Countermovement Jump Force-Time Curve Analyses: Reliability and Comparability Across Force Plate Systems

Effect of 6-week single leg countermovement jump training on force time metrics in elite female youth footballers

Female football participation has grown exponentially. Unfortunately, females exhibit greater injury risk than male athletes, and experience increased mechanical stress during adolescence. Force plates provide accurate and reliable force-time characteristics enabling profiling of injury risk and benchmarking using a variety of jump and isometric tasks. The purpose of this study was to determine whether test-retest reliability and force-time characteristics of SLCMJ, bilateral countermovement jump (CMJ), countermovement rebound jump (CMJ-R) and isometric mid-thigh pull (IMTP) change with six weeks of SLCMJ training. Twenty-eight elite youth female footballers (13.7 ± 1.1 years, 53.27 ± 8.82 kg, 162.20 ± 5.37 cm) completed six weeks of SLCMJ as part of a routine strength and plyometric training program. SLCMJ training did not influence test-retest reliability and resulted in favourable adaptations indicated through small to large changes in force-time characteristics for SLCMJ. Significant (p < 0.05) yet trivial to small favourable changes were observed for the CMJ and CMJ-R, with small increases observed for IMTP. The results of this study demonstrate that six weeks of SLCMJ training does not influence phase-specific test-rest reliability (i.e. braking and propulsion) and causes weekly fluctuations in force-time characteristics leading to improvements in SLCMJ, CMJ, CMJ-R and IMTP. Practitioners can use such information to inform training design and monitor athlete performance.

Impact of Early Season Jump Loads on Neuromuscular Performance in Division I Volleyball: Analyzing Force, Velocity, and Power From Countermovement Jump Tests

The study investigated daily jump load variations on neuromuscular fatigue in nine NCAA Division I female volleyball athletes during the first 22 days of the season. Using force plates and inertial measurement units, data from 17 sessions were analyzed to assess relationships between jump loads and neuromuscular performance. Pearson's correlations were calculated to assess the relationships between force, velocity, and power force plate metrics and jump variables (duration in minutes, total jump counts, and jump counts greater than 38.1 cm (Jumps 38+) and 50.8 cm (Jumps 50+)). Nine out of 14 force metrics showed weak-to-moderate negative correlations with Jumps 50+, indicating as the highest intensity of jump counts increased and force production decreased (r ranges from -0.194 to -0.570; p ≤ 0.025 for all). In contrast, nine out of 16 velocity and power metrics showed weak-to-moderate positive correlations with Jumps 50+ (r ranges from 0.175 to 0.466; p ≤ 0.044 for all). In total, 29 out of 36 force plate metrics were significantly correlated to Jumps 50+, the highest intensity jump threshold assessed. Monitoring high-intensity jump loads provides a more accurate and nuanced assessment of neuromuscular performance and fatigue than total jump counts or session duration, with implications for optimizing athlete readiness and performance.

Algorithmic Audits in Sports Medicine: An Examination of the SpartaScience™ Force Plate System

INTRODUCTION

Force plate systems are increasingly utilized in the armed forces that claim to identify individuals at risk of musculoskeletal injury. However, factors influencing injury risk scores from a force plate system (SpartaScience™) and the effects of experimental perturbations on these scores remain unclear.

METHODS

Healthy males ( n = 823; 22.7 ± 3.9 yr) performed a countermovement jump (CMJ) on SpartaScience™ force plates. Multiple regression analysis was used to identify predictors of the system's proprietary Musculoskeletal (MSK) Health score, which were then experimentally perturbed. Twelve males (30.9 ± 4.3 yr) participated in a test-retest reliability study, performing three standard CMJs and one experimentally manipulated jump (50% effort) due to the observed relationship between the MSK Health score, vertical jump height, and body weight.

