Lower-limb damping characteristics during various repetitive jumping forms: Reliability and sensitivity analysis.

Understanding the reliability of jump testing is essential to determine the neuromuscular progress of athletes and make informed decisions. This study aimed to assess the reliability of several countermovement jump (CMJ) and drop jump (DJ) test metrics in female volleyball players. Sixteen (n = 16) semi-professional female volleyball players participated in this test-retest study. Intrasession and intersession reliability of CMJ and DJ metrics were evaluated using a randomized cross-over design. A dual force platform was used to collect CMJ and DJ data, and several dependent variables were calculated using forward dynamics. Intraclass correlation coefficients (ICC), coefficients of variation (CV), and minimum difference (MD) were calculated to assess intra- and interday reliability. During the same testing, the third attempt consistently yielded the highest values for both tests in jump height but presented excellent reliability (CMJ: ICC [95%CI] = 0.97 [0.93–0.99]; CV [95%CI] = 4.1% [1.2–7.0]; MD95 = 3.5 cm; MD90 = 2.9 cm; DJ: ICC [95%CI] = 0.91 [0.77–0.97]; CV [95%CI] = 6.7% [1.9–11.5]; MD95 = 6.0 cm; MD90 = 5.0 cm). CMJ height exhibited excellent reliability between sessions (ICC [95%CI] = 0.93 [0.81–0.97]; CV [95%CI] = 3.8% [1.1–6.4]; MD95 = 3.5 cm; MD90 = 3.0 cm), whereas DJ height demonstrated slightly lower but still acceptable intersession reliability (ICC [95%CI] = 0.81 [0.55–0.93]; CV [95%CI] = 6.1% [1.7–10.4]; MD95 = 5.2 cm; MD90 = 4.4 cm). Intersession reliability for CMJ kinetics and kinematics was excellent for 13 of the 24 metrics assessed. For DJ, only concentric (ICC [95%CI] = 0.91 [0.76–0.97]; CV [95%CI] = 3.0% [0.9–5.2]; MD95 = 15 Ns; MD90 = 12.6 Ns) and eccentric impulses (ICC [95%CI] = 0.99 [0.96–0.99]; CV [95%CI] = 1.7% [0.5–2.9]; MD95 = 9.2 Ns; MD90 = 7.7 Ns) demonstrated excellent intersession reliability. Most CMJ variables showed excellent reliability within sessions, while DJ had lower reliability in most metrics. These findings provide valuable information to physical trainers to select the metrics to assess athletes’ performance as well as to identify a minimum cut-off value that serves as a reference for each of the metrics reported in both tests.

Heishman, AD, Daub, BD, Miller, RM, Freitas, EDS, Frantz, BA, and Bemben, MG. Countermovement jump reliability performed with and without an arm swing in NCAA Division 1 intercollegiate basketball players. J Strength Cond Res 34(2): 546-558, 2020-The countermovement jump (CMJ) is routinely used in athlete performance to quantify adaptions to training, as well as monitor neuromuscular readiness and fatigue. However, controversy remains in whether to incorporate an arm swing during the CMJ (CMJ AS) or keep the hands placed on the hips (CMJ NAS). Incorporating the arms provides a higher degree of sport-specificity that may yield improved reliability, especially in skilled jumpers. By contrast, the hands-on-hips approach isolates lower extremity force production and eliminates potential arm-swing variation. Therefore, the purpose of this study was to establish the reliability of CMJ typical (CMJ-TYP), CMJ concentric alternative (CMJ-Conc-ALT), and CMJ eccentric alternative (CMJ-Ecc-ALT) variables obtained during the CMJ AS and CMJ NAS. Twenty-two (men = 14, women = 8) NCAA Division 1 collegiate basketball players performed 3 CMJ AS and 3 CMJ NAS on a force plate, in a randomized order. To assess the test-retest reliability, participants returned 1 week later to perform 3 additional CMJ AS and 3 CMJ NAS. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were used to assess intersession and intrasession reliability for the various CMJ variables. A majority of CMJ-TYP and several CMJ-Conc-ALT and CMJ-Ecc-ALT variables exhibited adequate intersession and intrasession reliability (ICC > 0.700 and CV <10%) during both the CMJ AS and the CMJ NAS. Countermovement jump AS may provide more pertinent information about long-term changes in sport-specific performance, whereas the CMJ NAS may be more beneficial for detecting acute changes in neuromuscular fatigue and athlete readiness.

