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Geoff Lovell and Mike Lauder

Context:

Anecdotal evidence suggests a relationship between strength imbalances and injury incidence.

Objective:

To examine the relationship between bilateral strength imbalance and incidence of injury.

Participants and Design:

Thirty national- or international-standard flatwater kayakers were classified as noninjured, trunk injured, or upper-limb injured based on the number of days lost from training over the last 6 months. Bilateral strength imbalance was measured using a kayak ergometer, producing data for peak force and force impulse for each side of each stroke. Bilateral strength imbalance was then compared between the noninjured, trunk-injured, and upper-limb-injured groups by means of 2 one-way ANOVAs. No participants reported training days lost through lower-limb injury.

Results:

A significantly elevated bilateral peak-force strength imbalance was observed between the upper-limb-injured and the noninjured groups.

Conclusion:

These data support the existence of a relationship between strength imbalance and incidence of injury.

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Daniel D. Cohen, Bingnan Zhao, Brian Okwera, Martyn J. Matthews, and Anne Delextrat

Purpose:

To evaluate the effect of simulated soccer on the hamstrings eccentric torque-angle profile and angle of peak torque (APTeccH), and on the hamstrings:quadriceps torque ratio at specific joint angles (ASHecc:Qcon).

Methods:

The authors assessed dominant-limb isokinetic concentric and eccentric knee flexion and concentric knee extension at 120°/s in 9 semiprofessional male soccer players immediately before and after they completed the Loughborough Intermittent Shuttle Test (LIST).

Results:

The LIST resulted in significant decreases in eccentric hamstrings torque at 60°, 50°, and 10° and a significant (21.8%) decrease in ASHecc:Qcon at 10° (P < .05). APTeccH increased from 7.1° ± 1.0° to 18.8° ± 4.2° (P < .05). Eccentric hamstrings peak torque significantly declined from 185.1 ± 70.4 N·m pre-LIST to 150.9 ± 58.5 N·m post-LIST (P = .002), but there were no significant changes in hamstrings or quadriceps concentric peak torque (P = .312, .169, respectively).

Conclusions:

Simulated soccer results in a selective loss of eccentric hamstrings torque and hamstrings-to-quadriceps muscle balance at an extended joint position and a shift in the eccentric hamstrings APT to a shorter length, changes that could increase vulnerability to hamstrings injury. These findings suggest that injury-risk screening could be improved by evaluating the eccentric hamstrings torque-angle profile and hamstrings strength-endurance and that the development of hamstrings fatigue resistance and long-length eccentric strength may reduce injury incidence.

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Seong-won Han, Andrew Sawatsky, Azim Jinha, and Walter Herzog

origin and insertion sites of the individual muscles. Quadriceps muscle weakness in rabbits, induced by injections of botulinum toxin type A, has been found to be associated with the onset of knee osteoarthritis at 1 to 3 months postweakness induction. 37 – 39 Quadriceps muscle strength imbalance

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Martin Ramsi, Kathleen A. Swanik, Charles “Buz” Swanik, Steve Straub, and Carl Mattacola

Context:

Changes in strength over the course of a swim season could predispose the shoulder to strength imbalances and lead to injury.

Objective:

To examine isometric shoulder internal- (IR) and external-rotator (ER) strength in high school swimmers over a 12-week competitive season.

Design:

Three 3 × 2 × 2 ANOVAs with repeated measures were used to determine significant main effects for IR, ER, and IR:ER strength ratio.

Participants:

27 (14 female, 13 male) high school varsity swimmers.

Main Outcome Measures:

IR and ER strength during preseason, midseason, and postseason.

Results:

Significant increases in IR strength in both groups were revealed for all test sessions. ER strength significantly improved in both males and females from preseason to midseason and from preseason to postseason. IR:ER ratio revealed a significant increase from preseason to postseason.

Conclusions:

Increases in IR strength without equal gains in ER strength were revealed and could contribute to future shoulder pathologies in competitive swimmers

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Yuji Kobayashi, Junjiro Kubo, Takeo Matsubayashi, Akifumi Matsuo, Kando Kobayashi, and Naokata Ishii

The aims of the study were to investigate the differences in kinematics and kinetics between the dominant and nondominant leg during single-leg jumps without arm swing, and to determine the relationship between bilateral asymmetry in isokinetic knee strength and the single-leg jump. Isokinetic knee strength and single-leg jump kinematics and kinetics were measured in 11 male participants. The bilateral asymmetry index was calculated for each parameter. For isokinetic knee strength, there were no significant differences between the dominant and nondominant legs. Significant correlations were observed for the bilateral asymmetry index for isokinetic knee strength at 180 degrees per second and the bilateral asymmetry indexes for maximum flexion angle and the mean knee joint torque during the single-leg jumps. In conclusion, the findings of the current study suggest an association between knee strength imbalances and the joint angle, as well as the torque produced in single-leg jumps, although no relationship between knee strength and jump height was observed.