RESULTS

The MSK Health score was negatively correlated with vertical jump height and positively with body weight ( R2 = 0.59, P < 0.001). Each inch increase in jump height decreased the MSK Health score by an average of 1.27 units (95% confidence interval, 1.17-1.36), whereas each pound of body weight increased it by 0.12 units (95% confidence interval, 0.11-0.13). Notably, 83% of participants in the reliability study improved their MSK Health score on the 50% effort jump.

CONCLUSIONS

The study revealed atypical relationships between MSK Health scores, vertical jump height, and body weight, with vertical jump height playing a majority role in predicting the principal output (MSK Health score). Findings indicated a higher injury risk with greater jump height but a lower risk with increased body weight. In addition, MSK Health scores paradoxically improved with lower effort (i.e., lower vertical jump height), which highlights the dangers of using undisclosed and unvetted algorithms for the prediction of health outcomes.

Novel Use of Generalizability Theory to Optimize Countermovement Jump Data Collection

This study aimed to evaluate the reliability of countermovement jump (CMJ) performance metrics across five NCAA Division I varsity sports using Generalizability Theory (G-Theory). Three hundred male athletes from football, hockey, baseball, soccer, and lacrosse performed three or more CMJs on dual-force platforms. G-Theory was applied to identify variance components and determine reliability coefficients (Φ) for 14 key metrics. Metrics requiring more than three jumps to achieve Φ 0.80 were deemed unreliable. Metric reliability varied by sport and phase of movement. Metrics associated with the eccentric phase (e.g., Eccentric Duration, Deceleration Rate of Force Development Asymmetry) demonstrated lower reliability, often requiring >3 jumps. Reliable metrics across sports included Phase 1 Concentric Impulse and Scaled Power, requiring three trials or fewer. CMJ reliability is sport- and metric-specific. Practitioners should prioritize reliable metrics and adjust protocols to balance data quality and practicality, particularly when monitoring eccentric characteristics.

Estimation of maximum lower limb muscle strength from vertical jumps

Determining the one-repetition maximum (1RM) is crucial for organizing training loads, but it also is time-consuming, physically demanding, and poses a risk of injury. Vertical jumps are a less demanding and well-established method to test the ability of the lower limbs to generate great forces over a short time, which may allow for the estimation of 1RM in squatting. The purpose of this study was to develop a model for estimating 1RM back squat from ground reaction forces during vertical jumps. Thirteen healthy participants completed a 1RM back squat test, countermovement jumps, and squat jumps. Five kinematic and kinetic variables (e.g., peak and mean power, relative net impulse, jump height, and peak kinetic energy during various phases) were derived from ground reaction forces collected via a Kistler force plate (1000 Hz). Five out of 5 variables correlated with 1RM in countermovement jump and squat jump (ICC = .96-.98, r = .88-.95, p < .001 and ICC = .97-.99, r = .76-.90, p < .05, respectively). The most accurate stepwise regression model (adjusted R2 = .90, SEE =  13.24 kg, mean error =  7.4% of mean 1RMm, p < .001) estimated 1RM back squat based on peak kinetic energy during countermovement jumps. Estimation errors ranged from 7.4% to 10.7% of mean measured 1RM, with no differences between estimated and measured values (d <  0.01, p = .96-1.00). Estimating 1RM via jump tests may offer a practical alternative to traditional methods, reducing injury risks, testing intervals, and effort. Our study proposes a new possible approach for estimating 1RM back squat from jump forces, providing coaches and sports professionals with a more efficient tool to monitor and adjust training loads.

Comparison of Vertical Jump Force-Time Metrics Between ACL-Injured and Healthy Semi-Professional Male and Female Soccer Players

