Roles of deltoid and rotator cuff muscles in shoulder elevation

doi:10.1016/S0268-0033(96)00047-2

Clinical Biomechanics

Volume 12, Issue 1, January 1997, Pages 32-38

https://doi.org/10.1016/S0268-0033(96)00047-2 Get rights and content

Abstract

Objective. The objective of this study was to measure abduction moment arms of the supraspinatus, subscapularis, infraspinatus, and deltoid (anterior, middle, and posterior portions) muscles during humeral elevation in the scapular plane (abduction).

Design. Moment arms were measured by conducting an in vitro experiment.

Background. The moment arm of a muscle represents its mechanical advantage, which is an important determinant of muscle function.

Methods. Measurements were made on 10 fresh frozen cadaveric specimens. Tendon excursions were measured as the humerus was elevated in the plane of the scapula. The principle of virtual work was used to estimate the muscle moment arm of each muscle by computing the slope of the tendon excursion versus joint angle relationship.

Results. Moment arms were affected by joint angle in a non-linear fashion. The anterior deltoid, middle deltoid, subscapularis, and infraspinatus muscles had abduction moment arms throughout most of the range of motion studied. The posterior deltoid had an adduction moment arm. Internal and external humeral rotation affected the elevation moment arms of all six muscles.

Conclusions. Abduction moment arm magnitudes of the muscles studies vary throughout the arc of elevation. This study was limited by considering broad muscles to have a single line of action.

References (25)

R.W. Bassett et al.
Glenohumeral muscle force and moment mechanics in a position of shoulder instability
J Biomech
(1990)
K.N. An et al.
Tendon excursion and moment arm of index finger muscles
J Biomech
(1983)
K.N. An et al.
Application of a magnetic tracking device to kinesiologic studies
J Biomech
(1988)
H.E.J. Veeger et al.
Inertia and muscle contraction parameters for musculoskeletal modeling of the shoulder mechanism
J Biomech
(1991)
D. Karlsson et al.
Towards a model for force predictions in the human shoulder
J Biomech
(1992)
P.J. McMahon et al.
Shoulder muscle forces and tendon excursions during glenohumeral abduction in the scapular plane
J Shoulder Elbow Surg
(1995)
F.W. Jobe et al.
Delineation of diagnostic criteria and a rehabilitation program for rotator cuff injuries
Am J Sports Med
(1982)
M. Kronberg et al.
Muscle activity and coordination in the normal shoulder — An electromyographic study
Clin Orthop
(1990)
G. Sigholm et al.
Electormyographic analysis of shoulder muscle load
J Orthop Res
(1984)
H. Townsend et al.
Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program
Am J Sports Med
(1991)

J. Perry et al.

EMG-force relationship in skeletal muscle

CRC Crit Rev Biomed Eng

(1981)

J.F. Keating et al.

The relative strength of the rotator cuff muscles: a cadaver study

J Bone Joint Surg [Br]

(1993)

Cited by (139)

