Infraspinatus Muscle Activity Research Articles

A study of effective exercise methods and resistance intensity for selective strengthening of the infraspinatus muscle

Background To selectively strengthen target muscles, resistance intensity as well as limb position should be considered. Objective This study aimed to identify the most effective exercise positions and the optimal resistance intensity to selectively strengthen the infraspinatus muscle. Methods This study included 18 healthy men who underwent four different external rotation (ER) exercises in prone external rotation (PER), side-lying wiper, sitting external rotation, and standing external rotation (STER) exercise by varying the shoulder positions under low, medium, and high resistance intensity conditions randomly. Infraspinatus and posterior deltoid muscle activities and the infraspinatus to posterior deltoid activity ratio were measured based on ER exercise positions and resistance intensities. Results This study revealed a significant interaction and main effects of exercise position and resistance intensity on muscle activity and muscle activity ratio. Both muscle activities were increased as the resistance intensity increased, but the muscle activity ratio was decreased. Infraspinatus muscle activity and muscle activity ratio were higher in the PER and STER exercises than in other exercises. Conclusion We indicate that PER and STER are effective exercises to selectively strengthen the infraspinatus muscle. Additionally, performing the exercise at low or medium resistance intensity rather than high resistance intensity is recommended to activate the infraspinatus selectively while minimizing the involvement of the posterior deltoid.

Effects of isolated shoulder versus core-shoulder chain exercises on motor control and isokinetic torque in baseball pitchers with shoulder impingement syndrome: A single-blinded randomized controlled trial

ABSTRACT Recent biomechanical evidence suggests that shoulder impingement syndrome (SIS) is closely linked with altered core-shoulder kinetic chain, resulting pain, altered external shoulder muscle activation, and external muscle weakness. We aimed to compare the effects of conventional isolated shoulder exercise (ISE) and core-shoulder chain exercises (CCE) during isokinetic shoulder rotation in baseball pitchers with SIS. Forty male college baseball pitchers with SIS were randomly allocated to ISE and CCE groups and they performed the exercises 3 times a week for 6 weeks. The standardised numerical pain rating scale (NPRS), shoulder pain and disability index (SPADI), electromyography (EMG) amplitude, and concentric (CON) and eccentric (ECC) torques were measured. Substantial improvements in NPRS and SPADI scores were observed after CCE compared to ISE (p ≤ 0.046). Internal oblique/transversus abdominis, rectus abdominis, external oblique, serratus anterior, and infraspinatus muscle activation were significantly higher after CCE than ISE (p ≤ 0.033). CON and ECC torques were higher after CCE than ISE (p ≤ 0.002). The present findings demonstrated superior therapeutic effects of CCE in improving pain, disability level, shoulder muscle activation, and torque (muscle strength) in baseball pitchers with SIS compared to the conventional ISE, highlighting the importance of the chain exercise concept.

Comparison of the Effects of Isometric Horizontal Abduction on Shoulder Muscle Activity During Wall Push-Up Plus and Wall Slide in Individuals With Scapular Winging.

Wall push-up plus (WPP) and wall slide (WS) are commonly prescribed in early rehabilitation to increase serratus anterior (SA) muscle activity. For individuals with scapular winging (SW), synergistic muscles such as upper trapezius (UT) and pectoralis major (PM) may compensate for weak SA during scapular movement. However, no studies have applied isometric horizontal abduction (IHA) during WS in individuals with SW nor have compared it with WPP with IHA. This study compared the effects of IHA on shoulder muscle activity during WPP and WS exercises in individuals with SW. Cross-sectional study; 2-way repeated-measures analysis of variance was used to assess the statistical significance of observed differences in SA, UT, PM, lower trapezius (LT), and infraspinatus (IS) muscle activities. Research laboratory. We recruited 30 individuals with SW comprising 20 men and 10 women. The individuals performed WPP and WS exercises with and without IHA using Thera-Band. Surface electromyography was used to measure muscle activity of the SA, UT, PM, LT, and IS during the isometric phase of WPP and WS. Maximal voluntary isometric contractions were recorded to normalize electromyographic data. There was no significant interaction between IHA application and exercise type for any of the shoulder muscles. IHA application increased SA (P = .008), UT (P = .001), LT (P = .009), and IS (P = .000) activities and decreased PM (P = .001) activity compared with those without IHA. WS exercises elicited higher PM (P = .017) and LT (P = .011) activities than WPP. WPP and WS with IHA may be effective in increasing the muscle activities of shoulder stabilizers and preventing overactivation of PM activity. WPP may be recommended for individuals with overactivated PM, whereas WS may be used to increase LT activity.

