Comparative Electromyographic Study of Scapular Stabilizing Muscles During Five Main Rehabilitation Exercises.

OBJECTIVE: The aim of the study is to compare the surface electromyographic amplitude, activation ratio, and onset latency of the main scapular stabilizing muscles between five typical rehabilitative exercises. DESIGN: Twenty-seven healthy participants performed five scapular exercises (wall slide, wall push-up plus, prone horizontal abduction with external rotation, external rotation in side lying, and low row) while simultaneously recording surface electromyographic of serratus anterior, middle trapezius, lower trapezius, and upper trapezius. Surface electromyographic amplitudes, onset latencies, and activation ratios were calculated. RESULTS: Prone horizontal abduction with external rotation showed an excellent upper trapezius/middle trapezius (0.43) and upper trapezius/lower trapezius (0.30) muscle balance with high (>50% maximum voluntary isometric contraction) middle trapezius and lower trapezius amplitudes, a low (<20% maximum voluntary isometric contraction) upper trapezius amplitude, and an early activation of the scapular stabilizing muscles (-474.7 to 89.9 ms) relative to upper trapezius. External rotation in side lying showed excellent upper trapezius/serratus anterior (0.26), upper trapezius/middle trapezius (0.32), and upper trapezius/lower trapezius (0.21) activation ratios and, along with low row and wall slide, showed early activation of the scapular stabilizing muscles (-378.1 to -26.6 ms). CONCLUSIONS: Prone horizontal abduction with external rotation presented optimal scapular neuromuscular control. Although external rotation in side lying, low row, and wall slide did not meet all the criteria associated with optimal scapular neuromuscular control, these exercises could be used in early stages of shoulder rehabilitation because they favor early activation of the scapular stabilizing muscles.

Scapulothoracic muscle activity during kinetic chain variations of a prone elevation exercise.

BACKGROUND: Scapular rehabilitation exercises should target appropriate muscles. Recently, adding external rotation resistance to scapular exercises has gained interest. Moreover, clinical experts advise kinetic chain integration into shoulder rehabilitation exercises. OBJECTIVE: To investigate scapular muscle activity during kinetic chain variations of a prone elevation exercise. METHODS: Activity of the upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior (SA) muscles was determined with surface electromyography (EMG) in 31 asymptomatic participants during six prone elevation exercise variations. Variation was created by adding external rotation resistance, adding trunk extension, or changing exercise position (prone on a Swiss ball with knees or feet supported, or prone on a physiotable). All data were normalized as a percentage of maximal voluntary isometric contraction (% MVIC). For each muscle, a Friedman's ANOVA was conducted to analyse statistical differences in EMG signal intensity between exercises. RESULTS: The LT was moderately (42 - 48% MVIC) and MT highly (63 - 66% MVIC) activated during all exercise variations. No significant differences between exercises for these muscles could be detected. Adding external rotation to a prone elevation exercise decreased UT activity while adding trunk extension increased UT activity. Altering exercise position had no influence on scapular muscle activity except increased UT activity when lying prone on a physiotable with trunk extension. CONCLUSION: Prone elevation exercises are appropriate for facilitating LT and MT activity. Adding external rotation inhibits UT activity while UT facilitation could be achieved when adding trunk extension.

Electromyographic Muscle Activity and Three-Dimensional Scapular Kinematics in Patients With Multidirectional Shoulder Instability: A Study in the Hypermobile Type of the Ehlers-Danlos Syndrome and the Hypermobility Spectrum Disorders.

