Control strategy of maximum vertical jumps: The preferred countermovement depth may not be fully optimized for jump height

Effect of Countermovement Depth on the Neuromechanics of a Vertical Jump

The purpose of this study was to examine kinematic, kinetic, and muscle activation metrics during countermovement jumps (CMJs) with varying countermovement depths. The hypothesis was that a shallow countermovement depth would compromise jump height by disrupting neuromechanical control. Ten healthy men (age 26 ± 8 yr, height 1.81 ± 0.08 m, mass 83.5 ± 9.0 kg) performed maximal CMJs at self-selected countermovement depth (self-selected CMJ), at reduced countermovement depth (shallow CMJ), and at increased countermovement depth (deep CMJ). Three jumps were performed in each condition on force plates with ankle, knee, and hip motion recorded and electromyograms (EMG) recorded from the gluteus maximus (GM), vastus lateralis (VL), and medial gastrocnemius (MG) muscles. During CMJs, the knee flexion angle was recorded with an electrogoniometer. Jumpers were instructed to flex at least 15% less (shallow CMJ) and at least 15% more (deep CMJ) than the self-selected CMJs. Kinematic, kinetic, and EMG metrics were compared between the different CMJ depths using repeated measures ANOVA. Compared with self-selected CMJs, shallow CMJs had 26% less countermovement depth (P < 0.001, effect size 1.74) and the deep CMJs had 28% greater countermovement depth (P < 0.001, effect size 1.56). Jump height was 8% less for the shallow vs. self-selected CMJs (P = 0.007, effect size 1.09) but not different between self-selected and deep CMJs (P = 0.254). Shallow CMJs differed from self-selected CMJs at the initiation of the countermovement (unweighting). For self-selected CMJs, force dropped to 43% of body weight during unweighting but only to 58% for shallow CMJs (P = 0.015, effect size 0.95). During unweighting, VL EMG averaged 5.5% of MVC during self-selected CMJs versus 8.1% for shallow CMJs (P = 0.014, effect size 0.97). Percent decline in jump height with shallow versus self-selected CMJs was correlated with the difference in VL EMG during unweighting between shallow and self-selected CMJs (r = 0.651, P = 0.041). A deep countermovement prolonged the time to execute the jump by 38% (P < 0.010, effect size 1.04) but did not impair CMJ force metrics. In conclusion, self-selected countermovement depth represents a tradeoff between dropping the center of mass sufficiently far and executing the jump quickly. Unweighting at the initiation of a CMJ appears to be a critical element in the neuromechanics of the CMJ.

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

ABSTRACT

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.

Verbal instructions affect reactive strength index modified and time-series waveforms in basketball players

This study aimed to determine the effects of different verbal instructions, intended to affect the countermovement jump (CMJ) execution time, on the reactive strength index modified (RSIMod) and the time-series waveforms. Thirteen male basketball players performed six CMJs on a force plate with two different verbal instructions: 'jump as high as possible' (CMJhigh) and 'jump as high and as fast as possible' (CMJfast). Force-, power-, velocity-, and displacement-series waveforms, RSIMod and jump height were compared between conditions using statistical parametric mapping procedures. CMJfast showed greater values in RSIMod (p = 0.002) despite no differences in jump height (p = 0.345). Unweighting force (between 18% and 33% of total time) was lower in the CMJfast compared to CMJhigh. Larger force (between 53% and 63% of total time), velocity (between 31% and 48% of total time) and power (between 43% and 56% of total time) were found in the CMJfast compared to CMJhigh. These findings suggest that commanding athletes to jump as high and fast as possible increases rapid force production. Additionally, the results highlight the relevance of the countermovement phase in jumping and show that RSIMod could increase without power output modifications during propulsion, despite previous studies having reported positive associations between RSIMod propulsion power.

Predicting Time to Take-Off in a Countermovement Jump for Maximal Quickness From Upright and Squat Starting Positions

A countermovement jump (CMJ) is common in sport and often time-constrained. Little is known about contributors to quickness in jumps. This study examined effective predictors of time to take-off and effects of the starting position on reaction time and take-off time in a countermovement jump performed for quickness from upright and squat positions. Forty-nine collegiate athletes performed CMJs for quickness from upright and squatting starting positions to 75% of their maximal jump height. Several variables were calculated from the kinetic data related to jump performance. Correlation and multiple regression were used to determine variables related and predictive of time to take-off under both conditions. Paired t-tests evaluated differences in reaction and take-off times between conditions. In the upright condition, an increasing rate of force development and force, and decreasing time variables, impulses, and countermovement depth were associated with shorter time to take-off. The time to take-off prediction included rates of force development, force, time, and impulse. In the squat condition, shorter time to take-off was associated with lesser time variables, eccentric impulse, force at the end of the eccentric phase, and countermovement depth, and a greater rate of force development, concentric impulse, peak power, peak force, and reaction time. The time to take-off prediction equation included time to the bottom of the countermovement, time to peak force, and peak power. Reaction and take-off times were longer in the upright condition. Quick jump efficiency may be improved by strategies to increase maximum strength and the eccentric rate of force development while decreasing countermovement depth and time to bottom.

