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12 pages, 2434 KiB

Open AccessArticle

Surfing the Waves of the CMJ; Are There between-Sport Differences in the Waveform Data?

by James Parker and Lina E. Lundgren

Sports 2018, 6(4), 168; https://doi.org/10.3390/sports6040168 - 8 Dec 2018

Cited by 9 | Viewed by 6642

Abstract

The ability to analyse countermovement jump (CMJ) waveform data using statistical methods, like principal component analysis, can provide additional information regarding the different phases of the CMJ, compared to jump height or peak power alone. The aim of this study was to investigate [...] Read more.

The ability to analyse countermovement jump (CMJ) waveform data using statistical methods, like principal component analysis, can provide additional information regarding the different phases of the CMJ, compared to jump height or peak power alone. The aim of this study was to investigate the between-sport force-time curve differences in the CMJ. Eighteen high level golfers (male = 10, female = 8) and eighteen high level surfers (male = 10, female = 8) performed three separate countermovement jumps on a force platform. Time series of data from the force platform was normalized to body weight and each repetition was then normalized to 0–100 percent. Principal component analyses (PCA) were performed on force waveforms and the first six PCs explained 35% of the variance in force parameters. The main features of the movement cycles were characterized by magnitude (PC1 and PC5), waveform (PC2 and PC4), and phase shift features (PC3). Surf athletes differ in their CMJ technique and show a greater negative centre of mass displacement when compared to golfers (PC1), although these differences are not necessarily associated with greater jump height. Principal component 5 demonstrated the largest correlation with jump height (R² = 0.52). Further studies are recommended in this area, to reveal which features of the CMJ that relate to jumping performance, and sport specific adaptations. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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10 pages, 2690 KiB

Open AccessArticle

Using Portable Force Plates to Assess Vertical Jump Performance: A Metrological Appraisal

by François Raymond, Benoit Lussier, François Dugas, Mathieu Charbonneau, Félix Croteau, Cory Kennedy and Nicolas Berryman

Sports 2018, 6(4), 149; https://doi.org/10.3390/sports6040149 - 19 Nov 2018

Cited by 7 | Viewed by 5540

Abstract

The purpose of this study was to verify the metrological properties of portable force plates that are used to assess countermovement jump performance. While 88 participants (38 males, 50 females) were included in the agreement analyses, 84 participants (37 males and 47 females) [...] Read more.

The purpose of this study was to verify the metrological properties of portable force plates that are used to assess countermovement jump performance. While 88 participants (38 males, 50 females) were included in the agreement analyses, 84 participants (37 males and 47 females) completed the reliability part of the study. This randomized crossover design suggests that portable force plates could be used interchangeably with a reference system. Indeed, the differences between both devices were all considered trivial (effect size (ES) < 0.20), and the mean bias was never greater than 3.41% in comparison to the reference system. In addition, the absolute and relative reliability parameters were found to be acceptable for clinical use, even when used on different floor surfaces. However, it was found that the ratio between flight time and contraction time (FTCT) showed questionable reliability when tests were conducted on different surfaces (intraclass correlation coefficient = 0.49; coefficient of variation = 26.72%). Therefore, practitioners should be careful when installing the portable device on different floor surfaces in order to optimize the reliability and the ability to detect real change in the context of a countermovement jump monitoring process. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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8 pages, 688 KiB

Open AccessArticle

Within-Subject Consistency of Unimodal and Bimodal Force Application during the Countermovement Jump

by Jason P. Lake and John J. McMahon

Sports 2018, 6(4), 143; https://doi.org/10.3390/sports6040143 - 8 Nov 2018

Cited by 15 | Viewed by 5387

Abstract

Countermovement jump (CMJ) force data are often time-normalized so researchers and practitioners can study the effect that sex, training status, and training intervention have on CMJ strategy: the so-called force–time curve shape. Data are often collected on an individual basis and then averaged [...] Read more.

Countermovement jump (CMJ) force data are often time-normalized so researchers and practitioners can study the effect that sex, training status, and training intervention have on CMJ strategy: the so-called force–time curve shape. Data are often collected on an individual basis and then averaged across interest-groups. However, little is known about the agreement of the CMJ force–time curve shape within-subject, and this formed the aim of this study. Fifteen men performed 10 CMJs on in-ground force plates. The resulting force–time curves were plotted, with their shape categorized as exhibiting either a single peak (unimodal) or a double peak (bimodal). Percentage-agreement and the kappa-coefficient were used to assess within-subject agreement. Over two and three trials, 13% demonstrated a unimodal shape, 67% exhibited a bimodal shape, and 20% were inconsistent. When five trials were considered, the unimodal shape was not demonstrated consistently; 67% demonstrated a bimodal shape, and 33% were inconsistent. Over 10 trials, none demonstrated a unimodal shape, 60% demonstrated a bimodal shape, and 40% were inconsistent. The results of this study suggest that researchers and practitioners should ensure within-subject consistency before group averaging CMJ force–time data, to avoid errors. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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13 pages, 7172 KiB

