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Laura C. Slane, Stijn Bogaerts, Darryl G. Thelen and Lennart Scheys

passive knee flexion, 27 , 28 and typically treat the patellar tendon as uniform and inextensible, assumptions which could lead to significant inaccuracies. 29 Thus, the purpose of this study was to evaluate patellar tendon motion during passive knee flexion to observe whether nonuniformity in

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Salman Nazary-Moghadam, Mahyar Salavati, Ali Esteki, Behnam Akhbari, Sohrab Keyhani and Afsaneh Zeinalzadeh

knowledge of the authors, no study has been conducted to examine the reliability of the knee flexion–extension LyE in patients with ACLD and healthy subjects. It is well known that the reliability is a population- and condition-specific property. Therefore, it is necessary to establish the reliability of

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Maria Angelika Peer and Nigel Gleeson

preventing ligamentous injury. 3 Potentially harmful dynamic forces need counteracting by synergistic patterns of muscular activation and timely neuromuscular system responses in order to protect ligamentous tissue against injury. 3 , 4 The knee flexors restrain anterior tibio-femoral displacement and

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Jacob T. Hartzell, Kyle B. Kosik, Matthew C. Hoch and Phillip A. Gribble

history of an ankle sprain. 12 Adequate knee flexion is important for attenuating the large, potentially harmful, ground reaction forces encountered during a jump landing. Therefore, it has been suggested that less sagittal plane knee motion at initial contact is associated with the heightened risk of a

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Kenny Guex, Chantal Daucourt and Stéphane Borloz

Context:

In the field of sport rehabilitation, an easy, valid, and reliable assessment of maximal strength is crucial for efficient muscle rehabilitation. Classically, it is performed on fitness equipment that is not necessary available in the field. Thera-Band has developed elastic bands with different resistances depending on the color of the band and on the percentage of its stretch. This may allow testing maximal strength.

Objective:

To determine validity and reliability of maximal-strength assessment of knee flexors and extensors using elastic bands.

Design:

Reliability and validity study.

Participants:

22 healthy participants (31.3 ± 7.0 y, 175.5 ± 8.5 cm, 70.7 ± 12.9 kg).

Intervention:

Participants performed 2 maximal-strength assessments, separated by 7 d, of the knee flexors and extensors using elastic bands. After the 2nd trial, a maximal concentric isokinetic test at 60°/s was performed.

Main Outcome Measures:

Correlations between 1-repetition maximum using elastic bands and peak torque on an isokinetic dynamometer were used to determine the validity of the proposed method, while ICC, CV, and SEM were used to determine reliability between the 1st and 2nd trials.

Results:

The validity of the proposed method was found to be very high (r = .93 for both knee flexors and extensors). The relative reliability was found to be very high (ICC = .98 and .99 for knee flexors and extensors, respectively), while absolute reliability was also very satisfying (CV = 3.44% and 2.33%; SEM = 1.70 and 2.16 kg for knee flexors and extensors, respectively).

Conclusions:

Thera-Band is a valid and reliable alternative to the use of fitness equipment to test maximal strength of the knee flexors and extensors in healthy subjects. The ease of use, accessibility, and low cost of elastic bands should allow regular assessment during the rehabilitation process.

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Theophanis Siatras, Dimitra Mameletzi and Spiros Kellis

The purpose of the study was to determine young male gymnasts’ and swimmers’ knee flexor:extensor (F:E) ratios during isokinetic testing at different velocities. Nine gymnasts (10.3 ± 0.5 years) and 14 swimmers (10.5 ± 0.5 years) participated. Concentric isokinetic peak torque was measured by a Cybex® Norm dynamometer at different angular velocities (60,120, and 180°/s) during unilateral knee extensions and flexions after gravity correction. Significant differences were found only in gymnasts’ knee F:E peak-torque ratios between the angular velocities of 60 and 120°/s (p < 0.01), as well as 60–180°/s (p < .01), whereas swimmers’ ratios were unchanged. Gymnasts presented significantly higher F:E ratios than swimmers did at the angular velocities of 120°/s (p < .01) and 180°/s (p < .001). The reciprocal ratios provided some indication that the training context of young athletes can influence the balance between agonistic and antagonistic activity of the lower limbs’ major muscle groups.

