A non-invasive protocol to determine the personalized moment arms of knee and ankle muscles

One difficulty that comes with predicting muscular forces is the accuracy of experimental data, particularly the assessment of muscle moment arms with respect to each joint rotation axis. This paper presents a non-invasive experimental protocol to obtain the personalized muscle moment arms with respect to the ankle and knee joints. A specific pointer is used by a specialist of lower limb anatomy in order to define the local portion of the line of action of the different muscles closed to the joint on the standing subject's lower limb. With this pointer, the three-dimensional coordinates of several points representing the line of action of 12 ankle and knee muscles are collected by a Motion Analysis system. The collection is done five times by the same operator and one time by two different operators. From this data, the intra and inter operator repeatabilities are tested. Relative (ICC) and absolute (SEM) reliabilities are determined in order to evaluate the intra operator repeatability of this non-invasive protocol. The ICC values obtained are higher than 0.91 for 10 among 12 muscles. The intra operator repeatability is thus confirmed. From the records realized by the two operators, the differences are negligible. Thus, the inter operator repeatability is also confirmed. The moments arms obtained using this non-invasive experimental protocol are compared with those calculated from origin and insertion points reported in the literature, according to the work of Whites, Pierrynowskis and Kepples, respectively. The estimations obtained using the non-invasive experimental protocol are found, for some muscles, more realistic than those calculated using the literature data and are always coherent with the role of the muscles described in anatomical books.     

Intra-session repeatability of lower limb muscles activation pattern during pedaling

Assessment of intra-session repeatability of muscle activation pattern is of considerable relevance for research settings, especially when used to determine changes over time. However, the repeatability of lower limb muscles activation pattern during pedaling is not fully established. Thus, we tested the intra-session repeatability of the activation pattern of 10 lower limb muscles during a sub-maximal cycling exercise.Eleven triathletes participated to this study. The experimental session consisted in a reference sub-maximal cycling exercise (i.e. 150 W) performed before and after a 53-min simulated training session (mean power output = 200 ± 12 W). Repeatability of EMG patterns was assessed in terms of muscle activity level (i.e. RMS of the mean pedaling cycle and burst) and muscle activation timing (i.e. onset and offset of the EMG burst) for the 10 following lower limb muscles: gluteus maximus (GMax), semimembranosus (SM), Biceps femoris (BF), vastus medialis (VM), rectus femoris (RF), vastus lateralis (VL), gastrocnemius medianus (GM) and lateralis (GL), soleus (SOL) and tibialis anterior (TA).No significant differences concerning the muscle activation level were found between test and retest for all the muscles investigated. Only VM, SOL and TA showed significant differences in muscle activation timing parameters. Whereas ICC and SEM values confirmed this weak repeatability, cross-correlation coefficients suggest a good repeatability of the activation timing parameters for all the studied muscles.Overall, the main finding of this work is the good repeatability of the EMG pattern during pedaling both in term of muscle activity level and muscle activation timing.     

Biceps brachii can add to performance of tasks requiring supination in cerebral palsy patients

The aim of this study was to assess whether cerebral palsy patients can use biceps brachii for supination during movement tasks requiring supination and pronation. 3D upper extremity kinematic and EMG-data of 12 patients (mean age 13 y 8 mo ± 36 mo) were compared to 10 healthy age-matched controls. Significant difference in biceps brachii activation between maximal isolated pronation and supination in both groups showed that it is possible for CP patients to use biceps brachii for supination. Performance of reach-to-grasp with either pronation or supination showed similar activation patterns as during isolated tasks in both groups, although increased biceps brachii activation likely also hampered performance of reach-to-grasp in the patient group by causing increased, and possibly unwanted elbow flexion. However, the functional effect of this flexion for supination purposes cannot be ruled out. Therefore, one should be cautious with simply weakening biceps brachii when the purpose is to improve functional reach. Ideally treatment might focus more on changing the flexion moment/supination moment ratio of biceps toward a stronger supination function.     

