Intraobserver and interobserver reliability for the strength test in the Constant-Murley shoulder assessment

This study evaluates the standardized strength test in the Constant-Murley shoulder assessment of adults with healthy shoulders in a randomized, single-blind design. The following questions were to be answered: (1) Can the spring balance and a digital dynamometer both yield the same result? (2) What is the intraobserver and interobserver reliability of the strength test? (3) Is the strength test sensitive to change in technique or affected by calculation with mean or maximum values? Ten subjects were included in a comparison of the Handyscale (digital dynamometer) and the mechanical spring balance for concurrent validity, resulting in intraclass correlation coefficient values ranging from 0.96 to 0.99. For intraobserver and interobserver reliability, 2 observers tested 20 subjects with the Handyscale and retested them after 2 weeks. Regardless of technique during testing, this resulted in almost perfect agreement (intraclass correlation coefficient range, 0.89-0.98). The digital dynamometer can replace the conventional spring balance. The standardized strength test in the Constant-Murley shoulder assessment is reliable in young subjects with healthy shoulders, independent of technique or whether calculated with mean or maximum values.

Measurement of baseline shoulder function in subjects receiving workers' compensation versus noncompensated subjects

The purpose of this study was to ascertain whether a measurable difference existed in normative scores for the American Shoulder and Elbow Surgeons (ASES) questionnaire between subjects who had an active workers' compensation claim (WC) with no known shoulder injury and subjects without a compensation claim (non-WC). Subjects with non-shoulder-related orthopaedic injuries were recruited from a suburban orthopaedic sports medicine clinic and an urban occupational medicine clinic. They were asked to complete a composite questionnaire that consisted of demographic information and the ASES questionnaire. There were no significant differences in the ASES scores between subject groups. There were significant differences between subject groups with regard to work hours (P = .0001), work demands (P = .0001), and tobacco use (P = .0001). Subject group was also significantly associated with education level (P = .0001), marital status (P = .0001), work demands (P = .0001), gender (P = .0001), and sports participation (P = .0314). The ASES score was significantly affected by marital status (P = .0476), sports participation (P = .0008), and age (P = .0129).

Normalization of the Constant score

The strength of the normal shoulder may differ by gender and deteriorate with age. Thus, the Constant score may also decrease in absolute value while still reflecting a normal score. To account for age- and gender-related differences, normal results for this scale must be determined across a population of patients without shoulder disease. Patients presenting for evaluation of nonshoulder conditions participated. A subjective questionnaire was completed. Range of motion and strength were measured. This analysis includes the data of 441 patients. The mean Constant score for men was significantly greater than that for women in each age group ( P < .05). Significant age-related differences were noted in each group ( P < .05). Normative values for the Constant score based on age and gender were determined. The adjusted score represents the gender- and age-matched function of the shoulder and is useful in the evaluation of shoulder outcomes.

The effect of sampling frequency on EMG measures of occupational mechanical exposure

The purpose of the present study was to determine how much it is possible to downsample EMG without loosing the accuracy of some EMG measures of occupational mechanical exposure frequently used in the literature. The EMG signals of four muscles (two trapezius, right deltoid and right extensor digitorum) were collected (sampling frequency: 1024 Hz) from 20 subjects while performing a 20 min computer work task. The EMG RMS amplitude was computed from 0.125 s successive time-windows for the original (1024 Hz) and four additional digitally resampled (at 512, 256, 128 and 64 Hz) EMG signals. Three of the most frequently used data reduction methods (1. gaps analysis, 2. amplitude probability distribution function and 3. exposure variation analysis) were used to summarise the 20 min EMG activation profiles. The results from the exposure variation analysis were summarized into three variables using a new method detailed here. In general, the ANOVA for repeated measures demonstrated that a decrease of the sampling frequency significantly changed the EMG measures (relative to the 1024 Hz sampling condition) most of the time at 64 and 128 Hz, occasionally at 256 Hz, but practically never at 512 Hz. An analysis of the maximal errors (relative to the 1024 Hz condition) across all subjects supported these findings. Consequently, it was concluded that 512 Hz is quite conservative and should practically never lead to invalid EMG parameters estimations. Conversely, 256 Hz represents the lowest limit tolerable for some EMG parameters (gaps analysis, amplitude probability distribution function) while it is unacceptable for others (modified exposure variation analysis).

