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Jason D. Stone, Adam C. King, Shiho Goto, John D. Mata, Joseph Hannon, James C. Garrison, James Bothwell, Andrew R. Jagim, Margaret T. Jones and Jonathan M. Oliver

right and left end of the barbell. Three reflective markers (seventh cervical vertebra, bilateral anterosuperior iliac spine) were removed after the static trial. Kinetic data were obtained at a sampling frequency of 1200 Hz from bilateral force platforms (Advanced Medical Technology, Inc, Watertown, MA

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Jozo Grgic, Sandro Venier and Pavle Mikulic

performed on a force platform (BP600600; AMTI, Inc., Watertown, MA), accompanied with a custom-developed software for data acquisition and analysis. In each testing session, the subjects performed 3 countermovement jumps (CMJs) on this platform, with a detailed procedure explained elsewhere. 9 , 10 The

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Pedro Jiménez-Reyes, Fernando Pareja-Blanco, David Rodríguez-Rosell, Mario C. Marques and Juan José González-Badillo

Purpose:

To determine what variables determine the differences in performance on 2 tests of squat jump (SJ) performed under light load in highly trained athletes using maximal velocity (Vmax) or flight time (FT) as the discriminating factor of SJ performance.

Methods:

Thirty-two participants performed 2 maximal weighted SJs using a force platform synchronized with a linear transducer. Mean force (Fmean), mean and maximal power (Pmean, Pmax), peak force (PF), maximal rate of force development (RFDmax), and time required to attain PF (TPF) and RFDmax (TRFDmax) were analyzed. SJs were divided into 2 segments: from the initiation of force application to PF1 and from the moment after PF1 to Vmax.

Results:

Traditional significance statistics revealed significant differences in the same variables between best and worst SJs using both FT and Vmax. However, to use an approach based on the magnitude of the effect, the best SJ showed greater Pmax (83/17/0%), Pmean (85/15/0%), Fmean (71/29/0%), RFDmax1 (73/27/0%), and PF1 (53/47/0%) and lower TPF2 (0/61/39%) than the worst SJ when Vmax was used to discriminate SJ performance. However, using FT to differentiate SJ performance, no difference was observed between best and worst.

Conclusions:

Although jump height assessed through FT is a valid measure, these results suggest that Vmax is a more sensitive variable than FT to detect differences in loaded-SJ performance.

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Warren Young, Stuart Cormack and Michael Crichton

Purpose:

The main purpose of this study was to determine the relationships between countermovement jump (CMJ) variables and acceleration and maximum speed performance.

Methods:

Twenty-three elite Australian football players were tested on a CMJ, which yielded several kinematic and kinetic variables describing leg muscle function. A 40 m sprint was also conducted to assess acceleration (10 m time) and an estimate of maximum speed (fying 20 m time). Players from one Australian Football League (AFL) club were tested and Pearson correlations for CMJ variables and sprint performance were calculated.

Results:

Jump height, peak velocity, peak force, and peak power had less than 50% common variance, and therefore represented independent expressions of CMJ performance. Generally, the correlations between CMJ variables and sprinting performance were stronger for maximum speed (small to large effect sizes) than for acceleration (trivial to moderate sizes). The variable that produced the strongest correlation with acceleration was jump height (r = -0.430, P = .041) and with maximum speed was peak power/weight (r = -0.649, P = .001).

Conclusions:

The results indicate that if an integrated system comprising a position transducer and a force platform is available for CMJ assessment, jump height and peak power/weight are useful variables to describe leg muscle explosive function for athletes who perform sprints.

