Impact of a Neck Strap Intervention on Perceived Effort, Thumb Force, and Muscle Activity of Clarinetists

OBJECTIVE: Clarinetists often report discomfort of the right wrist and thumb and note that it is likely the result of the constant force applied to the area from the instrument’s weight and the musician’s technique. One preventative measure to reduce this discomfort is the use of a neck strap. The objective of the current study was to document the biomechanical impacts of this intervention. METHODS: Eight experienced clarinetists played a series of three etude pieces while playing both with and without a neck strap. For each condition, the force between the right thumb and clarinet was measured, electromyographic (EMG) data were collected from seven muscle groups, and subjective assessment of perceived effort was obtained. RESULTS: The results showed that when the neck strap was used, there was a significant decrease in the average force between the thumb and clarinet (p<0.05) and a decrease in the average perceived effort required for the right shoulder and thumb of the participants (p<0.05). Importantly, there were no statistically significant increases in the muscle activity of any of the neck and shoulder muscles with the introduction of the neck strap intervention. CONCLUSION: A neck strap intervention had positive effects on the right thumb while not causing any known adverse effects to other areas such as the neck, upper back, and shoulders.

Dynamic Spatial Tuning Patterns of Shoulder Muscles with Volunteers in a Driving Posture

Computational human body models (HBMs) of drivers for pre-crash simulations need active shoulder muscle control, and volunteer data are lacking. The goal of this paper was to build shoulder muscle dynamic spatial tuning patterns, with a secondary focus to present shoulder kinematic evaluation data. 8M and 9F volunteers sat in a driver posture, with their torso restrained, and were exposed to upper arm dynamic perturbations in eight directions perpendicular to the humerus. A dropping 8-kg weight connected to the elbow through pulleys applied the loads; the exact timing and direction were unknown. Activity in 11 shoulder muscles was measured using surface electrodes, and upper arm kinematics were measured with three cameras. We found directionally specific muscle activity and presented dynamic spatial tuning patterns for each muscle separated by sex. The preferred directions, i.e. the vector mean of a spatial tuning pattern, were similar between males and females, with the largest difference of 31° in the pectoralis major muscle. Males and females had similar elbow displacements. The maxima of elbow displacements in the loading plane for males was 189 ± 36 mm during flexion loading, and for females, it was 196 ± 36 mm during adduction loading. The data presented here can be used to design shoulder muscle controllers for HBMs and evaluate the performance of shoulder models.

Validity of freehand three-dimensional ultrasound system in measurement of three-dimensional surface shape of shoulder muscles

Accurate measurement of muscle morphology is crucial for assessing skeletal muscle capacity. Although the freehand three-dimensional ultrasound (3DUS) system is a promising technique for assessing muscle morphology, its accuracy has been validated mainly in terms of volume by examining lower limb muscles. The purpose of this study was to validate 3DUS in the measurements of 3D surface shape and volume by comparing them with MRI measurements while ensuring the reproducibility of participant posture by focusing on the shoulder muscles. The supraspinatus, infraspinatus, and posterior deltoid muscles of 10 healthy males were scanned using 3DUS and MRI while secured by an immobilization support customized for each participant. A 3D surface model of each muscle was created from the 3DUS and MRI methods, and the agreement between them was assessed. For the muscle volume, the mean difference between the two models was within 0.51 cm3 for all muscles. For the surface shape, the distances between the closest points of the two models was calculated for every point on the 3DUS surface model. The results showed that the median (third quartile) of the distances was less than 1.21 mm (1.89 mm) for all muscles. These results suggest that, given the above error is permitted, 3DUS can be used as an alternative to MRI in measuring volume and surface shape, even for the shoulder muscles.

Validity, Agreement and Accuracy of A Hand-Held Dynamometer for Shoulder Muscles Strength Assessment in Healthy Individuals

Background: The shoulder complex has a high prevalence of injuries. It is fundamental to quantify the muscle strength and identify muscular imbalances that predispose to lesions. The aim was to test concurrent validation of the muscle strength assessment with a hand held dynamometer (HHD) for shoulder joint muscles, and measure the accuracy and diagnostic agreement between instruments for assessing the strength of this joint with the hand held dynamometer and isokinetic dynamometer (ID) in a population of healthy individuals Methods: healthy individuals aged between 18 and 40 years were included. The HHD was used to test the isometric contraction of the main shoulder movements. Isometric contraction was performed for 3 seconds. Assessments with HHD and DI were performed on the same day, with a minimum interval of 90 minutes between tests. The study was approved by the Ethics Committee by report No.1537948. Concurrent validation was calculated with Pearson’s correlation, the accuracy obtained by the ROC curve and agreement by Kappa test. Results: The HHD showed concurrent validation between 0.51 – 0.83, with sensitivity between 0.90 and 0.98 and specificity between 0.64 and 0.89 for shoulder movements. The HHD demonstrated moderately-strong to excellent concurrent validity. Conclusion: These results are encouraging for the routine use of this portable and lower cost instrument in quantification of the pique torque of the shoulder muscles. Moreover, this instrument showed good accuracy and moderate to high agreement in comparison with diagnosis of the gold standard instrument.

