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Sean J. Maloney, Joanna Richards and Iain M. Fletcher

to perform short-duration maximal intensity actions. The drop jump is an exercise in which an athlete drops from a predetermined height and attempts to jump immediately upon landing. 11 As drop jumping is typically performed with a view to enhancing whole-body stiffness, 11 , 12 it may be

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Bradley S. Beardt, Myranda R. McCollum, Taylour J. Hinshaw, Jacob S. Layer, Margaret A. Wilson, Qin Zhu and Boyi Dai

with a noncontact mechanism. 10 – 13 The risk of suffering ACL injuries is greater for female athletes compared with male athletes. 14 Researchers have assessed the value of lower-extremity biomechanics during double-leg drop-jump tasks in predicting future ACL injuries, but observed inconsistent

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Guillaume P. Ducrocq, Thomas J. Hureau, Olivier Meste and Grégory M. Blain

repeated drop jumps (ie, interval drop jumping) might be an effective training method to combine improvements in V ˙ O 2 max and muscle power. However, performing drop jumps at a high work rate could impair muscle activation and force/power production—that is, fatigue could develop. 22 , 23 The

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Rodrigo Ramirez-Campillo, Cristian Alvarez, Felipe García-Pinillos, Paulo Gentil, Jason Moran, Lucas A. Pereira and Irineu Loturco

considered ( 37 ), such as the volume ( 10 , 40 ) and intensity of the jumps ( 1 , 38 ), the landing surfaces, the order of drills execution and recovery time ( 40 , 46 ), and the type of training exercises ( 6 , 42 ), including those that stress the musculotendinous unit ( 50 ) (eg, drop jump [DJ]) ( 6

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Harald Böhm, Gerald K. Cole, Gert-Peter Brüggemann and Hanns Ruder

The contribution of muscle in-series compliance on maximum performance of the muscle tendon complex was investigated using a forward dynamic computer simulation. The model of the human body contains 8 Hill-type muscles of the lower extremities. Muscle activation is optimized as a function of time, so that maximum drop jump height is achieved by the model. It is shown that the muscle series elastic energy stored in the downward phase provides a considerable contribution (32%) to the total muscle energy in the push-off phase. Furthermore, by the return of stored elastic energy all muscle contractile elements can reduce their shortening velocity up to 63% during push-off to develop a higher force due to their force velocity properties. The additional stretch taken up by the muscle series elastic element allows only m. rectus femoris to work closer to its optimal length, due to its force length properties. Therefore the contribution of the series elastic element to muscle performance in maximum height drop jumping is to store and return energy, and at the same time to increase the force producing ability of the contractile elements during push-off.

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Christopher Carcia, Jim Eggen and Sandra Shultz

Context:

The influence of hip-muscle function on knee-joint kinematics during landing has been inadequately investigated.

Objective:

To determine the effect of bilateral hip-abductor fatigue on frontal-plane tibiofemoral landing characteristics and vertical ground-reaction force (vGRF) during the landing phase of a drop jump.

Design:

Experimental, pretest–posttest.

Setting:

Research laboratory.

Participants:

20 recreationally active college-age students.

Intervention:

Isometric bilateral hip-abductor-fatigue protocol.

Main Outcome Measures:

Frontal-plane tibiofemoral landing angle, excursion, and vGRF during landing from a drop jump under prefatigue, postfatigue, and recovery conditions.

Results:

After the fatigue protocol, participants landed in a greater valgus orientation than in the prefatigued state. No differences in frontal-plane excursion or vGRF were noted.

Conclusions:

Isolated bilateral hip-abductor fatigue alters frontal-plane lower extremity orientation during a double-leg landing. Because an increase in valgus orientation has been observed at or near the time of noncontact anterior cruciate ligament injuries, we recommend improving hip-abductor muscle performance to lessen the risk of such injuries.

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Neil E. Fowler and Adrian Lees

The aim of this study was to compare the kinetic and kinematic characteristics of plyometric drop-jump and pendulum exercises. Exercises were filmed (100 Hz) from the sagittal view and manually digitized; the data were smoothed and differentiated using cross-validated quintic splines. Ground reaction force data were sampled using a Kistler force platform sampling at 500 Hz. Differences between movement amplitudes and coordination strategies were assessed using t tests and conjugate cross-correlations. Pendulum exercises involved a greater range of motion at the ankle and knee but less motion at the hip joint than drop-jumps. Although different in absolute terms, the exercises used a similar coordination strategy. Drop-jumps resulted in greater peak vertical ground reaction forces than the pendulum exercises although the latter involved a greater net impulse. The similarity between the movement patterns for the two modes of exercise led to the conclusion that pendulum exercises offer a training stimulus similar to that of drop-jumps.

