in any dependent variables (all p &gt; .05). A significant time effect was observed in 10 m (p &lt; .001, effect size [ES] = 0.70) and 30 m (p &lt; .001, ES = 0.79) linear sprint, CMJ height (p = .012, ES = 0.34), DJ contact time (p = .012, ES = 0.34), and triple-hop distance (p = .006, ES = 0.38). Both DJ and CMJ training interventions led to comparable improvements in linear sprints, CMJ height, DJ contact time, and triple-hop distance. These findings suggest that the duration of ground contact during intervention exercises (i.e., fast vs. slow stretch-shortening cycle) did not significantly influence initial (6 weeks) physical fitness adaptations in young females. However, extending these results to highly trained groups (e.g., athletes) warrants further investigation.

The Effects of Neuromuscular Training on Sand Versus Hard Surfaces on Physical Fitness in Young Male Tennis Players.

To examine the effects of a neuromuscular training program combining plyometric exercises with acceleration, deceleration, and change-of-direction drillsconducted on sand or hard surfaces on the fitness qualities of young male tennis players. Thirty-one young male players were allocated to a training group performing 12 training sessions on sand or hard surfaces, during a 6-week period. Tests included linear sprint (10-m acceleration with 5-m split times), change of direction (modified 5-0-5 test), vertical jumps (countermovement jump and the 10/5 repeated-jump test), isometric hip abduction and adduction strength, and dynamic balance (Y-balance test). Perceived training loads and muscle soreness were assessed during the intervention. Both training strategies were similarly effective in improving the analyzed fitness components. Group × time interaction effects were noticed, with countermovement jump (P = .032), repeated-jump test (P = .029), and reactive strength index (P = .008) favoring hardsurfaces and 5-m sprint (P = .009), dynamic balance (P < .05), adduction strength (P < .05), and abduction strength (P < .001) indices favoring sand. Furthermore, the sand group promoted greater perceived training loads and muscle soreness (P < .05) than the hard group across the intervention period. Neuromuscular training strategies characterized by a relatively low volume (∼35min), conducted on sand or hard surfaces, promoted similar improvements in the fitness qualities of young tennis players, with selected surface-interaction effects. Training on sand can cause transiently higher training loads and persistently higher muscle soreness, suggesting the need for an adequate familiarization period.

Reliability, interrelationships, and minimal detectable changes of strength and power metrics among well-trained rugby sevens players.

Despite the importance of strength and power in rugby skills and match outcomes, there exists a noticeable gap in the measurement consistency and estimation of a true change of typical assessments designed to assess these qualities. To address this gap, we investigated the between-session reliability, interrelationships, and minimal detectable changes (MDC) of commonly used strength and power measures in team sports. Sixteen national-level rugby 7 s players were tested on two occasions, one week apart. Both the best and average (of 2-3 trials) peak force, peak power, height, distance, and/or strength indices during countermovement jump (CMJ), drop jump (DJ), isometric mid-thigh pull (IMTP), plyometric push-up (PPU), and standing long jump (SLJ) were obtained. Furthermore, one-repetition maximum (1RM) strength for bench press and back squat, reactive strength index, and dynamic strength index were also determined. Reliability was assessed using intraclass correlation coefficients (ICC) and coefficients of variation (CV), and used for MDC calculations, and interrelationships between variables were determined using correlation coefficients. Reliability was excellent for bench press, back squat, and SLJ (ICCs > 0.91); high to excellent for IMTP peak force, all CMJ, and DJ (except best DJ height and contact time), and PPU peak force parameters (ICCs > 0.78), with < 10% CVs (except PPU peak power). MDCs were generally smaller for average than best values. Large to very large relationships (r = 0.60 to 0.85) were observed between bench press, back squat, and IMTP with selected parameters of CMJ and PPU (p < 0.05), but not in DJ and SLJ. In conclusion, selected measures of strength and power displayed high to excellent reproducibility, with average values (rather than best) offering more stable assessments, and "smaller" MDCs. Based upon the relationships, it can be inferred that maximising strength would likely contribute to enhanced explosive performance.

