The Reliability and Validity of the Rebound Countermovement Jump in National Collegiate Athletic Association Division I American Football Players.

ABSTRACT: Talpey, SW, Drake, M, Haintz, L, Belanger, A, O'Grady, MW, Young, WB, Mundy, PD, James L, Gabbett, TJ, Gardner, EC. The reliability and validity of the rebound countermovement jump in National Collegiate Athletic Association Division I American Football Players. J Strength Cond Res XX(X): 000-000, 2024-The purpose of this study was to investigate the reliability and validity of the rebound countermovement jump (R-CMJ), as an alternate test of leg muscle function to the CMJ and drop jumps (DJs). Because the first phase of the R-CMJ mimics that of the CMJ, it is hypothesized that variables obtained in phase I of the R-CMJ will be like those of a CMJ. Similarly, because the second phase of a R-CMJ mimics a DJ, it is believed that the variables obtained from phase II will be like those from a DJ. Collegiate male American football players (N = 46) aged 18-24 years completed CMJs and R-CMJs on a portable force plate. Tests were completed on 3 separate days to determine the repeatability of select variables and to establish their validity. In addition, a subgroup (N = 20) of players from the cohort completed DJs from both 30 cm (DJ30) and 45 cm (DJ45) to determine the concurrent validity of the variables obtained from the second phase of the R-CMJ. Most variables obtained from the CMJ and R-CMJ phase I were found to be reliable, except for time-to-take-off. The variables from the DJ30, DJ45, and R-CMJ phase II displayed moderate to good reliability; however, all coefficient of variations were >10%. Jump height achieved in the CMJ was significantly greater than that achieved in phase I of the R-CMJ. The reactive strength index was significantly different in the R-CMJ compared with the DJ from both 30 and 45 cm heights. Although the R-CMJ may be inviting for coaches to use owing to its ease and time efficiency, the results of this study highlight that it may not provide a valid representation of an athlete's reactive strength.

The Validity of Hawkin Dynamics Wireless Dual Force Plates for Measuring Countermovement Jump and Drop Jump Variables.

Force plate testing is becoming more commonplace in sport due to the advent of commercially available, portable, and affordable force plate systems (i.e., hardware and software). Following the validation of the Hawkin Dynamics Inc. (HD) proprietary software in recent literature, the aim of this study was to determine the concurrent validity of the HD wireless dual force plate hardware for assessing vertical jumps. During a single testing session, the HD force plates were placed directly atop two adjacent Advanced Mechanical Technology Inc. in-ground force plates (the "gold standard") to simultaneously collect vertical ground reaction forces produced by 20 participants (27 ± 6 years, 85 ± 14 kg, 176.5 ± 9.23 cm) during the countermovement jump (CMJ) and drop jump (DJ) tests (1000 Hz). Agreement between force plate systems was determined via ordinary least products regression using bootstrapped 95% confidence intervals. No bias was present between the two force plate systems for any of the CMJ and DJ variables, except DJ peak braking force (proportional bias) and DJ peak braking power (fixed and proportional bias). The HD system may be considered a valid alternative to the industry gold standard for assessing vertical jumps because fixed or proportional bias was identified for none of the CMJ variables (n = 17) and only 2 out of 18 DJ variables.

Effect of Barbell Load on Vertical Jump Landing Force-Time Characteristics.