Kinetic and Kinematic Analyses of Countermovement Jump in a Small Sample of Individuals with Congenital Vision Loss

In the present study, we aimed to explore whether countermovement jumps (CMJs) performed by young adults with and without visual impairment (VI) differ. We compared three participants with congenital VI to 10 participants without congenital VI when both groups performed CMJs with maximum effort. Although the maximum jump height did not differ between groups, all three participants with VI showed such reduced maximum downward velocity of the center of body mass and a relative net negative vertical impulse that, on these measures, they fell beyond two standard deviations from the mean scores of participants without VI. The range of motion for the leg joints and countermovement depth did not differ between groups. Although findings from our small sample should be cross-validated and trainers should take care to protect athletes from falls, it appears from our preliminary data that a path to improved CMJ performance for athletes with VI is to increase their movement velocity in the countermovement phase of the jump.

Are the Parameters of Novel Two-Point Force-Velocity Model Generalizable in Leg Muscles?

The two-point force-velocity model allows the assessment of the muscle mechanical capacities in fast, almost fatigue-free conditions. The aim of this study was to investigate the concurrent validity of the two-point parameters with directly measured force and power and to examine the generalization of the two-point parameters across the different functional movement tests of leg muscles. Twelve physically active participants were tested performing three functional lower limb maximal tests under two different magnitudes of loads: countermovement jumps, maximal cycling sprint, and maximal force under isokinetic conditions of the knee extensors. The results showed that all values from the two-point model were higher than the values from the standard tests (p < 0.05). We also found strong correlations between the same variables from different tests (r ≥ 0.84; p < 0.01), except for force in maximal cycling sprint, where it was low and negligible (r = −0.24). The results regarding our second aim showed that the correlation coefficients between the same two-point parameters of different lower limb tests ranged from moderate to strong (r −0.47 to 0.72). In particular, the relationships were stronger between power variables than between force variables and somewhat stronger between standard tests and two-point parameters. We can conclude that mechanical capacities of the leg muscles can be partially generalized between different functional tests.

Influence of countermovement depth on the countermovement jump-derived reactive strength index modified

This study aimed to investigate the effect of countermovement depth on the magnitude of the countermovement jump (CMJ) derived reactive strength index modified (RSI_mod), and to compare the RSI_mod between the CMJ performed with a self-preferred knee flexion angle (CMJ_pref) and the CMJ performed from a pre-determined knee flexion angle (CMJ_refer) with the countermovement depth more similar to the CMJ_pref. Sixteen subjects (11 males and 5 females; age 25.1 ± 6.3 years, body mass 69.7 ± 10.2 kg, body height 172.9 ± 8.1 m) randomly performed in a single session the CMJ_pref and CMJs from five pre-determined knee flexion angles (60°, 75°, 90°, 105°, and 120°). Our results showed that lower knee flexion angles were generally associated with greater RSI_mod values with the CMJ performed at 60° showing the greatest RSI_mod (P ≤ 0.049; effect size [ES] range = 0.19-0.63). The greatest RSI_mod for the CMJ performed at 60° was caused by the proportionally lower values of the time to take-off (ES range = 0.65-1.91) compared to the decrease observed in jump height (ES range = 0.11-0.25). The RSI_mod was higher for the CMJ_pref compared to the CMJ_refer (P < 0.001; ES = 0.34) due to a higher jump height (P = 0.021; ES = 0.14) and reduced time to take-off (P < 0.001; ES = 0.85). These results indicate that practitioners should be careful when interpreting an individual's changes in RSI_mod when the countermovement depth is not similar across the testing sessions. However, since the use of pre-determined knee flexion angles negatively impacts the RSI_mod, we encourage practitioners to use the CMJ_pref but only compare the RSI_mod when CMJs are performed using consistent countermovement depths.Highlights The magnitude of the countermovement jump-reactive reactive strength index modified is influenced by the knee flexion angle instruction.The magnitude of the countermovement jump-reactive reactive strength index tended to progressively increase with lower amounts of knee flexion.The magnitude of the countermovement jump-reactive reactive strength index is lower when an external reference is used to control the depth of the countermovement.