Coupled bilateral movements and active neuromuscular stimulation: intralimb transfer evidence during bimanual aiming

Motor improvements in chronic stroke recovery accrue from coupled protocols of bilateral movements and active neuromuscular stimulation. This experiment investigated coupled protocols and within-limb transfer between distal and proximal joint combinations. The leading question focused on within-limb transfer of coupled protocols on distal joints to a bimanual aiming task that involved proximal joints. Twenty-six volunteers completed one of three motor recovery protocols according to group assignments: (1) coupled bilateral involved concurrent wrist/finger movements on the unimpaired limb coupled with active stimulation on the impaired limb; (2) unilateral/active stimulation involved neuromuscular electromyogram-triggered stimulation on the impaired wrist/fingers; and (3) no protocol (control group). During the pretest and posttest, subjects performed transverse plane target aiming movements (29 cm) with vision available. The coupled bilateral group showed positive intralimb transfer post-treatment when both arms moved simultaneously. During the posttest, the coupled bilateral group displayed improved movement time, higher peak limb velocity, less variability in peak velocity, and less percentage of total movement time in the deceleration phase than during the pretest. The evidence confirms that within-limb transfer from distal joint training to proximal joint combinations is viable and generalizable in chronic stroke rehabilitation. Moreover, these intralimb transfer findings extend the evidence favoring motor improvements for coupled bilateral protocols during chronic stroke.

Variation in the cervical range of motion over time measured by the "flock of birds" electromagnetic tracking system

STUDY DESIGN

Observational longitudinal study.

OBJECTIVE

To establish the normal variation over time for active and passive cervical range of motion (ROM) measured with the Flock of Birds electromagnetic tracking system (FOB).

SUMMARY OF BACKGROUND DATA

Data about normal variation of cervical ROM over time are scarce but important for the interpretation of study results.

METHODS

Forty-eight subjects without a manifest dysfunction in neck and shoulder region (asymptomatic group) and 58 subjects with a dysfunction in the neck and shoulder region (symptomatic group) participated in this study. Cervical active and passive ROM was assessed in three different sessions 6 weeks apart. The following movements were measured: flexion-extension, lateral bending, and axial rotation in neutral, flexed, and extended position.

RESULTS

A wide range of variation of active and passive cervical ROM was found at the 6- and 12-week measurement in the asymptomatic group as well as in the symptomatic group. Highest variation was found during passive ROM testing as compared with active ROM testing. The symptomatic group showed larger variation than the asymptomatic group.

CONCLUSIONS

Cervical range of motion varies considerably over time. This variation should be taken into account when results of therapeutic trials with respect to cervical ROM are interpreted.

The effect of simulated school load carriage configurations on shoulder strap tension forces and shoulder interface pressure

Recently, several studies have addressed the physical demands of school student's load carriage, in particular the load weight carried, using physical demands indicators such as oxygen consumption, gait, and posture. The objective of this study was to determine the effects of different load carriage configurations on shoulder strap tension forces and shoulder interface pressure during simulated school student's load carriage. A load carriage simulator was used to compare shoulder strap forces and shoulder pressure for 32 combinations of gait speed, backpack weight, load distribution, shoulder strap length and use of a hip-belt. The results showed that the manipulation of backpack weight, hip-belt use and shoulder strap length had a strong effect on shoulder strap tension and shoulder pressure. Backpack weight had the greatest influence on shoulder strap tension and shoulder pressure, whereas hip-belt use and then shoulder strap adjustment had the next greatest effects, respectively. While it is clear that researchers and practitioners are justified in focusing on load magnitude in backpack studies as it has the greatest effect on shoulder forces, hip-belt use and shoulder strap adjustment should also be examined further as they too may have significant effects on the demands placed on backpack users. Based on the present findings, school students should wear their backpacks with the least weight possible, use the hip-belt if present, allow a reasonable amount of looseness in the shoulder straps and should position the heaviest items closest to their back. However, more detailed work using human participants needs to be undertaken before these recommendations can be confirmed.