Tennis players show a lower coactivation of the elbow antagonist muscles during isokinetic exercises

PurposePrevious studies have suggested that muscle coactivation could be reduced by a recurrent activity (training, daily activities). If this was correct, skilled athletes should show a specific muscle activation pattern with a low level of coactivation of muscles which are typically involved in their discipline. In particular, the aim of this study was to verify the hypothesis that the amount of antagonist activation of biceps brachii (BB) and triceps brachii (TB) is different between tennis players and non-players individuals during maximal isokinetic contractions.MethodsTen young healthy men and eight male tennis players participated in the study. The surface electromyographic signals (sEMG) were recorded from the BB and TB muscles during three maximal voluntary isometric contractions (MVC) of elbow flexors and extensors and a set of three maximal elbow flexions and extensions at 15°, 30°, 60°, 120°, 180° and 240°/s. Normalized root mean square (RMS) of sEMG was calculated as an index of sEMG amplitude.ResultsAntagonist activation (%RMSmax) of TB was significantly lower in tennis players (from 14.0 ± 7.9% at MVC to 16.3 ± 8.9% at 240°/s) with respect to non-players (from 27.7 ± 19.7% at MVC to 38.7 ± 17.6% at 240°/s) at all angular velocities. Contrary to non-players, tennis players did not show any difference in antagonist activation between BB and TB muscles.ConclusionsTennis players, with a constant practice in controlling forces around the elbow joint, learn how to reduce coactivation of muscles involved in the control of this joint. This has been shown by the lower antagonist muscular activity of triceps brachii muscle during isokinetic elbow flexion found in tennis players with respect to non-players.     

Effects of posture,movement and hand load on shoulder muscle activity

The influence of external factors such as arm posture, hand loading and dynamic exertion on shoulder muscle activity is needed to provide insight into the relationship between internal and external loading of the shoulder joint. Surface electromyography was collected from 8 upper extremity muscles on 16 participants who performed isometric and dynamic shoulder exertions in three shoulder planes (flexion, mid-abduction and abduction) covering four shoulder elevation angles (30°, 60°, 90° and 120°). Shoulder exertions were performed under three hand load conditions: no load, holding a 0.5 kg load and 30% grip. It was found that adding a 0.5 kg load to the hand increased shoulder muscle activity by 4% maximum voluntary excitation (MVE), across all postures and velocities. Performing a simultaneous shoulder exertion and hand grip led to posture specific redistribution of shoulder muscle activity that was consistent for both isometric and dynamic exertions. When gripping, anterior and middle deltoid activity decreased by 2% MVE, while posterior deltoid, infraspinatus and trapezius activity increased by 2% MVE and biceps brachii activity increased by 6% MVE. Increased biceps brachii activity with gripping may be an initiating factor for the changes in shoulder muscle activity. The finding that hand gripping altered muscle activation, and thus the internal loading, of the shoulder may play an important role in shoulder injury development and rehabilitation.     

Anticipatory postural adjustments to arm movement reveal complex control of paraspinal muscles in the thorax

Anatomical and empirical data suggest that deep and superficial muscles may have different functions for thoracic spine control. This study investigated thoracic paraspinal muscle activity during anticipatory postural adjustments associated with arm movement. Electromyographic (EMG) recordings were made from the right deep (multifidus/rotatores) and superficial (longissimus) muscles at T5, T8, and T11 levels using fine-wire electrodes. Ten healthy participants performed fast unilateral and bilateral flexion and extension arm movements in response to a light. EMG amplitude was measured during 25 ms epochs for 150 ms before and 400 ms after deltoid EMG onset. During arm flexion movements, multifidus and longissimus had two bursts of activity, one burst prior to deltoid and a late burst. With arm extension both muscles were active in a single burst after deltoid onset. There was differential activity with respect to direction of trunk rotation induced by arm movement. Right longissimus was most active with left arm movements and right multifidus was most active with right arm movements. All levels of the thorax responded similarly. We suggest that although thoracic multifidus and longissimus function similarly to control sagittal plane perturbations, these muscles are differentially active with rotational forces on the trunk.     

Bilateral impairments of shoulder abduction in chronic hemiparesis: Electromyographic patterns and isokinetic muscle performance

ObjectiveTo analyze electromyographic (EMG) patterns and isokinetic muscle performance of shoulder abduction movement in individuals who sustained a cerebrovascular accident (CVA).DesignTwenty-two individuals who sustained a CVA and 22 healthy subjects volunteered for EMG activity and isokinetic shoulder abduction assessments. EMG onset time, root mean square (RMS) for upper trapezius and deltoid muscles, as well as the isokinetic variables of peak torque, total work, average power and acceleration time were compared between limbs and groups.ResultsThe paretic side showed a different onset activation pattern in shoulder abduction, along with a lower RMS for both muscles (21.8 ± 13.4% of the maximal voluntary isometric contraction (MVIC) for the deltoid and 25.9 ± 15.3% MVIC for the upper trapezius, about 50% lower than the control group). The non-paretic side showed a delay in both muscles activation and a lower RMS for the deltoid (32.2 ± 13.7% MVIC, about 25% lower than the control group). Both sides of the group of individuals who sustained a CVA presented a significantly lower isokinetic performance compared to the control group (paretic side ～60% lower; non-paretic side ～35% lower).ConclusionsShoulder abduction muscle performance is impaired in both paretic and non-paretic limbs of individuals who sustained a CVA.     

