***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Aim . This study investigates consequences of chronic neck pain on muscle function and the rehabilitating effects of contrasting interventions . Methods . Women with trapezius myalgia ( MYA , n = 42 ) and healthy controls ( CON , n = 20 ) participated in a case-control study . Subsequently MYA were r and omized to 10 weeks of specific strength training ( SST , n = 18 ) , general fitness training ( GFT , n = 16 ) , or a reference group without physical training ( REF , n = 8) . Participants performed tests of 100 consecutive cycles of 2 s isometric maximal voluntary contractions ( MVC ) of shoulder elevation followed by 2 s relaxation at baseline and 10-week follow-up . Results . In the case-control study , peak force , rate of force development , and rate of force relaxation as well as EMG amplitude were lower in MYA than CON throughout all 100 MVC . Muscle fiber capillarization was not significantly different between MYA and CON . In the intervention study , SST improved all force parameters significantly more than the two other groups , to levels comparable to that of CON . This was seen along with muscle fiber hypertrophy and increased capillarization . Conclusion . Women with trapezius myalgia have lower strength capacity during repetitive MVC of the trapezius muscle than healthy controls . High-intensity strength training effectively improves strength capacity during repetitive MVC of the painful trapezius muscle This study aim ed at investigating whether patients with neck – shoulder complaints from different aetiologies ( work-related musculo-skeletal disorders , WMSD ; whiplash associated disorders , WAD ) show comparable muscle activation patterns , characterised by higher activation and lower relaxation levels of the trapezius muscles compared to healthy controls . Twenty healthy controls , 21 WMSD and 20 WAD patients with non-acute neck-shoulder pain were recruited for this cross-sectional study .  Surface electromyography ( sEMG ) recordings were performed at the upper trapezius muscles during reference contractions , st and ardised computer tasks ( typing and unilateral stress task ) , and rest measurements . sEMG was continuously recorded during these measurements .  Outcome measures were root mean square ( RMS ) to study muscle activity , and relative rest time ( RRT ) to study muscle relaxation . Statistical analysis comprised the bootstrap technique and Kruskall – Wallis tests . Results showed no clear evidence for abnormal muscle activation patterns in WMSD and WAD patients compared to healthy controls . However , a tendency was observed for higher RMS levels during the reference contractions and computer tasks in both patient groups compared to healthy controls , and lower RRT levels at the non-dominant side during stress . Both patient groups also showed larger variability in RMS and RRT values . This variability has more often been reported in literature and may suggest the existence of subgroups of pain patients with corresponding different muscle activation patterns not related to aetiology . Future research may focus on identifying these subgroups of patients with neck-shoulder pain The aim of this investigation was to study female workers active in the labour market for differences between those with trapezius myalgia ( MYA ) and without ( CON ) during repetitive pegboard ( PEG ) and stress ( STR ) tasks regarding ( 1 ) relative muscle load , ( 2 ) trapezius muscle blood flow , ( 3 ) metabolite accumulation , ( 4 ) oxygenation , and ( 5 ) pain development . Among 812 female employees ( age 30–60 years ) at 7 companies with high prevalence of neck/shoulder complaints , clinical examination identified 43 MYA and 19 CON .  At rest , during PEG , and STR the trapezius muscle was measured using ( 1 ) EMG and MMG , ( 2 ) microdialysis , and ( 3 ) NIRS . Further , subjective pain ratings were scored ( VAS ) . EMGrms in % MVE ( Maximal Voluntary EMG-activity ) , was significantly higher among MYA than CON during PEG ( 11.74 ± 9.09 vs. 7.42 ± 5.56%MVE ) and STR ( 5.47 ± 5.00 vs. 3.28 ± 1.94%MVE ) . MANOVA showed a group and time effect regarding data from the microdialysis : for MYA versus CON group differences demonstrated lower muscle blood flow and higher lactate and pyruvate concentrations . Potassium and glucose only showed time effects . NIRS showed similar initial decreases in oxygenation with PEG in both groups , but only in CON a significant increase back to baseline during PEG . VAS score at rest was highest among MYA and increased during PEG , but not for CON . The results showed significant differences between CON and MYA regarding muscle metabolism at rest and with PEG and STR . Higher relative muscle load during PEG and STR , insufficient muscle blood flow and oxygenation may account for the higher lactate , pyruvate and pain responses among MYA versus CON Abstract Objectives . The purpose of this prospect i ve laboratory study was to follow newly employed workers in