Countermovement Jump and Squat Jump Force-Time Curve Analysis in Control and Fatigue Conditions

Between-Session Reliability of Field-Based Assessments of Isometric Neck Strength

The reliability of the fixed-frame dynamometer for measuring isometric neck strength is established, but with limited field-based applications. This study aimed to establish the inter- and intra-session reliability of the peak force for neck flexors, extensors, and side flexors using the VALD ForceFrame and DynaMo and the force-time characteristics in the quadruped position (ForceFrame). Twenty-seven recreationally active males performed three repetitions of isometric neck flexion, extension, and side flexion over two sessions in random order using the VALD ForceFrame and DynaMo. Both devices demonstrated acceptable reliability, with the Forceframe ICC > 0.8 and CV% < 13.8% and the DynaMo ICC > 0.76 and CV% < 13.8%. No systematic or proportional differences were found using the Passing-Bablock procedure, and Bland-Altman analysis confirmed agreement across measures. Reliability was shown for right-side (ICC > 0.76) and left-side (ICC > 0.79) flexion and flexion (ICC > 0.75) across 50, 100, 150, and 200 ms. Statistical parametric mapping indicated no differences in ForceFrame-generated isometric force-time curves between sessions, though the CV was highest in the force development phase. The findings suggest that both tools can reliably assess neck strength, supporting their use in sports and clinical settings. However, assessment methods are not interchangeable, emphasising the need for standardised neck strength assessment approaches.

Effects of high-intensity sprint exercise on neuromuscular function in sprinters: the countermovement jump as a fatigue assessment tool

Background

High-intensity sprint exercises (HIS) are central to sprinter training and require careful monitoring of athlete muscle fatigue to improve performance and prevent injury. While the countermovement jump (CMJ) may be used to monitor neuromuscular fatigue (NMF), little is known about the specific effects from HIS. The purpose of this study is to investigate the effects of HIS on the CMJ to assess its utility for assessing NMF following HIS.

Methods

Ten male collegiate 400 m sprinters completed a 400 m sprint fatigue protocol and underwent five CMJ-testing sessions (baseline, 3 minutes, 10 minutes, 1 hour and 24 hours) over two days. Three CMJ trials, performed on a force plate, were completed each trial, with rating of perceived exertion (RPE) recorded as a subjective fatigue measure. Changes in RPE, CMJ variables, force-time and power-time curves at baseline and post fatigue were assessed.

Results

Significant changes were observed in most variables following the fatigue protocol. In particular, concentric mean power remained significantly lower after 24 hours compared to baseline. In addition, the force-time curves exhibited a significant reduction in all conditions following the fatigue protocol. This decline was most pronounced within 50-75%of the concentric phase relative to baseline measurements. Conclusion. Results indicate that the CMJ may be a useful tool for monitoring fatigue in at least 400 m sprinters. These data also indicate that HIS may disproportionately reduce force output in during concentric movement. These insights may improve training prescriptions and injury prevention strategies for sprint athletes.

Kinetic Analysis, Potentiation, and Fatigue During Vertical and Horizontal Plyometric Training: An In-Depth Investigation Into Session Volume

Despite previous support for plyometric training, optimal dosing strategies remain unclear.

PURPOSE

To investigate vertical and horizontal jump kinetic performance following a low-volume plyometric stimulus with progressively increased session jump volume.

METHODS

Sixteen academy rugby players (20.0 [2.0] y; 103.0 [17.6] kg; 184.3 [5.5] cm) volunteered for this study. Vertical and horizontal jump sessions were conducted 1 week apart and consisted of a 40-jump low-volume plyometric stimulus using 4 exercises, after which volume was progressively increased to 200 jumps, using countermovement jump (CMJ) for vertical sessions and horizontal broad jump (HBJ) for horizontal sessions. Jump performance was assessed via force-plate analysis at baseline (PRE-0), following the low-volume plyometric stimulus (P-40), and every subsequent 10 jumps until the end of the session (P-50, P-60, P-70, ... P-200).

RESULTS

The low-volume stimulus was effective in potentiating HBJ (2% to 5%) but not CMJ (0% to -7%) performance (P < .001). The HBJ performance enhancements were maintained throughout the entire high-volume session, while CMJ realized small but significant decrements (-5% to -7%) in jump height P-50 to P-80 before recovering to presession values. Moreover, increases in eccentric impulse (5% to 24%; P < .001) in both sessions were associated with decreased or maintained concentric impulse, indicating a breakdown in performance-augmenting mechanisms and less effective power transfer concentrically after moderate volumes.

CONCLUSION

Practitioners should consider kinetic differences between HBJ and CMJ with increasing volume to better inform and understand session dosing strategies.

