Motor control retraining exercises for shoulder impingement: effects on function, muscle activation, and biomechanics in young adults

Objective: Evidence for effective management of shoulder impingement is limited. The present study aimed to quantify the clinical, neurophysiological, and biomechanical effects of a scapular motor control retraining for young individuals with shoulder impingement signs.Method: Sixteen adults with shoulder impingement signs (mean age 22 ? 1.6 years) underwent the intervention and 16 healthy participants (24.8 ? 3.1years) provided reference data. Shoulder function and pain were assessed using the Shoulder Pain and Disability Index (SPADI) and other questionnaires. Electromyography (EMG) and 3 dimensional motion analysis was used to record muscle activation and kinematic data during arm elevation to 90? and lowering in 3 planes. Patients were assessed pre and post a 10-week motor control based intervention, utilizing scapular orientation retraining.Results: Pre-intervention, patients reported pain and reduced function compared to the healthy participants (SPADI in patients 20 ? 9.2; healthy 0 ? 0). Post intervention, the SPADI scores reduced significantly (P < .001) by a mean of 10 points (?4). EMG showed delayed onset and early termination of serratus anterior and lower trapezius muscle activity pre-intervention, which improved significantly post-intervention (P < .05). Pre intervention, patients exhibited on average 4.6-7.4? less posterior tilt, which was significantly lower in 2 arm elevation planes (P < .05) than healthy participants. Postintervention, upward rotation and posterior tilt increased significantly (P <.05) during 2 arm movements, approaching the healthy values.Conclusion: A 10-week motor control intervention for shoulder impingement increased function and reduced pain. Recovery mechanisms were indicated by changes in muscle recruitment andscapular kinematics. The efficacy of the intervention requires further examined in a randomizedcontrol trial

A comparison of isotonic and elastic resistance exercise on trapezius muscle balance in overhead athletes

The scaption exercise (elevation of the arm in the scapular plane) is often performed in shoulder rehabilitation and preventive exercise programs. Three studies were performed to better understand the activation characteristics of the upper trapezius (UT) and lower trapezius (LT) muscles during scaption. The purpose of these studies was to 1) quantify and compare trapezius muscle activation ratios and onset of activation in normal subjects, 2) compare the findings from normal subjects with overhead athletes, and 3) compare the activation ratios and onset of the trapezius with 2 modes of resistance (elastic and isotonic) in overhead athletes. Methods. Healthy college-aged subjects performed scaption to 90⁰ with (W) and without (UW) standardized resistance. The average activation of the UT and LT was determined with surface electromyography (EMG) over 30⁰ increments in concentric and eccentric directions. The UT:LT ratio was then determined for each interval and condition, as well as the average onset of activation. Statistical analysis using repeated measures and t-tests were used to determine significant differences. Results. The UT:LT ratios of both W and UW conditions demonstrated a u-shaped curve over 90⁰. The UW condition consistently demonstrated significantly higher UT:LT ratios ranging from 1.5 to 4.5, while the W ranged from 0.9 to 2.4. There was no significant difference in activation ratios between athletes and non-athletes, or between elastic and isotonic resistance. The UT demonstrated earlier activation than the LT in the UW condition. The LT reduced its latency with the addition of resistance, reversing the firing order in overhead athletes. Isotonic resistance provided slightly faster activation of the LT compared to elastic resistance. Conclusion. These 3 studies suggest that overhead athletes demonstrate the same UT:LT ratios as non-athletes over 90⁰ during scaption with and without resistance. Adding resistance to the scaption exercise significantly reduces the UT:LT ratio and reverses the firing order, activating the LT significantly earlier than the UT. Both elastic and isotonic resistances demonstrate similar activation ratios in overhead athletes, although isotonic resistance activates the LT faster than elastic resistance. Using these results, clinicians may improve their clinical decision-making in prescribing scaption exercises

Evaluation of control strategies for overhead work using electromyography of rotator cuff muscles

Work-related musculoskeletal disorders (MSDs) of shoulder have a significant impact on overall health and economics in the industrialized nations. Rotator cuff is the most frequently injured region in the shoulder complex. Overhead work is considered as one of the most predominant causes of rotator cuff injuries. The workers in construction, automotive, and aerospace industries are routinely exposed to overhead exertions. Elimination of overhead work is nearly impossible due to various task and technology constraints. Therefore, appropriate intervention strategies based on the engineering and administrative controls opt to be used to prevent the hazardous impact of overhead exertions. The objective of this study was to design administrative controls based on the principles of ergonomics and biomechanics and test their influence on the fatigue response of the rotator cuff muscles. As a first step towards developing such controls, a preliminary study was completed to understand baseline behavior of the rotator cuff muscles in terms of their strength, endurance, and fatigue response and subsequently two specific aims on control strategies were completed. The first specific aim evaluated the effect of four different task rotation sequences on the activation and fatigue response of rotator cuff muscles. In the sequences, three different exertions (Hard (H), Medium (M), and Low (L)) were performed in the following orders: increasing (LLMMHH), decreasing (HHMMLL), upward parabolic (HMLLMH), and downward parabolic (LMHHML). Trends in the median frequency of surface electromyography (EMG) data, maximum strength, and ratings of perceived exertion were used as the fatigue indicators. Despite the similar levels of muscle activation, the effect of task rotation sequence on muscle fatigue development was significant. The median frequency-based fatigue indicator reduced by 54% for supraspinatus, 53% for infraspinatus, and 39% for teres minor when high fatigue sequence (decreasing) was compared with low fatigue sequence (upward parabolic). In the second specific aim, a moderate gripping exertion was added to the task rotation sequences to evaluate the effectiveness of a refresher exertion on the active recovery and the fatigue response of the rotator cuff muscles. On average, presence of the griping task reduced the percent drop in the median frequency by 36% for supraspinatus, 56% for infraspinatus, and 58% for teres minor when compared with the task rotation without gripping exertions (aim 1 study). In conclusion, the results of this study indicate that performing tasks with a constant workload in different orders can alter rotator cuff muscles’ fatigue development. A shorter duty cycle for the intense tasks, warm up exertions prior to the intense tasks, and low intensity/refresher exertions between the work cycles seem to be the key factors in designing control strategies based on task rotations

