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Research ArticleHigh-Intensity Strength Training Improves Function ofChronically Painful Muscles: Case-Control and RCT Studies

Lars L. Andersen,1 Christoffer H. Andersen,1 Jrgen H. Skotte,1 Charlotte Suetta,2

Karen Sgaard,3 Bengt Saltin,4 and Gisela Sjgaard3

National Research Centre or the Working Environment, Lers Parkalle , Copenhagen, Denmark Section o Clinical Physiology and Nuclear Medicine, Department o Diagnostics, Glostrup Hospital, University o Copenhagen,

Glostrup, Denmark Institute o Sport Science and Clinical Biomechanics, University o Southern Denmark, Campusvej , Odense M, Denmark Copenhagen Muscle Research Centre, University o Copenhagen, Copenhagen, Denmark

Correspondence should be addressed to Lars L. Andersen; [email protected]

Received November ; Revised January ; Accepted January ; Published February

Academic Editor: David G. Behm

Copyright Lars L. Andersen et al. Tis is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Aim. Tis study investigates consequences o chronic neck pain on muscle unction and the rehabilitating effects o contrasting

interventions.Methods. Women with trapezius myalgia (MYA, = 42) and healthy controls (CON, = 20) participated in acase-control study. Subsequently MYA were randomized to weeks o specic strength training (SS, = 18), general tnesstraining (GF, = 16), or a reerence group without physical training (REF, = 8). Participants perormed tests o consecutivecycles o s isometric maximal voluntary contractions (MVC) o shoulder elevation ollowed by s relaxation at baseline and -week ollow-up. Results. In the case-control study, peak orce, rate o orce development, and rate o orce relaxation as well asEMG amplitude were lower in MYA than CON throughout all MVC. Muscle ber capillarization was not signicantly differentbetween MYA andCON. In the intervention study, SSimproved all orceparameterssignicantly more than the twoother groups,to levels comparable to that o CON. Tis was seen along with muscle ber hypertrophy and increased capillarization.Conclusion.Women with trapezius myalgia have lower strength capacity during repetitive MVC o the trapezius muscle than healthy controls.High-intensity strength training effectively improves strength capacity during repetitive MVC o the painul trapezius muscle.

1. Introduction

Neck/shoulder pain is a requent condition in the workingpopulation [] and pain, tightness, and tenderness o theupper trapezius muscletrapezius myalgiaare the mostcommon type o chronic neck/shoulder pain [, ]. Ina studyamong elderly emale computer workers with neck/shoulderpain % were clinically diagnosed with trapezius myalgia[]. In another study among office workers with requentneck/shoulder pain three out o our experienced tendernessby palpation o the upper trapezius muscle []. rapeziusmyalgia is associated with pathophysiological changes, suchas increased occurrence o ragged red bers, moth eatenbers, and cytochrome oxidase negative type I bers [,].Using the microdialysis technique, increased concentration

o the algesic substance serotonin during work, stress, andrest has also been shown []. Recent studies combining

muscle biopsies and microdialysis with gel electrophoresisand mass spectrometry identied several proteins involvedin inammatory processes in myalgic trapezius musclescompared with healthy controls [, ]. Women with trapeziusmyalgia also have reduced capillarization o type I musclebers [], increased proportion o poorly capillarized typeI megabers [], impaired regulation o microcirculationlocally in the painul trapezius muscle [], and reducedcapacity o carbohydrate oxidation []. Tese actors lead toelevated anaerobic metabolism and atigue during repetitivework [,].

In addition, trapezius myalgia negatively impacts muscleunctioning. Compared with healthy controls, women with

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014, Article ID 187324, 11 pageshttp://dx.doi.org/10.1155/2014/187324
http://dx.doi.org/10.1155/2014/187324http://dx.doi.org/10.1155/2014/187324

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BioMed Research International

trapezius myalgia show decreased maximal voluntary orce,rapid orce, motor control, endurance, and neck exibility[]. rapezius myalgia has also been associated with aninability to properly relax the muscle between repeated con-tractions [], which may aggravate development o atigue.Tus, prevention as well as rehabilitation o neck/shoulder

pain has ocused on improving different components ophysical unction such as the ability to relax the musclesusing bioeedback training [, ], muscle coordinationtraining [], muscle strength using high-intensity resistancetraining [], endurance using repeated low-intensitycontractions [, ], tness training [], and exibilityusing stretching []. Among these training modalitiesstrength training appears particularly effective in reducingpain and increasing muscle strength in trapezius myalgia[]. However, transer effects o strength training to improvework capacity o the painul trapezius muscle have only beenscarcelyinvestigated []. Tisis a potentialimportant aspect,as daily job tasks require repetitive muscle contractionsinducing a certain level o atigue, or example, repetitivearm movements during assembly line work or keyboardtyping. Studying the effect o strength training on strength-endurance during repetitive and atiguing contractions there-ore seems pertinent.