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Teddy W. Worrell, Steven Connelly and John Hilvert

The purpose of this study was to determine the intrasession and intersession reliability of EMG vastus medialis oblique:vastus lateralis (VMO:VL) ratios at four knee positions (0, 45, 60, and 90°) at 100 and 60% of maximal voluntary isometric contraction (MVIC). Once reliability was established, the second purpose was to determine VMO:VL ratios and torque at each knee position. Thirty-two subjects participated in two sessions; 19 subjects were tested at 100% MVIC and 13 were tested at .60% MVIC. Results revealed the following intraclass correlations: 100% MVIC intrasession .40-.80, intersession .40-.70; 60% MVIC intrasession .60-.90, intersession .50-.80. A significant difference in torque occurred at all knee positions except 60 versus 90°. No significant difference existed in VMO:VL ratios at the four positions of knee flexion. Pain and measurement error significantly increased during 100% MVIC testing. It was concluded that no selective VMO recruitment occurred as revealed by the VMO: VL ratios in asymptomatic subjects. Future study is needed that reports EMG reliability data during exercises that theorize selective VMO recruitment.

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Boyi Dai, Mitchell L. Stephenson, Samantha M. Ellis, Michael R. Donohue, Xiaopeng Ning and Qin Zhu

Increased knee flexion and decreased knee valgus angles and decreased impact ground reaction forces (GRF) are associated with decreased anterior cruciate ligament (ACL) loading during landing. The purpose of this study was to determine the effect of tactile feedback provided by a simple device on knee flexion and valgus angles and impact GRF during landing. Kinematic and kinetic data were collected when 28 participants performed baseline, training, and evaluation jump-landing trials. During the training trials, the device was placed on participants’ shanks so that participants received tactile feedback when they reached a peak knee flexion angle of a minimum of 100°. During the evaluation trials, participants were instructed to maintain the movement patterns as they learned from the training trials. Participants demonstrated significantly (P < .008) increased peak knee flexion angles, knee flexion range of motion during early landing (first 100 ms of landing) and stance time, decreased impact posterior and vertical GRF during early landing and jump height, and similar knee valgus angles during the evaluation trials compared with the baseline trials. Immediately following training with tactile feedback, participants demonstrated landing patterns associated with decreased ACL loading. This device may have advantages in application because it provides low-cost, independent, and real-time feedback.

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Jenny Toonstra and Carl G. Mattacola

Context: Physicians and clinicians need portable, efficient, and cost-effective assessment tools to determine the effectiveness of rehabilitation programs after knee injury. Progress in rehabilitation should be evaluated using valid and reliable measurement methods. Objective: To examine the test-retest reliability of portable fixed dynamometry (PFD), handheld dynamometry (HHD), and isokinetic dynamometry (IKD). In addition, the authors sought to examine the validity of PFD and HHD by comparing differences in peak torque of the knee flexors and extensors to that of the "gold standard" IKD. Design: Repeated measures. Participants: 16 healthy subjects (age 29.3 ± 7.2 y, height 167.4 ± 8.04 cm, mass 73.7 ± 20.0 kg). Main Outcome Measures: The dependent variables were trial (trial 1, trial 2) and instrument (IKD, PFD, and HHD). Results: Test-retest reliability was high for both PFD and IKD. However, fair to poor reliability was found for HHD. There were no differences in peak torque (Nm) between IKD and PFD. However, significant differences in peak torque were observed between IKD and HHD and between PFD and HHD. Conclusions: PFD provides reliable measures of strength and also demonstrates similar output measures as IKD. Its portability, ease of use, and cost provide clinicians an effective means of measuring strength.

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Martin Buchheit, Yannick Cholley, Mark Nagel and Nicholas Poulos

Purpose:

To examine the effect of body mass (BM) on eccentric knee-flexor strength using the Nordbord and offer simple guidelines to control for the effect of BM on knee-flexor strength.

Methods:

Data from 81 soccer players (U17, U19, U21, senior 4th French division, and professionals) and 41 Australian Football League (AFL) players were used for analysis. They all performed 1 set of 3 maximal repetitions of the bilateral Nordic hamstring exercise, with the greatest strength measure used for analysis. The main regression equation obtained from the overall sample was used to predict eccentric knee-flexor strength from a given BM (moderate TEE, 22%). Individual deviations from the BM-predicted score were used as a BM-free index of eccentric knee- flexor strength.

Results:

There was a large (r = .55, 90% confidence limits .42;.64) correlation between eccentric knee-flexor strength and BM. Heavier and older players (professionals, 4th French division, and AFL) outperformed their lighter and younger (U17–U21) counterparts, with the soccer professionals presenting the highest absolute strength. Professional soccer players were the only ones to show strength values likely slightly greater than those expected for their BM.

Conclusions:

Eccentric knee-flexor strength, as assessed with the Nordbord, is largely BM-dependent. To control for this effect, practitioners may compare actual test performances with the expected strength for a given BM, using the following predictive equation: Eccentric strength (N) = 4 × BM (kg) + 26.1. Professional soccer players with specific knee-flexor-training history and enhanced neuromuscular performance may show higher than expected values.