Individuals with rotator cuff tears unsuccessfully treated with exercise therapy have less inferiorly oriented net muscle forces during scapular plane abduction
2024, Journal of Biomechanics
Exercise therapy for individuals with rotator cuff tears fails in approximately 25.0 % of cases. One reason for failure of exercise therapy may be the inability to strengthen and balance the muscle forces crossing the glenohumeral joint that act to center the humeral head on the glenoid. The objective of the current study was to compare the magnitude and orientation of the net muscle force pre- and post-exercise therapy between subjects successfully and unsuccessfully (e.g. eventually underwent surgery) treated with a 12-week individualized exercise therapy program. Twelve computational musculoskeletal models (n = 6 successful, n = 6 unsuccessful) were developed in OpenSim (v4.0) that incorporated subject specific tear characteristics, muscle peak isometric force, in-vivo kinematics and bony morphology. The models were driven with experimental kinematics and the magnitude and orientation of the net muscle force was determined during scapular plane abduction at pre- and post-exercise therapy timepoints. Subjects unsuccessfully treated had less inferiorly oriented net muscle forces pre- and post-exercise therapy compared to subjects successfully treated (p = 0.039 & 0.045, respectively). No differences were observed in the magnitude of the net muscle force (p > 0.05). The current study developed novel computational musculoskeletal models with subject specific inputs capable of distinguishing between subjects successfully and unsuccessfully treated with exercise therapy. A less inferiorly oriented net muscle force in subjects unsuccessfully treated may increase the risk of superior migration leading to impingement. Adjustments to exercise therapy programs may be warranted to avoid surgery in subjects at risk of unsuccessful treatment.
Impact of reverse shoulder arthroplasty design and patient shoulder size on moment arms and muscle fiber lengths in shoulder abductors
2023, Journal of Shoulder and Elbow Surgery
Reverse shoulder arthroplasty (RSA) increases the moment arm of the deltoid; however, there is limited knowledge on the accompanying changes in muscle architecture that play a role in muscle force production. The purpose of this study was to use a geometric shoulder model to evaluate the anterior deltoid, middle deltoid, and supraspinatus regarding (1) the differences in moment arms and muscle-tendon lengths in small, medium, and large native shoulders and (2) the impact of 3 RSA designs on moment arms, muscle fiber lengths, and force-length (F-L) curves.
A geometric model of the native glenohumeral joint was developed, validated, and adjusted to represent small, medium, and large shoulders. Moment arms, muscle-tendon lengths, and normalized muscle fiber lengths were assessed for the supraspinatus, anterior deltoid, and middle deltoid from 0° to 90° of abduction. RSA designs were modeled and virtually implanted, including a lateralized glenosphere with an inlay 135° humeral component (lateral glenoid–medial humerus [LGMH]), a medialized glenosphere with an onlay 145° humeral component (medial glenoid–lateral humerus [MGLH]), and a medialized glenosphere with an inlay 155° humeral component (medial glenoid–medial humerus [MGMH]). Descriptive statistics were used to compare moment arms and normalized muscle fiber lengths.
As shoulder size increased, the moment arms and muscle-tendon lengths for the anterior deltoid, middle deltoid, and supraspinatus increased. All RSA designs achieved greater moment arms for the anterior and middle deltoid, with the MGLH design achieving the largest increase. The resting normalized muscle fiber length of the anterior and middle deltoid was substantially increased in the MGLH (1.29) and MGMH (1.24) designs, shifting the operating ranges of these muscles to the descending portions of their F-L curves, whereas the LGMH design maintained a resting deltoid fiber length (1.14) and operating range similar to the native shoulder. All RSA designs demonstrated a decrease in the native supraspinatus moment arm in early abduction, with the largest decrease in the MGLH design (−59%) and minimal decrease in the LGMH design (−14%). The supraspinatus operated on the ascending limb of its F-L curve in the native shoulder and remained on this portion of the F-L curve for all RSA designs.
Although the MGLH design maximizes the abduction moment arm for the anterior and middle deltoid, overlengthening of the muscle may compromise deltoid muscle force production by forcing the muscle to operate on the descending portion of its F-L curve. In contrast, the LGMH design increases the abduction moment arm for the anterior and middle deltoid more modestly while allowing the muscle to operate near the plateau of its F-L curve and maximizing its force-producing potential.
Electromyographic activities of glenohumeral joint muscles during shoulder forward flexion with isometric horizontal abduction loading
