Rehabilitation Exercises for Dysfunction of the Scapula: Exploration of Muscle Activity Using Fine-Wire EMG

Background: Scapular muscle activity during shoulder exercises has been explored with surface electromyography (EMG). However, knowledge about the activity of deeper-layer scapular muscles is still limited. Purpose: To investigate EMG activation of the deeper-layer scapular stabilizers (levator scapulae [LS], rhomboid major [RM], pectoralis minor [Pm] muscles) together with superficial muscle activity (upper [UT], middle [MT], and lower trapezius [LT] and serratus anterior [SA]) during 4 exercises often used for training scapular function. Based on the amplitude EMG of the deeper-layer muscles, scapular muscle activation ratios for the 4 exercises were calculated, hereby providing knowledge of the optimal muscle balance. Study Design: Descriptive laboratory study. Methods: A total of 26 healthy participants performed 4 shoulder exercises (side-lying external rotation [ER], side-lying forward flexion, prone horizontal abduction with ER, and prone extension) while simultaneously measuring scapular muscle activity. Intramuscular electrodes were used for the deeper layer, in contrast to surface electrodes for the superficial muscles. All data were normalized to percentage of maximal voluntary isometric contraction (%MVIC), and the activation ratios (the muscle activity of the deeper layer relative to the other muscles) were calculated. A 1-way analysis of variance with Bonferroni correction was applied for statistical analysis. Results: Moderate activity was found in all exercises for the LS and RM (25%-45% MVIC). The Pm resulted in low activity during both side-lying exercises (13%-18% MVIC). Ratios involving LS or RM showed values >1 for all exercises (1.28-12.41) except for LS/MT, LS/LT, and LS/RM (0.85-0.98) during side-lying ER, and LS/MT, RM/MT and RM/LS (0.85-0.99) during side-lying forward flexion. Likewise, values <1 were found when MT (0.85) and LS (0.99) were involved with RM in the numerator during side-lying forward flexion. Ratios with Pm in the numerator showed values <1, apart from the ratios with UT and SA in the denominator. Conclusion: The study provides extended knowledge about the deeper-layer scapular muscle activity and related ratios during the 4 shoulder exercises mentioned here. Putting theory into practice, based on our results, we advise both side-lying exercises to be performed to strengthen LT and MT, even in case of hyperactivity of the Pm. However, the 4 exercises should be given carefully to patients with hyperactivity in the LS and/or RM. Clinical Relevance: The findings of this study may assist clinical decision making in exercise selection for restoring scapular function.

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Torso and Hip Muscle Activity and Resulting Spine Load and Stability while Using the ProFitter 3-D Cross Trainer

Journal of Applied Biomechanics ◽

10.1123/jab.25.1.73 ◽

2009 ◽

Vol 25 (1) ◽

pp. 73-84 ◽

Cited By ~ 2

Author(s):

Priyanka Banerjee ◽

Stephen H.M Brown ◽

Samuel J. Howarth ◽

Stuart M. McGill

Keyword(s):

Muscle Activity ◽

Muscle Activation ◽

Clinical Decision Making ◽

Dynamic Balance ◽

Gluteus Medius ◽

Clinical Decision ◽

Whole Body ◽

Motor Patterns ◽

Hip Muscle ◽

Spine Mechanics

The ProFitter 3-D Cross Trainer is a labile surface device used in the clinic and claimed to train spine stability. The purpose of this study was to quantify the spine mechanics (compression and shear forces and stability), together with muscle activation mechanics (surface electromyography) of the torso and hip, during three ProFitter exercises. Trunk muscle activity was relatively low while exercising on the device (<25%MVC). Gluteus medius activity was phasic with the horizontal sliding position, especially for an experienced participant. Sufficient spinal stability was achieved in all three exercise conditions. Peak spinal compression values were below 3400 N (maximum 3188 N) and peak shear values were correspondingly low (under 500 N). The exercises challenge whole-body dynamic balance while producing very conservative spine loads. The motion simultaneously integrates hip and torso muscles in a way that appears to ensure stabilizing motor patterns in the spine. This information will assist with clinical decision making about the utility of the device and exercise technique in rehabilitation and training programs.

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Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

10.21203/rs.2.11994/v3 ◽

2019 ◽

Author(s):

Omar Baritello ◽

Mina Khajooei ◽

Tilman Engel ◽

Stephan Kopinski ◽

Andrew Quarmby ◽

...

