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Gareth Ryan, Heather Johnston and Janice Moreside

Up to 67% of individuals will experience some form of shoulder injury in their lifetime. 1 External rotation (ER) is one of the most commonly prescribed shoulder strengthening exercises for injury rehabilitation and prevention. 2 , 3 Although primarily intended to target the infraspinatus, the

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Brianna M. Papotto, Thomas Rice, Terry Malone, Timothy Butterfield and Tim L. Uhl

Context: Shoulder external rotators are challenged eccentrically throughout the deceleration phase of throwing, which is thought to contribute to overuse injuries. To evaluate the effectiveness of intervention programs, as well as identifying deficits, reliable and responsive measures of isometric and eccentric shoulder external rotation are necessary. Previously, isometric measures have primarily tested a single position, and eccentric measures have not been found to have high reliability. Objective: To examine the between-days reliability of multiple-angle isometric and dynamic eccentric isokinetic testing of shoulder external rotation. Design: Repeated measures. Participants: 10 healthy subjects (age 30 ± 12 y, height 166 ± 13 cm, mass 72 ± 10 kg). Main Outcome Measures: Average isometric peak torque of shoulder external rotation at 7 angles was measured. From these values, the angle of isometric peak torque was calculated. Dynamic eccentric average peak torque, average total work, and average angle of peak torque were measured. Results: Between-days reliability was high for average peak torque during isometric contractions at all angles (ICC ≥ .85), as it was for dynamic eccentric average peak torque (ICC ≥ .97). The estimated angle of isometric peak torque (ICC ≤ .65) was not highly reliable between days. The average angle of peak torque from the eccentric testing produced inconsistent results. Average total work of dynamic eccentric shoulder external rotation was found to be highly reliable between days (ICC ≥ . 97). Conclusion: Aspects of force such as peak torque and total work in isometric and eccentric testing of the shoulder external-rotator muscles can be measured reliably between days and used to objectively evaluate shoulder strength and identify changes when they occur. Angle measurements of peak torque could provide insight into the mechanical properties of the posterior shoulder muscles but were found to be inconsistent between days.

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Marcelo Peduzzi de Castro, Daniel Cury Ribeiro, Felipe de Camargo Forte, Joelly Mahnic de Toledo, Roberto Costa Krug and Jefferson Fagundes Loss

The aim of this study was to compare shoulder muscle force and moment production during external rotation performed in the transverse and sagittal planes. An optimization model was used for estimating shoulder muscle force production of infraspinatus, teres minor, supraspinatus, anterior deltoid, middle deltoid and posterior deltoid muscles. The model uses as input data the external rotation moment, muscle moment arm magnitude, muscle physiologic cross-sectional area and muscle specific tension. The external rotation moment data were gathered from eight subjects in transverse and six subjects in sagittal plane using an isokinetic dynamometer. In the sagittal plane, all studied muscles presented larger estimated force in comparison with the transverse plane. The infraspinatus, teres minor, supraspinatus and posterior deltoid muscles presented larger moment in sagittal when compared with transverse plane. When prescribing shoulder rehabilitation exercises, therapists should bear in mind the described changes in muscle force production.

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Kazuto Sakita, Matthew K. Seeley, Joseph William Myrer and J. Ty Hopkins

Context:

Standing and side-lying external-rotation exercises produce high activation of the deltoid and infraspinatus. Slight shoulder abduction during these exercises may decrease deltoid activity and increase infraspinatus activity.

Objective:

To determine if the addition of a towel under the arm during standing and side-lying external rotation affects infraspinatus, middle and posterior deltoid, and pectoralis major activation characteristics compared with a no-towel condition.

Design:

Controlled laboratory study.

Participants:

20 male volunteers (age 26 ± 3 y, height 1.80 ± 0.07 m, mass 77 ± 10 kg) who were right-hand dominant and had bilaterally healthy shoulders with no current cervical pathology and no skin infection or shoulder lesion.

Interventions:

External-rotation exercises without a towel roll (0° shoulder abduction) and with a towel roll (30° shoulder abduction) were performed in a standing and side-lying.

Main Outcome Measures:

Maximal voluntary isometric contraction for the infraspinatus, middle and posterior deltoid, and pectoralis major and external rotation in standing and side-lying with and without a towel roll were performed. Normalized average and peak surface EMG amplitude were compared between the towel conditions during standing and side-lying external rotation.

Results:

Both infraspinatus and pectoralis major activity had no significant differences between the towel conditions in standing and side-lying (P > .05). In standing and side-lying, posterior-deltoid activity was significantly greater with a towel roll (P < .05). Middle-deltoid activity had no significant differences between the towel conditions in standing (P > .05). However, in side-lying, middle-deltoid activity was significantly lower with a towel roll (P < .05).

Conclusion:

Middle-deltoid activity decreased with a towel roll during side-lying exercises. More data are needed to determine if a towel roll could be used to potentially reduce superior glide during external-rotation exercises.