A contrasting approach to specic strength training couldbe to train large muscles distant rom the painul site,or example, by general tness training perormed as legcycling. Previous research in other populations has indicatedphysiological adaptations in sites distant rom the trainedmuscles [,]. Increased blood ow to the orearms []and nonworking limb [] has also been shown in responseto leg exercise. Based on these studies, general tness trainingperormed as leg cycling may also improve endurance o thepainul trapezius muscle.

Te aims o the present study were () in a case-control design to compare muscle unction during atiguingmuscle contractions in women with trapezius myalgia andhealthy controls and () in a randomized controlled trialto investigate the effect o contrasting types o physicalrehabilitation in women with trapezius myalgia on muscleunction during atiguing muscle contractions. Addition-ally, analyses o electromyographic recordings and musclebiopsies were included to investigate neural and muscularadaptations. We hypothesized that specic strength trainingandgeneral tness training would be superior to the reerenceintervention with regard to improved muscle unction.

2. Methods

.. Study Design and Participants. Te study design, recruit-ment o participants, randomization o women, and mainresults have beendescribed in detail previously [, ].Inthepresent case-control study, women with trapezius myalgia(MYA, mean SD: 448 yrs, 1656 cm, 7215 kg, and dayswith neck pain during previous year 219 19 days) and women comparable with regard to job-type, age, weight, andheight but without neck muscle complications (CON, meanSD:45 9 yrs,167 6 cm,70 11 kg, and days with neckpain during previous year5 6days) participated. Exclusion

criteria were serious conditions such as previous trauma,lie threatening diseases, whiplash injury, cardiovasculardiseases, or arthritis in the neck and shoulder. All partici-pants were recruited rom workplaces with monotonous andrepetitive work tasks, mostly office- and computer-work. Allemales in MYA were clinically diagnosed with trapezius

myalgia, where the main criteria or a positive diagnosiswere () chronic pain in the neck area, () tightness o theupper trapezius muscle, and () palpable tenderness o theupper trapezius muscle []. In the -week interventionstudy, the women with trapezius myalgia were randomlyallocated in balanced design accounting or similar age,BMI, and neck/shoulder trouble to three different -weekinterventions, but dropped out initially in the REF groupresulting in women in this study. Te random allocationwas concealed; that is, the researcher who determined theeligibility o the subjects was unaware which group a subjectwas to be allocated to. Unortunately, the timewise successivebalanced recruitment resulted in a somewhat smaller REFgroup, or example, due to withdrawal o participants whoinitially stated they would volunteer or the study.

All subjectswere inormed about the purposeand contento the project and gave written inormed consent to partic-ipate in the study, which conormed to the Declaration oHelsinki and was approved by the Local Ethical Committee(KF -/). Te study was registered in the InternationalStandard Randomised Controlled rial Number Register(ISRCN).

.. Measurements and Data Acquisition. Muscle endurancewas measured during consecutive isometric shoulder ele-

vations using a custom-built setup with a steel rame, achair, and attached orce dynamometers (Figure ). Teparticipant was sitting upright in the height-adjustable chair,and two Boors dynamometers were placed bilaterally cmmedial to the lateral edge o the acromion with the directiono orce being upward []. Prior to the endurance test,the participant perormed maximal voluntary isometriccontractions (MVC) to determine peak orce. Te participantwas then instructed to perorm consecutive cycles o -second MVC ollowed by -second relaxation. Figure showsthe square wave on the computer screen providing visualeedback instructing the participant when to contract andwhen to relax, with the target value o the square wave setto the peak orce determined prior to the endurance test.Te participant was instructed to contract as hard and ast as

possible when the signal o the square wave wentrom zero tomax andto relax immediately andcompletely when the signalwent rom max to zero. Te contractions were completedin minutes and seconds.