OBJECTIVE: To investigate differences in electromyography (EMG), muscle activity, and scapular kinematics during elevation in the scapular plane between healthy controls, participants with multidirectional shoulder laxity (MDL), and patients with multidirectional shoulder instability (MDI) who are diagnosed with hypermobile Ehlers-Danlos syndrome (hEDS) or hypermobility spectrum disorder (HSD). METHODS: Twenty-seven women with hEDS/HSD and MDI, 27 female healthy control subjects, and 28 female subjects with MDL participated in this study. Scapular 3-dimensional kinematic data were obtained using 8 Oqus Qualisys cameras. Simultaneously, surface EMG was used to measure muscle activity of the upper, middle, and lower trapezius, infraspinatus, latissimus dorsi, serratus anterior, posterior deltoid, and pectoralis major during arm elevation in the scapular plane. Group differences were assessed using statistical parametric mapping. RESULTS: Regarding scapular kinematics, significantly less upward rotation was observed in hEDS/HSD patients with MDI compared to both healthy controls and MDL subjects. Significantly less posterior tilt was seen in hEDS/HSD patients compared to MDL subjects. Furthermore, significantly higher EMG activity of the infraspinatus, middle trapezius, and posterior deltoid was found in hEDS/HSD patients with MDI. CONCLUSION: hEDS/HSD patients with MDI demonstrate altered scapular kinematics and increased EMG muscle activity compared to subjects without MDI. These findings could serve as a stepping stone for future research regarding treatment strategies in patients whose conditions belong to the hypermobility spectrum.

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.

Electromyographic analysis of selected shoulder muscles during a series of exercises commonly used in patients with symptomatic degenerative rotator cuff tears.

BACKGROUND: In the nonoperative treatment of degenerative rotator cuff (RC) tears, exercise therapy is advocated. Exercises focusing on strengthening the anterior deltoid (AD) and the scapular muscles are proposed to compensate for RC dysfunction. However, the amount of electromyographic (EMG) activity in these muscles during these exercises remains unclear. Moreover, it is unknown whether muscle activity levels during these exercises alter with increasing age. Therefore, the purpose of this study was to evaluate EMG activity in the deltoid and scapular muscles during 2 series of commonly used shoulder rehabilitation exercises and assess possible age-related changes in muscle activity. METHODS: Fifty-five healthy participants (aged 18-60 years) participated in this study. Surface EMG activity was measured in 8 shoulder girdle muscles during a progression of a closed chain elevation program (bench and wall slides) and during a progression of previously published AD exercises. In addition, muscle activity was compared between 3 age categories (18-32 years, 33-46 years, and 47-60 years). RESULTS: The proposed progressions exhibited increasing activity from <10% of maximal voluntary isometric contraction to >20% of maximal voluntary isometric contraction for the AD for both exercise programs and for the middle deltoid, upper trapezius, and middle trapezius during the closed chain elevation exercises. Activity levels in the other muscles remained <20% throughout the progression. Age-related analysis revealed increased activity in the AD, infraspinatus, and middle trapezius and decreased lower trapezius activity during the bench and wall slides. No age-related changes were noted for the AD exercises. CONCLUSION: These findings may assist the clinician in prescribing appropriate progressive exercise programs for patients with symptomatic RC tears.

Analysis of Scapular Kinematics and Muscle Activity by Use of Fine-Wire Electrodes During Shoulder Exercises.

BACKGROUND: During nonoperative or postoperative rehabilitation after sports injuries, exercise selection is often based on minimal load on the injured/repaired glenohumeral structures, while optimally activating scapulothoracic muscles. Previous research explored scapular muscle activity during rehabilitation exercises using surface electromyography (EMG). However, limited information exists about the deeper lying muscle activity, measured with fine-wire electrodes, even more in combination with 3-dimensional scapular kinematics. PURPOSE: To report scapular kinematics synchronously with surface and fine-wire EMG during specific shoulder exercises for early rehabilitation. STUDY DESIGN: Descriptive laboratory study. METHODS: A total of 23 healthy male patients were recruited. Three-dimensional scapular kinematics were measured combined with EMG recording of 8 muscles during 4 commonly used shoulder exercises (inferior glide, low row, lawnmower, and robbery). Upper (UT), middle (MT), and lower (LT) trapezius and serratus anterior muscle activities were measured with bipolar surface electrodes. Intramuscular electrodes were placed in the levator scapulae (LS), rhomboid major (RM), pectoralis minor (Pm), and infraspinatus (IS) muscles. All data were normalized as a percentage of maximal voluntary isometric contraction (%MVIC). A linear mixed model with Bonferroni correction was applied for statistical analysis. RESULTS: Scapular kinematics revealed an anterior tilt position during the inferior glide, low row, and robbery (P < .05). An upward rotation position between 20° and 30° was reached in all exercises except low row. Inferior glide (31°) and low row (42°) represented a significantly increased internal rotation position compared with lawnmower and robbery. Lawnmower and robbery showed significantly (P < .05) more MT (lawnmower, 36% MVIC; robbery, 39% MVIC) and RM (lawnmower, 59% MVIC; robbery, 66% MVIC) activation compared with inferior glide and low row. Lawnmower and robbery showed significantly (P < .05) less Pm activation (9.5%-12% MVIC). LS was significantly more active during robbery (58% MVIC) compared with inferior glide and low row (27%-36% MVIC) (P < .05). IS showed moderate activity (24%-37% MVIC) for all exercises, except low row (13% MVIC). CONCLUSION/CLINICAL RELEVANCE: This study provides new insights about scapular positions and activation of the deeper layer muscles during 4 commonly used shoulder rehabilitation exercises. The lawnmower showed a favorable position of the scapula with less Pm activity in contrast to the low row. The inferior glide, lawnmower, and robbery should not be implemented in early phases of shoulder rehabilitation because of their moderate muscle activity.