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Peter Werner and Judith Rink

The purpose of this study was to describe the teaching behaviors of four teachers who had varying degrees of expertise in working with second grade students and to improve the teachers’ effectiveness. Four experienced teachers were asked to teach a six-lesson unit in jumping and landing skills to an intact class of their choice. Students were pre- and posttested on their ability to produce and reduce force using a force platform and a jump for distance without the platform. OSCD-PE (Rink, 1979) was used to describe the more general aspects of the teachers’ content development and managerial skills. Task presentation, nature of feedback, and appropriateness of student responses were obtained using the QMTPS (Rink & Werner, 1989). Additional information was obtained by counting practice trials and analyzing teacher written plans and approaches to content. Following the first teaching experience, the researchers gave feedback to the teachers and asked them to reteach the unit to a different class. Product and process measures were obtained in the same manner on the second teaching experience. Data were presented in a case study format. The results describe the importance of content knowledge, the ability to present information clearly, and holding students accountable for selected performance aspects.

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Simo Ihalainen, Vesa Linnamo, Kaisu Mononen and Sami Kuitunen

Purpose:

To describe the long-term changes in shooting technique in relation to competition performances in elite air-rifle shooters.

Methods:

Seventeen elite shooters completed simulated air-rifle shooting-competition series in 3 consecutive seasons, participating on 15 ± 7 testing occasions. Shooting score and aiming-point-trajectory variables were obtained with an optoelectronic shooting device, and postural-balance variables were measured with force platform. Shooters’ competition results were collected from all international and national competitions during the 3-y period.

Results:

Mean test score, stability of hold, aiming accuracy, cleanness of triggering, and postural balance improved during the 3-y period (ANOVA, time, P < .05−.01). Seasonal mean test results in stability of hold (R = −.70, P = .000) and cleanness of triggering (R = −.75, P = .000) were related to competition performances. Changes in stability of hold (R = −.61, P = .000) and cleanness of triggering (R = −.39, P = .022) were also related to the changes in competition performances. Postural balance in shooting direction was more related to cleanness of triggering (R = .57, P = .000), whereas balance in cross-shooting direction was more related to stability of hold (R = .70, P = .000).

Conclusion:

The shooting-technique testing used in the current study seems to be a valid and useful tool for long-term performance assessment. Stability of hold, cleanness of triggering, and postural balance can be further developed even at the elite level, resulting in improved competition performances.

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Thomas Dos’Santos, Paul A. Jones, Jonathan Kelly, John J. McMahon, Paul Comfort and Christopher Thomas

Purpose:

Skeletal-muscle function can be evaluated using force–times curves generated via the isometric midthigh pull (IMTP). Various sampling frequencies (500–1000 Hz) have been used for IMTP assessments; however, no research has investigated the influence of sampling frequency on IMTP kinetics. Therefore, the purpose of this study was to investigate the influence of sampling frequency on kinetic variables during the IMTP, including peak force, time-specific force values (100, 150, and 200 ms), and rate of force development (RFD) at 3 time bands (0–100, 0–150, 0–200 ms).

Methods:

Academy rugby league players (n = 30, age 17.5 ± 1.1 y, height 1.80 ± 0.06 m, mass 85.4 ± 10.3 kg) performed 3 IMTP trials on a force platform sampling at 2000 Hz, which was subsequently down-sampled to 1500, 1000, and 500 Hz for analysis.

Results:

Intraclass correlation coefficients (ICC) and coefficients of variation (CV) demonstrated high within-session reliability for all force and RFD variables across all sampling frequencies (ICC ≥ .80, CV ≤ 10.1%). Repeated-measures analysis of variance revealed no significant differences (P > .05, Cohen d ≤ 0.009) in kinetic variables between sampling frequencies. Overall, high reliability was observed across all sampling frequencies for all kinetic variables, with no significant differences (P > .05) for each kinetic variable across sampling frequencies.

Conclusions:

Practitioners and scientists may consider sampling as low as 500 Hz when measuring peak force, time-specific force values, and RFD at predetermined time bands during the IMTP for accurate and reliable data.

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John J. McMahon, Shannon Murphy, Sophie J.E. Rej and Paul Comfort

Purpose:

Gross measures of countermovement-jump (CMJ) performance are commonly used to track maturational changes in neuromuscular function in rugby league (RL). The purpose of this study was to conduct both a gross and a more detailed temporal-phase analysis of the CMJ performances of senior and academy RL players, to provide greater insight into how neuromuscular function differs between these groups.