Efficacy of Plyometric Warm Up Exercises on Aerobic Capacity and Anaerobic Capacity in Palestrato Population: A Pilot Study

Introduction: Plyometric training should be a fundamental part of any plan, whether it is used for performance enhancement, strength and conditioning, or later phases of rehabilitation. Plyometric training, also known as jump-based strength training, is a popular approach to enhancing neuromuscular strength. It utilises the Stretch-Shortening Cycle (SSC) in muscle contractions. This method can improve running economy and reactive strength index, potentially enhancing aerobic performance. Aim: To observe and compare the efficacy of plyometric warm up exercises on aerobic and anaerobic capacity in palestrato population. Materials and Methods: The participants were randomly assigned to two groups using convenience sampling; plyometric warm up group (n=6): Non-plyometric warm up group (n=6), a four week warm up intervention was given to the Plyometric group. Outcome measures included push-ups, squat thrusts, abdominal curls, and a 20-meter shuttle run test. Results: The experimental group (plyometric) showed significant improvement in all four measures: 20 m shuttle run test: Pre (30.7±2.7) and post (34.6±2.8) with p=0.02. Push-up test: Pre (32.8±9.3), post (35.5±8.4) with p=0.042. Abdominal curl: Pre (31.2±8.9), post (35.3±8.3) with p=0.042. Squat thrust: Pre (12.8±4.2), post (17.5±2.1) with p=0.027. Conclusion: Strength athletes can benefit from plyometrics to increase their muscle strength and power as well as their aerobic capacity.

The Influence of Maturity Status on Drop Jump Kinetics in Male Youth

Abstract Kumar, NTA, Radnor, JM, Oliver, JL, Lloyd, RS, CSCSD, Pedley, JS, Wong, MA, and Dobbs, IJ. The influence of maturity status on drop jump kinetics in male youth. J Strength Cond Res 38(1): 38–46, 2024—The aim of this study was to examine the effects of maturity status on drop jump (DJ) kinetics in young male athletes (categorized as early-pre–peak height velocity [PHV] [&lt;−2.51 years], late-pre-PHV [−1.99 to −1.00 years], circa-PHV [−0.50 to 0.50 years], and post-PHV [&gt;1.00 years]). All athletes performed a DJ from a 30-cm box onto force plates with performance variables (jump height, ground contact time, and reactive strength index) and absolute and relative kinetic variables during the braking and propulsive phases assessed. Subjects were categorized into GOOD (no impact-peak and spring-like), MODERATE (impact-peak and spring-like), or POOR (impact-peak and not spring-like) stretch-shortening cycle (SSC) function. The post-PHV group exhibited significantly greater values for most absolute kinetic variables compared with early-pre-PHV, late-pre-PHV, and circa-PHV (p &lt; 0.05). The differences observed between consecutive maturity groups were similar in magnitude for most absolute variables (Cohen's d = 0.53–1.70). Post-PHV male athletes outperform their less mature counterparts during a DJ, and this may be attributed to the growth and maturity-related structural and motor control strategy changes that occur in children. Stretch-shortening cycle function in boys seems to improve with maturity status reflected by a greater number of post-PHV participants displaying GOOD SSC function (65.8%) and a greater number of early-pre-PHV participants displaying POOR SSC function (54.4%). However, a number of mature boys displayed POOR SSC function (17.8%), suggesting that the development of SSC function is not exclusively related to maturation.

Validity and Reliability of the Measurement of the Reactive Strength Index during One-leg Continuous Hopping Using an Inertial Measurement Unit

Validity and Reliability of the Measurement of the Reactive Strength Index during One-leg Continuous Hopping Using an Inertial Measurement Unit

Comparing the effects of akimbo and bent-in-front arm positions on jump metrics: Validity and reliability of a modified 10/5 repeated jump test

The purpose of this study was to compare the effects of two arm positions, akimbo and the newly introduced bent-in-front, on jump metrics in the ten-to-five repeated jump test (10/5 RJT) and to evaluate the reliability and validity of new modified bent-in-front variation. In contrast to akimbo, bent-in-front arm variation allows participants to use their arms freely by holding them with free hands, with parallel arms bent in front of chest and elbows pointing downward without swinging. This new arm position was designed to alleviate postural control difficulties and ensure smooth movement during repeated jumps on the force plate. However, the 10/5 RJT was designed to measure lower-body stretch–shortening cycle (SSC) performance, and it is unknown whether the bent-in-front arm variation would affect jump performance, such as arm swing. If the arms can be freed without interfering with jump performance, it would be possible to determine lower-body SSC performance without the contribution of the arms and have the advantage of postural control assistance. Fifty-five healthy sports science students who regularly participated in intercollegiate or recreational sports performed 10/5 RJT with arms akimbo and bent-in-front during two sessions. Four jump metrics, including the reactive strength index, and four reliability and validity statistics, including intraclass-correlation-coefficients, were estimated. The results indicated no significant differences in the jump metrics between two arm variations. Bent-in-front arm variation can be deemed as a valid and reliable test. Therefore, the newly introduced 10/5 RJT with arms bent-in-front can be used to evaluate SSC performance in this cohort.