Effect of Neuromuscular Fatigue on the Countermovement Jump Characteristics: Basketball-Related High-Intensity Exercises

ABSTRACT

Yoshida, N, Hornsby, WG, Sole, CJ, Sato, K, and Stone, MH. Effect of neuromuscular fatigue on the countermovement jump characteristics: basketball related high-intensity exercises. J Strength Cond Res 38(1): 164-173, 2024-The purpose of this study was to investigate basketball specific neuromuscular (NM) fatigue effect on countermovement jump (CMJ) force-time (F-T) curve characteristics. Eleven male college-level basketball athletes performed 6 CMJ trials at 3 baseline (pre) and 6 postexercise time points. The fatiguing protocol consisted of high-intensity basketball related exercises commensurate with basketball game or practice. Typical CMJ (CMJ-TYP) and phase-specific CMJ variables were derived from the F-T curve. Meaningful differences in CMJ performance were examined using effect size (ES) compared with baseline and previous postexercise time point. Baseline with 3 separated measurements demonstrated suitable CMJ variables reproducibility (CV, coefficient of variation). Most CMJ-TYP output and performance variables displayed substantial alterations immediately postexercise (0 hour) and returned to baseline at 24 hours postexercise, whereas the time and rate-related CMJ-TYP and CMJ-phase variables tended to display delayed decline peaked at 2 hours and delayed recovery to baseline at 48 hours postexercise. In conjunction with the return of the time and rate-related variables, CMJ performance displayed supercompensation at 72 hours postexercise. The results indicate altered NM functions with desired CMJ performance, such as jump height, which imply an altered movement strategy at early stage of recovery process. Full recovery may take 48-72 hours. Practitioners are, therefore, advised to monitor variables reflecting NM functions for precise manipulation of the intensity and volume of exercise to avoid prolonging the recovery from NM fatigue.

Effects of Repeated Jump Testing and Diurnal Changes on Subsequent Countermovement Jump and Squat Jump Output and Force-Time Characteristics

ABSTRACT

Harrison, PW, James, LP, Jenkins, DG, Holmberg, PM, and Kelly, VG. Effects of repeated jump testing and diurnal changes on subsequent countermovement jump and squat jump output and force-time characteristics. J Strength Cond Res 38(1): 174-179, 2024-The aim of this brief study was to investigate the effects of repeated jump testing on performance over 2 consecutive days while considering the possibility of diurnal changes. Fourteen male subjects and 14 recreationally active female subjects completed countermovement jump (CMJ) and squat jump (SJ) testing on 5 occasions (baseline [0,800], 5 minutes [0,820], 8 hours [1,600], 24 hours [0,800], and 32 hours [1,600]) over 32 hours. An additional rested baseline test was conducted on a separate day in the afternoon (1,600) to compare jump performance between morning and afternoon baseline values. Excluding small decreases in CMJ height at 24 hours (p = 0.292, Cliff's delta = -0.225) in male subjects and similar decreases in CMJ height at 5 minutes (p = 0.034, Cliff's delta = -0.245) in addition to SJ height:contraction time at 32 hours (p = 0.126, Cliff's delta = 0.153) in female subjects, findings generally showed no changes in jump performance over multiple assessments. Squat jump metrics may have showed small improvements between morning and afternoon baseline values in male subjects (SJ height:contraction time [p = 0.030, Cliff's delta = 0.225]) and female subjects (SJ height [p = 0.013, Cliff's delta = 0.173] and SJ height:contraction time [p = 0.091, Cliff's delta = 0.163)]. As jump performance was largely unaffected by repeated jump testing, the present findings support the use of monitoring practices and research designs that require multiple jump assessments within acute periods (∼32 hours).

Individual Muscle Force Differences During Loaded Hexbar Jumps: A Statistical Parametric Mapping Analysis

Knowledge of individual muscle force during strength and conditioning exercises provides deeper understanding of how specific training decisions relate to desired training outcomes. The purpose of this study was to estimate individual muscle forces during hexbar jumps with 0%, 20%, 40%, and 60% of the hexbar deadlift 1-repetition maximum utilizing in vivo motion capture and computational modeling techniques of male participants. Muscle forces for the gluteus maximus, biceps femoris, rectus femoris, vastus intermedius, gastrocnemius, and soleus were estimated via static optimization. Changes in muscle forces over the concentric phase were analyzed across loading conditions using statistical parametric mapping, impulse, and peak values. Conclusions about the effects of load differ between the three analysis methods; therefore, careful selection of analysis method is essential. Peaks may be inadequate in assessing differences in muscle force during dynamic movements. If SPM, assessing point-by-point differences, is combined with impulse, where time of force application is considered, both timepoint and overall loading can be analyzed. The response of individual muscle forces to increases in external load, as assessed by impulse and SPM, includes increased total muscle output, proportionally highest at 20%1RM, and increased absolute force for the vasti and plantarflexors during the concentric phase of hexbar jumps.