Relative Scapular-Muscle Ratios During Maximal Isokinetic Shoulder-Girdle Strength Performance in Elite Field Hockey Players.

CONTEXT: The shoulder joint and girdle are highly loaded during field hockey play. To optimize performance and to better substantiate preventive programs, it is important to gain insight into shoulder-girdle muscle function and balance in this athlete population. OBJECTIVE: To evaluate relative scapular muscle-activity ratios through surface electromyography during maximal isokinetic strength testing in elite male field hockey players compared with nonathletes. DESIGN: Cross-sectional study. SETTING: Institutional laboratory. PATIENTS OR OTHER PARTICIPANTS: Twenty-five elite field hockey players from the Belgian National Team and 25 age- and sex-matched nonathletes. INTERVENTION(S): We measured bilateral activity in 4 scapular muscles (upper trapezius [UT], middle trapezius [MT], lower trapezius [LT], and serratus anterior [SA]) during an external-internal rotation and protraction-retraction isokinetic shoulder protocol. MAIN OUTCOME MEASURE(S): Relative scapular muscle-activity ratios, or balance ratios, of the UT : MT, UT : LT, UT : SA, SA : MT, and SA : LT. RESULTS: We noted lower ratios bilaterally in the athlete group compared with the control group for the UT : MT, UT : LT, and SA : MT ratios during protraction, retraction, and external rotation, respectively, and unilaterally (dominant side only) for the UT : LT ratio during protraction. No consistent trend was present for established side differences in the studied balance ratios. CONCLUSIONS: Compared with nonathletes, elite field hockey players had altered intramuscular (within the trapezius) and intermuscular (between the trapezius and SA) balance ratios during maximal shoulder-girdle contractions, with relatively more MT and LT activity. This may reflect a sport-specific adaptation to optimize coordinated activity of the scapulothoracic muscles, meeting the specific demands of field hockey movements and simultaneously better protecting the shoulder against injury. Our results can assist in optimizing high-performance training and in supporting injury-prevention programs, which are key to both successful and long-lasting athletic careers.

The isokinetic rotator cuff strength ratios in overhead athletes: Assessment and exercise effect.

OBJECTIVE: Muscle strength imbalance in the shoulder region can be considered as a predisposing factor in the development of movement dysfunctions, possibly leading to overuse injuries. Repetitive overhead throwing, performed in sports, may result in muscle imbalance between the external (ER) and internal (IR) rotators. Muscle strength measured with an isokinetic device, is reported as a concentric (CON) or eccentric (ECC) force. The balance between an agonist and an antagonist is mentioned as a ratio (CON/CON or ECC/CON). The aim of this systematic literature review is to provide an overview of the existing evidence considering the isokinetic muscle strength ratios of ER and IR of the shoulder in healthy overhead athletes. In addition, the effect of exercise programs on these ratios was investigated. METHODS: Two online databases (Web of Science and PubMed) were consulted using different search strategies. Articles were selected based on inclusion and exclusion criteria. All included articles were assessed on their methodological quality. RESULTS AND CONCLUSIONS: There is moderate evidence for a lower functional deceleration ratio (ECC ER/CON IR) at the dominant side. This lower ratio is due to a large overweight of CON IR strength on that side. There is no consensus about which exercise program is the most effective in altering the shoulder isokinetic strength ratios.