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Jeni R. McNeal, William A. Sands and Michael H. Stone

Purpose:

The aim of this study was to investigate the effects of a maximal repeated-jumps task on force production, muscle activation and kinematics, and to determine if changes in performance were dependent on gender.

Methods:

Eleven male and nine female athletes performed continuous countermovement jumps for 60 s on a force platform while muscle activation was assessed using surface electromyography. Performances were videotaped and digitized (60 Hz). Data were averaged across three jumps in 10-s intervals from the initial jump to the final 10 s of the test.

Results:

No interaction between time and gender was evident for any variable; therefore, all results represent data collapsed across gender. Preactivation magnitude decreased across time periods for anterior tibialis (AT, P < .001), gastrocnemius (GAS, P < .001) and biceps femoris (BF, P = .03), but not for vastus lateralis (VL, P = .16). Muscle activation during ground contact did not change across time for BF; however, VL, G, and AT showed significant reductions (all P < .001). Peak force was reduced at 40 s compared with the initial jumps, and continued to be reduced at 50 and 60 s (all P < .05). The time from peak force to takeoff was greater at 50 and 60 s compared with the initial jumps (P < .05). Both knee fexion and ankle dorsifexion were reduced across time (both P < .001), whereas no change in relative hip angle was evident (P = .10). Absolute angle of the trunk increased with time (P < .001), whereas the absolute angle of the shank decreased (P < .001).

Conclusions:

In response to the fatiguing task, subjects reduced muscle activation and force production and altered jumping technique; however, these changes were not dependent on gender.

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Saied Jalal Aboodarda, Ashril Yusof, N.A. Abu Osman, Martin W. Thompson and A. Halim Mokhtar

Purpose:

To identify the effect of additional elastic force on the kinetic and kinematic characteristics, as well as the magnitude of leg stiffness, during the performance of accentuated countermovement jumps (CMJs).

Methods:

Fifteen trained male subjects performed 3 types of CMJ including free CMJ (FCMJ; ie, body weight), ACMJ-20, and ACMJ-30 (ie, accentuated eccentric CMJ with downward tensile force equivalent to 20% and 30% body mass, respectively). A force platform synchronized with 6 high-speed infrared cameras was used to measure vertical ground-reaction force (VGRF) and displacement.

Results:

Using downward tensile force during the lowering phase of a CMJ and releasing the bands at the start of the concentric phase increased maximal concentric VGRF (6.34%), power output (23.21%), net impulse (16.65%), and jump height (9.52%) in ACMJ-30 compared with FCMJ (all P < .05). However, no significant difference was observed in the magnitude of leg stiffness between the 3 modes of jump. The results indicate that using downward recoil force of the elastic material during the eccentric phase of a CMJ could be an effective method to enhance jump performance by applying a greater eccentric loading on the parallel and series elastic components coupled with the release of stored elastic energy.

Conclusions:

The importance of this finding is related to the proposition that power output, net impulse, takeoff velocity, and jump height are the key parameters for successful athletic performance, and any training method that improves impulse and power production may improve sports performance, particularly in jumping aspects of sport.

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Dustin J. Oranchuk, Eric J. Drinkwater, Riki S. Lindsay, Eric R. Helms, Eric T. Harbour and Adam G. Storey

Purpose: The power clean and other weightlifting movements are commonly used in the development of muscle power. However, there is a paucity of research examining the use of the hook grip (HG) in weightlifting performance. Therefore, the purpose of this study was to compare 1-repetition maximum (1RM) and kinetic, kinematic, and qualitative variables across a range of loads (75–100%) during power-clean performance with an HG and a closed grip. Methods: A total of 11 well-trained men (power-clean 1RM = 113.4 [15.9] kg, 1.34 × body mass) with at least 3 mo of HG experience volunteered to participate. Following a familiarization session, 1RM testing with the HG and closed grip were completed 5–7 d apart in a randomized order. Barbell kinetic and kinematic variables were recorded via a force platform and dual linear position transducer system. Results: All subjects had a greater 1RM with the HG than with the closed grip (P < .001, effect size [ES] = 0.43). Peak velocity (ES = 0.41–0.70), peak power (ES = 0.43–0.61), peak force (ES = 0.50–0.57), and catch height (ES = 0.40–0.96) were significantly greater (P < .05) when using the HG at all or most of the submaximal intensities. In addition, subjects reported significantly greater perceptions of grip security, power, and technical competency at submaximal but not maximal loads. Conclusions: Athletes and coaches who implement weightlifting movements in their physical preparation should adopt the HG where possible. Furthermore, researchers and sport scientists should control and report the grip type used when performing weightlifting-type movements.

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Thomas A. Haugen, Espen Tønnessen and Stephen Seiler

Purpose:

The purpose of this investigation was to compare sprint and countermovement-jump (CMJ) performance among female 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 elite players over a 15-y period.

Methods:

194 female elite players (22± 4.1 y, 63 ± 5.6 kg), including an Olympic winning squad, tested 40-m sprint with electronic timing and CMJ on a force platform at the Norwegian Olympic training center from 1995 to 2010.