Acute Performance, Daily Well-Being, and Hormone Responses to Water Immersion After Resistance Exercise in Junior International and Subelite Male Volleyball Athletes

ABSTRACT

Horgan, BG, Tee, N, West, NP, Drinkwater, EJ, Halson, SL, Colomer, CME, Fonda, CJ, Tatham, J, Chapman, DW, and Haff, GG. Acute performance, daily well-being and hormone responses to water immersion after resistance exercise in junior international and subelite male volleyball athletes. J Strength Cond Res XX(X): 000-000, 2023-Athletes use postexercise hydrotherapy strategies to improve recovery and competition performance and to enhance adaptative responses to training. Using a randomized cross-over design, the acute effects of 3 postresistance exercise water immersion strategies on perceived recovery, neuromuscular performance, and hormone concentrations in junior international and subelite male volleyball athletes (n = 18) were investigated. After resistance exercise, subjects randomly completed either 15-minute passive control (CON), contrast water therapy (CWT), cold (CWI), or hot water immersion (HWI) interventions. A treatment effect occurred after HWI; reducing perceptions of fatigue (HWI > CWT: p = 0.05, g = 0.43); improved sleep quality, compared with CON (p < 0.001, g = 1.15), CWI (p = 0.017, g = 0.70), and CWT (p = 0.018, g = 0.51); as well as increasing testosterone concentration (HWI > CWT: p = 0.038, g = 0.24). There were trivial to small (p < 0.001-0.039, g = 0.02-0.34) improvements (treatment effect) in jump performance (i.e., squat jump and countermovement jump) after all water immersion strategies, as compared with CON, with high variability in the individual responses. There were no significant differences (interaction effect, p > 0.05) observed between the water immersion intervention strategies and CON in performance (p = 0.153-0.99), hormone (p = 0.207-0.938), nor perceptual (p = 0.368-0.955) measures. To optimize recovery and performance responses, e.g., during an in-season competition phase, postresistance exercise HWI may assist with providing small-to-large improvements for up to 38 hours in perceived recovery (i.e., increased sleep quality and reduced fatigue) and increases in circulating testosterone concentration. Practitioners should consider individual athlete neuromuscular performance responses when prescribing postexercise hydrotherapy. These findings apply to athletes who aim to improve their recovery status, where postresistance exercise HWI optimizes sleep quality and next-day perceptions of fatigue.

The Effects of Soccer Specific Exercise on Countermovement Jump Performance in Elite Youth Soccer Players

The aims of the study were to examine the test−retest reliability of force-time (F-T) characteristics and F-T curve waveform of bilateral and unilateral countermovement jumps (CMJ) in elite youth soccer players and to evaluate the effects of competitive match-play on CMJ performance. 16 male youth soccer players completed CMJs on two separate occasions to determine reliability, and immediately pre, post and 48 h following a competitive match. Coefficient of variation (CV%), Intra-class correlation coefficient (ICC) and limits of agreement were used to assess reliability of discreate CMJ variables. Single factor repeated measures ANOVA were used to determine the effects of match play. Statistical parametric mapping was used to evaluate the repeatability of the CMJ force-time waveform and the effects of match play. Jump height had limited reliability in all three jumps and only a select few jump specific F-T variables were found to be reliable (CV < 10%, ICC > 0.5). Select variables were reduced immediately post game but recovered 48 h post game. The F-T curve waveform was found to be repeatable but did not differ following match-play. This study suggest that select F-T variables change following match-play and may be suitable tools to allow practitioners to detect decrements in performance. These data may help inform practitioners to use the most appropriate F-T variables to assess fatigue and recovery, with implications for performance and injury risk.

Comparing biomechanical time series data across countermovement shrug loads

The effect of load on time-series data has yet to be investigated during weightlifting derivatives. This study compared the effect of load on the force-time and velocity-time curves during the countermovement shrug (CMS). Twenty-nine males performed the CMS at relative loads of 40%, 60%, 80%, 100%, 120%, and 140% one repetition maximum (1RM) power clean (PC). A force plate measured the vertical ground reaction force (VGRF), which was used to calculate the barbell-lifter system velocity. Time-series data were normalized to 100% of the movement duration and assessed via statistical parametric mapping (SPM). SPM analysis showed greater negative velocity at heavier loads early in the unweighting phase (12-38% of the movement), and greater positive velocity at lower loads during the last 16% of the movement. Relative loads of 40% 1RM PC maximised propulsion velocity, whilst 140% 1RM maximized force. At higher loads, the braking and propulsive phases commence at an earlier percentage of the time-normalized movement, and the total absolute durations increase with load. It may be more appropriate to prescribe the CMS during a maximal strength mesocycle given the ability to use supramaximal loads. Future research should assess training at different loads on the effects of performance.