Keyword(s):

Muscle Activation ◽

External Rotation ◽

Muscular Activity ◽

Shoulder Injury ◽

Serratus Anterior ◽

Maximal Voluntary Isometric Contraction ◽

Cross Sectional ◽

Neuromuscular Activity ◽

Custom Made ◽

Flexion Extension

Abstract Background:Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand. Methods:Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR : U.TA/L.TA; U.TA/SA) and contraction (CR : concentric/eccentric) ratios were analyzed (paired t-test; a = 0.05; Bonferroni adjusted a = 0.008). Results:PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p> 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion:Higher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an unstable weight mass increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

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Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

10.21203/rs.2.11994/v2 ◽

2019 ◽

Author(s):

Omar Baritello ◽

Mina Khajooei ◽

Tilman Engel ◽

Stephan Kopinski ◽

Andrew Quarmby ◽

...

Keyword(s):

Muscle Activation ◽

External Rotation ◽

Muscular Activity ◽

Shoulder Injury ◽

Serratus Anterior ◽

Maximal Voluntary Isometric Contraction ◽

Cross Sectional ◽

Neuromuscular Activity ◽

Custom Made ◽

Flexion Extension

Abstract Background Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass affects the muscular activity of the shoulder stabilizers (ST). Aim of the study was to analyzed the neuromuscular activity of the dynamic ST under four combinations of stable and unstable weight mass during three shoulder exercises. It was hypothesized that a combined condition of weight with unstable mass would elicit significantly greater activation due to the increased stabilization demand. Methods Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test;Bonferroni adjusted α=0.008) Results PWG showed significantly greater activation for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p>0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion Higher weight generated greater muscle activation whereas an unstable weight mass behavior raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an unstable weight mass increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.

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Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass

10.21203/rs.2.11994/v1 ◽

2019 ◽

Author(s):

Omar Baritello ◽

Mina Khajooei ◽

Tilman Engel ◽

Stephan Kopinski ◽

Andrew Quarmby ◽

...

Keyword(s):

Muscle Activation ◽

External Rotation ◽

Muscular Activity ◽

Shoulder Injury ◽

Serratus Anterior ◽

Maximal Voluntary Isometric Contraction ◽

Cross Sectional ◽

Neuromuscular Activity ◽

Custom Made ◽

Flexion Extension

Abstract Background Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass affects the muscular activity of the shoulder stabilizers. Aim of the study was to analyzed the neuromuscular activity of the dynamic shoulder stabilizers under four combinations of stable and unstable weight mass during three shoulder exercises. It was hypothesized that a combined condition of weight with unstable mass would elicit significantly greater activation due to the increased stabilization demand. Methods Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; α=0.05; Bonferroni adjusted α=0.008) Results PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p>0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion Higher weight generated greater muscle activation whereas an unstable weight mass behavior raised the neuromuscular activity, possibly due to increased stabilization demands. Application of an unstable weight mass may be beneficial to improve training effects in shoulder prevention and rehabilitation programs.

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Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass.

10.21203/rs.2.11994/v4 ◽

2020 ◽

Author(s):

Omar Baritello ◽

Mina Khajooei ◽

Tilman Engel ◽

Stephan Kopinski ◽

Andrew Quarmby ◽

...

Keyword(s):

Muscle Activation ◽

External Rotation ◽

Muscular Activity ◽

Shoulder Injury ◽

Serratus Anterior ◽

Maximal Voluntary Isometric Contraction ◽

Cross Sectional ◽

Neuromuscular Activity ◽

Custom Made ◽

Flexion Extension

Abstract Background:Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass affects the muscular activity of the shoulder stabilizers.Aim of the study was to analyze the neuromuscular activity of the dynamic shoulder stabilizers under four conditions of stable and unstable weight mass during three shoulder exercises. It was hypothesized that a combined condition of weight with unstable mass would elicit significantly greater activation due to the increased stabilization demand.MethodsSixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different training conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root mean square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; a = 0.05; Bonferroni adjusted a = 0.008) ResultsPWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles.ConclusionHigher weight generated greater muscle activation whereas an unstable weight mass behavior raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an unstable weight mass increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.Trial Registration: not applicable

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Scapular Bracing and Alteration of Posture and Muscle Activity in Overhead Athletes With Poor Posture

Journal of Athletic Training ◽

10.4085/1062-6050-48.1.13 ◽

2013 ◽

Vol 48 (1) ◽

pp. 12-24 ◽

Cited By ~ 28

Author(s):

Ashley K. Cole ◽

Melanie L. McGrath ◽

Shana E. Harrington ◽

Darin A. Padua ◽

Terri J. Rucinski ◽

...