Given the increasing use of innovative force plate systems in applied sports settings and the impact that anterior cruciate ligament (ACL) injuries have on team success, the purpose of the present study was to compare the lower-body neuromuscular performance characteristics of athletes who underwent ACL reconstruction (ACLR) and their non-injured counterparts (i.e., healthy controls). Forty-five male (thirteen injured) and twenty-six female (ten injured) semi-professional soccer players volunteered to participate in the present study. Each athlete performed three countermovement vertical jumps (CMJs) while standing on a uniaxial force plate system sampling at 1000 Hz. The injured athletes completed a nine-month recovery protocol and were screened 11-13 months post-ACLR. The dependent variables included the force-time metrics within both the eccentric and concentric phases of the CMJ. Independent t-tests or Mann-Whitney U-test were used to examine statistically significant (p < 0.05) differences in each variable (i.e., ACL-injured vs. healthy controls). The results revealed no significant between-group differences in any CMJ force-time metrics of interest (e.g., concentric peak force, eccentric mean power, countermovement depth) between ACL-injured and non-injured athletes, including inter-limb asymmetry measures (i.e., peak takeoff and landing force). Besides implying the effectiveness of the implemented rehabilitation protocol, these findings suggest that the CMJ may not present a sufficient neuromuscular performance stimulus needed to expose lower-limb asymmetries and strength and power deficiencies 11-13 months post-ACLR.

The Strength and Power Profile of Junior and Senior Female Rugby League Athletes

ABSTRACT

Flannery, L, Secomb, JL, West, MA, Compton, HR, and Dascombe, BJ. The strength and power profile of junior and senior female rugby league athletes. J Strength Cond Res 38(12): 2129-2135, 2024-The purpose of this study was to compare the lower-body strength and power profiles of the various female rugby league (RL) competition levels, thereby establishing normative data for these athletes. Seventy-nine female RL athletes from 3 different competition levels: junior-state ( n = 45, age: 17.5 ± 0.6 years), senior-state ( n = 15, age: 24.3 ± 3.7 years), and senior-national ( n = 19, age: 25.4 ± 4.0 years) participated in this study. All testing was completed in a single session at the beginning of preseason, with the following assessments performed: countermovement jump (CMJ), isometric mid-thigh pull (IMTP), and bilateral and unilateral isometric hip adduction and abduction strength. One-way analyses of variance with Bonferroni post hoc analyses, revealed that junior-state athletes exhibited significantly lower IMTP peak force (PF) and relative PF (rPF), and CMJ height compared with the senior-state and senior-national athletes. Importantly, senior-national athletes demonstrated significantly greater body mass (80.9 ± 14.6 kg) than senior-state athletes (70.9 ± 8.1 kg), but no significant differences were identified between these athletes for any IMTP or CMJ measure. Finally, the senior-national athletes possessed significantly lower unilateral hip adduction rPF (0.13 ± 0.04 N·BW -1 ) and adduction to abduction strength ratio (0.92 ± 0.14) than senior-state athletes (0.17 ± 0.03 N·BW -1 and 1.04 ± 0.13, respectively), which may have implications for noncontact lower-body injury risk. This study highlights the importance of practitioners prescribing training to increase the lower-body strength and power of junior-state RL athletes. Whereas, for senior-state athletes progressing to senior-national levels, the focus should on maintaining or improving relative strength and power, while increasing their body mass to enhance preparedness for the greater contact demands at that level.

The acute effects of nonsleep deep rest on perceptual responses, physical, and cognitive performance in physically active participants

This study aimed to examine the effect of nonsleep deep rest (NSDR) on physical and cognitive performance, as well as sleepiness, acute readiness, recovery, stress, and mood state in physically active participants. A total of 65 physically active participants (42 male, 23 female) were randomly assigned into two groups: an experimental group (NSDR, n = 34), in which participants completed a 10-min NSDR intervention, and a control group (CON, n = 31), whereby participants sat passively for 10 min. Testing measures were assessed immediately pre and 10 min post each condition and comprised completing a hand grip strength dynamometer test and a countermovement jump test on force plates, cognitive function measures via a psychomotor vigilance task (PVT-B), and a Simon task test, along with four questionnaires to assess sleep, recovery, and mood state. A significant Group × Time interaction favored the NSDR condition for handgrip strength, median reaction time during the PVT-B, and accuracy percentage during the Simon task. Questionnaire responses demonstrated NSDR to be associated with significant benefits to physical readiness, emotional balance, overall recovery, negative emotional state, overall stress, and tension in comparison to CON (p < .05). The NSDR intervention could be a valuable strategy for acutely enhancing overall well-being and readiness.