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Nelson Cortes and James Onate

Context:

Clinical assessment tools are needed to identify individual athletes who possess elevated risk for anterior cruciate ligament injury. Existing methods require expensive equipment and the investment of a large amount of time for data processing, which makes them unfeasible for preparticipation screening of a large number of athletes.

Objective:

To assess the extent of agreement between LESS and the iLESS classifications of jump landing performance and the level of agreement between ratings assigned by a novice evaluator and an expert evaluator.

Methods:

Ratings of drop-jump landings from 20 video recordings of NCAA Division I collegiate athletes, which were randomly selected from a large database.

Results:

The dichotomous iLESS score corresponded to the dichotomous classification of LESS score for 15 of 20 cases rated by the expert evaluator and 17 of 20 cases rated by the novice evaluator. For the iLESS, only 2 scores out of 20 differed between the evaluators.

Conclusions:

A high level of agreement was observed between the LESS and iLESS methods for classification of jump- landing performance. Because the iLESS method is inexpensive and efficient, it may prove to be valuable for preparticipation assessment of knee injury risk.

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William J. Markwick, Stephen P. Bird, James J. Tufano, Laurent B. Seitz and G. Gregory Haff

Purpose:

To evaluate the reliability of the Reactive Strength Index (RSI) and jump-height (JH) performance from multiple drop heights in an elite population.

Methods:

Thirteen professional basketball players (mean ±SD age 25.8 ± 3.5 y, height 1.96 ± 0.07 m, mass 94.8 ± 8.2 kg) completed 3 maximal drop-jump attempts onto a jump mat at 4 randomly assigned box heights and 3 countermovement-jump trials.

Results:

No statistical difference was observed between 3 trials for both the RSI and JH variable at all the tested drop heights. The RSI for drop-jump heights from 20 cm resulted in a coefficient of variation (CV) = 3.1% and an intraclass correlation (ICC α) = .96, 40 cm resulted in a CV = 3.0% and an ICC α = .95, and 50 cm resulted in a CV = 2.1% and an ICC α = .99. The JH variable at the 40-cm drop-jump height resulted in the highest reliability CV = 2.8% and an ICC α = .98.

Conclusion:

When assessing the RSI the 20-, 40-, and 50-cm drop heights are recommended with this population. When assessing large groups it appears that only 1 trial is required when assessing the RSI variable from the 20, 40-, and 50-cm drop heights.

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Allan Munro, Lee Herrington and Paul Comfort

Context:

Injuries to the anterior cruciate ligament (ACL) and patellofemoral joint (PFJ) are a significant problem in female athletes. A number of screening tasks have been used in the literature to identify those at greatest risk of injury. To date, no study has examined the relationship in 2-dimensional (2D) knee valgus between common screening tasks to determine whether individuals exhibit similar movement patterns across tasks.

Objective:

To establish whether frontal-plane projection angle (FPPA) during the single-leg squat (SLS), single-leg land (SLL), and drop jump (DJ) are related.

Design:

Cross-sectional study.

Setting:

University laboratory.

Participants:

52 national-league female football players and 36 national-league female basketball players.

Main Outcome Measures:

2D FPPA during the SLS, SLL, and DJ screening tasks.

Results:

Significant correlations were found between tasks. FPPA in the SLS was significantly correlated with SLL (r = .52) and DJ (r = .30), whereas FPPA in the SLL was also significantly correlated to DJ (r = .33). FPPA was significantly greater in the SLS than in the SLL (P < .001) and DJ (P < .001) and in the SLL than in the DJ (P < .001).

Conclusion:

The results showed that 2D FPPA is correlated across the SLS, SLL, and DJ tasks. However, significantly greater FPPA values in the unilateral tasks suggest that the DJ may not identify risk of injury in sports where primary injury mechanisms are during unilateral loading tasks. Therefore, it is recommended that both unilateral and bilateral tasks be included when screening for ACL and PFJ injury risk.