Analysis of phase detects altered timing of muscle activation in subjects with chronic shoulder pain.

Optimal exercise therapy for shoulder pain is unknown due to limited information regarding specific changes in muscle function associated with pain. Timing of muscle activity with respect to movement (phase) can provide information about muscle activation patterns without requiring electromyography data normalization which is problematic in the presence of pain. The aim of this study was to determine if a phase measure is able to detect differences in the timing of shoulder muscle activation in subjects with chronic shoulder pain.

Shoulder muscle activation patterns and levels differ between open and closed-chain abduction.

Objectives: Open and closed-chain abduction of the shoulder are commonly used in rehabilitation and exercise programs to assess and/or improve shoulder muscle function. However, it is not known if shoulder muscle activation patterns differ between these two exercises. Therefore the purpose of this study was to compare muscle activation patterns during closed-chain shoulder abduction performed using a shoulder press machine with open-chain abduction using free weights.

Is subscapularis recruited in a similar manner during shoulder internal rotation exercises and belly press and lift off tests?

Objectives: Although the belly press and lift off tests are recommended to assess subscapularis function, shoulder internal rotation (IR) exercises performed in other shoulder positions are more commonly used to restore subscapularis function. It is not known if shoulder IR exercises specifically activate subscapularis to the same degree as the lift off and belly press tests, and thus have the potential to effect subscapularis strength gains. Therefore, the aim was to compare subscapularis activation levels with those of other shoulder internal rotator muscles during the belly press and lift off tests and shoulder IR exercise positions.

Does load influence shoulder muscle recruitment patterns during scapular plane abduction?

Objectives: Load is used to increasingly challenge muscle function and has been shown to increase muscle activity levels with no change in activation patterns during shoulder flexion, extension, adduction and rotation. However, the effect of load during shoulder abduction, a movement commonly used in assessment of shoulder dysfunction and to improve shoulder function, has not been comprehensively examined. Therefore, the purpose of this study was to determine if load influences shoulder muscle activation patterns and levels during scapular plane abduction in normal subjects.

Does changing the plane of abduction influence shoulder muscle recruitment patterns in healthy individuals?

Study Design: Observational laboratory study.

Background: Abduction is a movement commonly used in the assessment of shoulder dysfunction and prescription of exercises to improve shoulder function. Abduction in the scapular and coronal planes are used interchangeably.

An Arabic version of the effort-reward imbalance questionnaire: translation and validation study.

An Arabic version of the Effort-Reward Imbalance Questionnaire was developed and validated through a translation process with cross-cultural considerations. The translated questionnaire was evaluated for reliability and validity. A Principal Components Analysis was conducted following assessment of the suitability of data for factor analysis.

Associations among work-related stress, cortisol, inflammation, and metabolic syndrome.

This cross-sectional study examined the relationship between work-related stress, cortisol, and C-reactive protein (CRP) in predicting metabolic syndrome (MtS). Self-reported work stress measured by the effort reward imbalance ratio (ERI), anthropometric data, CRP, and saliva cortisol were collected from 204 healthy Jordanian male workers. ERI and cortisol were significantly associated with the presence of MtS (OR = 4.

An electromyographic study of parkinsonian swallowing and its response to levodopa.

Background: Few studies have investigated the effect of levodopa on parkinsonian swallowing with findings thus far being equivocal.

Methods: We used surface electromyography and accelerometry to investigate submental and laryngeal muscle activation during swallowing in 14 parkinsonian subjects before and after levodopa and in 22 age-matched controls. Our aims were (1) to demonstrate the clinical utility of noninvasive electromyography, (2) to identify electromyographic features of parkinsonian swallowing, and (3) to investigate the effect of levodopa on parkinsonian swallowing.

Does supraspinatus initiate shoulder abduction?

Purpose: It is commonly stated that supraspinatus initiates abduction; however, there is no direct evidence to support this claim. Therefore, the aims of the present study were to determine whether supraspinatus initiates shoulder abduction by activating prior to movement and significantly earlier than other shoulder muscles and to determine if load or plane of movement influenced the recruitment timing of supraspinatus.