ABSTRACT: Lake, JP, Mundy, PD, Comfort, P, McMahon, JJ, Suchomel, TJ, and Carden, P. Effect of barbell load on vertical jump landing force-time characteristics. J Strength Cond Res 35(1): 25-32, 2021-The aim of this study was to quantify the effect that barbell load has on the jump height and force-time characteristics of the countermovement jump (CMJ). Fifteen strength-trained men (mean ± SD: age 23 ± 2 years, mass 84.9 ± 8.1 kg, and height 1.80 ± 0.05 m) performed 3 CMJs with no additional load, and with barbell loads of 25, 50, 75, and 100% of body mass on 2 force plates recording at 1,000 Hz. Propulsion and landing force-time characteristics were obtained from force-time data and compared using analysis of variance and effect sizes. Jump height decreased significantly as load increased (26-71%, d = 1.80-6.87). During propulsion, impulse increased with load up to 75% of body mass (6-9%, d = 0.71-1.08), mean net force decreased (10-43%, d = 0.50-2.45), and time increased (13-50%, d = 0.70-2.57). During landing, impulse increased as load increased up to 75% of body mass (5 to 12%, d = 0.54-1.01), mean net force decreased (13-38%, d = 0.41-1.24), and time increased (20-47%, d = 0.65-1.47). Adding barbell load to CMJ significantly decreases CMJ height. Furthermore, CMJ with additional barbell load increases landing phase impulse. However, while mean net force decreases as barbell load increases, landing time increases so that jumpers are exposed to mechanical load for longer. Practitioners should exercise caution when implementing loaded CMJ to assess their athletes.

The effects of barbell load on countermovement vertical jump power and net impulse.

The aim of this study was to examine the effects of barbell load on countermovement vertical jump (CMJ) power and net impulse within a theoretically valid framework, cognisant of the underpinning force, temporal, and spatial components. A total of 24 resistance-trained rugby union athletes (average ± SD: age: 23.1 ± 3.4 years; height: 1.83 ± 0.05 m; body mass (BM): 91.3 ± 10.5 kg) performed maximal CMJ under 5 experimental conditions in a randomised, counterbalanced order: unloaded, and with additional loads of 25%, 50%, 75%, and 100% of BM. Peak power and average power were maximised during the unloaded condition, both decreasing significantly (P < 0.05) as load increased. Net impulse was maximised with 75% of BM, which was significantly greater (P < 0.05) than the unloaded and 100% of BM conditions. Net mean force and mean velocity were maximised during the unloaded condition and decreased significantly (P < 0.05) as load increased, whereas phase duration increased significantly (P < 0.05) as load increased. As such, the interaction between barbell load and the underpinning force, time, and displacement components should be considered by strength and conditioning coaches when prescribing barbell loads.

Power and impulse applied during push press exercise.

The aim of this study was to quantify the load, which maximized peak and mean power, and impulse applied to these loads, during the push press and to compare them to equivalent jump squat data. Resistance-trained men performed 2 push press (n = 17; age: 25.4 ± 7.4 years; height: 183.4 ± 5 cm; body mass: 87 ± 15.6 kg) and jump squat (n = 8 of original 17; age: 28.7 ± 8.1 years; height: 184.3 ± 5.5 cm; mass: 98 ± 5.3 kg) singles with 10-90% of their push press and back squat 1 repetition maximum (1RM), respectively, in 10% 1RM increments while standing on a force platform. Push press peak and mean power was maximized with 75.3 ± 16.4 and 64.7 ± 20% 1RM, respectively, and impulses applied to these loads were 243 ± 29 N·s and 231 ± 36 N·s. Increasing and decreasing load, from the load that maximized peak and mean power, by 10 and 20% 1RM reduced peak and mean power by 6-15% (p ≤ 0.05). Push press and jump squat maximum peak power (7%, p = 0.08) and the impulse that was applied to the load that maximized peak (8%, p = 0.17) and mean (13%, p = 0.91) power were not significantly different, but push press maximum mean power was significantly greater than the jump squat equivalent (∼9.5%, p = 0.03). The mechanical demand of the push press is comparable with the jump squat and could provide a time-efficient combination of lower-body power and upper-body and trunk strength training.

The Influence of Recruitment Age and Anthropometric and Physical Characteristics on the Development Pathway of English Academy Football Players.