Validation of the Measuring Protocol for the Infraspinatus Muscle with M-Mode Ultrasound in Asymptomatic Subjects. Intra- and Inter-examiner Reliability Study

M-mode ultrasound is a reliable and valid instrument for assessing muscle activity. However, it has not been studied in any of the muscles belonging to the shoulder joint complex, particularly in the infraspinatus muscle. The aim of this study is the validation of the infraspinatus muscle activity measurement protocol with the M-mode ultrasound in asymptomatic subjects. Sixty asymptomatic volunteers were evaluated by two physiotherapists who were blinded; each of them carried out three measurements with the M-mode ultrasound in infraspinatus muscle and analysed the muscle thickness at rest and contraction, velocity of muscle activation and relaxation and Maximum Voluntary Isometric Contraction (MVIC). Intra-observer reliability was significant in both observers, showing good thickness at rest (ICC = 0.833-0.889), thickness in contraction (ICC = 0.861-0.933) and MVIC (ICC = 0.875-0.813); moderate in the activation velocity (ICC = 0.499-0.547) and relaxation velocity (ICC = 0.457-0.606). The inter-observer reliability also had good thickness at rest (ICC = 0.797), thickness in contraction (ICC = 0.89) and MVIC (ICC = 0.84); poor in relaxation time variable (ICC = 0.474) and not significant at the activation velocity (ICC = 0). The muscle activity measurement protocol of the infraspinatus muscle measured with M-mode ultrasound has been found to be reliable in asymptomatic subjects, for both the intra-examiner and inter-examiner.

Comparison of Infraspinatus and Posterior Deltoid Muscle Activities According to Exercise Methods and Forearm Positions During Shoulder External Rotation Exercises

Comparison of Infraspinatus and Posterior Deltoid Muscle Activities According to Exercise Methods and Forearm Positions During Shoulder External Rotation Exercises

Chronic Adaptations of Shoulder Muscle Synergies in Healthy Baseball Players.

Previous research has demonstrated that muscle synergy structure can adapt owing to training and injury; however, muscle synergies have not been evaluated in baseball players. The throwing arm would have a similar muscle synergy structure but different levels of individual muscle activity within each synergy, relative to the nonthrowing arm. Cross-sectional study in a controlled laboratory setting. Fourteen healthy competitive baseball players were included. Participants were tested bilaterally during a center-out planar reaching task using the KINARM robot, where kinematic data and surface electromyography data from 14 glenohumeral and scapular muscles were synchronized. Principal component analysis was used to extract muscle synergies, the variance accounted for (VAF) of each synergy, and individual muscle coefficients. The dominant (DOM) arm was compared with the nondominant (NDOM) arm using paired t tests for all dependent variables. The same number of muscle synergies were extracted on the DOM and NDOM arms, along with no differences in VAF. In the first synergy, the infraspinatus (DOM 0.798 vs NDOM 0.587, P = 0.038) and lower trapezius (DOM 0.872 vs NDOM 0.480, P = 0.005) muscle coefficients significantly increased on the DOM arm. The second synergy had a significantly increased anterior deltoid (DOM 0.764 vs NDOM 0.374, P = 0.003) and a significantly decreased posterior deltoid (DOM -0.069 vs NDOM 0.197, P = 0.041) muscle coefficient on the DOM arm. The DOM shoulder exhibits a higher proportion of infraspinatus and lower trapezius muscle activation during the external rotation and abduction synergy. Also, the DOM shoulder has increased muscle activation of the teres major and latissimus dorsi during the internal rotation synergy, and increased muscle activation of the pectoralis major during the cross-body adduction synergy, compared with the NDOM shoulder. By exploring these neuromuscular adaptations, the improved understanding of muscle synergy adaptations in baseball players will help optimize injury prevention and rehabilitation techniques.

Supine scapular punch: An exercise for early phases of shoulder rehabilitation?