Study protocol subacromial impingement syndrome: the identification of pathophysiologic mechanisms (SISTIM)

<p>Abstract</p> <p>Background</p> <p>The Subacromial Impingement Syndrome (SIS) is the most common diagnosed disorder of the shoulder in primary health care, but its aetiology is unclear. Conservative treatment regimes focus at reduction of subacromial inflammatory reactions or pathologic scapulohumeral motion patterns (<it>intrinsic </it>aetiology). Long-lasting symptoms are often treated with surgery, which is focused at enlarging the subacromial space by resection of the anterior part of the acromion (based on <it>extrinsic </it>aetiology). Despite that acromionplasty is in the top-10 of orthopaedic surgical procedures, there is no consensus on its indications and reported results are variable (successful in 48-90%). We hypothesize that the aetiology of SIS, i.e. an increase in subacromial pressure or decrease of subacromial space, is multi-factorial. SIS can be the consequence of pathologic scapulohumeral motion patterns leading to humerus cranialisation, anatomical variations of the scapula and the humerus (e.g. hooked acromion), a subacromial inflammatory reaction (e.g. due to overuse or micro-trauma), or adjoining pathology (e.g. osteoarthritis in the acromion-clavicular-joint with subacromial osteophytes).</p> <p>We believe patients should be treated according to their predominant etiological mechanism(s). Therefore, the objective of our study is to identify and discriminate etiological mechanisms occurring in SIS patients, in order to develop tailored diagnostic and therapeutic strategies.</p> <p>Methods</p> <p>In this cross-sectional descriptive study, applied clinical and experimental methods to identify intrinsic and extrinsic etiologic mechanisms comprise: MRI-arthrography (eligibility criteria, cuff status, 3D-segmented bony contours); 3D-motion tracking (scapulohumeral rhythm, arm range of motion, dynamic subacromial volume assessment by combining the 3D bony contours and 3D-kinematics); EMG (adductor co-activation) and dynamometry instrumented shoulder radiographs during arm tasks (force and muscle activation controlled acromiohumeral translation assessments); Clinical phenotyping (Constant Score, DASH, WORC, and SF-36 scores).</p> <p>Discussion</p> <p>By relating anatomic properties, kinematics and muscle dynamics to subacromial volume, we expect to identify one or more predominant pathophysiological mechanisms in every SIS patient. These differences in underlying mechanisms are a reflection of the variations in symptoms, clinical scores and outcomes reported in literature. More insight in these mechanisms is necessary in order to optimize future diagnostic and treatment strategies for patients with SIS symptoms.</p> <p>Trial registration</p> <p>Dutch Trial Registry (Nederlands Trial Register) <a href="http://www.trialregister.nl/trialreg/admin/rctview.asp?TC=2283">NTR2283</a>.</p

Effect of rotator cuff muscle fatigue on shoulder muscle activation and posture during driving

Rotator cuff (RC) muscle dysfunction impacts the ability to perform daily functional tasks, such as driving. It has been suggested that RC muscle fatigue can mimic rotator cuff tears (RCT) during sudden steering in terms of kinematics. It has also been found that two RC muscles (infraspinatus and supraspinatus) are highly active during driving. However, it is unknown whether fatigue of these muscles would change the kinematic strategy during driving. The aim of this research was to analyze changes in joint angle and electromyography (EMG) signals of the upper extremity in simulated driving to identify compensatory mechanism of rotator cuff muscles. Mean, maximum, standard deviation, and range of motion (ROM) of joint angles for four degrees of freedom (shoulder plane, shoulder elevation, shoulder rotation, and elbow flexion) were examined for four steering patterns (straight, left, right, and complex) and compared between before and after fatigue. Along with kinematic analyses, EMG signals of four muscles (deltoid, supraspinatus, infraspinatus, and biceps) were measured to analyze the relationship between kinematics and muscle usage before and after fatigue. In straight and left turns, usage of the right deltoid significantly increased (p≤0.05) in all three measurements (mean, standard deviation, and maximum) whereas in complex turn, the right bicep was used more (p≤0.05). However, kinematics in corresponding muscles did not show significant change, which indicates change in muscle usage did not impact driver's kinematic strategy. The results suggest that in simple steering, the deltoid compensates for fatigue of RC muscles while in more dynamic steering, the biceps compensate for fatigue of RC muscles. However, the extent of this compensation was minimal as activation level of infraspinatus reached close to its maximum contraction (~96.5% MVC) while non-RC muscles were generally below 30% MVC in all turns