Electromyography (EMG) signals were recorded syn-chronously rom the upper trapezius muscle with a bipolarsurace EMG conguration (Neuroline -K, MedicotestA/S, lstykke, Denmark) and an interelectrode distanceo cm []. Te electrodes were positioned according toSENIAM guidelines []. Te skin was abraded prior toapplying the electrodes to ensure an impedance o less than k (typically the impedance was - k). I the impedancewas higher than k the procedure was repeated until

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(a) (b)

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F: Illustration o experimental setup, the square wave signal (green tracing), and a typical orce signal (white tracing) in the beginning(lef) and during the end (right) o the consecutive contractions.

impedance was less than k. Te EMG electrodes wereconnected directly to small preampliers located near therecording site. Te raw analogue EMG signals were ledthrough shielded wires to instrumental differentiation ampli-ers, with a bandwidth o Hz and a common moderejection ratio better than dB. Force and EMG signalswere sampled synchronously at Hz using a -bit A/Dconverter (DAQ Card-Al-XE-, National Instruments,USA) and stored on a laptop or urther analysis.

.. Data Analysis. Data were analyzed only or the signalsrom the most painul shoulder. In case o similar pain

intensities in both shoulders the dominant side was used orthe analyses. During lateroffline analyses,the orcesignalwaslow-pass ltered at Hz, andthen three parameters were cal-culated or each o the MVCs: () peak orce, determinedas the maximal orce value within each cycle, () rate o orcedevelopment (RFD) determined as the maximal positiveslope over msec o theorce signalduring thebeginningoeach MVC, and () rate o orce relaxation (RFR) determinedas the maximal negative slope over msec o the orcesignal during the end o each MVC. All RFR values weresubsequently multiplied by to ease comparison with RFD.

Likewise, the raw EMG signals were ltered using linearEMG envelopes, which consisted o () high-pass ltering at

Hz, () ull-wave rectication, and () low-pass lteringat Hz. Te ltering algorithms were based on a ourth-order zero phase lag Butterworth lter []. From the lteredEMG signal the ollowing parameter was calculated or eacho the MVCs: () peak EMG, determined as the maximal

value o the ltered signal during the top phase o the squaresignal, that is, when muscle orce is peaking, () integratedEMG during the rst 1/2 second o the top phase o thesquare signal, that is, during the very beginning o musclecontraction, and () resting EMG determined as the average

value o the ltered signal during the mid1/2second o thebottom phase o the square signal, that is, during relaxation

between contractions.Te power spectral density o the EMG signals was

calculatedas the median power requency (MPF) in epochs o ms in the midphase o each o the contractions. Tepower density spectra were estimated by Welchs averaged,modied periodogram method in which each epoch wasdivided into eight Hamming windowed sections with %overlap.

.. Muscle Biopsies. Using the needle biopsy technique,muscle biopsies were obtained ultrasound guided rom theupper trapezius muscle at the midbelly between the thcervical vertebrae and the acromion. Te tissue samples

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were mounted with issue-ek within - min, rozen inisopentane precooled with liquid nitrogen, and stored in areezer at C until processed. All biopsy samples weregivena unique identication number and blinded. ransverseserial sections ( m) o the embedded muscle biopsy werecut in a cryostat (Microm, Germany) (C) and mounted

on glass slides. Standard APase analysis was perormed aferpreincubation at pH values o ., ., and . []. Tebiopsy sections were visualized on a computer screen usinga Carl Zeiss light microscope (Zeiss Axiolab), a JVC high-resolution color digital camera (JVC, K-CEG), andan -bit Matrox Meteor Framegrabber (Matrox ElectronicSystems, Quebec, Canada). Quantitative analysis o all musclesamples or ber type percentage, ber cross-sectional area(CSA), capillaries per ber (CAF), and capillaries per berCSA (CAFA) was perormed using a digital image analysisprogram (EMA ., Scanbeam, Hadsund, Denmark). All

values are reported or types I and II bers separately.Te results on ber type percentage (case-control study),ber type area percentage (intervention study), CSA (case-control and intervention study), and CAF and CAFA (case-control study) have been reported previously [,] and arereported here only or comparison with the results rom theendurance test. Results rom the intervention study or bertype percentage, CAF, and CAFA have not been reportedpreviously and are reported here as original data.