Muscle Fiber Contribution to Rotator Cuff Moment Arms During Abduction for Intact Rotator Cuff, Complete Supraspinatus Tear, Superior Capsular Reconstruction, and Reverse Shoulder Arthroplasty. (225)

Objectives: The Rotator Cuff (RC) is formed from the subscapularis, supraspinatus, infraspinatus, and teres minor muscles and their tendinous extensions. The 4 RC tendons insert on the humeral head such that they contribute to the dynamic stability of the glenohumeral joint along with their rotational actions on the shoulder. The moment arm can be used to demonstrate the work effort potential that a specific muscle is contributing to a musculoskeletal joint rotation. The objective of this study was to break out RC muscles into multiple fibers, providing more clarity as to how individual fibers contribute to a muscle’s overall moment arm during abduction. The aims of this study are: 1.) to illustrate within each RC muscle how multiple muscle fiber lines of action work together to produce abduction in an intact shoulder 2.) to estimate the moment arm changes that take place when the intact rotator cuff goes through surgical repair with either SCR or RSA after complete supraspinatus tear. We hypothesized that the rotator cuff muscles work differently and in combination at the fiber level to bring about a resultant movement that can be assessed through the proposed method of moment arm calculation for intact RC, complete supraspinatus tear, SCR and RSA. Methods: Five fresh cadaveric shoulder specimens were used in an apparatus where each muscle was maintained in tension with the line of action towards its origin on the scapula (Figure 1). An Optotrack camera kept track of digitized points along both the origin and insertion of the rotator cuff muscles as the shoulder was abducted. Using these digitized points, multiple lines of action were created across the breadth of each muscle. Each muscle force action line was then used to calculate moment arm values during 0-90º abduction (Figure 2). Results: Moment arms calculated for multiple fiber lines spanning the tendon attachment site displayed the variance of fiber contribution and function within each muscle during abduction. Our results indicate that rather than providing a return to anatomical shoulder muscle function, RSA and SCR models produce moment arms that vary between muscles, with some contributing more to abduction and some contributing less. Highlighted below are the infraspinatus results for moment arms of individual fiber lines of action (Figure 3) and calculated mean moment arms (Figure 4) over abduction.ANOVA testing demonstrated a significant difference (p<0.001) when analyzing moment arms of intact, complete supraspinatus tear, SCR, and RSA models in teres minor and infraspinatus. There was no significant difference in moment arm values between the models in the subscapularis (p=0.148). Highlighted in Table 1 are the ANOVA testing results for infraspinatus. Conclusions: Our biomechanical analysis demonstrated sufficient sensitivity to detect differences in moment arms of the four rotator cuff muscles across a variety of models, suggesting changes to even one muscle of the shoulder will have significant implications on the function of other shoulder muscles. Furthermore, our analysis of fiber divisions within the same muscle illustrates the complex nature of the shoulder muscles themselves, and future studies should aim to better explore and model their function. The calculated percent differences from intact beautifully illustrated this complexity, as corrective RSA and SCR procedures provided better resemblance of intact anatomy within some rotator cuff muscles while creating a larger percent difference in other muscle groups. By breaking out RC muscles into multiple fibers, more clarity can be gained as to how individual fibers contribute to a muscle’s overall moment arm during abduction. This may further aid surgical decision-making, specifically for RSA where there is continued debate about whether to reconstruct portions of the RC. Given that the supraspinatus tendon is the most frequently torn tendon in the rotator cuff, especially for athletes who apply repetitive stress to the tendon, the results of this study may help inform post-operative rehabilitation by illustrating how abduction and stability are achieved after SCR and RSA.

Carcass Yields and Physical-Chemical Meat Quality Characteristics of Namibian Red Hartebeest (Alcelaphus buselaphus) as Influenced by Sex and Muscle

This study determined the carcass yields of red hartebeest from Namibia and compared the physical-chemical meat quality characteristics of six different muscles (biceps femoris, infraspinatus, longissimus thoracis et lumborum, semimembranosus, semitendinosus, and supraspinatus) for both males and females. Red hartebeest males were heavier (133.92 kg) than females (114.20 kg) but the average dressing percentage did not differ between the two sexes. Muscles from females had a lower mean shear force value of 3.59 kg/1.27 cm ø, compared to males (4.23 kg/1.27 cm ø). The most tender muscle was the infraspinatus of the female treatment group, while the semimembranosus of the male treatment group was the least tender muscle. Drip loss, cooking loss and L* (lightness) values were not affected by sex. The largest hue angle was observed in the semitendinosus muscle of the female treatment group (28.94°), and it was thus the lightest red muscle. The highest chroma values (17.3) were observed in the semimembranosus muscle. Muscle protein content averaged 20.5% over all treatment combinations, and the mean intra-muscular fat content for both male and female muscles was low (2.4%). The shoulder muscles, infraspinatus and supraspinatus, of the females had the highest fat content (2.7%). The results indicate that red hartebeest meat should be market according to specific muscles and that sex of the animals need not be considered during marketing.