Methods: Electromyographic recordings were taken from seven shoulder muscles of fourteen volunteers during shoulder abduction in the coronal and scapular planes and a plane 30° anterior to the scapular plane, at 25%, 50% and 75% of maximum load.

Systematic nonlinear relations between joint mechanics and the neural reflex response with changes in stretch amplitude at the wrist.

The effects on both joint mechanics and the neural stretch reflex of changes in amplitude of stretch ranging from within the region of short range stiffness up to 3% of resting muscle length were quantified. The level of activation of the primary agonist was held constant but there was a small but systematic increase in activation of the other flexor and extensor muscles as stretch amplitude increased. The patterns of change with stretch amplitude in both the joint mechanics and stretch reflex properties were non-linear but systematic and were well described by power relationships that accounted for high proportions of variance.

Rotator cuff muscles perform different functional roles during shoulder external rotation exercises.

The aim of this study was to compare activity in shoulder muscles during an external rotation task under conditions of increasing arm support to investigate whether changing support requirements would influence muscle recruitment levels, particularly in the rotator cuff (RC) muscles. Electromyographic recordings were collected from seven shoulder muscles using surface and indwelling electrodes. The dominant shoulder of 14 healthy participants were examined during dynamic shoulder external rotation performed at 90° abduction with the arm fully supported, partially supported, and unsupported.

The association between work stress and inflammatory biomarkers in Jordanian male workers.

The study aimed to establish the association of work stress, expressed as effort-reward imbalance (ERI), and C-reactive protein (CRP) in 152 healthy Jordanian male employees. Self-report work stress, anthropometric data, and blood for CRP analysis were collected. A significant correlation between ERI and CRP (r = 0.

Direction-specific recruitment of rotator cuff muscles during bench press and row.

Recent studies indicate that rotator cuff (RC) muscles are recruited in a reciprocal, direction-specific pattern during shoulder flexion and extension exercises. The main purpose of this study was to determine if similar reciprocal RC recruitment occurs during bench press (flexion-like) and row (extension-like) exercises. In addition, shoulder muscle activity was comprehensively compared between bench press and flexion; row and extension; and bench press and row exercises.

An Arabic version of the perceived stress scale: translation and validation study.

Background: The Perceived Stress Scale has been designed to measure the degree to which situations in a person's life are perceived as stressful.

Objective: The paper describes the development of an Arabic version of the Perceived Stress Scale.

Design: A translation process with cross-cultural considerations was employed to produce an Arabic version of the Perceived Stress Scale.

A comprehensive analysis of muscle recruitment patterns during shoulder flexion: an electromyographic study.

Although flexion is a common component of the routine clinical assessment of the shoulder the muscle recruitment patterns during this movement are not clearly understood making valid interpretation of potential muscle dysfunction problematic. The purpose of this study was to comprehensively examine shoulder muscle activity during flexion in order to compare the activity levels and recruitment patterns of shoulder flexor, scapular lateral rotator and rotator cuff muscles. Electromyographic (EMG) data were recorded from 12 shoulder muscles sites in 15 volunteers.

The rotator cuff muscles have a direction specific recruitment pattern during shoulder flexion and extension exercises.

A recent study has shown that posterior rotator cuff (RC) muscles are recruited at significantly higher levels than the anterior RC during shoulder flexion. It was proposed that the mechanism whereby the posterior RC muscles were providing shoulder stability during flexion was to counterbalance potential anterior humeral head translation caused by flexion torque producing muscles. This hypothesis implies that anterior RC activity should be higher than posterior RC activity during extension to prevent posterior humeral head translation.

Does passive mobilization of shoulder region joints provide additional benefit over advice and exercise alone for people who have shoulder pain and minimal movement restriction? A randomized controlled trial.

Background: Passive mobilization of shoulder region joints, often in conjunction with other treatment modalities, is used for the treatment of people with shoulder pain and minimal movement restriction. However, there is only limited evidence supporting the efficacy of this treatment modality.