Countermovement Jump Force-Time Curve Analysis between Strength-Matched Male and Female Soccer Players

The purpose of this study was to compare countermovement jump force-time measures between strength-matched male and female soccer players. Males (n = 11) and females (n = 11) were strength-matched via isometric mid-thigh pull testing, whereby peak force values were normalised to body mass. Subjects performed three maximal-effort countermovement jumps (CMJs) on a force platform from which a range of kinetic and kinematic variables were calculated via forward dynamics. Thereafter, differences in gross measures were examined via independent t-tests, while differences in force-, power-, velocity-, and displacement-time curves throughout the entire CMJ were analysed using statistical parametric mapping (SPM). Jump height, reactive strength index modified, propulsion mean force, propulsion impulse, and propulsion mean velocity were all greater for males (d = 1.50 to 3.07). Relative force- and velocity-time curves were greater for males at 86-93% (latter half of the concentric phase) and 85-100% (latter half of the concentric phase) of normalized movement time, respectively. Time to take-off, braking phase time, braking mean velocity and impulse, propulsion phase time and centre of mass displacement were similar between males and females (d = -0.23 to 0.97). This research demonstrates the strength of SPM to identify changes between entire force-time curves. Continued development and the use of SPM analysis could present the opportunity for a refined comparison of strength-matched male and female CMJ performance with the analysis of entire force-time curves.

Comparisons of Countermovement Jump Force-Time Characteristics Among National Collegiate Athletic Association Division I American Football Athletes: Use of Principal Component Analysis

ABSTRACT

Merrigan, JJ, Rentz, LE, Hornsby, WG, Wagle, JP, Stone, JD, Smith, HT, Galster, SM, Joseph, M, and Hagen, JA. Comparisons of countermovement jump force-time characteristics among NCAA Division I American football athletes: use of principal component analysis. J Strength Cond Res 36(2): 411-419, 2022-This study aimed to reduce the dimensionality of countermovement jump (CMJ) force-time characteristics and evaluate differences among positional groups (skills, hybrid, linemen, and specialists) within National Collegiate Athletic Association (NCAA) division I American football. Eighty-two football athletes performed 2 maximal effort, no arm-swing, CMJs on force plates. The average absolute and relative (e.g., power/body mass) metrics were analyzed using analysis of variance and principal component analysis procedures (p < 0.05). Linemen had the heaviest body mass and produced greater absolute forces than hybrid and skills but had lower propulsive abilities demonstrated by longer propulsive phase durations and greater eccentric to concentric mean force ratios. Skills and hybrid produced the most relative concentric and eccentric forces and power, as well as modified reactive strength indexes (RSIMOD). Skills (46.7 ± 4.6 cm) achieved the highest jump height compared with hybrid (42.8 ± 5.5 cm), specialists (38.7 ± 4.0 cm), and linemen (34.1 ± 5.3 cm). Four principal components explained 89.5% of the variance in force-time metrics. Dimensions were described as the (a) explosive transferability to concentric power (RSIMOD, concentric power, and eccentric to concentric forces) (b) powerful eccentric loading (eccentric power and velocity), (c) countermovement strategy (depth and duration), and (d) jump height and power. The many positional differences in CMJ force-time characteristics may inform strength and conditioning program designs tailored to each position and identify important explanatory metrics to routinely monitor by position. The overwhelming number of force-time metrics to select from may be reduced using principal component analysis methods, although practitioners should still consider the various metric's applicability and reliability.

Gender Differences in Physical Fitness Characteristics in Professional Padel Players

The aims of the present study were to examine the fitness characteristics of professional padel players and to determine differences in physical performance regarding players' gender. Thirty professional padel players (men: n = 15, age = 27.4 ± 6.8 years, height = 177.9 ± 4.0 cm; women: n = 15, age = 30.0 ± 4.2 years, height = 166.6 ± 4.8 cm) completed a 4-day evaluation process, including: isometric handgrip strength, sit and reach, 10 × 5 shuttle test, countermovement jump (CMJ), squat jump (SJ), Abalakov test, one-repetition maximum test (bench press, leg extension, leg curl, lat pulldowns, overhead press, and shoulder press), anthropometry and VO2 max tests. The men players had higher values in terms of weight, height, one maximum repetition, jump tests (CMJ and ABK) and VO2 max test than the women (p < 0.005). By contrast, the women had higher values for fat mass (p = 0.005; ES: 2.49). The values from this multifaceted test battery can be a useful guide for coaches regarding players' development in future evaluations and monitoring.