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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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Alejandro Pérez-Castilla, F. Javier Rojas, John F.T. Fernandes, Federico Gómez-Martínez, and Amador García-Ramos

which muscles are powerfully contracted immediately after being rapidly stretched ( Comyns, Brady, & Molloy, 2019 ). The drop jump (DJ) is one of the plyometric exercises most commonly used to enhance an athlete’s performance, as well as to assess injury risk ( Collings, Gorman, Stuelcken, Mellifont

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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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Mark C. Richardson, Andrew Wilkinson, Paul Chesterton, and William Evans

accelerate the rehabilitation process would be desirable in both populations. Increased knee valgus on landing is a biomechanical risk factor for nonimpact ACL injury among athletes. 9 Specifically, increased knee valgus during drop jump (DJ) tasks on firm ground has been prospectively associated with ACL

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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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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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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.