Alternating stimulation of synergistic muscles during functional electrical stimulation cycling improves endurance in persons with spinal cord injury

Therapeutic effects of functional electrical stimulation (FES) cycling for persons with spinal cord injury (SCI) are limited by high rates of muscular fatigue. FES-cycling performance limits and surface mechanomyography (MMG) of 12 persons with SCI were compared under two different stimulation protocols of the quadriceps muscles. One strategy used the standard “co-activation” protocol from the manufacturer of the FES cycle which involved intermittent simultaneous activation of the entire quadriceps muscle group for 400 ms. The other strategy was an “alternation” stimulation protocol which involved alternately stimulating the rectus femoris (RF) muscle for 100 ms and the vastus medialis (VM) and vastus lateralis (VL) muscles for 100 ms, with two sets with a 400 ms burst. Thus, during the alternation protocol, each of the muscle groups rested for two 100 ms “off” periods in each 400 ms burst. There was no difference in average cycling cadence (28 RPM) between the two protocols. The alternation stimulation protocol produced longer ride times and longer virtual distances traveled and used lower stimulation intensity levels with no differences in average MMG amplitudes compared to the co-activation protocol. These results demonstrate that FES-cycling performance can be enhanced by a synergistic muscle alternation stimulation strategy.     

Reliability and minimal detectable change in scapulothoracic neuromuscular activity

Alterations in scapular muscle activity, including excess activation of the upper trapezius (UT) and onset latencies of the lower trapezius (LT) and serratus anterior (SA) muscles, are associated with abnormal scapular motion and shoulder impingement. Limited information exists on the reliability of neuromuscular activity to demonstrate the efficacy of interventions. The purpose of this study was to characterize the reproducibility of scapular muscle activity (mean activity, relative onset timing) over time and establish the minimal detectable change (MDC). Surface electromyography (sEMG) of the UT, LT, SA and anterior deltoid (AD) muscles in 16 adults were captured during an overhead lifting task in two sessions, one-week apart. sEMG data were also normalized to maximum isometric contraction and the relative onset and mean muscle activity during concentric and eccentric phases of the scapular muscles were calculated. Additionally, reliability of the absolute sEMG data during the lifting task and MVIC was evaluated. Both intrasession and intersession reliability of normalized and absolute mean scapular muscle activity, assessed with intraclass correlation coefficients (ICC), ranged from 0.62 to 0.99; MDC values were between 1.3% and 11.7% MVIC and 24 to 135 mV absolute sEMG. Reliability of sEMG during MVIC was ICC = 0.82–0.99, with the exception of intersession upper trapezius reliability (ICC = 0.36). Within session reliability of muscle onset times was ICC = 0.88–0.97, but between session reliability was lower with ICC = 0.43–0.73; MDC were between 39 and 237 ms. Small changes in scapular neuromuscular mean activity (>11.7% MVIC) can be interpreted as meaningful change, while change in muscle onset timing in light of specific processing parameters used in this study is more variable.     

Intra-session and inter-day reliability of forearm surface EMG during varying hand grip forces

Surface electromyography (EMG) is widely used to evaluate forearm muscle function and predict hand grip forces; however, there is a lack of literature on its intra-session and inter-day reliability. The aim of this study was to determine reliability of surface EMG of finger and wrist flexor muscles across varying grip forces. Surface EMG was measured from six forearm flexor muscles of 23 healthy adults. Eleven of these subjects undertook inter-day test–retest. Six repetitions of five randomized isometric grip forces between 0% and 80% of maximum force (MVC) were recorded and normalized to MVC. Intra- and inter-day reliability were calculated through the intraclass correlation coefficient (ICC) and standard error of measurement (SEM).Normalized EMG produced excellent intra-session ICC of 0.90 when repeated measurements were averaged. Intra-session SEM was low at low grip forces, however, corresponding normalized SEM was high (23–45%) due to the small magnitude of EMG signals. This may limit the ability to evaluate finer forearm muscle function and hand grip forces in daily tasks. Combining EMG of functionally related muscles improved intra-session SEM, improving within-subject reliability without taking multiple measurements. Removing and replacing electrodes inter-day produced poor ICC (ICC < 0.50) but did not substantially affect SEM.     