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Pascal David, Mohamad Halimi, Isabelle Mora, Pierre-Louis Doutrellot, and Michel Petitjean

Ankle sprains are among the most common sport-related injuries and can lead to chronic ankle instability. Impaired sensorimotor function of the ankle musculature is often suggested as a cause. The current study sought to assess and compare the isokinetic performance and electromyographic patterns of evertor and invertor muscles in patients with chronic ankle instability and in a control group. Twelve patients with chronic ankle instability and twelve healthy subjects were included. Isokinetic eccentric and concentric testing at various angular velocities was performed for eversion and inversion movements. The corresponding myoelectric activities of the fibularis longus and tibialis anterior muscles were quantified from surface electromyographic recordings by computing average root mean square values. Patients had lower myoelectric activity of the evertor and invertor muscles than controls did; this difference could account for the eccentric weakness associated with ankle instability. Functional strength ratios revealed a dynamic strength imbalance in unstable ankle patients and that may contribute to recurrent injury. Our findings suggest that rehabilitation programs for unstable ankle patients must be focused on the motor control of eccentric contractions of the ankle evertors and invertors, to boost these muscles’ contribution to ankle stabilization.

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Bin Chen, Yichao Zhao, Xianxin Cao, Guojiong Hu, Lincoln B. Chen, and Wenxin Niu

Context: One of the possible mechanisms leading to secondary impingement syndrome may be the strength imbalance of shoulder rotators which is known as functional control ratio (FCR). The FCR is a ratio dividing the eccentric peak torque of the external rotators by the concentric peak torque of the internal rotators. Previous studies have focused on the reproducibility and reliability of isokinetic assessment, but there is little information on the influence of variable shoulder positions on FCR. Objective: To compare shoulder FCR across 3 different shoulder abduction positions during isokinetic assessment. Design: Cross-sectional study. Setting: Biomechanics laboratory. Participants: Thirty-one healthy young university students (age 22.35 [0.95] y, weight 60.52 [9.31] kg, height 168.23 [9.47] cm). Interventions: The concentric peak torque of internal rotators and eccentric peak torque of external rotators of right shoulder were measured on an isokinetic dynamometer. Main Outcome Measures: Concentric peak torque of the internal rotators and eccentric peak torque of the external rotators, measured using an isokinetic dynamometer. Results: The concentric peak torque of internal rotators was significantly lower at 120° shoulder abduction compared with other positions (P < .001). The FCR was significantly higher at 120° shoulder abduction than 90° (P = .002) or 60° (P < .001) shoulder abduction because of the lower concentric peak torque. No significant difference was found in the FCR between the other 2 shoulder positions (P = .14). Conclusions: Shoulder position variations may influence FCR because of weakness of the internal rotators. Rehabilitation and injury prevention training programs should specifically focus on strengthening the internal rotators at more elevated angles of shoulder abduction.

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Charles Goulet and Isabelle Rogowski

muscle strength imbalance implied by the weakness of the external rotator muscles compared to the internal rotators is potentially a risk factor for shoulder injury. 6 Additional strength training of the shoulder external rotator muscles is commonly recommended to prevent this shoulder muscle strength

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Thales M. Medeiros, João B. Ribeiro-Alvares, Carolina G. Fritsch, Gabriel S. Oliveira, Lucas Severo-Silveira, Evangelos Pappas, and Bruno M. Baroni

while prospective studies have demonstrated that players with eccentric hamstring weakness, 9 – 12 muscle strength imbalance (hamstring to quadriceps [H:Q] ratio), 12 – 14 and reduced BF LH fascicle length 11 are also more prone to sustaining HSIs. Hamstring strain injuries are potentially

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Melissa Theige and Shannon David

apprehension, and (3) desire to preserve hip function. Intervention investigated All 4 patients underwent a 3-phase physical therapy protocol. Phase 1 addressed pain control, core stabilization, and movement pattern correction. Phase 2 focused on restoring ROM and correcting muscle strength imbalances. Phase 3