PURPOSE: To investigate the differences in joint mechanics between adolescent and adult males performing countermovement and drop jump tasks. METHODS: Eleven adolescent basketball players (age: 16.5 ± 0.7 years; height: 1.78 ± 0.07 m; mass: 68.9 ± 8.8 kg) and eleven resistance-trained adults (age: 22.3 ± 1.9 years; height: 1.80 ± 0.10 m; mass: 84.3 ± 9.3 kg) performed two trials of a countermovement jump (CMJ) and a drop jump from a height of 0.40 m (DJ). Force plates (1000 Hz) and an 8-camera 3-D motion analysis system (200 Hz) were used to determine the following kinetic variables for the hip, knee, and ankle joints during the propulsive phase of each jump: normalized work performed by the moment (JWNORM), normalized power output of the moment (JPONORM), and normalized joint stiffness (JSNORM). RESULTS: The adults produced significantly greater JWNORM across the two jumps (mean difference [MD]: 0.32 J/kg, p=0.014). JWNORM at the knee was greater than that at the hip (MD: 2.09 J/kg, p<0.001) and the ankle (MD: 2.61 J/kg, p<0.001), while JWNORM was greater at the hip compared to the ankle (MD: 0.52 J/kg, p=0.001). The adults performed greater JWNORM at the hip compared to the adolescents (MD: 0.75 J/kg, p=0.005). JPONORM at the knee was greater than that at the hip (MD: 4.49 W/kg, p<0.001) and ankle (MD: 4.32 W/kg, p<0.001) across the two jumps while JPONORM was significantly greater in DJ compared to CMJ (MD: 0.49 W/kg, p=0.10). The adolescents produced significantly greater JPONORM at the ankle compared to the adults (MD: 1.35 W/k, p=0.002). The adolescents produced significantly greater JSNORM compared to the adults (MD: 0.021 Nm/kg/deg, p<0.001). Both groups produced significantly greater JSNORM in DJ compared to CMJ (MD: 0.015 Nm/kg/deg, p=0.001) with significant increases in JSNORM at the knee joint from CMJ to DJ (MD: 0.02 Nm/kg/deg, p<0.001). The increase in JSNORM at the hip (MD: 0.025 Nm/kg/deg, p=0.033) and knee (MD: 0.023 Nm/kg/deg, p=0.046) between CMJ and DJ was significantly greater in adolescents compared to adults. CONCLUSION: Adolescent males produce different joint mechanics compared to adults during jumping tasks and rely on a strategy of increasing joint stiffness at the hip and knee joints when performing DJ. These differences may have implications for musculoskeletal injuries in adolescent males.

The purpose of the present study was to establish the intrasession and intersession reliability of variables obtained from a force plate that was used to quantitate lower extremity inter-limb asymmetry during the bilateral countermovement jump (CMJ). Secondarily, a comparison was performed to determine the influence of the jump protocol CMJ with or without an arm swing (CMJ AS and CMJ NAS, respectively) on inter-limb asymmetries. Twenty-two collegiate basketball players performed three CMJ AS and three CMJ NAS on dual force platforms during two separate testing sessions. A majority of variables met the acceptable criterion of intersession and intrasession relative reliability (ICC > 0.700), while fewer than half met standards established for absolute reliability (CV < 10%). CMJ protocol appeared to influence asymmetries; Concentric Impulse-100 ms, Eccentric Braking Rate of Force Development, Eccentric Deceleration, and Force at Zero velocity were significantly different between jumping conditions (CMJAS versus CMJ NAS; p < 0.05). The present data establish the reliability and smallest worthwhile change of inter-limb asymmetries during the CMJ, while also identifying the influence of CMJ protocol on inter-limb asymmetries, which can be useful to practitioners and clinicians in order to effectively monitor changes associated with performance, injury risk, and return-to-play strategies.

