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Il-young Yu, Dong-kyu Lee, Myoung-Joo Kang and Jae-seop Oh

The rotator cuff (RC) muscles comprise the supraspinatus, subscapularis, infraspinatus, and teres minor, 1 providing dynamic stability of the shoulder joint. 2 , 3 The infraspinatus muscle plays a particularly important role in producing primary external rotation (ER) torque and dynamic stability

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Samuele Contemori, Andrea Biscarini, Fabio M. Botti, Daniele Busti, Roberto Panichi and Vito E. Pettorossi

structural shoulder alterations that are not directly related to clear detectable clinical symptoms. 6 , 7 These alterations, though asymptomatic, may have a subtle negative impact on performance and may gradually progress in functional loss or limitation. Isolated infraspinatus muscle atrophy (IIMA) is

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Julien Le Gal, Mickael Begon, Benoit Gillet and Isabelle Rogowski

follow-through phase of the tennis stroke 9 may lead to microtraumatisms in the soft tissues. 10 The subsequent scarring process may induce tightening of the posterior shoulder, such as the posterior glenohumeral capsule, infraspinatus muscle, and connective tissue, which also contributes to the

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Gareth Ryan, Heather Johnston and Janice Moreside

posterior deltoid is also recruited significantly. 4 Infraspinatus muscle fibers run superolaterally from the inferior scapula to the greater tubercle of the humerus and translate the head of the humerus inferiorly upon contraction. In some patients, this can help prevent subacromial impingement by

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Eadric Bressel and Gary D. Heise

The purpose of this study was to compare muscle activity, kinematic, and oxygen consumption characteristics between forward and reverse arm cranking. Twenty able-bodied men performed 5-min exercise bouts of forward and reverse arm cranking while electromyographic (EMG), kinematic, and oxygen consumption data were collected. EMG activity of biceps brachii, triceps brachii, deltoid, and infraspinatus muscles were recorded and analyzed to reflect on-time durations and amplitudes for each half-cycle (first 180° and second 180° of crank cycle). Kinematic data were quantified from digitization of video images, and oxygen consumption was calculated from expired gases. Dependent measures were analyzed with a MANOVA and follow-up univariate procedures; alpha was set at .01. The biceps brachii, deltoid, and infraspinatus muscles displayed greater on-time durations and amplitudes for select half-cycles of reverse arm cranking compared to forward arm cranking (p < 0.01). Peak wrist flexion was 9% less in reverse arm cranking (p < 0.01), and oxygen consumption values did not differ between conditions (p = 0.25). Although there were no differences in oxygen consumption and only minor differences kinematically, reverse arm cranking requires greater muscle activity from the biceps brachii, deltoid, and infraspinatus muscles. These results may allow clinicians to more effectively choose an arm cranking direction that either minimizes or maximizes upper extremity muscle activity depending on the treatment objectives.

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Timothy J. Henry, Scott M. Lephart, Jorge Giraldo, David Stone and Freddie H. Fu

Context:

Muscle fatigue is an important concept in regard to the muscle function of the shoulder joint. Its effect on the muscle force couples of the glenohumeral joint has not been fully identified.

Objective:

To examine the effects of muscle fatigue on muscle force-couple activation in the normal shoulder.

Design:

Pretest, posttest.

Patients:

Ten male subjects, age 18–30 years, with no previous history of shoulder problems.

Main Outcome Measures:

EMG (area) values were assessed for the anterior and middle deltoid, subscapularis, and infraspinatus muscles during 4 dynamic stabilizing exercises before and after muscle fatigue. The exercises examined were a push-up, horizontal abduction, segmental stabilization, and rotational movement on a slide board.

Results:

No significant differences were observed for any of the muscles tested.

Conclusions:

The results of our study indicate that force-couple coactivation of the glenohumeral joint is not significantly altered after muscle fatigue.

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Jun G. San Juan, Peter Kosek and Andrew R. Karduna

Subacromial impingement syndrome is the most common shoulder disorder. Abnormal superior translation of the humeral head is believed to be a major cause of this pathology. The first purpose of the study was to examine the effects of suprascapular nerve block on superior translation of the humeral head and scapular upward rotation during dynamic shoulder elevation. The secondary purpose was to assess muscle activation patterns during these motions. Twenty healthy subjects participated in the study. Using fluoroscopy and electromyography, humeral head translation and muscle activation were measured before and after a suprascapular nerve block. The humeral head was superiorly located at 60 degrees of humeral elevation, and the scapula was more upwardly rotated from 30 to 90 degrees of humeral elevation after the block. The differences were observed during midrange of motion. In addition, the deltoid muscle group demonstrated increased muscle activation after the nerve block. The study’s results showed a compensatory increase in humeral head translation, scapular upward rotation, and deltoid muscle activation due to the nerve block. These outcomes suggest that increasing muscular strength and endurance of the supraspinatus and infraspinatus muscles could prevent any increased superior humeral head translation. This may be beneficial in reducing shoulder impingement or rotator cuff tears over time.

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Daniele Coraci, Silvia Giovannini, Giulia Piccinini, Claudia Loreti, Valter Santilli and Luca Padua

Dear Editor, We have read with high consideration and pleasure the article, “Sensorimotor Control of the Shoulder in Professional Volleyball Players with Isolated Infraspinatus Muscle Atrophy,” by Contemori and colleagues. 1 The authors investigated the static and dynamic shoulder stability, by

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Kellie C. Huxel Bliven and Kelsey J. Picha

muscle alterations exist in the presence of shoulder pain and pathology; however, recent focus on the infraspinatus muscle—deficiencies, alterations and adaptations, and response to treatment—is reflected in 4 of this issue’s articles (Contemori and Biscarini, 1 Kamali et al, 2 Pexa et al, 3 and Yu et

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Samuele Contemori and Andrea Biscarini

neuropathy of the suprascapular nerve. This neuropathy leads to paralysis and atrophy of the infraspinatus muscle. 14 – 20 Indeed, overhead activity athletes with suprascapular nerve palsy exhibit an evident reduction of the soft tissue bulk in the infraspinatus fossa of the HS compared with the healthy