Age-related differences in the control of multijoint movements

The present study investigates whether regulation of interactive torque during multijoint movements decays with advanced age as a result of declines in the motor system. Young and elderly adults repeatedly drew a circle and ovals oriented in different directions using shoulder and elbow joint movements. Each template was traced at three levels of cycling frequency with and without vision. Although vision did not affect performance, increases in cycling frequency caused distortions of movement trajectories in both groups. The pattern of distortions differed, however, between the groups. These differences were accounted for by differences in elbow control. Young adults provided regulation of elbow amplitude and timing by matching muscle torque magnitude with increased interactive torque. In contrast, elderly adults did not increase muscle torque magnitude and modulated torque timing for elbow motion regulation. This strategy is discussed as adaptation to decrements in the aging motor system.

Ability of very young children to produce reliable isometric force measurements

PURPOSE

This study was designed to examine the reliability of measuring isometric muscle force in very young children with a hand-held dynamometer (HHD).

METHODS

Forty-five children aged two, three, or four years old and with typical development, were divided into three groups of 15 subjects each. Group 1 included two-year-old children (X age = 32 +/- 2.4 months), group 2 contained three-year-old children (X age = 43 +/- 3.8 months), and group 3 included four-year-old children (X age = 54 +/- 3.7 months). Isometric force for shoulder flexion, elbow flexion, elbow extension, knee flexion, and knee extension were measured with a HHD on two occasions separated by five to nine days. The frequency of challenging child behaviors and extra test trails also were recorded.

RESULTS

Intraclass correlation coefficients (ICCs) (2, 1) for the combined group (n = 45) ranged from 0.90 to 0.95. The ICCs (2, 1) for the two-year-old children ranged from 0.76 to 0.91, for the three-year-old group from 0.85 to 0.92, and for the four-year-old children from 0.54 to 0.94. The frequency of challenging behaviors did not appear to be related to the level of reliability.

CONCLUSION

Using a HHD and standardized procedures, isometric force of children who are typically developing and as young as two years of age can be measured with fair to excellent reliability.

The effect of single- or multiple-layered garments on interface pressure measured at the backpack-shoulder interface

Experiments were aimed at determining whether interface pressure measurements are a true reflection of skin contact pressure when made over different layers of clothing. Interface pressures were recorded at the skin interface and above clothing layers, with 11 participants wearing 10 different clothing combinations. The clothing used was standard issue British military clothing, including body armour (without ballistic plate). Participants wore both single and multiple clothing layers whilst walking on a treadmill carrying a loaded backpack (23.5 kg, British military issue). Results showed no significant differences (p=>0.05) in pressure between different clothing layers either singly, or worn in multiple. In conclusion, the soldier (or leisure user) will gain no or very little relief from applied pressure by wearing garments, even in layers, when carrying a backpack. Also, the findings suggest that interface pressure may adequately be assessed using a sensor placed above the clothing layer(s) rather than at skin surface.