BackgroundSerratus anterior strengthening generally appears in shoulder rehabilitation protocols. This study's aim was to measure electromyographic activity of the serratus anterior, upper trapezius, and infraspinatus muscles during the Supine Scapular Punch exercise in healthy volunteers and those with unilateral shoulder pain. MethodsFifty-four participants were included and grouped as without (n = 34, age = 25.8 years) or with unilateral shoulder pain (n = 20, age = 26.3 years, visual analogue scale = 4.15 cm). Electromyographic activity of the serratus anterior, upper trapezius, and infraspinatus muscles was assessed during Supine Scapular Punch (four phases: P1 = press up concentric, P2 = Supine Scapular Punch concentric, P3 = Supine Scapular Punch eccentric, P4 = press up eccentric) performed under two conditions, with and without additional load. FindingsOverall muscle activity during P1 and P4 was negligible (< 10% maximal voluntary isometric contractions). During P2 and P3, no statistically significant differences in serratus anterior and upper trapezius muscle activity were found between groups, with moderate to high serratus anterior activity (28.94% to 44.3%) and very low upper trapezius activity (< 6%). Upper trapezius/serratus anterior activity ratios ranged from 0.09 to 0.18. Overall infraspinatus muscle activity was always very low (< 10%). InterpretationThe Supine Scapular Punch induces moderate to high serratus anterior muscle activity with very low upper trapezius and infraspinatus activation. Based on these results, the Supine Scapular Punch is a safe exercise that can be used in the early phases of shoulder rehabilitation.

A comparison of teres minor and infraspinatus muscle activation in the prone position.

BackgroundThe electromyography (EMG) activity of the teres minor (TMi) and infraspinatus (IS) muscle has been demonstrated to vary depending on the arm position, such as in the coronal or scapular position, during intervention exercises. This may be reflected by different EMG activities demonstrated between the TMi and IS muscle during the acceleration and deceleration phases of the pitching motion. Tenderness in the scapular attachment site of the TMi muscle is often seen in baseball pitchers after pitching but not the attachment site of the IS muscle. However, few studies have investigated an interaction between TMi and IS muscle activity across different resistance exercises with different arm positions. The purpose of this study was to identify the feature of TMi and IS muscle activity in the presence of manual resistance applied in the prone position.MethodsEighteen collegiate baseball players volunteered their participation. Raw EMG amplitudes of the TMi, IS, posterior deltoid, middle deltoid, and upper trapezius muscles on the dominant shoulder were measured during intervention exercises. All subjects performed manual isometric resistance exercises: horizontal abduction (HABD) and external rotation (ER) of the glenohumeral joint with 40% of the manual maximum strength test in prone. The subjects also performed each of the HABD and ER resistance exercises with the arm actively positioned at 0° and 45° of ER of the glenohumeral joint in the coronal and scapular planes.ResultsBoth TMi and IS muscle activities significantly increased with the arm positioned at 45° of ER compared with 0° of ER regardless of the exercise (P < .05). TMi activity was significantly greater with HABD resistance than IS muscle activity regardless of the arm positions, whereas it was significantly less with ER resistance than IS muscle activity.ConclusionThe findings of this study indicated that the TMi and IS muscles were most highly activated during the HABD resistance with the arm actively positioned at 45° of ER in the coronal plane. The results of this study have clinical implications regarding the careful selection of arm position in both exercise and clinical examination for the TMi and IS muscles.

Regional Electromyography of the Infraspinatus and Supraspinatus Muscles During Standing Isometric External Rotation Exercises.