the fish or poultry industry for 6 months and investigate possible changes in sensory manifestations and motor performance during low load , repetitive work simulation . It was investigated whether the changes were an effect of employment duration and of development of neck – shoulder complaints . Methods . Twelve newly employed female filleting employees without any sign of neck – shoulder tenderness/pain at the time of employment of 0 months took part in two laboratory recording sessions planned within 1 month of employment and after 6 months of employment at the plant . After 6 months , six workers out of 12 had developed pain and /or tenderness in the neck – shoulder region . The recording sessions evaluated sensory-motor aspects by measuring pressure pain threshold , work-task timing , cutting forces , surface electromyographic activity of four shoulder muscles , displacement of the centre of pressure , and 3D movements of the arm and trunk during simulation of low load , repetitive filleting . Results . Effects due to the duration of employment were observed in both groups , i.e. decreased sensibility to pressure , decrease in the duration of the work cycle , increased arm starting position with respect to the upright position , and decreased range of motion of the arm and trunk ( P<0.05 ) after 6 months . Among the workers with neck – shoulder complaints , increased sensibility to pressure , lower force level , higher electromyographic activity , decreased amplitude of arm movement , and increased trunk posture and movement amplitude ( P<0.05 ) were observed , compared with workers without complaints . Conclusions . Differences in terms of sensory manifestations and motor control strategy were seen after 6 months of employment with or without neck – shoulder complaints . In general , changes in sensory manifestations and motor control strategy after 6 months work were most likely of importance , as they underlined a learning process as employment duration increased . Moreover , the present sensory – motor changes observed among workers with neck – shoulder complaints highlighted the potential physical risk factors associated with low load , repetitive work Abstract Little is known about the mechanisms leading to chronic neck-shoulder musculoskeletal disorders  ( MSD ) . The aim of the present study was to investigate and compare motor function during controlled , low load , repetitive work together with chronic or acute experimental neck-shoulder pain . The clinical study was performed on workers with ( n = 12 ) and without ( n = 6 ) chronic neck-shoulder pain . In the experimental study , experimental muscle pain was induced in healthy subjects by intra-muscular injection of hypertonic saline into the trapezius muscle ( n = 10 ) . The assessed parameters related to motor performance were : work task event duration , cutting forces , surface electromyogram ( EMG ) activity in four shoulder muscles , displacement of the centre of pressure , and arm and trunk 3D movements . For controlled cutting force levels , chronic and acute experimental pain provoked a series of changes : a decreased working rhythm and a protective reorganisation of muscle synergy ( experimental study ) , higher EMG frequency contents which may indicate altered motor unit recruitment , and greater postural activity and a tendency towards increased arm and trunk movements . These pain-related changes can play a role in the development of MSD . The present clinical and experimental study demonstrated similar interactions between motor co-ordination and neck-shoulder pain in occupational setting s. We therefore suggest that this experimental model can be used to study mechanisms related to MSD . Information on such modulatory processes may help in the design of new strategies aim ed at reducing the development of MSD The aim of the present study was to investigate reactions in trapezius muscle blood flow ( MBF ) , muscle activity , heart rate variability ( HRV ) and systemic blood pressure ( BP ) to autonomic tests in subjects with chronic neck – shoulder pain and healthy controls . Changes in muscle activity and blood flow due to stress and unfavourable muscle loads are known underlying factors of work-related muscle pain . Aberration of the autonomic nervous system ( ANS ) is considered a possible mechanism . In the present study , participants ( n = 23 Pain , n = 22 Control ) performed autonomic tests which included a resting condition , static h and grip test ( HGT ) at 30 % of maximal voluntary contraction , a cold pressor test ( CPT ) and a deep breathing test ( DBT ) . HRV was analysed in time and frequency domains . MBF and muscle activity were recorded from the upper trapezius muscles using photoplethysmography and electromyography ( EMG ) . The pain group showed reduced low frequency-HRV ( LF ) and SDNN during rest , as well as a blunted BP response and increased LF-HRV during HGT ( ∆systolic 22 mm Hg ; ∆LF(nu ) 27 % ) compared with controls ( ∆systolic 27 ; ∆LF(nu ) 6 % ) . Locally , the pain group had attenuated trapezius MBF in response to HGT ( Pain 122 % Control 140 % ) with elevated trapezius EMG following HGT and during CPT . In conclusion , only HGT showed differences between groups in systemic BP and HRV and alterations in local trapezius MBF and EMG in the pain group . Findings support the hypothesis of ANS involvement at systemic and local levels in chronic neck – shoulder pain The present study investigated the effect of chronic neck muscle pain ( defined as trapezius myalgia ) on neck/shoulder muscle function during concentric , eccentric and static contraction . Forty-two female office workers with trapezius myalgia ( MYA ) and 20 healthy matched controls ( CON ) participated . Isokinetic ( -60 , 60 and 180 degrees s(-1 ) ) and static maximal voluntary shoulder abductions were performed in a Biodex dynamometer , and electromyography ( EMG ) obtained in the trapezius and deltoideus muscles . Muscle thickness in the trapezius was measured with ultrasound .  Pain and perceived exertion were registered before and after the dynamometer test . The main findings were that shoulder abduction torque ( at -60 and 60 degrees s(-1 ) ) and trapezius EMG amplitude ( at -60 , 0 and 60 degrees s(-1 ) ) were significantly lower in MYA compared with CON ( p<0.001 - 0.05 ) . Deltoideus EMG and trapezius muscle thickness were not significantly different between the groups . While perceived exertion increased in both groups in response to the test ( p<0.0001 ) , pain increased in MYA only ( p<0.0001 ) . In conclusion , having trapezius myalgia was associated with decreased strength capacity and lowered activity of the painful trapezius muscle . The most consistent differences-in terms of both torque and EMG-were found during slow concentric and eccentric contractions . Activity of the synergistic pain free deltoideus muscle was not significantly lower , indicating specific inhibitory feedback of the painful trapezius muscle only . Parallel increase in pain and perceived exertion among MYA were observed in response to the maximal contractions , emphasizing that heavy physical exertion provokes pain increase only in conditions of myalgia Abstract This cross-sectional study aim ed at investigating the influence of occupational exposure to static and highly repetitive work involving the neck and shoulder muscles , myalgia of and tender point in the trapezius muscle on biomechanical output , and electromyogram ( EMG ) variables ( mean frequency MNF , signal amplitude and ability to relax ) during maximal forward flexions of the shoulder muscles . Groups of 25 cleaners suffering from chronic myalgia of the trapezius muscle , 25 cleaners free from myalgia of the trapezius muscle and 21 teachers performed 150 forward flexions using an isokinetic dynamometer .  Perception of fatigue was reported and surface EMG was recorded from four muscles during the endurance test . The cleaners were stronger than the teachers . Myalgia was associated with lower levels of endurance and a high degree of perceived fatigue . The ability to relax the trapezius muscle decreased with age and was even lower in cleaners with and without myalgia . Higher MNF of the deltoid muscle but not of the trapezius muscle was found in the group suffering from myalgia compared to the groups free from myalgia . This cross-sectional study indicated that myalgia of the trapezius muscle did not influence the strength but did influence the endurance of the forward flexor muscles of cleaners . The observed decrease in the ability to relax the trapezius muscle in cleaners compared to healthy teachers might be indicative of a future insufficiency in the muscle . Prospect i ve studies are needed to define the significance of the results presented here The aim of this prospect i ve study was to detect a possible development of trapezius myalgia  likely to be work-related in initially healthy female packers . Symptoms were recorded on a five-step intensity scale in a daily diary and in an interview at ten-week intervals . All of the subjects were interviewed concerning assumed risk factors during work and leisure time , and a clinical examination was performed . Within their first year of employment , 17 of 30 subjects developed work-related trapezius myalgia of sufficient intensity to be classified as patients . The median time before a clinical ly confirmed patient status was 23 ( range 6 - 51 ) weeks . The symptoms showed a fluctuating pattern , decreasing on the weekends and during some holidays . In conclusion , likely work-related trapezius myalgia of 
    Output:
    
During rest and activities below shoulder height , no clear differences in mean Upper Trapezius ( = UT ) EMG activity exist between patients with idiopathic neck pain and a healthy control group .
During overhead activities , no conclusion for scapular EMG amplitude can be drawn as a large variation of results were reported .
Adaptation strategies during overhead tasks are not the same between studies .