Results:

Moderate to large velocity differences across performance levels and positions were observed. National-team players were 2% faster than 1st-division players (P = .027, d = 0.5) and 5% faster than 2nd-division players (P < .001, d = 1.3) over 0–20 m. National-team players jumped 8–9% higher than 1st-division players (P = .001, d = 0.6) and junior elite players (P = .023, d = 0.5). Forwards were 3–4% faster than midfielders (P < .001, d = 0.8) and goalkeepers (P = .003, d = 0.9) over 0–20 m. No differences in velocity or CMJ height were observed among the age categories. Players from 2006–2010 were 2% faster (P < .05, d = 0.6) than players from 1995–1999 over 20 m, whereas no differences in 20- to 40-m velocity or CMJ performance were observed.

Conclusions:

This study provides effect-magnitude estimates for the influence of performance level, age, and player position on sprint and CMJ performance in female soccer players. While 20- to 40-m velocity and CMJ performance have remained stable over the time, there has been a moderate but positive development in 0- to 20-m velocity among elite performers.

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Conall F. Murtagh, Christopher Nulty, Jos Vanrenterghem, Andrew O’Boyle, Ryland Morgans, Barry Drust and Robert M. Erskine

Purpose: To investigate differences in neuromuscular factors between elite and nonelite players and to establish which factors underpin direction-specific unilateral jump performance. Methods: Elite (n = 23; age, 18.1 [1.0] y; body mass index, 23.1 [1.8] kg·m−2) and nonelite (n = 20; age, 22.3 [2.7] y; body mass index, 23.8 [1.8] kg·m−2) soccer players performed 3 unilateral countermovement jumps (CMJs) on a force platform in the vertical, horizontal-forward, and medial directions. Knee extension isometric maximum voluntary contraction torque was assessed using isokinetic dynamometry. Vastus lateralis fascicle length, angle of pennation, quadriceps femoris muscle volume (M vol), and physiological cross-sectional area (PCSA) were assessed using ultrasonography. Vastus lateralis activation was assessed using electromyography. Results: Elite soccer players presented greater knee extensor isometric maximum voluntary contraction torque (365.7 [66.6] vs 320.1 [62.6] N·m; P = .045), M vol (2853 [508] vs 2429 [232] cm3; P = .001), and PCSA (227 [42] vs 193 [25] cm2; P = .003) than nonelite. In both cohorts, unilateral vertical and unilateral medial CMJ performance correlated with M vol and PCSA (r ≥ .310, P ≤ .043). In elite soccer players, unilateral vertical and unilateral medial CMJ performance correlated with upward phase vastus lateralis activation and angle of pennation (r ≥ .478, P ≤ .028). Unilateral horizontal-forward CMJ peak vertical power did not correlate with any measure of muscle size or activation but correlated inversely with angle of pennation (r = −.413, P = .037). Conclusions: While larger and stronger quadriceps differentiated elite from nonelite players, relationships between neuromuscular factors and unilateral jump performance were shown to be direction-specific. These findings support a notion that improving direction-specific muscular power in soccer requires improving a distinct neuromuscular profile.

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Seiichiro Takei, Kuniaki Hirayama and Junichi Okada

previously described. 6 – 10 , 15 Briefly, (1) the subjects stood still on a force platform while holding the bar at their upper thigh, (2) moved the bar down to the upper part of their knees, (3) pulled the bar drastically upward with countermovement, and (4) then lowered themselves into a quarter

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Paul Comfort, Christopher Thomas, Thomas Dos’Santos, Paul A. Jones, Timothy J. Suchomel and John J. McMahon

Testing Both the SJ and CMJ trials were performed with the subjects standing on a force platform (type: 9286AA, dimensions 600 × 400 mm, Kistler Instruments Inc, Amherst, NY, USA) sampling at 1000 Hz, interfaced with laptop computer running Bioware software (version 5.11, Kistler Instruments Inc, Amherst

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Abderrahmane Rahmani, Pierre Samozino, Jean-Benoit Morin and Baptiste Morel

Bench-press exercise is often used as a simple test to evaluate the upper-limb force, velocity, and power output. 1 – 3 These muscle parameters are usually determined using a force platform 4 , 5 or kinematic systems such as optical encoders 6 , 7 or linear transducers. 1 , 8 – 10 Although

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Paul Comfort, Thomas Dos’Santos, Paul A. Jones, John J. McMahon, Timothy J. Suchomel, Caleb Bazyler and Michael H. Stone

of the clean on a custom rack above a force platform. Once the bar height was established, the subjects stood on the force platform with their hands strapped to the bar using standard lifting straps. 1 Each subject adopted the posture that they would use for the start of the second pull phase of the

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Jacob A. Goldsmith, Cameron Trepeck, Jessica L. Halle, Kristin M. Mendez, Alex Klemp, Daniel M. Cooke, Michael H. Haischer, Ryan K. Byrnes, Robert F. Zoeller, Michael Whitehurst and Michael C. Zourdos

position transducers (LPTs) and wearable velocity calculators have been developed, 1 , 2 which have a lower cost (Tendo Weightlifting Analyzer System [TWAS], ∼$1500; GymAware, ∼$2000) than criterion measurement systems: force platforms and 3-dimensional motion capture ($10,000–40,000). In terms of