Kinematics,kinetics and muscle activation patterns of the upper extremity during simulated forward falls

The purpose of this study was to explore the effects of fall type and fall height on the kinematics, kinetics, and muscle activation of the upper extremity during simulated forward falls using a novel fall simulation method.Twenty participants were released in a prone position from a Propelled Upper Limb Fall ARrest Impact System. Impacts occurred to the hands from two fall heights (0.05 m and 0.10 m) and three fall types (straight-arm, bent-arm, self-selected). Muscle activation from six muscles (biceps brachii, brachioradialis, triceps brachii, anconeus, flexor carpi radialis and extensor carpi radialis) was collected and upper extremity joint kinematics were calculated.Peak Fx (medio-lateral), as well as Fx and Fz (inferior–superior) load rate increased between the 0.05 m and 0.10 m heights. With respect to fall type, the straight-arm falls resulted in significantly greater Fy (anterior–posterior) impulse and Fy and Fz load rates. The change in elbow flexion angle was greater during the self-selected and bent-arm falls compared to the straight-arm falls; a pattern also seen in the wrist flexion/extension angles. All muscles experienced peak % MVIC prior to the time of the peak force.The results of this study suggest that, to some extent, individuals are capable of selecting an upper extremity posture that allows them to minimize the effects of an impact and it has confirmed the presence of a preparatory muscle activation response.     

Alternative methods of normalising EMG during cycling

We evaluated possible methods of normalisation for EMG measured during cycling. The MVC method, Sprint method and 70% Peak Power Output Method were investigated and their repeatability, reliability and sensitivity to change in workload were compared.Thirteen cyclists performed the same experimental protocol on three separate occasions. Each day, subjects firstly performed MVCs, followed by a 10 s maximal sprint on a cycle ergometer. Subjects then performed a Peak Power Output (PPO) test until exhaustion. After which they cycled at 70% of PPO for 5 min at 90 rpm. Results indicated that normalising EMG data to 70% PPO is more repeatable, the intra-class correlation (ICC) of 70% PPO (0.87) was significantly higher than for MVC (0.66) (p = 0.03) and 10 s sprint (0.65) (p = 0.04). The 70% PPO method also demonstrated the least intra-subject variability for five out of the six muscles. The Sprint and 70% PPO method highlighted greater sensitivity to changes in muscle activity than the MVC method. The MVC method showed the highest intra-subject variability for most muscles except VM.The data suggests that normalising EMG to dynamic methods is the most appropriate for examining muscle activity during cycling over different days and for once-off measurements.     

The recruitment order of scapular muscles depends on the characteristics of the postural task

Previous studies show that the scapular muscle recruitment order could possibly change according to the characteristics of the postural task. We aimed to compare the activation latencies of serratus anterior (SA), upper, middle, and lower trapezius (UT, MT and LT, respectively) between an unpredictable perturbation (sudden arm destabilization) and a predictable task (voluntary arm raise) and, to determine the differences in the muscle recruitment order in each task. The electromyographic signals of 23 participants were recorded while the tasks were performed. All scapular muscles showed earlier onset latency in the voluntary arm raise than in the sudden arm destabilization. No significant differences were observed in the muscle recruitment order for the sudden arm destabilization (p > 0.05). Conversely, for voluntary arm raise the MT, LT SA and anterior deltoid (AD) were activated significantly earlier than the UT (p < 0.001). Scapular muscles present a specific recruitment order during a predictable task: SA was activated prior to the AD and the UT after the AD, in a recruitment order of SA, AD, UT, MT, and LT. While in an unpredictable motor task, all muscles were activated after the destabilization without a specific recruitment order, but rather a simultaneous activation.     