Cricket

We investigated the techniques used by nine right-handed, international batsmen to perform front foot off-side drives in first class and international matches. All strokes were captured using two synchronised high-speed video cameras; nine were selected for kinematic analysis. These movement sequences were then manually digitised at a sampling frequency of 125 Hz using APAS motion analysis software. The results of this study indicated that the batsmen used movement patterns that enabled important aspects of stroke production, such as the front stride and the downswing of the bat, to be delayed so that additional information from ball flight could be assimilated. Front upper limb segments were constrained to work in a unitary fashion, with the peak horizontal end point speed of each segment occurring almost simultaneously just before impact. It has been suggested that these strategies serve to enhance stroke accuracy. Other aspects of their techniques included a distinctively looped bat path, a front foot placement that occurred only just before impact, and a front ankle that was positioned well inside the line of the ball at impact. Various technical parameters, such as the alignment of the trunk relative to ground and the continuous flow of the bat between the backswing and downswing, were similar to findings in previous batting research. Other characteristics of stroke production not previously addressed, including the path of the bat and the timing of the front stride, may challenge some long held beliefs evident in current coaching literature.

Tennis

Isokinetic dynamometry is used in the assessment and rehabilitation of shoulder function in tennis players. The aim of this study was to validate a newly installed Biodex III Isokinetic Dynamometer for internal and external shoulder rotation. A non-injured male performed this movement which replicates an integral section of the tennis service action (Cohen et al., 1994). Three maximal trials were performed at six randomly assigned angular velocities (0.52, 1.05, 1.57, 2.09, 2.62 and 3.14 rad x s(-1)) with 90 s rest between each set. Trials were recorded using an on-line motion analysis system and kinematic data were obtained. Kinematic angular displacement of the lever arm was slightly greater (> or = 0.01 rad x s(-1)) than for the isokinetic dynamometer at all test angular velocities. Mean angular velocities from the kinematic data were almost identical to those from the isokinetic dynamometer but less than the target values, and this difference (e.g. 2.55 rad x s(-1) at 3.14 rad x s(-1)) was greater at higher angular velocities owing to the greater acceleration phases required. Peak angular velocity was similar on the isokinetic dynamometer to the target values, but substantially less than those from the kinematic data (e.g. 0.68 rad x s(-1) at 0.52 rad x s(-1)). This suggests that the isokinetic data are over-smoothed and may mask important information. In summary, criterion validity of this isokinetic dynamometer is supported for displacement and mean angular velocity, but not for peak angular velocity. Shoulder rotations in tennis are often at angular velocities greater than the Biodex can reproduce, but for the purpose of monitoring the shoulder strength and range of motion of tennis players and providing safe functional rehabilitation, the use of slower angular velocities is acceptable.

[Evoked potentials of the somatic cortex, thalamus, and electromyographic reactions of the cat shoulder muscles elicited by elbow joint straightening in norm and after injection of neurotoxin]

EMG activity from the elbow joint muscles and evoked potentials (ep) from the somatic cortex (fields 4, 6) and thalamic nuclei (vl, vpl) elicited by passive extension were recorded in the unanesthetized cats before and after MPTP injection (total dose 10 mg/kg). It was shown, that after MPTP injection changes of the EMG response in cats are similar to that observed in parkinsonian patients: The increase of amplitude and duration of the stretch-related m2-3 -components of EMG, as well as excitation increase in thalamus and cortex was shown after MPTP. Perturbation of an external extensor loading applied to the forearm with different fixed force moments elicited m. biceps brachii EMG reactions which amplitude in norm correlated with a muscle stretch size. The MPTP injection influenced this dependence. Contrary to EMG responses n26-60 amplitude of the thalamic and cortical EP did not depend on the level of muscle stretch neither in norm nor after MPTP injection. Hence it supposed that an afferent excitation, which was responsible for this EP, did not take part in a generation of the m2-components of the stretch reflex. Late (n100) component's amplitude of the thalamic nuclei EP depended on the muscle stretch level. After MPTP injection this relation disappeared just as in the EMG responses. Since m2 components aroused in the spinal cord motor neurons earlier than n100 components in thalamus it is supposed that excitation of shoulder muscle receptors and spinal neurons, which provided with origin of m2 components consisting of EMG responses, were responsible for generation of the EP late components of thalamic nuclei VL and VPL.