Background:Whole-muscle electromyography (EMG) data of the rotator cuff support external rotation (ER) strengthening exercises during shoulder rehabilitation. However, distinct neuroanatomic regions in the supraspinatus and infraspinatus exist. Differences in regional muscle activity occur during rehabilitation exercises, but little information is available for ER exertions.Hypothesis:Regional infraspinatus and supraspinatus muscle activity during standing ER exertions will differ with posture and intensity.Study Design:Descriptive laboratory study.Level of Evidence:Level 5.Methods:Twenty healthy individuals (12 men, 8 women) participated. Fine wire electrodes were inserted into 2 supraspinatus and 3 infraspinatus muscle regions. EMG data were recorded during standing isometric ER exertions at 2 intensities (maximal, submaximal) and in 7 postures defined by the angle (0°, 30°, 90°) and plane (abduction, scaption, flexion) of arm elevation. EMG data were normalized to maximum voluntary isometric contraction (% MVIC) to examine the influences of posture, intensity and their interaction on muscle activity.Results:Superior infraspinatus activity was higher in 0° of elevation (50.9% ± 5.7% MVIC) versus 30° of flexion (37.4% ± 3.9% MVIC) at maximal intensity. Inferior infraspinatus activity was higher in 90° of scaption (max = 59.8% ± 2.8% MVIC, submax = 29.4% ± 1.9% MVIC) versus 0° of elevation (max = 42.3% ± 4.5% MVIC, submax = 22.4% ± 2.8% MVIC) (P = 0.02, P = 0.05, respectively). Anterior supraspinatus activity was highest in 90° of adbuction (max = 61.6% ± 3.1% MVIC; submax = 39.1% ± 3.8% MVIC) and lowest in 30° of flexion (max = 29.0% ± 3.4% MVIC, submax = 15.6% ± 1.7% MVIC) and 90° of flexion (max = 34.6% ± 2.4% MVIC, submax = 14.8% ± 1.9% MVIC). Posterior suprasptinatus activity was lowest in 0° of elevation (34.2% ± 3.0% MVIC), 30° of flexion (33.0% ± 3.6% MVIC) and highest in 90° of abduction (56.2% ± 4.1% MVIC) and 90° of scaption (46.7% ± 2.8% MVIC) (all Ps < 0.04).Conclusion:Regional infraspinatus and supraspinatus muscle activity differed with posture and intensity. Superior and middle infraspinatus muscle activities were similar across postures, but inferior infraspinatus activity was highest in 90° of arm elevation. Anterior and posterior supraspinatus activities were higher in the abduction and scaption planes, especially at 90° of elevation, as compared with the flexion plane.Clinical Relevance:In shoulder rehabilitation of supraspinatus tendon injuries, ER exercises in the flexion plane challenge the whole infraspinatus muscle and require lower supraspinatus muscle activity.

The infraspinatus muscle activity during pitching motion in baseball players with shoulder instability.

BackgroundShoulder microinstability is often overlooked, which can be problematic, especially in overhead athletes. The slipping phenomenon is defined as posterior or lateral sliding of the humeral head in an elevated arm. When the shoulder is close to the end range of stability, the infraspinatus is highly activated and keeps the shoulder in the glenoid cavity. This study aimed to examine the characteristic physical function and infraspinatus activity during the pitching motion in baseball pitchers with shoulder instability.MethodsTwenty-one male baseball pitchers participated and were divided into 2 groups based on radiograph findings at zero position: slipped (group S) and nonslipped (group N) groups. Physical function using Hara test and infraspinatus muscle activity during pitching were evaluated.ResultsThe infraspinatus muscle activity during the acceleration phase was significantly greater in group S (59.5 ± 33.0%MVC) than in group N (33.0 ± 16.9%MVC) (P < .05). Positive rate of the Hara test in group S was significantly high in the loose test and elbow push test.ConclusionsThis study shows that baseball pitchers with slipping phenomenon have capsular laxity and scapular instability that indicate high infraspinatus muscle activity during the acceleration phase. Therefore, repetitive pitching with hyperactivity of the infraspinatus on the slipping shoulder may cause fatigue and dysfunction.

Strategies for controlling axial shoulder rotation change shoulder muscle activity during external rotation exercises

The infraspinatus muscle has a crucial role in shoulder stability. Although axial shoulder rotation is useful for selective activation of the infraspinatus, no study has examined the influence of exercise position on axial shoulder rotation during shoulder external rotation (ER) exercises. Thus, this study investigated the muscle activity in the infraspinatus, posterior deltoid, and middle trapezius during shoulder ER exercises performed with and without controlled axial shoulder rotation in 2 different positions. Twenty healthy subjects performed prone external rotation (PER) exercises with and without pressure biofeedback and seated external rotation (SITER) exercises with and without posterior humeral head gliding. Muscle activity during each ER exercise was measured using surface electromyography. Exercise strategy (P < .001) and position (P < .001) had a significant main effect on muscle activity in the infraspinatus and posterior deltoid. However, no significant interaction between strategy and position was observed. For muscle activity in the middle trapezius, strategy and position had a significant interaction effect (P = .014). Muscle activity in the infraspinatus increased significantly with the use of strategies to control axial shoulder rotation, whereas muscle activity in the posterior deltoid and middle trapezius decreased significantly. For all 3 muscles, greater activity was observed in the prone position than the seated position. We suggest that PER with pressure biofeedback can be useful to improve selective activation of the infraspinatus muscle while further eliciting infraspinatus muscle activity.