Influence of gravity compensation on muscle activity during reach and retrieval in healthy elderly

IntroductionArm support like gravity compensation may improve arm movements during stroke rehabilitation. It is unknown how gravity compensation affects muscle activation patterns during reach and retrieval movements. Since muscle activity during reach is represented by a component varying with movement velocity and a component supposedly counteracting gravity, we hypothesized that gravity compensation decreases the amplitude of muscle activity, but does not affect the pattern. To examine this, we compared muscle activity during well defined movements with and without gravity compensation in healthy elderly.MethodsTen subjects performed reach and retrieval movements with and without gravity compensation. Muscle activity of biceps, triceps, anterior, middle and posterior parts of deltoid and upper trapezius was compared between the two conditions.ResultsThe level of muscle activity was lower with gravity compensation in all muscles, reaching significance in biceps, anterior deltoid and trapezius (p ? 0.026). The muscle activation pattern did not differ between movements with and without gravity compensation (p ? 0.662).DiscussionGravity compensation only influenced the level of muscle activity but not the muscle activation pattern in terms of timing. Future studies should examine if the influence of gravity compensation is comparable for stroke patients. This may stimulate early and intensive training during rehabilitation.     

Electromyographic analysis during pull,forward punch,elevation and overhead throw after conservative treatment or capsular shift at patient with multidirectional shoulder joint instability

PurposeThe aim of this study was to compare the muscle activity of patients with multidirectional instability treated in a conservative or complex manner (capsular shift with postoperative rehabilitation) and the muscle activity of stable shoulder joints before and after treatment during pull, push, and elevation of upper extremities and during overhead throw.ScopeThe study was carried out on 34 patients with multidirectional shoulder instability treated non-operatively, on 31 patients with multidirectional shoulder instability treated operatively, and on 50 healthy subjects. Signals were recorded by surface EMG from eight different muscles. The mean and standard deviation of the maximum amplitude of normalized voluntary electrical activity for the different movement types and time broadness values during overhead throw were determined for each muscle in all groups and compared with each other.ConclusionThe centralization of the glenohumeral joint and the reduction of instability is attempted to be ensured by the organism through increasing the role of rotator cuff muscles (p = 0.009) and decreasing the role of the deltoid, biceps brachii, and pectoralis maior muscles (p = 0.007). At patients after short-term and long-term conservative treatment, the maximum amplitude of normalized voluntary electrical activity of stabilizer muscles is significantly higher (p = 0.006), and that of accelerator muscles is significantly lower (p = 0.005) and the time broadness is significantly longer (p = 0.01) than that of the control group. At patients after complex treatment (open capsular shift with postoperative conservative rehabilitation) the characteristic of the muscle pattern is similar (p = 0.19) to the control group.The complex treatment resolves the labral ligamentous abnormalities by operative treatment and restores the impaired muscular control by postoperative rehabilitation, whereas the conservative treatment restores only the muscular control.     

Neuromuscular fatigue following high versus low-intensity eccentric exercise of biceps brachii muscle

PurposeThis study investigated neuromuscular fatigue following high versus low-intensity eccentric exercise corresponding to the same amount of work.MethodsTen volunteers performed two eccentric exercises of the elbow flexors: a high-intensity versus a low-intensity exercise. Maximal voluntary contraction torque and surface electromyography of the biceps brachii muscle were recorded before, immediately and 48 h after exercises. Maximal voluntary activation level, neural (M-wave) and contractile (muscular twitch) properties of the biceps brachii muscle were analysed using electrical stimulation techniques.ResultsMaximal voluntary contraction torque was significantly (P < 0.01) reduced immediately and 48 h after exercise but the reduction was not different between the two conditions. Electromyography associated with maximal voluntary contraction significantly decreased (P < 0.05) immediately and 48 h after exercise for both conditions while maximal voluntary activation level was only significantly reduced immediately after the high-intensity exercise. Peak twitch alterations were observed immediately and 48 h after exercise for both conditions while M-wave did not change.ConclusionHigh and low-intensity eccentric exercises with the same amount of work induced the same reduction in maximal strength capacities of the biceps brachii muscles. The magnitude of peripheral and central fatigue was very similar in both conditions.     

Does supraspinatus initiate shoulder abduction?

PurposeIt 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.MethodsElectromyographic 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. Initial activation timing of a muscle was determined as the time at which the average activation (over a 25 ms moving window) was greater than three standard deviations above baseline measures.ResultsAll muscles tested were activated prior to movement onset. Subscapularis was activated significantly later than supraspinatus, infraspinatus, deltoid and upper trapezius, while supraspinatus, infraspinatus, upper trapezius, lower trapezius, serratus anterior and deltoid all had similar initial activation times. The effects of load or plane of movement were not significant.ConclusionsSupraspinatus is recruited prior to movement of the humerus into abduction but not earlier than many other shoulder muscles, including infraspinatus, deltoid and axioscapular muscles. The common statement that supraspinatus initiates abduction is therefore, misleading.     