Perceived work demands, felt stress, and musculoskeletal neck/shoulder symptoms among elderly female computer users. The NEW study

The aim of the present study was to test a structural model of the relationship between the perceived quantitative (time pressure and unevenly distributed workload) and emotional work demands and self-reported musculoskeletal symptoms from the neck and shoulder region with felt stress (rested, relaxed, calm, tense, stressed, and pressured at the end of a normal workday) as a mediating variable. As part of the NEW (Neuromuscular assessment in the Elderly Worker) study, a European case-control study, the present cross-sectional study was based on a questionnaire survey among Danish, Dutch, Swedish and Swiss female computer users aged 45 or older (n =148). The hypothesized structural model was tested using structural equation modelling. The results indicate that perceived work demands influence neck/shoulder musculoskeletal symptoms through their effect on felt stress. The results further indicate complete mediation, which means that all of the effect of the perceived work demands on symptoms could be attributed to the stress mechanism. As regards the percentage of explained variance in the endogenous variables, 36% of the variation in felt stress was explained by the perceived work demands, and about 20% of the variation in musculoskeletal neck/shoulder symptoms was explained by the combination of the perceived work demands and the felt stress.

Activation characteristics of shoulder muscles during maximal and submaximal efforts

Determination of individual maximum voluntary contraction (MVC) force is used as the gold standard for normalising surface EMG (SEMG) data. Assuming a linear amplitude-force relationship, individual strain levels are defined according to percentage rates of the measured MVC levels. The purpose of the study was to investigate if the assumed force-strain relationship can be applied without qualification. Therefore, healthy volunteers (nine men, ten women) were investigated during isometric exercises of shoulder muscles at MVC and 50% levels. Tasks were performed at four different angular positions in frontal, sagittal and horizontal planes. In each plane, both possible force directions were investigated. SEMG was taken simultaneously from 13 muscles of the shoulder and upper arms from both sides of the body. At a force level of 50% MVC, SEMG amplitude levels were compared to the expected 50% level. Differences in muscular co-ordination patterns were also determined. During retroversion and horizontal flexion, amplitude levels significantly remained at levels below 50%. This was seen for all the muscles investigated, independent of relative contribution to force production. During horizontal extension and abduction, the main force-producing muscles showed amplitude levels that significantly exceeded the expected 50% level. Co-ordination patterns differed significantly between MVC and submaximal conditions for anteversion, retroversion and horizontal extension. Specifically, four shoulder muscles showed higher proportions at the 50% level compared to MVC. Therefore, certain percentage rates of MVC force levels exhibit quite different strain rates, as identified by SEMG. Depending on force direction, differences in co-ordination patterns exist between MVC and submaximal test conditions. Both findings have implications for therapeutic and training applications.

The influence of contraction amplitude and firing history on spike-triggered averaged trapezius motor unit potentials

The spike-triggered averaged (STA) technique was used to examine trapezius motor unit potentials and their dependence on contraction amplitude and firing history. Individual motor unit firings were identified by a fine-wire intramuscular electrode, while STA-derived potentials were extracted from the simultaneously recorded surface electromyographic (SEMG) signal. Amplitude-controlled contractions and contractions with typing tasks and mental stress were carried out. STA potentials were mostly derived from 20 s intervals of firing. Motor unit synchrony was estimated by peristimulus time histograms (PSTHs). An association between SEMG amplitude and STA-derived motor unit potentials was found: motor unit area showed a four-fold increase when SEMG amplitude increased from 1.5 to 10.5% of the root mean square-detected SEMG signal at maximal voluntary contraction (%EMG(max)). Low- and higher threshold motor unit potentials, all with recruitment thresholds <10% EMG(max), had similar area at the same contraction amplitude. A significant increase in the STA-derived potentials was observed after 3 min of constant-amplitude contractions; however, this difference was reduced after 10 min and no longer present after 30 min of contraction. Motor unit synchrony accounted for, on average, 2.8% additional firings within 2 ms of the triggering motor unit. We conclude that the increase in STA-derived potentials with contraction amplitude is, to a major extent, due to motor unit synchrony, limiting the applicability of this method in postural muscles presenting wide motor unit potentials. The similar area of motor units at same SEMG amplitude may indicate that trapezius motor units recruited below 10% EMG(max) are of similar size and thus not organized according to the Henneman size principle.