Evaluation of the Electromyographic Amplitude-to-Work Ratio in the Infraspinatus Muscle During External Shoulder Rotation Exercises: A Comparison of Concentric Isotonic and Isokinetic Exercises

Background:Isotonic exercise is commonly adopted for shoulder rehabilitation, but the efficacy of isokinetic exercise for rehabilitation has not been evaluated.Purpose:To evaluate the efficacy of isotonic and isokinetic external shoulder rotation exercises.Study Design:Controlled laboratory study.Methods:Using surface electromyography (EMG) and the Biodex system, we investigated the EMG amplitude of the infraspinatus (IS), total work (tWK), and EMG(IS)/tWK ratio and examined the relative IS and posterior deltoid (PD) contributions to all exercises. A total of 24 healthy participants without musculoskeletal injuries were included. Participants performed isotonic external shoulder rotation at 10%, 20%, 30%, 40%, and 50% of the maximum voluntary isometric contraction (MVIC) as well as isokinetic external shoulder rotation at angular velocities of 60, 120, 180, 240, and 300 deg/s. Levels of intensity were classified from 1 to 5: level 1 corresponded to 10% of the MVIC and a 300-deg/s angular velocity; level 2 corresponded to 20% MVIC and 240 deg/s; level 3 corresponded to 30% MVIC and 180 deg/s; level 4 corresponded to 40% MVIC and 120 deg/s; and level 5 corresponded to 50% MVIC and 60 deg/s. Normalized IS and tWK amplitudes were calculated for each exercise.Results:During isotonic exercise, the EMG(IS)/tWK ratio significantly decreased from level 5 to 3, 2, and 1; from level 4 to 2 and 1; and from level 3 to 1. During isokinetic exercise, the EMG(IS)/tWK ratio at level 3 was greater than that at all other levels except level 1. Statistical differences were found between isotonic and isokinetic modes at levels 1, 2, and 3. The IS/PD activation ratios were not significantly different between exercise modes at any level.Conclusion:Isokinetic resistance may provide more effective stimulation of the IS muscle compared with isotonic resistance.Clinical Relevance:Isokinetic exercise needs to be considered as a method of rehabilitation that effectively increases infraspinatus muscle activity.

Comparative Study of Infraspinatus and Posterior Deltoid Muscle Activation According to Angle of External Rotation of Glenohumeral Joint

Background: Based on the understanding of the muscle activation relationship between the infraspinatus and posterior deltoid muscles to according to the angle of motion during external rotation on glenohumeral joint, effective shoulder joint strengthening exercise for the prevention and rehabilitation of shoulder injury due to muscle strength imbalance can be performed by achieving the ideal muscle activity ratio during exercise. Objectives: To compare and analyze the muscle activation changes and activity ratio of the infraspinatus and posterior deltoid muscles according to the glenohumeral external rotation angle. Design: Quasi-randomized trial. Methods: The study included 48 healthy male and female adults who provided informed consent for participation in the study. All the subjects performed isometric glenohumeral external rotation by setting the angle of motion to 30°, 45°, and 60° using a 5 kg resistance weight pulley. On surface electromyography, the differences in muscle activation and activity ratio between the infraspinatus and posterior deltoid muscles were investigated. Results: A significant difference in muscle activation was found in the comparison between the infraspinatus and posterior deltoid muscles according to the glenohumeral external rotation angle (P<.05). The muscle activation levels of the infraspinatus and posterior deltoid muscles were highest at the external rotation angles of 30° and 60°, respectively. The muscle activity ratio between the infraspinatus and posterior deltoid muscles also showed a significant difference (P<.05) and was highest at the shoulder external rotation angle of 30°. Conclusion: The findings of this study suggest that muscle activity is the highest at the shoulder external rotation angle of 30° in healthy individuals.