2023, Journal of Shoulder and Elbow Surgery
Isometric horizontal abduction loading has been applied to improve imbalanced scapular muscle activities during shoulder exercises; however, the effect on glenohumeral joint muscle activity remains unclear. The purpose of this study was to investigate the changes in electromyographic activity of shoulder muscles during forward flexion with isometric horizontal abduction loading in healthy participants.
Thirteen healthy men were recruited for this study. Participants performed shoulder forward flexion with isometric horizontal abduction loading using an elastic band (Flex-band condition) and forward flexion without shoulder loading (Normal-flex condition). Muscle activities were evaluated while maintaining shoulder flexion at 60°, 90°, 120°, and 150° (static task) and during active shoulder flexion from 0° to maximum elevation (dynamic task). Surface electrodes were placed on the deltoid, pectoralis major, infraspinatus, and teres minor muscles to measure the activities of the shoulder muscles during each task. The muscle activities during the static task were compared using a 2-way analysis of variance with repeated measures of the 2 factors, loading condition and flexion position, and a paired t test was used for comparisons between the 2 conditions during the dynamic task (significance level set at P < .05).
For the static task, the Flex-band condition significantly increased the deltoid middle and posterior activities by 2-15 times and the infraspinatus and teres minor activities by 2-3 times compared with the Normal-flex condition at all positions. In contrast, the Flex-band condition significantly decreased (by about half) the activities of the deltoid anterior (at 120° and 150°) and pectoralis major (at all positions) compared with the Normal-flex condition. For the dynamic task, the Flex-band condition significantly increased the deltoid middle, deltoid posterior, infraspinatus, and teres minor activities by 2-7 times and decreased the deltoid anterior activity by approximately two-thirds.
Applying isometric horizontal abduction loading during shoulder forward flexion may be useful in improving the imbalanced muscle activities of the glenohumeral joint, such as excessive activity of the deltoid anterior and pectoralis major and dysfunction of the deltoid middle, deltoid posterior, and shoulder external rotator muscles. Shoulder forward flexion with horizontal abduction loading could be available for exercise in patients who have massive rotator cuff tears or who have undergone rotator cuff repair and shoulder arthroplasty.
Effect of shape and size of supraspinatus tears on rotator cuff strain distribution: an in vitro study
2023, Journal of Shoulder and Elbow Surgery
The impact of the size and shape of a supraspinatus tear on the strain of the intact rotator cuff and the kinematics of the shoulder is still unknown. This, however, can be relevant when deciding whether surgical reconstruction is required to prevent an increase in a tendon defect. In this study, the effect of tear width and shape on rotator cuff strain and glenohumeral kinematics was evaluated during active abduction.
Twelve fresh-frozen cadaveric shoulders with intact rotator cuffs were used in this study. We created 50% and 100% wide (full-thickness) crescent-shaped (CS) tears (n = 6) and reverse L–shaped (rLS) tears (n = 6) in the supraspinatus tendon and measured strain and kinematics during active humeral elevation until 30°.
Both tear shapes and sizes led to an increase in internal rotation, supraspinatus loading force, and superior translation of the humerus. For the 100% wide tear size, anterior translation was observed in the CS tear group, whereas in the rLS tear group, this translation occurred mainly in the posterior direction. Strain was higher in the infraspinatus during the first 25° of abduction in comparison with the supraspinatus tendon in both tear shape groups. An analysis of the anterior and posterior tear borders showed a higher strain concentration on the same side of the tear in the CS tear group with 50% and 100% wide tears.
The influence of different tear shapes on translation in the anterior-posterior direction was evident as both CS and rLS tears led to an oppositely directed translation of the humeral head. The strain analysis showed a stress-shielding effect of the infraspinatus at the beginning of abduction. Therefore, special attention must be paid to correctly identify the tear extension and adequately reconstruct the rotator cuff footprint. Moreover, the constant location of maximum strain in the CS tear group may lead to an earlier progression than in the rLS tear group.
The effect of task rotation on activation and fatigue response of rotator cuff muscles during overhead work
2021, Applied Ergonomics
