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John R. Harry, Max R. Paquette, Brian K. Schilling, Leland A. Barker, C. Roger James and Janet S. Dufek

energy to be converted to downward kinetic energy and then elastic strain energy. 1 , 9 Accordingly, it has been suggested that the countermovement phase be divided into “unloading,” “eccentric,” and “concentric” subphases (Figure  1 ). 1 The eccentric and concentric subphases have been directly

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Jonathan S. Goodwin, Robert A. Creighton, Brian G. Pietrosimone, Jeffery T. Spang and J. Troy Blackburn

loading during weight-bearing activities. 6 – 8 Orthotic devices such as medial unloader knee braces and lateral wedges placed in shoes are often utilized to minimize compressive loading of the medial compartment. These devices are designed to induce valgus loading to counter compressive loading of the

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Stefan M. Gabriel, Anton G. Clifford, William J. Maloney, Mary K. O’Connell and Paul Tornetta III

Medial knee osteoarthritis (OA) is a common disorder often associated with pathologic joint loading. Insoles, braces, and high tibial osteotomy are OA treatments aimed at reducing medial joint loads, but their use and effectiveness are limited. The KineSpring System implant also intends to reduce knee loads in OA patients while overcoming those limitations. The current study was undertaken to test the implant’s effect on loads at the knee. Six cadaver knees with Outerbridge Grade I-II medial OA were subjected to simulated gait using a kinematic test system. Knees were tested with and without the medial knee implant while thin film sensors measured medial and lateral femorotibial contact pressures. Significant medial compartment load reductions (134 ± 53 N [P = .002]) were found throughout the stance phase of gait in the treated knee. Significant total joint load decreases (91 ± 40 N [P = .002]) were also observed without substantial changes in lateral compartment loads. These significant reductions of medial and total intra-articular loads are also within clinically effective ranges of other unloading systems. This suggests that the KineSpring System could be a viable treatment for medial knee OA.

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Arnold G. Nelson

It has been shown that the rate of tension generation (dP/dt) continues to increase with increasing stimulation rates, even after maximal tetanic tension has been achieved. Since dP/dt is directly proportional to unloaded shortening velocity, it was questioned whether supramaximal stimulation rates would increase shortening velocity. To test the relationship of velocity and stimulation rate, slack tests were performed on motor units isolated in the rat soleus muscles. For each motor unit tested, two slack tests were performed at two different stimulation rates: one rate yielded a maximal tetanic tension with a "slow" dP/dt (PO) and the other rate yielded a maximal tetanic tension with a "fast" dP/dt (RG). The two stimulation rates (PO and RG) had significantly different effects (p < .05) on motor unit shortening velocity, with the RG rate yielding a shortening velocity greater than that of PO by an average of 13 ± 6%. This suggests that rate coding could be used to grade motor unit power production by grading force production and/or shortening velocity.

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Yassine Negra, Helmi Chaabene, Senda Sammoud, Olaf Prieske, Jason Moran, Rodrigo Ramirez-Campillo, Ali Nejmaoui and Urs Granacher

soccer player. Previous studies have shown that unloaded plyometric jump training (UPJT), during which the performer must propel their own body mass, is an easy-to-administer, safe, effective, and efficient training method to improve physical fitness during different stages of maturation and long

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Ina Janssen, Jeremy M. Sheppard, Andrew A. Dingley, Dale W. Chapman and Wayne Spratford

Countermovement jumps loaded with a weighted vest are often used for the training of lower body power to improve jump performance. However, it is currently unknown how this added load affects the lower extremity kinematics and kinetics, in particular whether this results in an increased injury risk. Therefore, the purpose of this investigation was to determine how lower extremity kinematics and kinetics during landing are affected by loaded jumps as demonstrated in a volleyball block jump landing. Ten elite male volleyball players performed block jump landings in an unloaded and loaded (9.89 kg) condition. Kinematic and kinetic landing data from the three highest jumps were collected and assessed. Paired samples t test was used to establish whether load condition had a significant effect on lower extremity kinematics and kinetics. Hip flexion was significantly greater in the unloaded condition compared with the loaded condition (p = .004). There was no significant difference in any other kinematic or kinetic variables measures between the unloaded and loaded conditions. These results suggest that landing from loaded volleyball block jumps does not increase injury risk compared with unloaded jumps in elite male volleyball players.

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Mathieu Lacome, Ben M. Simpson, Yannick Cholley and Martin Buchheit

to unload both locomotor and MechL was substantially higher in GS compared with PO games (Figure  1 ). This may be related to the fact that during both types of SSGs, floaters are only in possession of the ball, and thus, their role is more likely comparable with that of regular players during PO

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Ricky Anderson, Carol Courtney and Eli Carmeli

The purpose of this study was to see if vastus medialis oblique/vastus lateralis (VMO:VL) ratios could be increased by widening the squat stance and if the VMO activity increases with deeper ranges of knee flexion. Fifteen healthy subjects performed unloaded narrow and wide stance squats through three ranges of knee flexion: 30°, 60°, and 90°. The two squat stances were compared using a 2 × 3 ANOVA to see if the wide-stance squat had any significant difference in EMG activity for VMO: VL ratios compared to the narrow-stance squat. The difference in EMG activity of the VMO between the various angles for both squat stances was also compared. The ANOVA revealed no significant differences between the squat stances for VMO:VL ratios but did show the VMO:VL ratios to be significantly higher with increasing knee flexion angles. These findings suggest that the VMO is active throughout the 90° range and that increasing knee flexion angles can elicit greater activity of the VMO relative to the VL.

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Daniel O’Sullivan and Stephen P. Bird

Edited by Tricia Hubbard

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Aviroop Dutt-Mazumder, Richard L. Segal and Aiko K. Thompson

ankle angles on the soleus H-reflex recruitment curve during standing, with the test leg loaded (i.e., weight symmetrically borne with both legs) and unloaded (i.e., full body weight solely borne with the contralateral leg). The unloaded condition was to examine the effects of imposed ankle angles with