Keyword(s):

Muscle Activity ◽

Muscle Activation ◽

Surface Emg ◽

Lateral View ◽

Controlled Clinical Trial ◽

Serratus Anterior ◽

Overhead Athletes ◽

Forward Flexion ◽

Upper Trapezius ◽

Lower Trapezius

Context: Overhead athletes commonly have poor posture. Commercial braces are used to improve posture and function, but few researchers have examined the effects of shoulder or scapular bracing on posture and scapular muscle activity. Objective: To examine whether a scapular stabilization brace acutely alters posture and scapular muscle activity in healthy overhead athletes with forward-head, rounded-shoulder posture (FHRSP). Design: Randomized controlled clinical trial. Setting: Applied biomechanics laboratory. Patients or Other Participants: Thirty-eight healthy overhead athletes with FHRSP. Intervention(s): Participants were assigned randomly to 2 groups: compression shirt with no strap tension (S) and compression shirt with the straps fully tensioned (S + T). Posture was measured using lateral-view photography with retroreflective markers. Electromyography (EMG) of the upper trapezius (UT), middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) in the dominant upper extremity was measured during 4 exercises (scapular punches, W's, Y's, T's) and 2 glenohumeral motions (forward flexion, shoulder extension). Posture and exercise EMG measurements were taken with and without the brace applied. Main Outcome Measure(s): Head and shoulder angles were measured from lateral-view digital photographs. Normalized surface EMG was used to assess mean muscle activation of the UT, MT, LT, and SA. Results: Application of the brace decreased forward shoulder angle in the S + T condition. Brace application also caused a small increase in LT EMG during forward flexion and Y's and a small decrease in UT and MT EMG during shoulder extension. Brace application in the S + T group decreased UT EMG during W's, whereas UT EMG increased during W's in the S group. Conclusions: Application of the scapular brace improved shoulder posture and scapular muscle activity, but EMG changes were highly variable. Use of a scapular brace might improve shoulder posture and muscle activity in overhead athletes with poor posture.

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Neuromuscular shoulder activity during exercises with different combinations of stable and unstable weight mass.

10.21203/rs.2.11994/v5 ◽

2020 ◽

Author(s):

Omar Baritello ◽

Mina Khajooei ◽

Tilman Engel ◽

Stephan Kopinski ◽

Andrew Quarmby ◽

...

Keyword(s):

Muscle Activation ◽

External Rotation ◽

Muscular Activity ◽

Shoulder Injury ◽

Serratus Anterior ◽

Maximal Voluntary Isometric Contraction ◽

Cross Sectional ◽

Neuromuscular Activity ◽

Custom Made ◽

Flexion Extension

Abstract Background: Recent shoulder injury prevention programs have utilized resistance exercises combined with different forms of instability, with the goal of eliciting functional adaptations and thereby reducing the risk of injury. However, it is still unknown how an unstable weight mass (UWM) affects the muscular activity of the shoulder stabilizers. Aim of the study was to assess neuromuscular activity of dynamic shoulder stabilizers under four conditions of stable and UWM during three shoulder exercises. It was hypothesized that a combined condition of weight with UWM would elicit greater activation due to the increased stabilization demand. Methods: Sixteen participants (7 m/9 f) were included in this cross-sectional study and prepared with an EMG-setup for the: Mm. upper/lower trapezius (U.TA/L.TA), lateral deltoid (DE), latissimus dorsi (LD), serratus anterior (SA) and pectoralis major (PE). A maximal voluntary isometric contraction test (MVIC; 5 sec.) was performed on an isokinetic dynamometer. Next, internal/external rotation (In/Ex), abduction/adduction (Ab/Ad) and diagonal flexion/extension (F/E) exercises (5 reps.) were performed with four custom-made-pipes representing different exercise conditions. First, the empty-pipe (P; 0.5 kg) and then, randomly ordered, water-filled-pipe (PW; 1 kg), weight-pipe (PG; 4.5 kg) and weight + water-filled-pipe (PWG; 4.5 kg), while EMG was recorded. Raw root-mean-square values (RMS) were normalized to MVIC (%MVIC). Differences between conditions for RMS%MVIC, scapular stabilizer (SR: U.TA/L.TA; U.TA/SA) and contraction (CR: concentric/eccentric) ratios were analyzed (paired t-test; p ≤ 0.05; Bonferroni adjusted α = 0.008). Results: PWG showed significantly greater muscle activity for all exercises and all muscles except for PE compared to P and PW. Condition PG elicited muscular activity comparable to PWG (p > 0.008) with significantly lower activation of L.TA and SA in the In/Ex rotation. The SR ratio was significantly higher in PWG compared to P and PW. No significant differences were found for the CR ratio in all exercises and for all muscles. Conclusion: Higher weight generated greater muscle activation whereas an UWM raised the neuromuscular activity, increasing the stabilization demands. Especially in the In/Ex rotation, an UWM increased the RMS%MVIC and SR ratio. This might improve training effects in shoulder prevention and rehabilitation programs.Trial Registration: not applicable

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Hip Muscle Activity During 3 Side-Lying Hip-Strengthening Exercises in Distance Runners