The Impact of the Official Basketball Champions League Game on Lower-Body Neuromuscular Performance Characteristics

ABSTRACT

Cabarkapa, D, Cabarkapa, DV, Aleksic, J, Mihajlovic, F, and Fry, AC. The impact of the official Basketball Champions League game on lower-body neuromuscular performance characteristics. J Strength Cond Res 38(10): e595-e599, 2024-Considering the extensive use of force plate technology in an applied sports setting and the lack of scientific literature during the actual competition, the purpose of the present study was to investigate the acute impact of an official basketball game on lower-body neuromuscular performance characteristics. Eight professional male basketball players volunteered to participate in this investigation. Upon completion of a standardized warm-up procedure, each athlete performed 3 maximum-effort countermovement vertical jumps (CVJs) with no arm swing while standing on a uniaxial force plate system sampling at 1,000 Hz. Then, 3 days after the baseline testing procedures, the athletes completed an identical CVJ testing protocol immediately after the completion of an official basketball game. Paired sample t-tests were used to examine statistically significant pregame and postgame differences in CVJ performance (p < 0.05). The findings reveal that force-time metrics examined during both eccentric and concentric phases of the CVJ tend to remain relatively unchanged in response to the game stimulus. Also, no differences in outcome metrics such as vertical jump height and reactive strength index-modified have been observed. However, despite not reaching the level of statistical significance, it should be noted that eccentric peak velocity, force, and power did demonstrate a moderate decrease postgame when compared with the baseline measurements (g = 0.509-0.627), suggesting that the eccentric phase of the jumping movement might be more sensitive in detecting acute fatigue-induced performance changes within this specific group of professional athletes.

The impact of simulated 3x3 tournament on vertical jump force-time metrics in national team male basketball players

With innovative portable force plate systems being widely implemented for lower-body neuromuscular performance assessment in an applied sports setting and the existing gap in the scientific literature regarding player performance during in-game competitive scenarios, the purpose of the present study was to compare changes in countermovement vertical jump (CVJ) performance pre-post a simulated 3×3 basketball tournament. Seven current or former members of a 3×3 national basketball team volunteered to participate in the present investigation. Upon completing standardized warm-up procedures, athletes stepped on a uni-axial force plate system sampling at 1,000 Hz and performed three maximal-effort CVJs with no arm swing. Then, the athletes proceeded to play a simulated 3×3 basketball tournament composed of two consecutive games, separated by a 15-min rest interval. Immediately following the completion of the second game, the identical CVJ testing procedures were repeated. Paired sample t-tests were used to examine pre-post-tournament differences in nineteen CVJ performance metrics (p < 0.05). The results reveal that force-time metrics during both eccentric and concentric phases of the CVJ remain relatively unchanged pre-post simulated 3×3 basketball tournament. However, multiple force-time metrics within the eccentric phase of the CVJ changed by 12.1%-19.1% (e.g., eccentric peak power and peak velocity, eccentric duration), suggesting that the eccentric phase of CVJ might be responsive to performance stimulus to a greater extent than the concentric phase. Overall, these findings further support the importance of comprehensive CVJ analysis when intending to measure changes in neuromuscular performance.

Concurrent validity and test-retest reliability of VALD ForceDecks' strength, balance, and movement assessment tests

OBJECTIVES

To evaluate the concurrent validity and test-retest reliability of common movement, strength, and balance tests using portable uniaxial dual force plates.

DESIGN

Repeated measures cross-sectional study.

METHODS

Sixteen healthy individuals participated in two testing sessions, where they performed 12 different movement, strength, and balance tests. Vertical ground reaction force and centre of pressure data were collected using the VALD ForceDecks simultaneously with ground-embedded laboratory force plates. Concurrent validity was assessed using root mean square error for raw time-series data and Bland-Altman plots for discrete metrics. Test-retest reliability was assessed using intraclass correlation coefficients and minimal detectable changes.