.. Interventions. Afer thecase-control study, the womenwith trapezius myalgia were randomly allocated to threedifferent-week interventions. Te specic strength traininggroup (SS, = 18) perormed ve dumbbell exercisesspecically or the shoulder and neck muscles (shoulder

abduction, shoulder elevation, -arm row, reverse yes, andupright row) or min three times a week. Te high levelo activity o the neck and shoulders muscles using theseexercises has been documented elsewhere []. Tree othe ve exercises were perormed during each session orthree sets o each exercise using relative loadings o repetitions maximum (RM). Te strength training scheduleollowed principles o progressive overload and periodizationas recommended by the ACSM []. Te general tnesstraining group (GF, = 16) perormed leg-bicycling inan upright position with relaxed shoulders on a stationaryergometer at relative loadings o % to % o maximaloxygen uptake or min three times a week. Te loading

was estimated based on relative workload = (working heartrate resting heart rate)/(max heart rate resting heart rate),where resting heart rate was set to bpm and max heart ratewas estimated as age []. Te reerence group (REF, = 8) received inormation concerninghealthpromotion orone hour per week but were not offered any physical training.Unortunately, the timewise successive balanced recruitmentresultedin a somewhat smaller REFgroup compared with thetwo other groups, or example, due to withdrawal o partici-pants who initially stated they would volunteer or the study.

.. Statistics. In the case-control study, differences betweenMYA and CON were tested with two-way ANOVA (Proc

Mixed o SAS). Te dependent variables were peak orce,RFD, RFR, and peak EMG, respectively. Independent xedactors included in the model were group (MYA, CON),number( contractions), andgroup by numberinteraction.

In the intervention study, differences over time betweenthe three groups were tested with repeated measures two-

way ANCOVA (Proc Mixed o SAS). Te dependent variableswere the changes rom baseline to ollow-up in peak orce,RFD, RFR, and peak EMG, respectively. Independent xedactors included in the model were group (GF, SS, andREF), number ( contractions), and group by numberinteraction. Te baseline value o the dependent variablewas included as a covariate due to the numerical differences

visualized in Figure. Participant was entered in the modelas a nested random effect using the repeatedstatement.

Te alpha level was set to ., and results are reported asmeansSE in the gures and as means and % condenceintervals in the text.

Finally, when statistically signicant changes were oundwe calculated effect sizes as Cohensd(difference rom base-line to ollow-up divided by the pooled standard deviationat baseline) []. According to Cohen, effect sizes o . aresmall, . moderate and . large.

3. Results

.. Case-Control Study. Tere was a signicantgroupeffector all three orce parameters ( < 0.001). Post hoc analysesshowed that peak orce, rate o orce development, and rateo orce relaxation were lower in MYA compared with CON(Figure, lef). Tere was a signicant group effect or twoo the our EMG parameters. Post hoc analyses showed

that peak EMG and rate o EMG rise were lower in MYAcompared with CON (Figure , lef). Tere was no signicant

group effect or resting EMG (Figure , lef) or MPF (Figure ,lef). Tere was no group by number interaction; that is, theslope over the repetitions did not signicantly differbetween the two groups, although there was a borderline

group by numberinteraction or MPF ( = 0.05).Capillarization per ber as well as per ber area did not

signicantly differ between MYA and CON, neither or typeI nor type II bers (able).

.. Intervention Study. Tere was a signicantgroup effector the change rom baseline to ollow-up or all three orce

parameters ( < 0.01.). Post hoc analyses showed thatthe strength training group improved signicantly more thanthe two other groups or peak orce (SS versus GF N[% CI ], SS versus REF N [% CI ]), rateo orce development (SS versus GF Ns1 [% CI ],SSversusREFNs1 [% CI ]),and rate oorce relaxation (SS versus GF Ns1 [% CI()], SS versus REF Ns1 [% CI()])(Figure,right). Te effect sizes or these changes in the SSgroup were ., ., and . or peak orce, rate o orcedevelopment, and rate o orce relaxation, respectively. Tus,the effects o SS can be considered moderate (peak orce) tolarge (rate o orce development and rate o orce relaxation).

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: Muscle ber cross-sectional area, ber type percentage, capillaries per ber (CAF), and capillaries per ber area (CAFA) in healthycontrols (CON) and women with trapezius myalgia (MYA) at baseline and beore and afer -week intervention in the specic strengthtraining (SS), general tness training (GF), and reerence (REF) groups.