Analysis of Scapular Muscle EMG Activity During Elastic Resistance Oscillation Exercises From the Perspective of Different Arm Positions.

Little is known about the optimal exercise intensity and the effects of arm position on elastic resistance exercise. The purpose of this study was to investigate scapular muscle activity in different arm positions utilized during standing elastic resistance exercise. Lower trapezius (LT), serratus anterior (SA), and infraspinatus (IS) muscle activity will vary across arm positions above shoulder level. Also, oscillation resistance exercise will result in increased muscle activity compared with isometric contraction. Controlled laboratory study. Level 4. A total of 19 uninjured male collegiate baseball players volunteered to participate in this study. The electromyography (EMG) activity of the LT, upper trapezius (UT), middle deltoid (MD), SA, and IS muscles was determined using surface EMG in 3 arm positions: diagonal pattern 1 (D1), 120° of shoulder abduction (120), and 90° shoulder abduction with external rotation and elbow flexion (90/90) during both isometric contraction and oscillation resistance exercise. No difference in EMG activity of the LT muscle was found between the 120 and 90/90 position. However, the 120 position increased UT and MD muscle activity significantly more than those of the 90/90 position. The D1 arm position significantly increased SA muscle activity more than the 120 and 90/90 positions while the LT muscle activity was nearly silent. The standing 90/90 position effectively generated both LT and IS muscle EMG activity while minimizing both UT and MD muscle activity. The use of oscillation movements under elastic loading can create high muscle activation in the LT muscle without an adverse effect of the humeral head position and scapular rotation.

Effect of short-term intervention on infraspinatus muscle activity during throwing motion and physical examination in baseball players with throwing disorder

Effect of short-term intervention on infraspinatus muscle activity during throwing motion and physical examination in baseball players with throwing disorder

The Effect of 8 Weeks of Rotator Cuff Muscle Specific Exercises on the Range of Motion, Strength, and Electrical Activity of Selected Shoulder Muscles in Man Volleyball Players with Glenohumeral Internal Rotation Deficit

Introduction: Disorder and injury in the shoulder joint have a high prevalence in overhead throwing athletes such as volleyball players. The glenohumeral internal rotation deficit is directly related to shoulder injuries. Therefore, the purpose of this study was to assess the effect of 8 weeks of rotator cuff muscle specific exercises on the range of motion, strength, and electrical activity of selected shoulder muscles in man volleyball players with shoulder internal rotation deficit. Materials and Methods: Thirty man athletes with glenohumeral internal rotation deficit participated in this study. After initial screening and identifying qualified athletes, the subjects were divided into equal groups of experimental and control. Specific rotator cuff exercises included stretching, strength, neuromuscular, and performance exercises. The range of motion was measured with goniometer, strength with isokinetic device, and electrical activity of the muscles with electromyographic device. Results: Specific exercises of rotator cuff muscles improved muscle strength in concentric and eccentric contractions (P < 0.001), decreased supraspinatus (P = 0.001), infraspinatus (P = 0.001), anterior deltoid (P = 0.005), and posterior deltoid (P = 0.004) muscle activity, and increased internal rotaion range of motion of shoulder joint (P < 0.001). Conclusion: According to positive influence of specific rotator cuff exercises on the range of motion, strength, and electrical activity of selected shoulder muscles, adding these programs to the volleyball rehabilitation therapy programs of athletes with an glenohumeral internal rotation deficit is recommended to improve the limitations of injury.

Relationship Between Middle Trapezius Muscle Activation and Acromiohumeral Distance Change During Shoulder Elevation With Scapular Retraction.