This study assessed the intra- and inter-session reliability of the inertial measurement unit (IMU) in measuring countermovement jump (CMJ) and 10m-walking gait-related outcomes. Thirty collegiate-level athletes (15 males [age: 21.0 ± 2.5 years] and 15 females [age: 21.5 ± 2.1 years]) were recruited to perform CMJs and 10m-walking test that were simultaneously recorded using the commercially available body-worn IMU – BTS G-walk. The coefficient of variation (CV), the analysis of variance with repeated measures (ANOVA), and the interclass correlation coefficient (ICC) were used for intra-session reliability. While the Pearson’s correlation coefficient (r) and the ICC were used to analyze inter-session reliability. Measurement of CMJ and 10m-walking test gait variables using the IMU resulted in moderate to excellent intra-session reliability for CMJ (ICC = 0.881 to 0.988) and gait analysis (ICC = 0.807 to 0.978) with acceptable CV (≤10%). Inter-session reliability for CMJ variables ranged from poor to excellent (ICC = 0.134 to 0.963), and 10-m walking test gait analysis variables were moderate to excellent (ICC = 0.683 to 0.931). The IMU (BTS G-walk) provides reliable data for most CMJ and gait variables. Future studies may determine the accuracy of the equipment to monitor changes over time (e.g., after a training intervention).

Prediction of lower limb joint stiffness and optimization of anthropometric parameters in countermovement jump using an anthropometry-informed neural network.

Gallardo-Fuentes, F, Gallardo-Fuentes, J, Ramírez-Campillo, R, Balsalobre-Fernández, C, Martínez, C, Caniuqueo, A, Cañas, R, Banzer, W, Loturco, I, Nakamura, FY, and Izquierdo, M. Intersession and intrasession reliability and validity of the My Jump app for measuring different jump actions in trained male and female athletes. J Strength Cond Res 30(7): 2049-2056, 2016-The purpose of this study was to analyze the concurrent validity and reliability of the iPhone app named My Jump for measuring jump height in 40-cm drop jumps (DJs), countermovement jumps (CMJs), and squat jumps (SJs). To do this, 21 male and female athletes (age, 22.1 ± 3.6 years) completed 5 maximal DJs, CMJs, and SJs on 2 separate days, which were evaluated using a contact platform and the app My Jump, developed to calculate jump height from flight time using the high-speed video recording facility on the iPhone. A total of 630 jumps were compared using the intraclass correlation coefficient (ICC), Bland-Altman plots, Pearson's product moment correlation coefficient (r), Cronbach's alpha (α), and coefficient of variation (CV). There was almost perfect agreement between the measurement instruments for all jump height values (ICC = 0.97-0.99), with no differences between the instruments (p > 0.05; mean difference of 0.2 cm). Almost perfect correlation was observed between the measurement instruments for SJs, CMJs, and DJs (r = 0.96-0.99). My Jump showed very good within-subject reliability (α = 0.94-0.99; CV = 3.8-7.6) and interday reliability (r = 0.86-0.95) for SJs, CMJs, and DJs in all subjects. Therefore, the iPhone app named My Jump provides reliable intersession and intrasession data, as well as valid measurements for maximal jump height during fast (i.e., DJs) and slow (i.e., CMJs) stretch-shortening cycle muscle actions, and during concentric-only explosive muscle actions (i.e., SJs), in both male and female athletes in comparison with a professional contact platform.