Single-Injection Paravertebral Block Before General Anesthesia Enhances Analgesia After Breast Cancer Surgery With and Without Associated Lymph Node Biopsy

Paravertebral block (PVB) seems to decrease postoperative pain and postoperative nausea and vomiting (PONV) after breast surgery, but the studies have not been placebo controlled. We studied 60 patients scheduled for breast cancer surgery randomly given single-injection PVB at T3 with bupivacaine 5 mg/mL (1.5 mg/kg) or saline before general anesthesia. The patient and attending investigators were blinded; the PVB or the sham block was performed behind a curtain by an anesthesiologist not involved in the study. The patients given PVB with bupivacaine needed 40% less IV opioid medication (primary outcome variable) in the postanesthesia care unit, had a longer latency to the first opioid dose, and had less pain at rest after 24 h than the control patients (P < 0.01). They also had less PONV in the postanesthesia care unit (P < 0.05), were less sedated until 90 min (P < 0.05), and performed better in the digit symbol substitution test at 90 min and the ocular coordination test 60-120 min after surgery (P < 0.05). The average peak bupivacaine plasma concentration was 750 ng/mL. One patient had bilateral convulsions immediately after bupivacaine injection. We conclude that PVB before general anesthesia for breast cancer surgery reduced postoperative pain, opioid consumption, and occurrence of PONV and improved recovery from anesthesia.

Activation of shoulder muscles in healthy men and women under isometric conditions

PURPOSE

Due to the low osseous lead of the shoulder joint a large portion of the shoulder muscles, in addition to executing movements, deals with stabilising tasks. This requires a permanent readjustment of the intermuscular co-ordination of all involved muscles. The aim of the study was to verify the existence of gender dependent differences in intramuscular co-ordination patterns of shoulder muscles.

METHOD

Fifteen healthy men and nine healthy women, who executed 24 isometric exercises in sagittal, frontal and horizontal planes with a loading of 50% of their individual isometric maximum force, were investigated. In every plane, four angular positions were chosen and both opposite force directions were measured, respectively. SEMG was taken from 13 muscles of the shoulder and the upper arm. Due to inter-individual differences SEMG amplitudes were normalised.

RESULTS

Gender specific differences of functional intermuscular co-ordination patterns could be proven systematically. Women showed less activation of muscles acting in the main force direction. In addition, those muscles less necessary for the actual force production were more activated in women than in men.

CONCLUSIONS

Functionally comparable shoulder function showed a gender dependency in terms of functional intermuscular co-ordination.

Critical points in the forelimb fictive locomotor cycle and motor coordination: effects of phasic retractions and protractions of the shoulder in the cat

This study investigates the responses to phasic shoulder retractions or protractions given at different times in the fictive locomotor cycle of the forelimbs of decerebrate cats. Generally, the responses in flexor and extensor muscles acting at the shoulder or elbow were bilaterally coordinated according to a negative feedback scheme. Perturbations in the direction of the movements that would have taken place if the animal had not been paralyzed tended to shorten the duration of the burst of activity of the muscles active during that phase and vice versa in the opposite phase. Changes in response patterns took place around critical points corresponding to the critical points B-D described in the companion paper using tonic perturbations of the limb. Past point C, at 58% of the ipsilateral extensor burst, protractions no longer prolonged the burst and no longer delayed onset of the contralateral extensor. At point B, occurring at 41% of the contralateral extensor burst, ipsilateral protractions maximally shortened the ipsilateral flexor phase, advancing ipsilateral extensor onset (point D) to point C of the contralateral extensor burst. During a critical period from the end of the ipsilateral flexor (point D) until the contralateral flexor onset, retractions elicited two alternative responses. Either the contralateral extensor activity was abolished and the contralateral flexor turned on, or it persisted for another cycle. We argue that the critical points found here correspond to critical biomechanical events in real locomotion and may underlie a phase-dependent motor coordination.