Differences in the magnitude and reliability of velocity variables collected during 3 variants of the bench press exercise

This study aimed to compare the reliability and magnitude of velocity variables between 3 variants of the bench press (BP) exercise in participants with and without BP training experience. Thirty males, 15 with and 15 without BP experience, randomly performed 3 variants of the BP on separate sessions: (I) concentric-only, (II) fast-eccentric and (III) controlled-eccentric. The mean velocity (MV) and maximum velocity (V_max) of the concentric phase were collected against 3 loads (≈30%1RM, 50%1RM, and 75%1RM) with a linear velocity transducer. Reliability was high regardless of the variable, BP variant, and load (coefficient of variation [CV] ≤ 4.47%, intraclass correlation coefficient [ICC] ≥ 0.87). The comparison of the CVs suggested a higher reliability for the fast-eccentric BP (8 out of 12 comparisons), followed by the concentric-only BP (5 out of 12 comparisons), and finally the controlled-eccentric BP (never provided a higher reliability). No differences in reliability were observed between experienced (CV ≤ 4.71%; ICC ≥ 0.79) and non-experienced (CV ≤ 6.29%; ICC ≥ 0.76) participants. The fast-eccentric BP provided the highest MV (p < 0.05) and no differences were observed for V_max. These results support the assessment of movement velocity during the fast-eccentric BP even in participants without experience.

Sleep restriction impairs maximal jump performance and joint coordination in elite athletes

The study objective was to examine the effects of three days of sleep restriction on maximal jump performance and joint coordination. Eleven elite cyclists obtained a one-week baseline of habitual sleep then restricted sleep to 4 h/night (SR) for three nights assessed through self-report and actigraphy. Pre and post-intervention measures were a box drop maximal vertical jump with 3D motion capture to assess physical performance and biomechanical changes, and Psychomotor Vigilance Task (PVT) assessed changes in response time. Associations between biomechanical, physical, and cognitive performance measures were assessed. Participants restricted reported sleep from 7.4 ± 0.5 h/night at baseline to 4.0 ± 0.2 h/night and actigraphy indicated 6.7 ± 0.7 to 3.7 ± 0.2 h/night. Following SR, jump height decreased (0.44 ± 0.09 vs. 0.42 ± 0.10 m, p = 0.02, g = 0.21). Hip sagittal/knee frontal (Δ15.5°, p = 0.04, g = 0.40) and hip frontal/knee frontal (Δ11.0°, p < 0.01, g = 0.44) plane coordination variability increased after SR. Hip sagittal/knee frontal plane coordination variability after SR was associated with increasingly slower PVT response time (r = 0.63, p = 0.03). These findings suggest SR for three days decreased maximal jump performance. SR increased joint coordination variability and was associated with greater impairment in response time. SR leads to deviations from preferred movement patterns, which may have implications for decrements in athlete performance and increased injury risk.

Self-Preferred Initial Position Could Be a Viable Alternative to the Standard Squat Jump Testing Procedure

Petronijevic, MS, Garcia Ramos, A, Mirkov, DM, Jaric, S, Valdevit, Z, and Knezevic, OM. Self-preferred initial position could be a viable alternative to the standard squat jump testing procedure. J Strength Cond Res 32(11): 3267-3275, 2018-The purpose of this study was to compare both the magnitude and reliability of different variables (knee angle, squat depth, jump height [Hmax], maximum force [Fmax], and maximum power [Pmax]) between the standardized squat jump (SJ) and the SJ performed from the self-preferred position. Eleven team handball players (age: 19.5 ± 1.1 years; height: 1.88 ± 0.06 m; and body mass: 82.1 ± 8.7 kg) and 13 physically active students (age: 20.5 ± 0.9 years; height: 1.81 ± 0.06 m; and body mass: 76.6 ± 6.6 kg) were evaluated on 2 sessions during the standardized SJ (knee angle fixed at 90°) and the self-preferred SJ (self-selected knee angle to maximize Hmax). Two blocks of both 3 standardized SJ and 3 self-preferred SJ were performed on the first session, whereas only 1 block was performed in the second session. The squat depth was smaller for the self-preferred SJ, whereas the knee angle, Fmax, and Pmax were higher for the self-preferred SJ (p < 0.025). The magnitude of Hmax did not significantly differ between both jump types. Most importantly, the reliability of the mechanical outputs (Hmax, Fmax, and Pmax) was generally higher for the self-preferred SJ (9 of 12 comparisons), whereas only in 2 of 12 comparisons the reliability was meaningfully higher for the standardized SJ. No differences were observed between presumably more (handball players) and less skilled individuals (physically active subjects). These results suggest that the self-preferred SJ should be recommended over the standardized SJ (90° knee angle) because it is not only quicker and more ecologically valid, but could also provide the performance variables with higher reliability.

