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Gulcan Harput, A. Ruhi Soylu, Hayri Ertan, Nevin Ergun and Carl G. Mattacola

Context:

Coactivation ratio of quadriceps to hamstring muscles (Q:H) and medial to lateral knee muscles (M:L) contributes to the dynamic stability of the knee joint during movement patterns recommended during rehabilitation and important for daily function.

Objective:

To compare the quadriceps-to-hamstring and medial-to-lateral knee muscles' coactivation ratios between men and women during the following closed kinetic chain exercises performed on a balance board: forward lunge, side lunge, single-leg stance, and single-leg squat.

Design:

Cross-sectional.

Participants:

20 healthy subjects (10 female and 10 male).

Main Outcome Measures:

Surface electromyography was used to measure the activation level of quadriceps (vastus lateralis and medialis) and hamstrings (biceps femoris and medial hamstrings) during forward- and side-lunge, single-leg-stance, and single-leg-squat exercises. Subjects were instructed during each exercise to move into the test position and to hold that position for 15 s. EMG was recorded during the 15-s isometric period where subjects tried to maintain a “set” position while the foot was on a balance board. Analysis of variance was used for statistical analysis.

Results:

There was a significant exercise-by-gender interaction for Q:H ratio (F 3,48 = 6.63, P = .001), but the exercise-by-gender interaction for M:L ratio was not significant (F 3,48 = 1.67, P = .18). Women showed larger Q:H ratio in side-lunge exercises than men (P = .002). Both genders showed larger M:L and lower Q:H ratio in a single-leg-stance exercise than in the other exercises.

Conclusions:

The results indicate that the forward- and side-lunge and single-leg-squat exercises should not be recommended as exercise where a balanced coactivation between quadriceps and hamstring muscles is warranted. Single-leg-stance exercise could be used when seeking an exercise where the ratio is balanced for both women and men.

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Alan Hreljac, Alan Arata, Reed Ferber, John A. Mercer and Brandi S. Row

Previous research has demonstrated that the preferred transition speed during human locomotion is the speed at which critical levels of ankle angular velocity and acceleration (in the dorsiflexor direction) are reached, leading to the hypothesis that gait transition occurs to alleviate muscular stress on the dorsiflexors. Furthermore, it has been shown that the metabolic cost of running at the preferred transition speed is greater than that of walking at that speed. This increase in energetic cost at gait transition has been hypothesized to occur due to a greater demand being placed on the larger muscles of the lower extremity when gait changes from a walk to a run. This hypothesis was tested by monitoring electromyographic (EMG) activity of the tibialis anterior, medial gastrocnemius, vastus lateralis, biceps femoris, and gluteus maximus while participants (6 M, 3 F) walked at speeds of 70, 80, 90, and 100% of their preferred transition speed, and ran at their preferred transition speed. The EMG activity of the tibialis anterior increased as walking speed increased, then decreased when gait changed to a run at the preferred transition speed. Concurrently, the EMG activity of all other muscles that were monitored increased with increasing walking speed, and at a greater rate when gait changed to a run at the preferred transition speed. The results of this study supported the hypothesis presented.

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William H. Clark and Jason R. Franz

increases with walking speed and positively correlates with positive work performed about the ankle during push off. 5 , 7 In addition, the profile of k A across the stance phase mirrors that of net ankle moment and triceps surae muscle activation. Together, these findings allude to activation

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Mostafa Yaghoubi, Philip W. Fink, Wyatt H. Page and Sarah P. Shultz

during locomotion ( 27 ) and exhibit increased lower extremity joint moments ( 22 ) and power ( 44 ), ground reaction forces (GRFs) ( 20 ), and muscle activation during gait ( 9 ). In addition, it has been suggested that changes in the locomotor strategy by OW children reduce mechanical efficiency and

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Jay A. Collison, Jason Moran, Inge Zijdewind and Florentina J. Hettinga

defined as a decline in an objective measure of performance over time and can be quantified by reductions in voluntary muscle force or changes in voluntary muscle activation (VA). 5 Performing bouts of resistance exercise induce performance fatigability, and ensuring that performance fatigability is

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Ji-Hyun Lee and Tae-Lim Yoon

). Eventually, patients with CAI experience postural-control deficit, and their functional performance could be damaged (self-reported disability). 7 , 9 Many previous studies introduced various exercises for improving balance and functional performance by improving muscle activation in patients with CAI

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Yi-Fen Shih, Ya-Fang Lee and Wen-Yin Chen

the functions of the shoulder complex. 1 Scapular dyskinesis, or alterations in scapular kinematics and muscle activation, has been shown to occur with SIS in previous studies. 1 , 3 – 5 Kibler and McMullen 6 further suggested that proprioception deficits might play a role in the development of

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Hooman Minoonejad, Mohammad Karimizadeh Ardakani, Reza Rajabi, Erik A. Wikstrom and Ali Sharifnezhad

). **Significant difference between the pretest and posttest collapsed means ( P  < .01). ***Significant difference between the experimental and control group collapsed means ( P  < .02). Table 4 Preparatory Muscle Activation Means, SDs, and Effects Sizes per Group Before and After the Hop Stabilization

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Rebecca L. Krupenevich, William H. Clark, Gregory S. Sawicki and Jason R. Franz

muscle stiffness via changes in triceps surae muscle activation. 6 , 8 Furthermore, this activation-dependent modulation of triceps surae muscle stiffness occurs in response to simulated changes in Achilles tendon stiffness when the task demand requires requisite ankle joint quasi-stiffness to preserve

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Smokey Fermin, Lindsay Larkins, Sarah Beene and David Wetzel

pain and/or ROM deficits, will CE decrease pain and increase ROM? Summary of Search, Best Evidence Appraised, and Key Findings • Ipsilateral muscle activation and muscular strength is significantly increased after performing contralateral maneuvers. • Ipsilateral movement has a significant impact on