PURPOSE: To investigate the influence of recruitment age on retention and release across the development pathway and to explore the influence of anthropometric and physical characteristics on retention and release at different ages throughout the development pathway and the likelihood of obtaining a professional contract. METHODS: Following receipt of ethics approval, a cross-sectional study tracking 4 cohorts of players over 5 years assessed 76 male youth football players (11-16 y) from an English football academy on 3 occasions annually in anthropometry, countermovement jump height, and linear (30 and 15 m) and multidirectional sprint time. Players were categorized based on their start and release date. RESULTS: Starting early (ie, before U12) in an academy was a key indicator of obtaining a professional contract, representing 87% of the players signed. Bayesian regression models suggest that the majority of differences in physical characteristics between players that were released and retained are trivial, small, and/or uncertain. Players who attained a professional contract at 18 had slower 15- and 30-m sprint times at U13 to U15 (P > 0 = .87-.99), slower multidirectional sprint times at U14 (P > 0 = .99), and lower countermovement jump height at U13 to U16 (P > 0 = .88-.99) compared with players who did not gain a contract. CONCLUSION: Players recruited early have an increased likelihood of gaining a professional contract. Physical assessments lack utility when used in isolation as a talent-identification tool.

Do the peak and mean force methods of assessing vertical jump force asymmetry agree?

The aim of this study was to assess agreement between peak and mean force methods of quantifying force asymmetry during the countermovement jump (CMJ). Forty-five men performed four CMJ with each foot on one of two force plates recording at 1,000 Hz. Peak and mean were obtained from both sides during the braking and propulsion phases. The dominant side was obtained for the braking and propulsion phase as the side with the largest peak or mean force and agreement was assessed using percentage agreement and the kappa coefficient. Braking phase peak and mean force methods demonstrated a percentage agreement of 84% and a kappa value of 0.67 (95% confidence limits: 0.45-0.90), indicating substantial agreement. Propulsion phase peak and mean force methods demonstrated a percentage agreement of 87% and a kappa value of 0.72 (95% confidence limits: 0.51-0.93), indicating substantial agreement. While agreement was substantial, side-to-side differences were not reflected equally when peak and mean force methods of assessing CMJ asymmetry were used. These methods should not be used interchangeably, but rather a combined approach should be used where practitioners consider both peak and mean force to obtain the fullest picture of athlete asymmetry.

The Kinematic and Kinetic Development of Sprinting and Countermovement Jump Performance in Boys.

BACKGROUND: The aim of the study was to examine the kinematics and kinetics of sprint running and countermovement jump performance between the ages of 8-9, and 11-12 years old boys in order to understand the developmental plateau in performance. METHODS: 18 physically active boys (Age: 10.1 ± 1.6), in an under 9 years old (U9) and an under 12 years old (U12) group performed 15 m sprints and countermovement jumps. A 3D motion analysis system (200 Hz), synchronized with four force platforms (1,000 Hz), was used to collect kinematic and kinetic data during the first stance phase of the sprint run and the countermovement jump. RESULTS: The U12 group had a significantly greater height (U9: 1.364 ± 0.064 m; U12: 1.548 ± 0.046 mm), larger mass (U9: 30.9 ± 3.5 kg; U12: 43.9 ± 5.0 kg), superior sprint performance over 0-5 m (U9: 1.31 ± 0.007 s; U12: 1.23 ± 0.009 s) and 0-15 m (U9: 3.20 ± 0.17 s; U12: 3.01 ± 0.20 s), and increased jump height (U9: 0.17 ± 0.06 m; U12: 0.24 ± 0.10 m) than the under nine group. During the first stance phase of the sprint the U12 group had a significantly greater vertical (U9: 0.22 ± 0.02 BW/s; U12: 0.25 ± 0.03 BW.s) and horizontal impulse (U9: 0.07 ± 0.02 BW/s; U12: 0.09 ± 0.03 BW.s) than the U9 group. When performing a countermovement jump the U12 group had a significantly greater mean average eccentric force (U9: 407.3 ± 55.0 N; U12: 542.2 ± 65.1 N) and mean average concentric force (U9: 495.8 ± 41.3 N; U12: 684.0 ± 62.1 N). Joint kinematics for the countermovement jump were significantly different between age groups for the ankle range of motion (U9: 80.6 ± 17.4°; U12: 64.1 ± 9°) and knee minimum joint angle (U9: -5.7 ± 3.9°; U12: 0.0 ± 4.4°). Conclusion: The study demonstrates for the first time that the development of physically active boys between the ages of 8-9 to 11-12 years increased the ground reaction forces and impulses during sprint running and countermovement jumps, but that sprint running technique had not developed during this period. Furthermore, countermovement jump technique was still emerging at the age of 8-9 years old. Practitioners need to implement on-going fine-grained sprint running and CMJ technique sessions to ensure that the increased force producing capabilities that come with age are appropriately utilized.