Larger Countermovement Increases the Jump Height of Countermovement Jump

Simulation studies show that jump performance can be improved by increasing the depth of countermovement. The purpose of this study was to determine how modifications to the depth of countermovement lead to changes in jump height and the biomechanical parameters related to center of mass displacement and force application. Twenty-nine competitive males participated in this investigation, performing nine countermovement jumps using a self-selected, a deep, and a shallow crouch position. Jump height and relative net vertical impulse were greater when using a deeper crouch position, compared to the self-selected position. Force application variables did not report differences, when the deeper countermovement was compared to the self-selected countermovement; although, the shallower countermovement showed higher values in force application parameters. The deeper countermovement jumps achieved higher velocities of the center of mass than the self-selected jumps, while shallower jumps produced lower velocities than the self-selected jumps. The results of this investigation were consistent with simulation studies, showing that deep countermovements increase net vertical impulse, leading to a higher jump height. In addition, the maximum downward velocity was higher, when the crouch position was deeper. Conversely, force-applied variables did not change when jump performance was increased.

Effects of Reduced Effort on Mechanical Output Obtained From Maximum Vertical Jumps

The aim of this study was to evaluate the effect of reduced effort on maximum countermovement jumps. Groups of unskilled and skilled jumpers performed countermovement jumps without an arm swing at 100% and 50% effort. The results revealed markedly reduced jump height and work performed at 50% effort, although the maximum force and power output remained virtually unchanged. The observed differences were consistent across individuals with different jumping skills. A possible cause of differences in changes across the tested variables was a reduced countermovement depth associated with the 50% effort jumps. It is known to cause an increase in maximum force and power outputs, but not in jump height. Therefore, the jump height and work performed may be more closely related to our sense of effort when jumping, rather than our maximum force and power output. From a practical perspective, the present findings reiterate the importance of maximizing effort for making valid assessments of muscle mechanical capacities, as tested by maximal vertical jumps and, possibly, other maximum performance tasks.

Is a Bimodal Force-Time Curve Related to Countermovement Jump Performance?

A countermovement jump (CMJ) represents one of the most frequently used performance tests for monitoring neuromuscular function in athletes. An often-overlooked feature that may provide some useful diagnostic information is the actual shape of the force-time curve. The aim of this study was therefore to consider how the shape of the force-time curve influences jump performance. Thirty-three male rugby union players performed two CMJs on a force plate, with discrete variables and continuous curve analysis used. The subjects were dichotomized based on shape of the force-time curve during the propulsion phase and by jump height. The differences between the unimodal and bimodal groups were unclear for jump height (ES = 0.28, ±0.58) and reactive strength index-modified (ES = −0.30, ±0.59). A substantial difference between high (40.2 ± 2.9 cm) and low (31.2 ± 3.2 cm) jumpers only existed in the late propulsion phase by 79.0% to 97.0% of the normalized force-time curve. A bimodal force-time curve is not representative of an optimal pattern of performance and simply reflects an inefficient stretch-shortening cycle. The inter-individual variability that exists in braking COM displacement renders temporal phase analysis impractical in cross-sectional type studies.

Differences in Vertical Jump Force-Time Characteristics between Stronger and Weaker Adolescent Basketball Players

The countermovement jump (CMJ) and isometric mid-thigh pull (IMTP) are commonly used to compare one’s force capacity during dynamic and isometric assessments, respectively. However, little research has investigated the influence of maximum isometric strength on drop-jump (DJ) performance. Therefore, the purpose of this study was to explore differences in CMJ and DJ force-time characteristics between stronger and weaker adolescent male basketball players. Sixteen adolescent male basketball players performed the IMTP to assess measures of peak force (IMTP PF), whereas CMJ and DJ calculated a range of kinetic and kinematic variables. Peak concentric force (CMJ-PF) in the CMJ was greater for stronger players (d = 1.99). However, no differences in DJ force-time characteristics existed between stronger and weaker players. Future research should be undertaken to investigate the role of maximum strength on DJ force-time characteristics in adolescent male basketball players. Such studies may help direct the creation of athlete training and monitoring programs more effectively to represent accurate player profiling.