Examination of Differences in Leg Stiffness and Reactive Strength Index an Ski Athletes

Bu araştırma, elit düzeydeki kayakçılarda, bacak sertliği ve reaktif kuvvet indeksi (RKİ) arasındaki farklılıklarının incelenmesi amacıyla yapıldı. Araştırmaya yaş ortalaması (18,55±2,86 yıl) boy ortalamaları (172,10±6,05 cm), vücut ağırlığı ortalamaları (65,73±10,79) olmak üzere 5 farklı branşta toplam 40 erkek kayak sporcusu katıldı. Bacak sertliği ölçümü için gerekli veriler Opto Jump protokolleri üzerinden alındı. Bacak sertliği Dalleau G, ve arkadaşlarının oluşturduğu bir eşitlik ile hesaplandı. Reaktif kuvvet indeksi 40 cm standart derinlik sıçrama üzerinden alındı. Değişkenler arasındaki ilişkilerin analizinde pearson momentler çarpımı korelasyon katsayısı uygulandı. Reaktif kuvvet ile bacak sertliği değişkenlerine incelendiğinde; alp disiplini branşında (r=0,801) yüksek, snowboard branşında (r=0,636) orta, biathlon branşında negatif yönde (r=-0,402) zayıf, kayaklı koşu branşında negatif yönde (r=-0,306) düşük, kayakla atlama branşında pozitif yönde (r=0,261) zayıf ilişki tespit edildi (p= 0,001). Diğer branşlar arasında bacak sertliği ve reaktif kuvvet indeksi değişkenleri arasında anlamlı ilişki görülmemiştir. Bu araştırmanın bulguları ile biathlon, kayakla atlama ve kayaklı koşu branşı sporcularında temel güç antrenmanlarını artırarak yüksek kas katılığını üretebileceği ve yüksek katılığı sürdürmede ise patlayıcı egzersizlerin önemli bir faktör olduğu düşünülmektedir. Bunlarla birlikte kas katılığı ile hız, ani yön değiştirme ve reaktif hız performansları arasında ilişki olduğu düşünülmektedir.

The Countermovement Rebound Jump: Between-Session Reliability and a Comparison With the Countermovement and Drop Jump Tests.

Xu, J, Turner, A, Comyns, TM, Chavda, S, and Bishop, C. The countermovement rebound jump: Between-session reliability and a comparison with the countermovement and drop jump tests. J Strength Cond Res 38(4): e150-e159, 2024-The countermovement jump (CMJ) and drop jump (DJ) are widely used jump tests to evaluate an athlete's neuromuscular performance. Nevertheless, conducting both the CMJ and the DJ assessments during one testing session can demand a considerable time investment that practitioners or coaches might not always have available. This study investigated whether the countermovement rebound jump (CMRJ) could be considered a viable alternative to the CMJ and DJ tests, respectively. Thirty-three physically active students volunteered as subjects (age: 27.2 ± 5.9 years, height: 1.78 ± 0.8 cm, body mass: 77.5 ± 11.5 kg), with 18 jumps completed for each subject across 2 testing sessions. The jump height (JH) and strategy-based metrics (time to take-off [TTTO], countermovement depth [CM depth], and reactive strength index [RSI] modified for CMJ and the first jump of the CMRJ; leg stiffness [ Kleg ], ground contact time [GCT], and RSI for DJ and the second jump for the CMRJ) were calculated simultaneously via the impulse-momentum, flight time, double integration, and motion capture methods. All variables were examined by repeated-measures analysis of variance, 2-way random effects model intraclass correlation coefficient (ICC), coefficient of variation (CV), and standard error of measurement, with the significance set at p ≤ 0.05. All 3 jump tests showed good-to-excellent relative reliability (ICC = 0.79-0.98) and good-to-moderate CV (≤9.83), with the only exception being Kleg measured during the DJ and in the second jump of the CMRJ assessment (CV ≤ 16.01%). Of all measured metrics, significant differences were only observed regarding TTTO between jumps ( p ≤ 0.027, effect size [ES] ≤ 0.49). The comparison of calculation methods indicated that the JH calculated by 4 methods were not significantly different between jump actions ( p ≥ 0.254). These findings support the use of the CMRJ as a reliable alternative to the CMJ and DJ tests. However, practitioners should be mindful of using Kleg as a metric, whereas practitioners are also advised to allocate sufficient familiarization trials before implementing the CMRJ into their routine test batteries.