Carbohydrate mouth rinse improves morning high-intensity exercise performance.

Oral carbohydrate (CHO) rinsing has been demonstrated to provide beneficial effects on exercise performance of durations of up to one hour. The aim of the present study was to investigate the effects of CHO mouth rinsing on morning high-intensity exercise performance. Following institutional ethical approval and familiarisation, 12 healthy males (mean ± SD age: 23 ± 3 years, height: 175.5 ± 7.4 cm, body mass: 75.4 ± 7.5 kg) participated in this study. Countermovement jump (CMJ) height, isometric mid-thigh pull peak force, 10 m sprint time and bench press and back squat repetitions to failure were assessed following CHO and placebo (PLA) rinsing or a control condition (CON). All testing took place at 07:30 following an 11 hour overnight fast. Performance of CMJ height (CHO: 39 ± 7 cm; PLA: 38 ± 7 cm; CON: 36 ± 6 cm; P = .003, [Formula: see text] = 0.40), 10 m sprint time (CHO: 1.78 ± 0.07 s; PLA: 1.81 ± 0.07 s; CON: 1.85 ± 0.05 s; P = .001, [Formula: see text] = 0.47), the number of bench press (CHO: 25 ± 3; PLA: 24 ± 4; CON: 22 ± 4; P < .001, [Formula: see text] = 0.55) and squat (CHO: 31 ± 4; PLA: 29 ± 5; CON: 26 ± 6; P < .001, [Formula: see text] = 0.70) repetitions and mean felt arousal (CHO: 5 ± 1; PLA: 4 ± 0; CON: 4 ± 0; P = .009, [Formula: see text] = 0.25) improved following CHO rinsing. However, isometric mid-thigh pull peak force was unchanged (CHO: 2262 ± 288 N; PLA: 2236 ± 354 N; CON: 2212 ± 321 N; P = .368, [Formula: see text] = 0.08). These results suggest that oral CHO rinsing solution significantly improved the morning performance of CMJ height, 10 m sprint times, bench press and squat repetitions to failure and felt arousal, although peak force during an isometric mid-thigh pull, rating of perceived exertion and heart rate were unaffected.

Agreement between the force platform method and the combined method measurements of power output during the loaded countermovement jump.

There are two perceived criterion methods for measuring power output during the loaded countermovement jump (CMJ): the force platform method and the combined method (force platform + optoelectronic motion capture system). Therefore, the primary aim of the present study was to assess agreement between the force platform method and the combined method measurements of peak power and mean power output during the CMJ across a spectrum of loads. Forty resistance-trained team sport athletes performed maximal effort CMJ with additional loads of 0 (body mass only), 25, 50, 75 and 100% of body mass (BM). Bias was present for peak velocity, mean velocity, peak power and mean power at all loads investigated, and present for mean force up to 75% of BM. Peak velocity, mean velocity, peak power and mean power 95% ratio limits of agreement were clinically unacceptable at all loads investigated. The 95% ratio limits of agreement were widest at 0% of BM and decreased linearly as load increased. Therefore, the force platform method and the combined method cannot be used interchangeably for measuring power output during the loaded CMJ. As such, if power output is to be meaningfully investigated, a standardised method must be adopted.