Functional modulation of shoulder girdle stability

We have previously reported that electrical stimulation of the ulnar nerve at group I strength evokes reflex excitation of the trapezius muscle in normal human subjects. In the present study this reflex has been evoked while subjects were performing a number of different tasks. When subjects performed a task involving a high degree of manual dexterity, the reflex was larger. On the other hand, when subjects performed a task that can be achieved with virtually no movement of the hand or wrist musculature, the reflex does not appear to show any task dependency. These results support the view that in delicate tasks of the hand, such compensatory reflexes are more important than in basic mechanisms such as lifting an object. The functional consequences of these findings and their significance in relation to the possibility that these task-related reflex gain changes produce intention tremor is discussed.

Surface electromyography of nine shoulder muscles in two iron cross conditions in gymnastics

AIM

The rules of gymnastics impose an element of static strength such as an iron cross (IC) on the rings. For IC training, coaches use a custom made device -- the herdos -- to simulate the conditions of competition. The purpose was to compare muscle activity and coordination during IC performed both on the rings and using herdos. Secondly, we tried to determine whether herdos usage induced functional adaptations of the shoulder muscles.

METHODS

Six male gymnasts performed 10 IC in each condition. Surface electromyogram of muscles pectoralis major, latissimus dorsi, teres major, infraspinatus, rhomboideus, trapezius, serratus anterior, biceps brachii, and triceps brachii in the right shoulder were analysed using root-mean-square (RMS), and muscle part's in each condition. Muscle part represents the contribution of each of the 9 shoulder muscles studied in each condition. Total muscle activity (SUM) was also used to compare the 2 conditions.

RESULTS

Except for the muscle teres major, the RMS decreases (p<0.05) when using the herdos. The SUM also decreases (p<0.05) when using this device. The muscle parts indicate that the contribution of the muscle latissimus dorsi decreases (p<0.05) when using the herdos. These results suggest that the herdos modified shoulder coordination. But their usage does not seem to induce any functional adaptations of these muscles.

CONCLUSIONS

The herdos do not seem to provide a valid method to reproduce the same shoulder coordination as on the rings. Therefore IC training with this special device could be called in question.

Reflexes in the shoulder muscles elicited from the human coracoacromial ligament

Morphological studies have demonstrated mechanoreceptors in the capsuloligamentous structures of the shoulder joint, however knowledge of the role these joint receptors play in the control of shoulder stability is limited. We therefore investigated the effect of electrically induced afferent activity from mechanoreceptors in the coracoacromial ligament (CAL) on the activity of voluntary activated shoulder muscles in healthy humans. In study I, wire electrodes, for electrical stimulation, were inserted into the CAL in eight normal shoulders. In study II, a needle electrode was inserted into the CAL in seven normal shoulders. Electric activity was recorded from eight shoulder muscles by surface and intramuscular electrodes. During isometric contractions, electrical stimulation was applied to the CAL at two different stimulus intensities, a weak stimulus (stim-1) and a stronger stimulus (stim-2). In both experiments, electrical stimulation of the CAL elicited a general inhibition in the voluntary activated shoulder muscles. In study I the average latencies (mean+/-SE) of the muscular inhibition were 66+/-4 ms (stim-1) and 62+/-4 ms (stim-2) during isometric flexion and 73+/-3 ms (stim-1) and 73+/-5 ms (stim-2) during isometric extension. In study II the average latency (mean+/-SE) of the response was 66+/-4 ms (stim-1) during isometric flexion. Our results demonstrated a response, probably of reflex origin, from mechanoreceptors in the CAL to the shoulder muscles. The existence of this synaptic connection between mechanoreceptors in CAL and the shoulder muscles suggest a role of these receptors in muscle coordination and in the functional joint stability.