The scapular retraction exercises are widely used among clinicians to balance the activity of the scapular muscles as well as the rotator cuff muscles in different shoulder abduction positions. The aim of this study was to investigate the relationship between scapular (middle and upper trapezius) and shoulder muscles (middle deltoid and infraspinatus) activation level differences and acromiohumeral distance changes during shoulder abduction with scapular retraction. Cross-sectional study. University research laboratory. Nineteen asymptomatic individuals were included (mean [SD]: age = 22.4 [1.8]y). The acromiohumeral distance was measured at 0° and 90° shoulder abduction when the scapula was in nonretracted and retracted position with ultrasound imaging. The relationship between muscle activation level changes and acromiohumeral distance difference was analyzed with the Pearson correlation test. Middle trapezius muscle activity change correlated with acromiohumeral distance difference (r = .55, P = .02) from 0° to 90° shoulder abduction when scapula was retracted. For both nonretracted and retracted scapular positions, no correlations were found between middle deltoid, infraspinatus, and upper trapezius muscle activity changes with acromiohumeral distance differences during shoulder abduction (P > .05). Active scapular retraction exercise, especially focusing on the middle trapezius muscle activation, seems to be an effective treatment option to optimize the acromiohumeral distance during shoulder abduction.

P 177 – The infraspinatus muscle activity during throwing motion in baseball player with throwing injury

P 177 – The infraspinatus muscle activity during throwing motion in baseball player with throwing injury

The effects of pressure biofeedback training on infraspinatus muscle activity and muscle thickness

The aim of this study was to investigate muscle activity in the infraspinatus and posterior deltoid and infraspinatus muscle thickness during a prone external rotation (PER) exercise using pressure biofeedback. Fifteen healthy men participated in this study, performing PER exercise with pressure biofeedback under four conditions (comfortable, 2 mm Hg, 4 mm Hg, and 8 mm Hg). Surface electromyography (EMG) was used to monitor infraspinatus and posterior deltoid muscle activity, and ultrasonography was used to collect infraspinatus muscle thickness data. Infraspinatus activity and muscle thickness were greatest at 2 mm Hg pressure feedback, and both measures were significantly different from those under other pressure feedback conditions (p < 0.05). In contrast, posterior deltoid activity was lower at 2 mm Hg. However, there was no significant difference between any of the four pressure feedback conditions. These findings suggest that PER exercise with pressure biofeedback, particularly at 2 mm Hg, is effective in selectively activating the infraspinatus muscle.

The immediate effect of muscle release intervention on muscle activity and shoulder kinematics in patients with frozen shoulder: a cross-sectional, exploratory study

BackgroundContractile tissue plays an important role in mobility deficits in frozen shoulder (FS). However, no study has assessed the effect of the muscle release technique on the muscle activation and kinematics in individuals with FS. The purposes of this study were to assess the differences in shoulder muscle activity and kinematics between the FS and asymptomatic groups; and to determine the immediate effects of muscle release intervention in the FS group.MethodsTwenty patients with FS and 20 asymptomatic controls were recruited. The outcome measures included muscle activity of the upper and lower trapezius (UT and LT), infraspinatus (ISp), pectoralis major (PM), and teres major (TM), shoulder kinematics (humeral elevation, scapular posterior tilt (PT) and upward rotation (UR), shoulder mobility, and pain. Participants in the FS group received one-session of heat and manual muscle release. Measurements were obtained at baseline, and immediately after intervention. Multivariate analysis of variance was used for data analysis. The level of significance was set at α=0.05.ResultsCompared to the controls, the FS group revealed significantly decreased LT (difference =55.89%, P=0.001) and ISp muscle activity (difference =26.32%, P =0.043) during the scaption task, and increased PM activity (difference =6.31%, P =0.014) during the thumb to waist task. The FS group showed decreased humeral elevation, scapular PT, and UR (difference = 35.36°, 10.18°, 6.73° respectively, P <0.05). Muscle release intervention immediately decreased pain (VAS drop 1.7, P <0.001); improved muscle activity during scaption (UT: 12.68% increase, LT: 35.46% increase, P <0.05) and hand to neck (UT: 12.14% increase, LT: 34.04% increase, P <0.05) task; and increased peak humeral elevation and scapular PT during scaption (95.18°±15.83° to 98.24°±15.57°, P=0.034; 11.06°±3.94° to 14.36°±4.65°, P=0.002), and increased scapular PT during the hand to neck (9.47°±3.86° to 12.80°±8.33°, P=0.025) task. No statistical significance was found for other group comparisons or intervention effect.ConclusionPatients with FS presented with altered shoulder muscle activity and kinematics, and one-session of heat and manual muscle release showed beneficial effects on shoulder muscle performance, kinematics, mobility, and pain.Trial registrationRetrospectively registered on Jan 18, 2016 (ACTRN 12616000031460).