A simple method for evaluating force (F), velocity (V) and power (P) output during a squat jump (SJ) was validated by Samozino et al. (2008, J Biomech, 41: 2940–5), who...

To compare the effects of unilateral and bilateral resistance training on single-leg power output, between-limbs imbalance (BLI), bilateral deficit (BLD), change of direction (COD), and linear sprinting and jumping performance in young elite basketball players. Twenty-two young (U-16-U-19) male basketball players were randomly assigned either to an exclusive unilateral (UNI) (n = 11) or a bilateral (BIL) (n = 11) resistance-training group during a 6-wk period. Both groups training consisted of 3 unilateral or bilateral 90° back-squat sets. A postdetermined number of repetitions was set until power output dropped to <10% of maximum power (MP) output. In addition, both groups performed 2 sets of 5 unilateral or bilateral drop jumps and 2 sets of 5 unilateral or bilateral countermovement jumps (CMJ). Pre- and posttraining, performance was assessed by an incremental bilateral and unilateral squat-load test, a multiple-COD test (V-cut test), a 15-m-sprint test (7.5 + 7.5 m) with one 180° COD performed with both right (180° RCOD) and left (180° LCOD) legs, a 25-m-sprint test (5- and 15-m split time), and a CMJ test. Within-group analyses showed substantial improvements in 180° RCOD, bilateral and unilateral MP, 25-m-sprint test, and CMJ in both groups. Between-groups analyses showed substantially better results in 180° LCOD, MP with right and left legs, BLI, and BLD in UNI than in BIL. Both training programs substantially improved most of the physical-fitness tests, but only UNI reduced between-limbs asymmetry and achieved greater enhancements in actions that mostly required applying force unilaterally in basketball players.

Carroll, KM, Wagle, JP, Sole, CJ, and Stone, MH. Intrasession and intersession reliability of countermovement jump testing in Division-I volleyball athletes. J Strength Cond Res 33(11): 2932-2935, 2019-The countermovement jump (CMJ) is a reliable and noninvasive test of lower-body neuromuscular performance. Many of the investigations used to establish the reliability of CMJ have been conducted in a controlled environment (i.e., laboratory setting). To better inform coaches, reliability of key CMJ variables should be examined in a practical environment. This study assessed intrasession and intersession reliability of CMJ variables in NCAA D-I volleyball athletes. Eleven female volleyball players (age = 19.8 ± 0.8 years, height = 1.75 ± 0.07 m, body mass = 71.6 ± 8.9 kg) performed twice weekly CMJ testing on force platforms across 14 weeks of training. Dependent variables were CMJ height (CMJH), reactive strength index modified (RSIMOD), relative peak power (rPP), and countermovement depth (CM depth). Intraclass correlation coefficients (ICCs), coefficient of variation (CV), and typical error (TE) were calculated, along with Pearson correlation coefficients. Intrasession reliability revealed excellent reliability values for CMJH (ICC = 0.94, CV = 2.9 ± 2.4%, TE = 1.25) and RSIMOD (ICC = 0.93, CV = 4.7 ± 4.9, TE = 0.03). Good reliability values were observed for rPP (ICC = 0.79, CV = 6.1 ± 10.9%, TE = 4.48), with only moderate reliability for CM depth (ICC = 0.61, CV = 7.1 ± 10.9%, TE = 16.9). Intersession reliability indicated excellent reliability for CMJH (ICC = 0.92, CV = 3.2 ± 2.8%, TE = 1.4) and RSIMOD (ICC = 0.92, CV = 5.4 ± 4.3%, TE = 0.03). However, poor reliability was observed for rPP (ICC = 0.41, CV = 10.4 ± 15.4%, TE = 7.95) and CM depth (ICC = 0.39, CV = 7.7 ± 10.8%, TE = 6.42). These results suggest that in the context of weekly athlete monitoring, measures such as CMJH and RSIMOD exhibit the greatest reliability. Conversely, measures such as CM depth and rPP exhibit high levels of variability. Practitioners seeking to track jump performance over time should be cognizant of CM depth variability and its potential impact on CMJ variables.