Methods:

Twenty senior and 14 academy (under-19) male RL players performed 3 maximal-effort CMJs on a force platform, with forward dynamics subsequently employed to allow gross performance measures and entire kinetic– and kinematic–time curves to be compared between groups.

Results:

Jump height (JH), reactive strength index modified, concentric displacement, and relative concentric impulse (C-IMP) were the only gross measures that were greater for senior players (d = 0.58–0.91) than for academy players. The relative force- and displacement–time curves were similar between groups, but the relative power– and velocity–time curves were greater (d = 0.59–0.97) for the senior players at 94–96% and 89–100% of the total movement time, respectively.

Conclusions:

The CMJ distinguished between senior and academy RL players, with seniors demonstrating greater JH through applying a larger C-IMP and thus achieving greater velocity throughout the majority of the concentric phase and at takeoff. Therefore, academy RL players should train to improve triple (ie, ankle, knee, and hip) extension velocity during the CMJ to bring their JH scores in line with those attained by senior players.

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Thomas A. Haugen, Espen Tønnessen and Stephen Seiler

Purpose:

To compare sprint and countermovement-jump (CMJ) performance among competitive soccer players as a function of performance level, field position, and age. In addition, the authors wanted to quantify the evolution of these physical characteristics among professional players over a 15-y period.

Methods:

939 athletes (22.1 ± 4.3 y), including national-team players, tested 40-m sprint with electronic timing and CMJ on a force platform at the Norwegian Olympic Training Center between 1995 and 2010.

Results:

National-team and 1st-division players were faster (P < .05) than 2nd-division (1.0–1.4%), 3rd- to 5th-division (3.0–3.8%), junior national-team (1.7–2.2%), and junior players (2.8–3.7%). Forwards were faster than defenders (1.4%), midfielders (2.5%), and goalkeepers (3.2%) over 0–20 m (P < .001). Midfielders jumped ~2.0 cm lower than the other playing positions (P < .05). Sprinting velocity peaked in the age range 20–28 y and declined significantly thereafter (P < .05). Players from 2006–2010 had 1–2% faster 0–20 m and peak velocity than players from the 1995–1999 and 2000–2005 epochs, whereas no differences in CMJ performance were observed.

Conclusions:

This study provides effect-magnitude estimates for the influence of performance level, position, and age on sprint and CMJ performance in soccer. While CMJ performance has remained stable over the time, there has been a small but positive development in sprinting velocity among professional players.

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Timothy J. Suchomel and Christopher J. Sole

The force-production characteristics of 3 weight-lifting derivatives were examined by comparing the force–time curves of each exercise. Sixteen resistance-trained men performed repetitions of the hang power clean (HPC), jump shrug (JS), and hang high pull (HHP) on a force platform at several relative loads. Relative peak force (PFRel), relative impulse (IMPRel), peak rate of force development (PRFD), and time-normalized force–time curves of each exercise were compared. The JS produced greater PFRel than the HPC (P < .001, d = 1.38) and HHP (P < .001, d = 1.14), while there was no difference between the HPC and HHP (P = .338, d = 0.26). Similarly, the JS produced greater IMPRel than the HPC (P < .001, d = 0.52) and HHP (P = .019, d = 0.36). The HHP also produced greater IMPRel than the HPC (P = .040, d = 0.18). Finally, the JS produced greater PRFD than the HPC (P < .001, d = 0.73) and HHP (P = .001, d = 0.47), while there was no difference between the HPC and HHP (P = .192, d = 0.22). The HPC, JS, and HHP force–time profiles were similar during the first 75–80% of the movement; however, the JS produced markedly different force–time characteristics in the final 20–25% of the movement. The JS produced superior force-production characteristics, namely PFRel, IMPRel, and PRFD, as well as a unique force–time profile, compared with the HPC and HHP across several loads.