Overhead work is known as one of the ergonomic risk factors that can lead to shoulder overload and injury. Anatomical alignment of rotator cuff muscles makes them the most vulnerable to injuries during overhead work. In this study, the effect of task rotation, as one of the administrative controls to reduce the risk of injury during overhead work, on the fatigue response of rotator cuff muscles was investigated. Twelve participants performed three submaximal exertions (5, 20, and 35% of maximum voluntary contraction (MVC)) using four task rotation sequences (increasing, decreasing, upward parabolic, and downward parabolic). Median frequency of surface electromyography (EMG), shoulder strength, and ratings of perceived exertion (RPE) were used to study the fatigue response of rotator cuff muscles. Although the average normalized muscle activity was similar in all sequences, the task rotation sequence had a significant effect on the median frequency. The effect of task rotation sequence on the strength and RPE was similar to that of the median frequency but was statistically not significant. The upward parabolic task rotation sequence resulted in the lowest fatigue among all the task sequences. Performing intense exertions apart from each other, warm-up exertions, and the presence of active recovery after the intense exertions could be the factors that produced the lowest fatigue during this sequence.
Changes in shoulder muscle activities and glenohumeral motion after rotator cuff repair: an assessment using ultrasound real-time tissue elastography
2021, Journal of Shoulder and Elbow Surgery
Although rotator cuff repair is performed to restore the function of the rotator cuff muscles and glenohumeral (GH) joint motion, little has been known regarding the recovery process. The purpose of this study was (1) to investigate changes over time in activities of the supraspinatus and deltoid muscles assessed by ultrasound real-time tissue elastography (RTE) after rotator cuff repair and (2) to determine contributions of the activities of these muscles to the GH joint motion.
Twenty patients after rotator cuff repair and 13 control participants were enrolled in this study. Elasticity of the supraspinatus and middle deltoid muscles were measured at rest and 30° of humerothoracic elevation in the scapular plane (scaption) by using RTE. The elasticity at 30° of scaption was normalized to that at rest in each muscle to quantify their muscle activities. In addition, the supraspinatus-to-middle deltoid (SSP/MD) ratio for the normalized elasticity was calculated. The GH elevation angle was measured with a digital inclinometer, which was calculated by subtracting the scapular upward rotation angle from 30° of scaption. For patients after rotator cuff repair, all measurements were performed at 6 weeks, 8 weeks, 3 months, and 6 months after surgery. Rotator cuff integrity was examined with magnetic resonance imaging at 6 months after surgery.
Fifteen of 20 patients who remained intact at 6 months after surgery completed this study. The supraspinatus activity at 6 weeks was significantly smaller than that at 3 months (P = .006) and 6 months (P = .010). There was no significant difference in the supraspinatus activity between the patients at 3 months and the control participants (P = .586). The middle deltoid activity at 6 weeks was significantly greater than that at 6 months (P = .003). There was positive correlation between GH elevation angle and the activity of the supraspinatus relative to the deltoid at 6 weeks (r = 0.75, P = .001) and 8 weeks (r = 0.53, P = .041).
The supraspinatus activity increased from 6 weeks to 3 months after surgery. The supraspinatus activity at 3 months after surgery was the same level as that in healthy individuals. On the other hand, the deltoid activity decreased from 6 weeks to 6 months after surgery. The increase in activity of the supraspinatus relative to the deltoid was likely to be related to the increase in GH elevation during postoperative at 8 weeks.

View all citing articles on Scopus

^†: Dr Jain Liu was primarily responsible for conceiving, conducting, and writing this research. Tragically, he was struck and killed by lightning in June 1995, soon after completing this manuscript. The co-authors wish to recognize his enthusiasm, intelligence, wit, and hard work.

View full text

PaperRoles of deltoid and rotator cuff muscles in shoulder elevation

Abstract

J Biomech

J Biomech

J Biomech

J Biomech

J Biomech

J Shoulder Elbow Surg

Delineation of diagnostic criteria and a rehabilitation program for rotator cuff injuries

Am J Sports Med

Muscle activity and coordination in the normal shoulder — An electromyographic study

Clin Orthop

Electormyographic analysis of shoulder muscle load

J Orthop Res

Electromyographic analysis of the glenohumeral muscles during a baseball rehabilitation program

Am J Sports Med

EMG-force relationship in skeletal muscle

CRC Crit Rev Biomed Eng

The relative strength of the rotator cuff muscles: a cadaver study

J Bone Joint Surg [Br]

Paper
Roles of deltoid and rotator cuff muscles in shoulder elevation