Journal of Athletic Training ◽

10.4085/1062-6050-47.1.15 ◽

2012 ◽

Vol 47 (1) ◽

pp. 15-23 ◽

Cited By ~ 28

Author(s):

Joseph M. McBeth ◽

Jennifer E. Earl-Boehm ◽

Stephen C. Cobb ◽

Wendy E. Huddleston

Keyword(s):

Muscle Activity ◽

Repeated Measures ◽

External Rotation ◽

Gluteus Maximus ◽

Gluteus Medius ◽

Electromyographic Activity ◽

Maximal Voluntary Isometric Contraction ◽

Strengthening Exercises ◽

Hip Abduction ◽

Hip Strengthening

Context: Lower extremity overuse injuries are associated with gluteus medius (GMed) weakness. Understanding the activation of muscles about the hip during strengthening exercises is important for rehabilitation. Objective: To compare the electromyographic activity produced by the gluteus medius (GMed), tensor fascia latae (TFL), anterior hip flexors (AHF), and gluteus maximus (GMax) during 3 hip-strengthening exercises: hip abduction (ABD), hip abduction with external rotation (ABD-ER), and clamshell (CLAM) exercises. Design: Controlled laboratory study. Setting: Laboratory. Patients or Other Participants: Twenty healthy runners (9 men, 11 women; age = 25.45 ± 5.80 years, height = 1.71 ± 0.07 m, mass = 64.43 ± 7.75 kg) participated. Intervention(s): A weight equal to 5% body mass was affixed to the ankle for the ABD and ABD-ER exercises, and an equivalent load was affixed for the CLAM exercise. A pressure biofeedback unit was placed beneath the trunk to provide positional feedback. Main Outcome Measure(s): Surface electromyography (root mean square normalized to maximal voluntary isometric contraction) was recorded over the GMed, TFL, AHF, and GMax. Results: Three 1-way, repeated-measures analyses of variance indicated differences for muscle activity among the ABD (F3,57 = 25.903, P<.001), ABD-ER (F3,57 = 10.458, P<.001), and CLAM (F3,57 = 4.640, P=.006) exercises. For the ABD exercise, the GMed (70.1 ± 29.9%), TFL (54.3 ± 19.1%), and AHF (28.2 ± 21.5%) differed in muscle activity. The GMax (25.3 ± 24.6%) was less active than the GMed and TFL but was not different from the AHF. For the ABD-ER exercise, the TFL (70.9 ± 17.2%) was more active than the AHF (54.3 ± 24.8%), GMed (53.03 ± 28.4%), and GMax (31.7 ± 24.1 %). For the CLAM exercise, the AHF (54.2 ± 25.2%) was more active than the TFL (34.4 ± 20.1%) and GMed (32.6 ± 16.9%) but was not different from the GMax (34.2 ± 24.8%). Conclusions: The ABD exercise is preferred if targeted activation of the GMed is a goal. Activation of the other muscles in the ABD-ER and CLAM exercises exceeded that of GMed, which might indicate the exercises are less appropriate when the primary goal is the GMed activation and strengthening.

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Biomechanical Analysis of Glenohumeral Internal Rotation Deficit in a Cadaveric Model

ASME 2010 5th Frontiers in Biomedical Devices Conference and Exhibition ◽

10.1115/biomed2010-32052 ◽

2010 ◽

Author(s):

Akash Gupta ◽

Jeffrey Gates ◽

Michelle H. McGarry ◽

James E. Tibone ◽

Thay Q. Lee

Keyword(s):

Internal Rotation ◽

Clinical Decision Making ◽

Glenohumeral Joint ◽

External Rotation ◽

Clinical Decision ◽

Biomechanical Analysis ◽

Glenohumeral Internal Rotation Deficit ◽

Posterior Translation ◽

Throwers Shoulder ◽

Cadaveric Model

Overhead throwing athletes have been shown to develop adaptive changes in humeral rotation to allow for higher throwing velocities. This manifests as an increase in humeral external rotation and a decrease in internal rotation, which is called glenohumeral internal rotation deficit (GIRD). The percentage of GIRD that significantly affects glenohumeral joint kinematics is not known. The objective of the study was to create a throwers shoulder model with fixed percentages of GIRD to determine at which point kinematic changes start occurring. The results showed that there was a significant decrease in posterior translation starting at 10% GIRD. With inferior translational loads, significantly less inferior translation starts occurring at 20% GIRD. The humeral head apex position at maximum external rotation moves superiorly, posteriorly and laterally, with significant changes in the superior direction occurring with 10% GIRD onwards. Overall, significant kinematic changes begin at 10% GIRD and this should be taken into account for clinical decision-making as to when intervention is necessary.

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