Open AccessFeature PaperArticle

The Validity of the Push Band 2.0 during Vertical Jump Performance

by Jason P. Lake, Simon Augustus, Kieran Austin, Peter Mundy, John J. McMahon, Paul Comfort and Guy G. Haff

Sports 2018, 6(4), 140; https://doi.org/10.3390/sports6040140 - 5 Nov 2018

Cited by 34 | Viewed by 6032

Abstract

The Push Band has the potential to provide a cheap and practical method of measuring velocity and power during countermovement vertical jumping (CMJ). However, very little is known about whether it conforms to laboratory-based gold standards. The aim of this study was to [...] Read more.

The Push Band has the potential to provide a cheap and practical method of measuring velocity and power during countermovement vertical jumping (CMJ). However, very little is known about whether it conforms to laboratory-based gold standards. The aim of this study was to assess the agreement between peak and mean velocity and power obtained from the belt-worn Push Band, and derived from three-dimensional motion capture, and vertical force from an in-ground force platform. Twenty-two volunteers performed 3 CMJ on a force platform, while a belt-worn Push Band and a motion capture system (a marker affixed to the Push Band) simultaneously recorded data that enabled peak and mean velocity and power to be calculated and then compared using ordinary least products regression. While the Push Band is reliable, it tends to overestimate peak (9–17%) and mean (24–27%) velocity, and when compared to force plate-derived peak and mean power, it tends to underestimate (40–45%) and demonstrates fixed and proportional bias. This suggests that while the Push Band may provide a useful method for measuring peak and mean velocity during the CMJ, researchers and practitioners should be mindful of its tendency to systematically overestimate and that its measures of peak and mean power should not be used. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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12 pages, 230 KiB

Open AccessArticle

Assessing Plyometric Ability during Vertical Jumps Performed by Adults and Adolescents

by Brandon W. Snyder, Shawn N. Munford, Chris Connaboy, Hugh S. Lamont, Shala E. Davis and Gavin L. Moir

Sports 2018, 6(4), 132; https://doi.org/10.3390/sports6040132 - 27 Oct 2018

Cited by 10 | Viewed by 4871

Abstract

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players [...] Read more.

The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (W_NORM), and power output (PO_NORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSI_MOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. W_NORM (MD: 4.2 J/kg) and PO_NORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSI_MOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

8 pages, 544 KiB

Open AccessArticle

Larger Countermovement Increases the Jump Height of Countermovement Jump

by Alberto Sánchez-Sixto, Andrew J. Harrison and Pablo Floría

Sports 2018, 6(4), 131; https://doi.org/10.3390/sports6040131 - 26 Oct 2018

Cited by 43 | Viewed by 13776

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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11 pages, 743 KiB

Open AccessArticle

Using Drop Jumps and Jump Squats to Assess Eccentric and Concentric Force-Velocity Characteristics

by Gavin L. Moir, Brandon W. Snyder, Chris Connaboy, Hugh S. Lamont and Shala E. Davis

Sports 2018, 6(4), 125; https://doi.org/10.3390/sports6040125 - 24 Oct 2018

Cited by 8 | Viewed by 5168

Abstract

The purpose of this study was to investigate the eccentric and concentric force-velocity (Fv) characteristics recorded during drop jumps (DJ) from different heights and loaded jump squats (JS) and to determine the number of jumps required to accurately model the eccentric and concentric [...] Read more.

The purpose of this study was to investigate the eccentric and concentric force-velocity (Fv) characteristics recorded during drop jumps (DJ) from different heights and loaded jump squats (JS) and to determine the number of jumps required to accurately model the eccentric and concentric Fv relationships. Fourteen resistance-trained men (age: 21.9 ± 1.8 years) performed a countermovement jump (CMJ) and DJ from heights of 0.40, 0.60, and 0.80 m. JS with loads equivalent to 0%, 27%, 56%, and 85% 1-repetition maximum were performed in a separate session. Force platforms and a 3-D motion analysis system were used to record the average force (

\bar{F}

) and velocity (

\bar{v}

) during the absorption (CMJ, DJ₄₀, DJ₆₀, DJ₈₀) and propulsion (JS₀, JS₂₇, JS₅₆, JS₈₅) phases of the jumps. Eccentric (absorption phase) and concentric (propulsion phase) Fv characteristics were then calculated and linear regression equations were determined when the number of jumps included was varied.