RESULTS

ForceDecks recorded vertical ground reaction forces and center of pressure with high accuracy compared to laboratory force plates. The mean bias between systems was negligible (<2 N or 0.1 mm), with small limits of agreement (<5 N or 1 mm). Overall, 530/674 (79%) showed good or excellent validity (<10% difference) and 611/773 (79%) had good or excellent reliability (intraclass correlation coefficient >0.75). ForceDecks reliability was similar to laboratory force plates (<0.07 intraclass correlation coefficient median difference for all metrics).

CONCLUSIONS

Portable uniaxial force plates record highly accurate vertical ground reaction forces and center of pressure during a range of movement, strength, and balance tests. The VALD ForcDecks are a valid and reliable alternative to laboratory force plates when strict standardized testing and data analysis procedures are followed. Users should be aware of the validity and reliability characteristics of the tests and metrics they choose.

Relationship between vertical jump performance and playing time and efficiency in professional male basketball players

With innovative force plate technology being available to many sports organizations worldwide that allow for time-efficient in-depth neuromuscular performance assessment, the purpose of the present study was to examine the relationship between some of the most commonly analyzed countermovement vertical jump (CVJ) force-time metrics and basketball playing time and efficiency. Twenty-four professional male basketball players volunteered to participate in the present study. The CVJ testing procedures were conducted within the first quarter of the competitive season span. Following a standardized warm-up protocol, each athlete stepped on a dual uni-axial force plate system sampling at 1,000 Hz and performed three maximum-effort CVJs with no arm swing. To minimize the possible influence of fatigue, each jump trial was separated by a 10-15 s rest interval and the average value across three jumps was used for performance analysis purposes. Basketball playing efficiency and average playing time were obtained at the end of the regular season competitive period from the coaching staff records and the official team records. Pearson product-moment correlation coefficients (r) were used to examine the strength of the relationships between force-time metrics and basketball playing time and efficiency, separately for each dependent variable (p < 0.05). A significant positive association was observed between playing efficiency and eccentric mean force and eccentric mean and peak power (r = 0.406-0.552). Similarly, an increase in eccentric mean power was positively correlated with the number of minutes played during the competitive season (r = 0.464). Moreover, the aforementioned relationship remained present even when eccentric mean power was expressed relative to the player's body mass (r = 0.406). Thus, the findings of the present study indicate that, at the professional level of men's basketball competition, CVJ eccentric strength and power have a positive impact on both playing time and efficiency.

Differences in countermovement vertical jump force-time metrics between starting and non-starting professional male basketball players

With force plates being widely implemented for neuromuscular performance assessment in sport-specific settings and various force-time metrics being able to differentiate athletes based on their performance capabilities, the purpose of the present study was to examine the differences in countermovement vertical jump (CVJ) characteristics between starting and non-starting professional male basketball players (e.g., ABA League). Twenty-three athletes (height = 199.2 ± 7.7 kg, body mass = 94.2 ± 8.2 kg, age = 23.8 ± 4.9 years) volunteered to participate in the present investigation. Upon completion of a standardized warm-up protocol, each athlete performed three maximal-effort CVJs without an arm swing while standing on a uni-axial force plate system sampling at 1,000 Hz. Independent t-tests were used to examine statistically significant differences (p < 0.05) in each force-time metric between starters (n = 10) and non-starters (n = 13). No significant differences in any of the CVJ force-time metrics of interest were observed between the two groups, during both the eccentric and concentric phases of the movement (i.e., impulse, duration, peak velocity, and mean and peak force and power). Moreover, starters and non-starters demonstrated similar performance on CVJ outcome (e.g., jump height) and strategy metrics (e.g., countermovement depth). Overall, these findings suggest that at the professional level of play, the ability to secure a spot in the starting lineup is not primarily determined by the players' CVJ performance characteristics.