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Joelly Mahnic de Toledo, Roberto Costa Krug, Marcelo Peduzzi Castro, Daniel Cury Ribeiro and Jefferson Fagundes Loss

In joints with 3 degrees of freedom, such as the shoulder joint, the association of different movements results in changes in the behavior of the moment arm of the muscles. The capacity of torque production for the same movement can be changed when movements take place in a different plane. The objective of this study is to quantify differences between torque production and resultant force estimated during the shoulder external rotation in two movement planes: the transverse and sagittal planes (with 90° of shoulder abduction). Eight individuals were evaluated using an isokinetic dynamometer and an eletrogoniometer for movements in the transverse plane and six individuals for movements in the sagittal plane. The results showed that the execution of the external rotation in the sagittal plane allowed greater torque magnitudes and resultant force compared with those in the transverse plane, probably owing to a prestretching of infraspinatus and teres minor.

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Kevin G. Laudner, Mike Moline and Keith Meister

Context:

Posterior shoulder tightness has been associated with altered shoulder range of motion (ROM) and several pathologic entities in baseball players. This tightness is hypothesized to be the result of the cumulative stress placed on the posterior shoulder during the deceleration phase of the throwing motion. The role of the posterior shoulder static restraints is to absorb this load while the glenohumeral (GH) external rotators eccentrically decelerate the arm after ball release and therefore also help dissipate this force. As such, the authors hypothesized that if the GH external rotators are weak, an excessive amount of this deceleration force is placed on the static restraints, which may lead to subsequent tightness.

Objective:

To compare the relationship between GH external-rotation strength and posterior shoulder tightness as measured by GH horizontal-adduction and internal-rotation ROM.

Design:

Descriptive study.

Setting:

Laboratory.

Participants:

45 professional baseball players.

Main Outcome Measures:

GH external-rotation strength and GH horizontal-adduction and internalrotation ROM.

Results:

GH external-rotation strength showed no relationship with either GH horizontal-adduction ROM (r 2 = .02, P = .40) or GH internal-rotation ROM (r 2 = .002, P = .77).

Conclusion:

There is little to no relationship between GH external-rotation strength and posterior shoulder tightness in professional baseball players. The posterior static restraints of the shoulder may absorb a large majority of the deceleration forces during the throwing motion. Although strengthening of the posterior shoulder dynamic restraints should not be overlooked, routine stretching of the static restraints may be more beneficial for decreasing posterior shoulder tightness and the subsequent risks associated with this tightness, although future research is warranted.

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Yanxin Zhang, David G. Lloyd, Amity C. Campbell and Jacqueline A. Alderson

The purpose of this study was to quantify the effect of soft tissue artifact during three-dimensional motion capture and assess the effectiveness of an optimization method to reduce this effect. Four subjects were captured performing upper-arm internal-external rotation with retro-reflective marker sets attached to their upper extremities. A mechanical arm, with the same marker set attached, replicated the tasks human subjects performed. Artificial sinusoidal noise was then added to the recorded mechanical arm data to simulate soft tissue artifact. All data were processed by an optimization model. The result from both human and mechanical arm kinematic data demonstrates that soft tissue artifact can be reduced by an optimization model, although this error cannot be successfully eliminated. The soft tissue artifact from human subjects and the simulated soft tissue artifact from artificial sinusoidal noise were demonstrated to be considerably different. It was therefore concluded that the kinematic noise caused by skin movement artifact during upper-arm internal-external rotation does not follow a sinusoidal pattern and cannot be effectively eliminated by an optimization model.

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Megan Q. Beard, Samantha A. Boland and Phillip A. Gribble

(HABD) and hip external rotation (HER) strength. 1 , 2 Furthermore, reduction in hip strength has been prospectively linked to increased risk in sustaining an anterior cruciate ligament injury. 3 The ability for clinicians to measure hip strength in an objective manner allows better detection of

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Dong-Rour Lee and Laurentius Jongsoon Kim

Context:

Many studies have explored closed kinetic chain (CKC) shoulder exercises (SEs) with a sling because they are safer and more effective than open-chain exercises, especially in early stages of treatment. However, the application of CKC SE in youth baseball players has rarely been attempted, although teenage baseball players also experience shoulder pain.

Objective:

To investigate the effects of CKC SE on the peak torque of shoulder internal rotation (IR) and external rotation (ER) in youth baseball players.

Design:

Single-group pretest, posttest.

Setting:

Biomechanics laboratory.

Participants:

23 Little League Baseball players with subacromial impingement syndrome.

Interventions:

The CKC SE with a sling was CKC shoulder-flexion exercise, extension exercise, IR exercise, and ER exercise. This exercise regimen was conducted 2 or 3 times/wk for 8 wk.

Main Outcome Measures:

The peak torque of shoulder IR and ER was measured using an isokinetic dynamometer. Concentric shoulder rotation was performed, with 5 repetitions at an angular velocity of 60°/s and 15 at 180°/s.

Results:

The IR and ER peak torque significantly increased at each angular velocity after the exercise program. In particular, the increase in IR and ER peak torque values was statistically significant at an angular velocity of 180°/s.

Conclusions:

CKC SE was effective in increasing shoulder IR and ER strength, demonstrating its potential benefits in the prevention and treatment of shoulder injury. In addition, increased IR peak torque appears to improve throwing velocity in baseball players.