Trial-by-trial modulation of express visuomotor responses induced by symbolic or barely detectable cues

Human cerebral cortex can produce visuomotor responses that are modulated by contextual and task-specific constraints. However, the distributed cortical network for visuomotor transformations limits the minimal response time of that pathway. Notably, humans can generate express visuomotor responses in arm muscles that are inflexibly tuned to the target location and occur 80-120ms from stimulus presentation (stimulus-locked responses, SLRs). This suggests a subcortical pathway for visuomotor transformations that might involve the superior colliculus and its downstream reticulo-spinal projections. Here we investigated whether cognitive expectations can modulate the SLR. In one experiment, we recorded surface EMG from shoulder muscles as participants reached toward a visual target whose location was unpredictable in control conditions, and partially predictable in cue conditions by interpreting a symbolic cue (75% validity). Valid symbolic cues led to earlier and larger SLRs than control conditions; invalid symbolic cues produced later and smaller SLRs than control conditions. This is consistent with a cortical top-down modulation of the putative subcortical SLR-network. In a second experiment, we presented high-contrast targets in isolation (control) or ~24ms after low-contrast stimuli, which could appear at the same (valid cue) or opposite (invalid cue) location as the target, and with equal probability (50% cue validity). We observed earlier SLRs than control with the valid low-contrast cues, whereas the invalid cues led to the opposite results. These findings may reflect bottom-up attentional mechanisms, potentially evolving subcortically via the superior colliculus. Overall, our results support both top-down and bottom-up modulations of the putative subcortical SLR network in humans.

Theraband applications for improved wall slide exercise

Context: The wall slide exercise is commonly used in clinic and research settings. Theraband positioning variations for hip exercises are investigated and used, but theraband positioning variations for upper extremity wall slide exercise, though not commonly used, are not investigated. Objective: To investigate the effect of different theraband positions (elbow and wrist) on scapular and shoulder muscles' activation in wall slide exercises and compare them to the regular wall slide exercise for the upper limbs. Study Design: Descriptive Laboratory Study. Setting: University Laboratory Patients or Other Participants: 20 participants with healthy shoulders Interventions: Participants performed regular and two different variations of wall slide exercises (theraband at wrist and theraband at elbow) in randomized order. Main Outcome Measures: Surface EMG activity of the trapezius muscles (upper [UT], middle [MT], and lower trapezius [LT]), infraspinatus (IS), middle deltoid (MD), and serratus anterior (SA). Results: Regular wall slide exercise elicited low activity in MD and moderate activity in SA muscles (32% MVIC), while theraband at wrist and elbow variations elicited low activity in MT, LT, IS, and MD muscles and moderate activity in SA muscles (46% and 34% MVICs, respectively). UT activation was absent to minimal (0–15% MVIC) in all wall slide exercise variations. Theraband at wrist produced lower UT/MT, UT/LT, and UT/SA levels. Conclusion: In shoulder rehabilitation, clinicians desiring to activate scapular stabilization muscles should consider using theraband at wrist variation; clinicians desiring to achieve more shoulder abduction activation and less scapular stabilization should consider theraband at elbow variation of upper extremity wall slide exercise.

Muscular loads associated with floor vacuuming with cordless stick cleaners

The muscular loads of the upper extremity and chest muscles were assessed during floor vacuuming with stick vacuum cleaners. Ten participants conducted vacuuming with two stick cleaners (weight: 3.03 kg, 3.56 kg) on tiled and carpeted floors while the myoelectric activity of the upper extremity and chest muscles were collected. The mean muscle activation levels ranged from 15.5% to 45.7% of the maximum voluntary capacity. Greater muscular loads were observed on the forearm and shoulder muscles when vacuuming with repeated curved strokes (vs. straight storkes), and on the chest muscle when vacuuming the carpeted floor. The range of muscular loads were higher than that of occupational tasks such as house painting and dental drilling, which have been known as intensive activities for upper extremities. The results suggest that floor vacuuming with stick vacuum cleaners is physically demanding for household consumers. Ergonomic interventions such as more user-friendly design should be considered.