Dynamic knee valgus is linked to reduced hip abduction strength, a critical factor in knee stability during unilateral movements. While interventions to reduce dynamic knee valgus often use traditional hip abduction training, many neglect the eccentric function of hip abductors, essential for controlling femoral medial translation. This pilot study compared the effects of a four-week-long eccentric vs. concentric hip abduction training on hip abduction torque, countermovement jump performance, dynamic knee valgus measured during one-legged jumping and drop landing, and determined if reductions in dynamic knee valgus correlated with increases in hip abduction torque and countermovement jump performance. Asymptomatic, physically active female college students (n = 20, 21.3 ± 2.51 years) with dynamic knee valgus were randomized to either eccentric or concentric hip abduction strength training. Testing included maximum hip abduction torque on an isokinetic dynamometer, single-leg countermovement jumps, and single-leg drop landings analyzed with 3D motion tracking. Participants trained three times per week for four weeks, performing four sets of 10 maximal effort repetitions. The two groups did not differ at baseline in any outcomes (all p > 0.05). Eccentric hip abduction torque improved over time (F = 39.7, p < 0.001) without a group-by-time interaction. Dynamic knee valgus decreased during single-leg countermovement jumps (time main effect: F = 33.5, p < 0.05) and single-leg drop landings (time main effect: F = 14.8, p < 0.05). The reductions in dynamic knee valgus, measured during single-leg countermovement jumps, were greater (p < 0.05) after eccentric vs. concentric training (group by time interaction: F = 5.57, p < 0.05). Countermovement jump improved similarly in the two groups (time main effect: F = 5.1, p < 0.05), without group by time interaction. Improvements in hip abduction maximal torque and countermovement jump performance, and changes in dynamic knee valgus outcomes did not correlate (p > 0.05). High-intensity eccentric versus concentric hip abductor strength training was superior in dynamic knee valgus improvement measured during single-leg countermovement jump but not during drop landings in asymptomatic young women, while both training modalities improved single leg countermovement jump performance.

OpenCap is a web-based markerless motion capture platform that estimates 3D kinematics from videos recorded from at least two iOS devices. This study aimed to determine the concurrent validity and inter-session reliability of OpenCap for measuring trunk and lower-limb kinematics during squatting, hopping, countermovement jumping, and cutting. Nineteen participants (10 males, 9 females; age 27.7 ± 4.1 years) were included. Countermovement jump, single-leg triple vertical hop, single-leg squat, sidestep cutting and side hop tasks were assessed. For validity, OpenCap was compared to a marker-based motion capture system using root-mean-square error. Test–retest reliability of OpenCap was determined using intraclass correlations and minimum detectable change (MDC) from two testing sessions. The squat had the lowest RMSE across joint angles (mean = 7.0°, range = 2.9° to 13.6°). For peak angles, the countermovement jump (jump phase) (ICC = 0.62–0.93) and the squat (ICC = 0.60–0.92) had the best reliability across all joints. For initial contact, the side hop had the best inter-session reliability (ICC = 0.70–0.94) across all joint angles. As such, OpenCap validity and reliability are joint and task specific.