Musculoskeletal parameters of muscles crossing the shoulder and elbow and the effect of sarcomere length sample size on estimation of optimal muscle length

BACKGROUND

Knowledge of musculoskeletal parameters is essential to understanding and modeling a muscle's force generating capability. A study of musculoskeletal parameters was conducted in two parts: (I) Empirical measurement of upper extremity musculoskeletal parameters. (II) Computational bootstrap simulation to examine statistical power of detecting optimal muscle length as a function of sarcomere length sample size and effect size.

METHODS

Parameters were determined with a cadaver model. Sarcomere lengths were measured for 120 samples per muscle using laser diffraction and the mean sarcomere length used to estimate optimal muscle length. A bootstrap computational simulation was conducted to estimate variance in mean sarcomere length as a function of sample size. Statistical power for detecting optimal muscle length as a function of sample size and effect size was then determined.

FINDINGS

Parameters are reported in tabular format. Power is 80% at approximately 85, 50, 40 and 25 samples for effect sizes of 0.5, 0.75, 1.0 and 1.5 mm respectively.

INTERPRETATION

Musculoskeletal parameters for predicting muscle forces can be adequately measured in a cadaver model. Measurement of 40-60 sarcomere lengths per muscle is sufficient to calculate mean sarcomere length for estimating optimal muscle length with power of 80% for an effect size of 0.75-1.0 mm.

Measures of accuracy for active shoulder movements at 3 different speeds with kinesthetic and visual feedback

STUDY DESIGN

Repeated-measures experiment.

OBJECTIVE

To compare measures of end point accuracy (EPA) for 2 feedback conditions: (1) visual and kinesthetic feedback and (2) kinesthetic feedback alone, during shoulder movements, at 3 different speeds.

BACKGROUND

Shoulder joint kinesthesia is typically reported with EPA measures, such as constant error. Reporting multiple measures of EPA, such as variable error and absolute error, could provide a more detailed description of performance.

METHODS AND MEASURES

Subjects were seated with the shoulder abducted 90 degrees in the scapular plane and externally rotated 75 degrees, with the forearm placed in a custom shoulder wheel. Subjects internally rotated the shoulder 27 degrees to a target position at 48 degrees of shoulder external rotation for both conditions. Motion analysis was used to determine peak angular velocity and 3 EPA measures for shoulder movements. Each EPA measure was compared between the 2 feedback conditions and among the 3 speeds with a separate 2-way analysis of variance.

RESULTS

Movements performed with kinesthetic feedback alone, measured by constant error (P<.01), variable error (P<.01), and absolute error (P<.01), were less accurate than movements performed with visual and kinesthetic feedback. Faster movements were less accurate when measured by constant error (P = .01) and absolute error (P<.01) than slower movements. Subjects tended to overshoot the target in the absence of visual feedback; however, movement speed played minimal role in the overshooting.

CONCLUSIONS

Multiple measures of EPA, such as constant, variable, and absolute error during simple restricted shoulder movements may provide additional information regarding the evaluation of a motor performance or identify different central nervous system control mechanisms for joint kinesthesia.

The effect of the amplitude of motor action on anticipatory postural adjustments

The purpose of this study was to determine whether changes in the amplitude of a motor action triggering the same perturbation affect anticipatory postural adjustments (APAs). Healthy subjects performed releases of the same load with shoulder abduction movements of different amplitudes. Changes in the electrical activity of trunk and leg muscles, as well as displacements of the center of pressure were recorded. Generally, there were no differences in anticipatory activity of muscles and displacements of the center of pressure between series of load releases induced by motor actions of different amplitudes. We suggest that the CNS arranges APAs based on the magnitude of the perturbation if the same muscle groups generate motor actions of different amplitudes.