\bar{F}

during the absorption phase significantly increased from CMJ to DJ₆₀ while

\bar{v}

increased significantly from CMJ to DJ₈₀. The two-point method (CMJ, DJ₈₀) resulted in a significantly lower y-intercept (mean difference [MD]: 0.7 N/kg) and a greater slope (MD: 0.7 Ns/m) for the eccentric Fv characteristics compared to the multiple-point method.

\bar{F}

increased significantly and

\bar{v}

decreased significantly with increasing external load in the JS conditions. The two-point method (JS₀, JS₈₅) resulted in a significantly greater y-intercept (MD: 1.1 N/kg) compared to the multiple-point method for the concentric Fv characteristics. Both DJ and loaded JS may provide means of assessing the eccentric and concentric Fv characteristics with only two jumps being required. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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15 pages, 615 KiB

Open AccessArticle

Countermovement Jump Analysis Using Different Portable Devices: Implications for Field Testing

by Vincenzo Rago, João Brito, Pedro Figueiredo, Thiago Carvalho, Tiago Fernandes, Pedro Fonseca and António Rebelo

Sports 2018, 6(3), 91; https://doi.org/10.3390/sports6030091 - 31 Aug 2018

Cited by 73 | Viewed by 12401

Abstract

The aim of this study was to analyze the concurrent validity, test–retest reliability, and capacity to detect changes of four different portable devices used to measure a wide range of neuromuscular parameters derived from countermovement jump (CMJ). An accelerometric device (Myotest), a jump [...] Read more.

The aim of this study was to analyze the concurrent validity, test–retest reliability, and capacity to detect changes of four different portable devices used to measure a wide range of neuromuscular parameters derived from countermovement jump (CMJ). An accelerometric device (Myotest), a jump mat (Ergojump), an optical device (Optojump), and a smartphone app (MyJump) were simultaneously examined for concurrent validity against gold-standard measures (motion-capture system and a force platform). Twenty-two CMJ-derived variables were collected from 15 healthy male subjects (n = 60 CMJs). Contraction time (CT) and eccentric duration (EccD) measurements obtained from the Myotest were moderately to largely associated with and not different from force platform measurements (r = 0.31 to 0.64, ES = 0.11 to 0.18) and showed moderate test-retest reliability (intraclass correlation coefficient (ICC) = 0.92 to 0.97, coefficient of variation (CV) = 3.8 to 8.0%). Flight time (FT) and jump height (JH) from Ergojump, Optojump, and MyJump showed moderate to strong associations with gold-standard measurements (r = 0.57 to 0.98) and good test–retest reliability (ICC = 0.54 to 0.97, CV = 1.8 to 4.2). However, all portable devices underestimated JH (ES = 1.25 to 2.75). Independent of the instrument used, the analyzed CMJ variables showed good capacity to detect changes (standard error of measurement (SEM) < smallest worthwhile change (SWC)), with the exception of rate of force and rate of power development parameters, which showed marginal capacity (SEM > SWC). The Myotest is preferable to measure temporal parameters during ground contact, whereas Ergojump, Optojump, and MyJump devices may be preferable to measure FT and JH, with the Optojump being the most accurate. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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10 pages, 1396 KiB

Open AccessFeature PaperArticle

Reliability of and Relationship between Flight Time to Contraction Time Ratio and Reactive Strength Index Modified

by John J. McMahon, Jason P. Lake and Paul Comfort

Sports 2018, 6(3), 81; https://doi.org/10.3390/sports6030081 - 15 Aug 2018

Cited by 25 | Viewed by 7977

Abstract

Countermovement jump (CMJ) force-time testing is commonly used to monitor seasonal alterations in athletes’ CMJ strategy (to infer alterations in neuromuscular function). The flight time to contraction time (FT:CT) ratio and reactive strength index modified (RSI_mod) are considered to be two [...] Read more.

Countermovement jump (CMJ) force-time testing is commonly used to monitor seasonal alterations in athletes’ CMJ strategy (to infer alterations in neuromuscular function). The flight time to contraction time (FT:CT) ratio and reactive strength index modified (RSI_mod) are considered to be two primary CMJ variables of interest. Due to similar calculations, it is likely that the FT:CT ratio and RSI_mod share similar reliability and an almost perfect relationship. Consequently, there may be no requirement to include both variables in CMJ monitoring reports. This study aimed to investigate this by recruiting twenty-five males to perform three CMJs on a force platform across two sessions that were separated by one week. The FT:CT ratio and two calculations of RSI_mod (based on the jump height from either flight time or take-off velocity) were then calculated using robust methods. The between-day reliability was good-excellent for all of the variables (95% confidence interval range of the coefficient of variation = 2.02–9.22%) with no significant between-day differences noted (p ≥ 0.231). There was an almost perfect positive relationship between the FT:CT ratio and RSI_mod regardless of the calculation method (r = 0.944–0.947, p < 0.001). As the FT:CT ratio and RSI_mod yield similar absolute reliability and share 90% of common variance, there is little reason to include both variables in CMJ monitoring reports. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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8 pages, 1029 KiB