Vertical stiffness has been highlighted as a potential determinant of performance and may be estimated across a range of different performance tasks. The aim of the current study was to investigate the relationship between vertical stiffness determined during 9 different hopping tests and performance of vertical jumps. Twenty healthy, active males performed vertical hopping tests with three different strategies (self-selected, maximal, and controlled) and three different limb configurations (bilateral, unilateral preferred, and unilateral non-preferred), resulting in nine different variations, during which vertical stiffness was determined. In addition, participants performed squat jump (SQJ) and countermovement jump (CMJ) during which jump height, CMJ stiffness, and eccentric utilization ratio (EUR) were determined. Vertical stiffness in bilateral and unilateral preferred tasks performed with a self-selected and maximal, but not controlled, strategy was associated with stiffness in the CMJ (r = 0.61–0.64; p < 0.05). However, stiffness obtained during unilateral preferred and non-preferred hopping with self-selected strategy was negatively associated with performance in SQJ and CMJ tasks (r = −0.50 to −0.57; p < 0.05). These findings suggest that high levels of vertical stiffness may be disadvantageous to static vertical jumping performance. In addition, unilateral hopping with a self-selected strategy may be the most appropriate task variation if seeking to determine relationships with vertical jumping performance. Highlights Stiffness obtained during unilateral hopping with a preferred strategy was negatively associated with vertical jumping performances Stiffness obtained during hopping with preferred and maximal strategies was associated with stiffness obtained during a countermovement jump In this population, hopping stiffness may therefore be reflective of an individual's countermovement jump strategy High levels of stiffness may be disadvantageous to static-start vertical jumping

Forefoot and toes are prominent regions for locomotion and individual metatarsophalangeal joint (MTPJ) stiffness may be linked to jump take-off mechanics and performances. However, little is known about the relationships between MTPJ stiffness and take-off related variables. This study examined the relationship between individual MTPJ stiffness and biomechanical variables under various vertical countermovement jumps (CMJ) conditions. We measured MTPJ stiffness on 21 male university basketball players and then asked them to perform jumps under single, consecutive and running CMJ conditions. Pearson’s correlation coefficient was employed to examine the relationships between MTP passive stiffness and each jumping performance, ground reaction force (GRF) and joint kinematic and kinetic variables. The results indicated that MTPJ stiffness significantly correlated with maximum jump height (r = 0.49, moderate), peak take-off velocity (r = 0.47, moderate), peak take-off ankle plantarflexion moment (r = 0.68, strong), peak dorsiflexion moment (r = 0.60, strong) and peak take-off ankle power (r = 0.44, moderate) in consecutive CMJ. Only a moderate correlation between MTPJ stiffness and peak MTPJ extension take-off velocity (r = −0.46, moderate) was determined in a single CMJ. There were no significant correlations found in running CMJ conditions. These findings imply that higher MTPJ stiffness of participants was related to improved jump performances in consecutive jumps.

Background: The incidence rate of elbow injuries has been rising in recent years among professional baseball pitchers. Determining valid screening procedures that allow practitioners to identify pitchers at an increased risk of such injuries is therefore of critical importance. Purpose: To validate the use of countermovement jump (CMJ) tests as a diagnostic tool for pitcher conditioning. Study Design: Case-control study; Level of evidence, 3. Methods: More than 500 pitchers at a single professional baseball organization performed preseason CMJ assessments on a force plate before the 2013 to 2018 seasons. Three measurements were extracted from ground-reaction force data during the test: eccentric rate of force development (ERFD), average vertical concentric force (AVCF), and concentric vertical impulse (CVI). Athletic trainers at the organization collected detailed information on elbow and shoulder injury rates as well as workload (pitch count) throughout the rest of the season. Poisson regression models were fit to investigate the dependency of injury rates on CMJ test performance. Results: ERFD, CVI, and AVCF were all significant predictors of elbow injury risk after accounting for pitcher age, weight, and workload. The analysis identified 3 specific indicators of heightened risk based on the results of a CMJ scan: low ERFD, a combination of low AVCF and high CVI, and a combination of high AVCF and low CVI. In contrast, shoulder injury risk was roughly independent of all 3 CMJ test measurements. Conclusion: This study supports the hypothesis of the entire kinetic chain’s involvement in pitching by establishing a link between CMJ test performance and elbow injury risk in professional baseball pitchers. CMJ assessment may be a powerful addition to injury risk alert and prevention protocols. Pitchers in high-risk groups can be prescribed specific exercise plans to improve movement imbalances.