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Existing kinematic studies of the shoulder girdle focus on humerothoracic movements. Isolated scapulothoracic movements are also performed during daily activities and rehabilitation but kinematic values are lacking.

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). 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. 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. 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.

Context: Shoulder strength assessment plays an important role in the clinical examination of the shoulder region. Eccentric strength measurements are of special importance in guiding the clinician in injury prevention or return-to-play decisions after injury.Objective: To examine the absolute and relative reliability and validity of a standardized eccentric strength-measurement protocol for the glenohumeral external rotators.Design: Descriptive laboratory study.Setting: Testing environment at the Department of Rehabilitation Sciences and Physiotherapy of Ghent University, Belgium.Patients or Other Participants: Twenty-five healthy participants (9 men and 16 women) without any history of shoulder pain were tested by 2 independent assessors using a handheld dynamometer (HHD) and underwent an isokinetic testing procedure.Intervention(s): The clinical protocol used an HHD, a DynaPort accelerometer to measure acceleration and angular velocity of testing 30°/s over 90° of range of motion, and a Biodex dynamometer to measure isokinetic activity.Main Outcome Measure(s): Three eccentric strength measurements: (1) tester 1 with the HHD, (2) tester 2 with the HHD, and (3) Biodex isokinetic strength measurement.Results: The intratester reliability was excellent (0.879 and 0.858), whereas the intertester reliability was good, with an intraclass correlation coefficient between testers of 0.714. Pearson product moment correlation coefficients of 0.78 and 0.70 were noted between the HHD and the isokinetic data, showing good validity of this new procedure.Conclusions: Standardized eccentric rotator cuff strength can be tested and measured in the clinical setting with good-to-excellent reliability and validity using an HHD.

Context:Muscle fatigue due to repetitive and prolonged overhead sports activity is considered an important factor contributing to impingement-related rotator cuff pathologic conditions in overhead athletes. The evidence on scapular and glenohumeral kinematic changes after fatigue is contradicting and prohibits conclusions about how shoulder muscle fatigue affects acromiohumeral distance.Objective:To investigate the effect of a fatigue protocol resembling overhead sports activity on acromiohumeral distance and 3-dimensional scapular position in overhead athletes.Design:Cross-sectional study.Setting:Institutional laboratory.Patients or Other Participants:A total of 29 healthy recreational overhead athletes (14 men, 15 women; age 22.23 ± 2.82 years, height 178.3 ± 7.8 cm, mass 71.6 ± 9.5 kg).Intervention(s): The athletes were tested before and after a shoulder muscle-fatiguing protocol.Main Outcome Measure(s):  Acromiohumeral distance was measured using ultrasound, and scapular position was determined with an electromagnetic motion-tracking system. Both measurements were performed at 3 elevation positions (0°, 45°, and 60° of abduction). We used a 3-factor mixed model for data analysis.Results:After fatigue, the acromiohumeral distance increased when the upper extremity was actively positioned at 45° (Δ 0.78 ± 0.24 mm, P .002) or 60° (Δ 0.58 ± 0.23 mm, P .02) of abduction. Scapular position changed after fatigue to a more externally rotated position at 45° (Δ 4.97° ± 1.13°, P< .001) and 60° (Δ 4.61° ± 1.90°, P .001) of abduction, a more upwardly rotated position at 45° (Δ 6.10° ± 1.30°, P< .001) and 60° (Δ 7.20° ± 1.65°, P< .001) of abduction, and a more posteriorly tilted position at 0°, 45°, and 60° of abduction (Δ 1.98° ± 0.41°, P< .001).Conclusions:After a fatiguing protocol, we found changes in acromiohumeral distance and scapular position that corresponded with an impingement-sparing situation.

Context: Tennis requires repetitive overhead movements that can lead to upper extremity injury. The scapula and the shoulder play a vital role in injury-free playing. Scapular dysfunction and glenohumeral changes in strength and range of motion (ROM) have been associated with shoulder injury in the overhead athlete.Objective: To compare scapular position and strength and shoulder ROM and strength between Swedish elite tennis players of 3 age categories (<14, 14–16, and >16 years).Design: Cross-sectional study.Setting: Tennis training sports facilities.Patients or Other Participants: Fifty-nine adolescent Swedish elite tennis players (ages 10–20 years) selected based on their national ranking.Main Outcome Measure(s): We used a clinical screening protocol with a digital inclinometer and a handheld dynamometer to measure scapular upward rotation at several angles of arm elevation, isometric scapular muscle strength, glenohumeral ROM, and isometric rotator cuff strength.Results: Players older than 16 years showed less scapular upward rotation on the dominant side at 90° and 180° (P< .05). Although all absolute scapular muscle strength values increased with age, there was no change in the body-weight–normalized strength of the middle (P .9) and lower (P .81) trapezius or serratus anterior (P .17). Glenohumeral internal-rotation ROM and total ROM tended to decrease, but this finding was not statistically significant (P .052 and P .06, respectively). Whereas normalized internal-rotator strength increased from 14 to 16 years to older than 16 years (P .009), normalized external-rotator and supraspinatus strength remained unchanged.Conclusions: Age-related changes in shoulder and scapular strength and ROM were apparent in elite adolescent tennis players. Future authors should examine the association of these adaptations with performance data and injury incidence.

BackgroundHamstring injuries remain a substantial problem in male football. Proximal neuromuscular control (‘core stability’) is considered to be of key importance in hamstring injury prevention, although scientific evidence regarding the exact nature of the core-hamstring association is non-existing at present.ObjectiveTo investigate whether core muscle activation patterns during sprinting are associated with hamstring injury risk.DesignCohort study.SettingAmateur football division.Participants60 male football players with no recent history of hamstring injury were recruited for the multi-muscle EMG time series analysis during sprint.AssessmentHamstring-, gluteal and trunk muscle activity time-series during the airborne- and stance phases of over-ground sprint acceleration were collected prior to follow up (1.5 seasons).Main Outcome MeasurementsEMG signals of the above-mentioned muscles were processed and explored in function of (1) the time within the running cycle and (2) injury occurrence during follow up.ResultsPlayers that remained injury free, presented significantly higher amounts of gluteal muscle activity during the front swing phase (p=0.018), and higher amounts of trunk muscle activity during the backswing phase of sprinting (p=0.0011). In particular, the risk of sustaining a hamstring injury during follow up lowered 87% and 46%, with each increment in normalized muscle activity of the Gluteus Maximus during front swing and the trunk muscles during backswing, respectively (p<0.02).ConclusionsMuscle activity of the proximal core unit during explosive running presented to be associated with hamstring injury occurrence. Higher amounts of gluteal – and trunk muscle activity during the airborne phases of sprinting were able to protect participants against injury during follow up. Hence, the present results provide a basis for improved, evidence based, rehabilitation and prevention, particularly focusing on increasing neuromuscular control of the gluts and trunk muscle during sport specific activities (eg. sprint drills, agility drills).