Open AccessFeature PaperArticle

Portable Force Plates: A Viable and Practical Alternative to Rapidly and Accurately Monitor Elite Sprint Performance

by Irineu Loturco, Lucas A. Pereira, Ronaldo Kobal, Cesar C. Cal Abad, Victor Fernandes, Rodrigo Ramirez-Campillo and Timothy Suchomel

Sports 2018, 6(3), 61; https://doi.org/10.3390/sports6030061 - 12 Jul 2018

Cited by 16 | Viewed by 6346

Abstract

This study aimed to examine the associations between a series of mechanical variables automatically generated by a portable force plate (PFP) and the actual performance of professional sprinters over a 150 m course. To test these correlations, 12 top-level sprinters performed vertical jumps [...] Read more.

This study aimed to examine the associations between a series of mechanical variables automatically generated by a portable force plate (PFP) and the actual performance of professional sprinters over a 150 m course. To test these correlations, 12 top-level sprinters performed vertical jumps (squat and countermovement jumps; SJ and CMJ, respectively), a 60 m sprint test, and a 150 m sprint test. Pearson product-moment coefficient of correlation and multiple regression analyses were used to determine the relationships between the sprinting velocities and vertical jump outputs. The SJ parameters were moderately to near perfectly associated with the different sprint distances, and the SJ height presented the highest correlation scores (r = 0.90 with velocities over 10- and 20-m). The correlation coefficients between the CMJ outcomes and sprint results varied between moderate and very large (from 0.38 to 0.88). Finally, the coefficients of determination (R²) ranged from 0.71 to 0.85 for the different multiple regressions involving PFP automatic measures. The PFP can provide practitioners with quick and accurate information regarding competitive athletes. Due to the strong correlations observed, coaches are encouraged to frequently adjust and tailor the training strategies of their sprinters, using practical and timesaving PFP measurements. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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13 pages, 2161 KiB

Open AccessFeature PaperArticle

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

by Rodney A. Kennedy and David Drake

Sports 2018, 6(2), 36; https://doi.org/10.3390/sports6020036 - 18 Apr 2018

Cited by 18 | Viewed by 7854

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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Other

Jump to: Research

10 pages, 1136 KiB

Open AccessFeature PaperBrief Report

Preliminary Scale of Reference Values for Evaluating Reactive Strength Index-Modified in Male and Female NCAA Division I Athletes

by Christopher J. Sole, Timothy J. Suchomel and Michael H. Stone

Sports 2018, 6(4), 133; https://doi.org/10.3390/sports6040133 - 29 Oct 2018

Cited by 15 | Viewed by 5716

Abstract

The purpose of this analysis was to construct a preliminary scale of reference values for reactive strength index-modified (RSI_mod). Countermovement jump data from 151 National Collegiate Athletic Association (NCAA) Division I collegiate athletes (male n = 76; female n = 75) [...] Read more.

The purpose of this analysis was to construct a preliminary scale of reference values for reactive strength index-modified (RSI_mod). Countermovement jump data from 151 National Collegiate Athletic Association (NCAA) Division I collegiate athletes (male n = 76; female n = 75) were analyzed. Using percentiles, scales for both male and female samples were constructed. For further analysis, athletes were separated into four performance groups based on RSI_mod and comparisons of jump height (JH), and time to takeoff (TTT) were performed. RSI_mod values ranged from 0.208 to 0.704 and 0.135 to 0.553 in males and females, respectively. Males had greater RSI_mod (p < 0.001, d = 1.15) and JH (p < 0.001, d = 1.41) as compared to females. No statistically significant difference was observed for TTT between males and females (p = 0.909, d = 0.02). Only JH was found to be statistically different between all performance groups. For TTT no statistical differences were observed when comparing the top two and middle two groups for males and top two, bottom two, and middle two groups for females. Similarities in TTT between sexes and across performance groups suggests JH is a primary factor contributing to differences in RSI_mod. The results of this analysis provide practitioners with additional insight as well as a scale of reference values for evaluating RSI_mod scores in collegiate athletes. Full article

(This article belongs to the Special Issue Kinetic Assessment of Vertical Jumping: Application to Training and Monitoring Athletes)

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