Objective: The purpose of this study was to determine whether passive mobilization of shoulder region joints adds treatment benefit over exercise and advice alone for people with shoulder pain and minimal movement restriction.

The role of shoulder muscles is task specific.

The aim of this study was to compare activity in shoulder muscles during unsupported internal and external rotation to examine their functional roles, and determine whether they retain their 'stabiliser' or 'mover' role regardless of the shoulder task. Electromyographic recordings in the dominant shoulder of 15 normal subjects were taken from 13 shoulder muscle sites using a combination of surface and intramuscular electrodes during isometric shoulder internal and external rotation in an unsupported abducted position under conditions of increasing load. During internal rotation significantly higher activity levels were found in subscapularis (p<0.

Which is the optimal exercise to strengthen supraspinatus?

Purpose: Supraspinatus strengthening is an important part of shoulder rehabilitation programs. Because of the force-couple relationship between supraspinatus and deltoid during shoulder abduction, it has been proposed that the optimal exercise to strengthen supraspinatus is one that would maximize supraspinatus activity while minimizing surrounding muscle activity, particularly deltoid. The aim of this study was to simultaneously examine all exercises known to recruit supraspinatus at high levels and to compare the level of recruitment in supraspinatus, deltoid, and infraspinatus.

The 'empty can' and 'full can' tests do not selectively activate supraspinatus.

Based on previous electromyographic studies the 'empty can' (EC) and 'full can' (FC) tests have been promoted as being able to isolate activity to supraspinatus and are therefore diagnostic of supraspinatus dysfunction. However, there is evidence to suggest that these positions do not selectively activate supraspinatus, and that they may have poor diagnostic accuracy, bringing into question the validity of these tests. Due to limitations in the original EMG papers describing the EC and FC tests the current study aimed to further examine shoulder muscle activity during these tests to determine their ability to selectively activate supraspinatus.

Standard maximum isometric voluntary contraction tests for normalizing shoulder muscle EMG.

A comparison of electromyographic (EMG) activity of muscles between and within subjects, and during separate occasions of testing, requires normalization. The most common way for generating the reference level used for normalizing shoulder EMG data is with a maximum isometric voluntary contraction (MVIC). The purpose of this study was to develop a parsimonious set of standardized tests that generate an MVIC in all the major muscle groups of the shoulder.

Voluntary modulation of human stretch reflexes.

It has been postulated that the central nervous system (CNS) can tune the mechanical behavior of a joint by altering reflex stiffness in a task-dependant manner. However, most of the evidence supporting this hypothesis has come from the analysis of H-reflexes or electromyogram (EMG) responses. Changes in overall stiffness have been documented but, as yet, there is no direct evidence that the CNS can control reflex stiffness independently of the intrinsic stiffness.

Entrainment to extinction of physiological tremor by spindle afferent input.

In this study the systematic modulation of wrist flexor muscle activity by imposed joint movement was examined. Ten subjects maintained a constant contraction level (25% of the maximum; trial duration: 20 s) in flexor carpi radialis while their wrists were perturbed with 50 different quasi-sinusoidal signals (frequency range: 0.5-9.

Systematic nonlinear relations between displacement amplitude and joint mechanics at the human wrist.

This study quantified the systematic effects on wrist joint mechanics of changes in amplitude of displacement ranging from within the region of short-range stiffness (0.2% of resting muscle length) up to 3% of resting muscle length. The joint mechanics were modelled using a second-order system from which estimates of joint stiffness, viscosity, inertia, natural resonant frequency and damping ratio were obtained.

Otolith and canal reflexes in human standing.

We used galvanic vestibular stimulation (GVS) to identify human balance reflexes of the semicircular canals and otolith organs. The experiment used a model of vestibular signals arising from GVS modulation of the net signal from vestibular afferents. With the head upright, the model predicts that the GVS-evoked canal signal indicates lateral head rotation while the otolith signal indicates lateral tilt or acceleration.