Shear wave elastography of the supraspinatus muscle and tendon: Repeatability and preliminary findings

Shear wave elastography (SWE) is a promising tool for estimating musculoskeletal tissue properties, but few studies have rigorously assessed its repeatability and sources of error. The objectives of this study were to assess: (1) the extent to which probe positioning error and human user error influence measurement accuracy, (2) intra-user, inter-user, and day-to-day repeatability, and (3) the extent to which active and passive conditions affect shear wave speed (SWS) repeatability. Probe positioning and human usage errors were assessed by acquiring SWE images from custom ultrasound phantoms. Intra- and inter-user repeatability were assessed by two users acquiring five trials of supraspinatus muscle and tendon SWE images from ten human subjects. To assess day-to-day repeatability, five of the subjects were tested a second time, approximately 24 h later. Imaging of the phantoms indicated high inter-user repeatability, with intraclass correlation coefficient (ICC) values of 0.68–0.85, and RMS errors of no more than 4.1%. SWE imaging of the supraspinatus muscle and tendon had high repeatability, with intra- and inter-user ICC values of greater than 0.87 and 0.73, respectively. Day-to-day repeatability demonstrated ICC values greater than 0.33 for passive muscle, 0.48 for passive tendon, 0.65 for active muscle, and 0.94 for active tendon. This study indicates the technique has good to very good intra- and inter-user repeatability, and day-to-day repeatability is appreciably higher when SWE images are acquired under a low level of muscle activation. The findings from this study establish the feasibility and repeatability of SWE for acquiring data longitudinally in human subjects.     

Quantifying ‘normal’ shoulder muscle activity during abduction

The purpose of this experiment was to obtain electromyographic (EMG) activity from a sample of healthy shoulders to allow a reference database to be developed and used for comparison with pathological shoulders. Temporal and intensity shoulder muscle activation characteristics during a coronal plane abduction/adduction movement were evaluated in the dominant healthy shoulder of 24 subjects. Surface and intramuscular fine wire electrodes recorded EMG activity from 15 shoulder muscles (deltoid × 3, trapezius × 3, subscapularis × 2, latissimus dorsi, pectoralis major, pectoralis minor, supraspinatus, infraspinatus, serratus anterior and rhomboids) at 2000 Hz for 10 s whilst each subject performed 10 dynamic coronal plane abduction/adduction movements from 0° to 166° to 0° with a light dumbbell. Results revealed that supraspinatus (?.102 s before movement onset) initiated the movement with middle trapezius (?.019 s) and middle deltoid (?.014 s) also activated before the movement onset. Similar patterns were also found in the time of peak amplitude and %MVC with a pattern emerging where the prime movers (supraspinatus and middle deltoid) were among the first to reach peak amplitude or display the highest %MVC values. In conclusion, the most reproducible patterns of activation arose from the more prime mover muscle sites in all EMG variables analysed and although variability was present, there emerged ‘invariant characteristics’ that were considered ‘normal’ for this group of non pathological shoulders. The authors believe that the methodology and certain parts of the analysis in this study can be duplicated and used by future researchers who require a reference database of muscle activity for use as a control group in comparisons to their respective pathological shoulder group.     

Effects of neck flexion on contingent negative variation and anticipatory postural control during arm movement while standing

We investigated the effects of neck flexion on contingent negative variation (CNV) and anticipatory postural control using an arm flexion task in standing. CNV was adopted to evaluate the state of activation of brain areas related to anticipatory postural control. Subjects were required to flex the arms in response to a sound stimulus preceded by a warning sound stimulus. Two different intervals (2.0 and 3.5 s) between these two stimuli were used in neck position in quiet standing (neck resting) and neck position at 80% angle of maximal neck flexion. The mean amplitude of CNV 100-ms before the response stimulus, recorded from a Cz electrode, was calculated. Onset timing of activation of the postural muscles (lumbar paraspinal, biceps femoris and gastrocnemius) with respect to the anterior deltoid was analyzed. Reaction time at the anterior deltoid was significantly shorter in the 2.0 s period than in the 3.5 s period, and in the neck flexion than in the neck resting in both periods. In the 2.0 s, but not in the 3.5 s period, neck flexion resulted in an increased CNV amplitude and an increased duration of preceding activation of the postural muscles, and the correlation between these increases was significant.