Application of a New Monitoring Variable: Effects of Power Loss During Squat Training on Strength Gains and Sports Performance.

Zhang, M, Chen, L, Dai, J, Yang, Q, Huang, Z, He, J, Ji, H, Sun, J, and Li, D. Application of a new monitoring variable: Effects of power loss during squat training on strength gains and sports performance. J Strength Cond Res 38(4): 656-670, 2024-This study aimed to compare the effects of power loss (PL) autoregulated volume (PL10 and PL20) with standardized fixed-load (FL) prescription on strength, sports performance, and lean body mass (LBM). Thirty-five female basketball players from a sports college were randomly assigned to 3 experimental groups (PL10, n = 12; PL20, n = 12; and FL, n = 11, respectively) that performed a resistance training (RT) program with wave-like periodization for 10 weeks using the back squat exercise. Assessments performed before (Pre) and after (Post) intervention included assessed 1 repetition maximum (1RM), body composition, 20-m sprint (T20M), change of direction (COD), and jump performance, including countermovement jump with arm swing, maximum vertical jump, and reactive strength index. Three groups showed significant improvements in strength (effect size [ES]: PL10 = 2.98, PL20 = 3.14, and FL = 1.90; p < 0.001) and jump performance (ES: PL10 = 0.74, PL20 = 1.50, and FL = 0.50; p <0.05-0.001). However, PL10 and PL20 demonstrated different advantages in sports performance compared with FL (group × time interaction, p <0.05). Specifically, PL10 significantly improved COD performance (ES = -0.79 ∼ -0.53, p <0.01), whereas PL20 showed greater improvements in sprint (ES = -0.57, p <0.05) and jump performance (ES = 0.67-1.64, p <0.01-0.001). Moreover, PL10 resulted in similar gains to PL20 and beneficial improvements compared with FL in LBM, despite performing the least repetitions. Overall, the study indicates that power loss-based autoregulation induces greater gains in LBM and sports performance, as well as eliciting a higher efficiency dose response than standardized FL prescriptions, particularly for PL10. Therefore, incorporating PL monitoring in training programs is recommended, and further studies on power-based RT would be worthwhile.

Vertical Jump Neuromuscular Performance Characteristics Determining On-Court Contribution in Male and Female NCAA Division 1 Basketball Players.

While various quantifiable physical attributes have been found to contribute to athletes' performance, there is a lack of scientific literature focused on examining how they relate to success during competition performance. The aim of this study was to investigate different countermovement jump (CMJ)-derived force-time characteristics and their utility in distinguishing high from low performers within a measure of on-court contribution (i.e., minutes per game played). Twenty-nine collegiate athletes (n = 15 males and n = 14 females) volunteered to participate in this investigation and performed CMJs on dual force plates sampling at 1000 Hz, weekly over the course of their basketball season. The athletes' average of their three best test-days across the season was used for further analysis. To identify their on-court contribution, athletes were divided into groups with high and low minutes per game, based on a median-split analysis. The findings suggest that at the overall group level (i.e., both genders), the modified reactive strength index (mRSI) and braking rate of force development (RFD) revealed the greatest between-group magnitudes of difference, with athletes playing more minutes per game showing greater performance. At the team-specific level, the braking RFD, average braking velocity, and mRSI were shown to be the greatest differentiators between groups for the men's team. The women's high-minutes group displayed greater magnitudes of mRSI and jump height. By identifying the neuromuscular qualities seen in top performers within their respective populations, the attributed physical performance underpinning these qualities may be identified, providing practitioners with insights into physical performance qualities and training methodologies that have the potential to influence basketball performance.