Area (m) Fiber type percentage (%) Capillaries per ber (CAF) Capillaries per ber area (CAFA)

ype I ype II ype I ype II ype I ype II ype I ype II

CON 5057 1120 4000 1104 67 11 33 11 4.23 0.74 3.15 0.72 0.89 0.15 0.84 0.17

MYA 5193 1110 3501 977 69 11 31 11 4.12 0.87 2.79 0.70 0.83 0.14 0.86 0.20REF

Beore 4941 399 3334 489 66 13 34 13 3.72 0.49 2.41 0.33 0.81 0.14 0.78 0.14

Afer 5299 1134 3471 684 66 14 34 14 3.97 0.53 2.60 0.61 0.83 0.18 0.78 0.16

GF

Beore 5555 1201 3794 796 69 11 31 11 4.39 0.80 3.10 0.51 0.85 0.19 0.89 0.25

Afer 5108 1030 3612 1070 72 11 28 11 4.18 0.43 2.93 0.57 0.85 0.15 0.87 0.34

SS

Beore 5043 1294 3439 1331 69 12 31 12 4.15 1.09 2.80 0.95 0.85 0.13 0.88 0.22

Afer 5516 1188# 4133 1145 70 10 31 10 4.53 0.82# 3.31 0.64 0.88 0.13 0.85 0.17#endency or increase rom baseline to ollow-up in SS, < 0.10.

Signicant increase rom baseline to ollow-up in SS, < 0.05.

Tere was no signicant group effect or the changerom baseline to ollow-up or any o the EMG parameters(Figure,right,and Figure,right). Tere was no group bynumberinteraction orthe changerom baseline to ollow-up;thatis, the change in the slope over the repetitions did notsignicantly differ between the three intervention groups.

Capillarization per ber as well as muscle ber cross-sectional area increased signicantly in the SS group ortype II bers ( < 0.05) and tended to increase or typeI bers ( < 0.10). In SS, capillarization per ber area

remained unchanged in both types I and II bers (able ).No signicant changes occurred in the two other groups.

.. est-Retest Reliability. est-retest reliability o the out-come measures was not determined prior to the study.However, we perormed reliability analyses afer the studyusing the data rom the two groups that did not respondto the intervention, that is, the GF and REF groups. Forthese analyses the values or each subject were averaged orthe contractions at baseline and ollow-up, respectively.

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Te intraclass correlation coefficient (ICC) between baselineand -week ollow-up was . or peak orce, . or rateo orce development, and . or rate o orce relaxation.

.. Post Hoc Power Analysis. Due to the nonsignicantchanges in the EMG parameters we perormed a post hoc

power analysis using the EMG data (averaged or the contractions or each subject) rom the two groups that didnot respond to the intervention, that is, the GF and REFgroups. At baseline peak EMG was uV (mean value)and the standard deviation o the change rom baseline toollow-up was uV. Requesting % power to detect %difference rom baseline to ollow-up with a type I errorprobability o % would then require subjects in eachgroup. Correspondingly, with only subjects in each groupthe power to detect % difference is only .%; that is, it islikely that in studies with similar sample size would reportnull ndings.

4. DiscussionTe main ndings o the present study were () that womenwith trapezius myalgia showed reduced orce capacity duringrepetitive maximal contractions o the trapezius musclecompared with healthy controls (case-control study) and ()that weeks o high-intensity specic strength training ledto improved orce capacity o the trapezius muscle in womenwith trapezius myalgia. By contrast, leg cycling did notimprove trapezius muscle unction. Tese results along withneural and muscular ndings are discussed in the ollowing.

In the case-control study, peak orce, rate o orce devel-opment, and rate o orce relaxation as well as peak EMGand integrated EMG during the rising phase o contractionwere lower in women with trapezius myalgia comparedwith healthy controls. We have previously shownin thesame group o subjectsthat peak orce and rate o orcedevelopment during a single maximal voluntary contractionare lower in women with trapezius myalgia []. In thepresentstudy we elaborate on these ndings by showing that all theseorce parameters are lower throughout all contractions.However, the slopes o curves or the peak orce values didnot differ between the groups. Tis nding suggests thatlower strength-endurance capacity in women with trapeziusmyalgia is related to the generally lower level o musclestrength generally requesting a higher relative load duringdaily lie and occupational tasks []rather than aster

development o atigue.Some o our case-control results contrast previous nd-

ings. In contrast to the ndings by Larsson and coworkers[] we did not nd reduced capillarization o type I musclebers in women with trapezius myalgia compared withhealthy controls. Tis is surprising since we have also inprevious studies ound a decreased oxygenation in womenwith trapezius myalgia compared to healthy controls duringa more unctional and submaximal test using a pegboard task[]. Tismay suggest that impaired regulation o microcircu-lation, rather than reduced capillarization, may contribute todevelopment o pain and atigue during repetitive work tasksin women with trapezius myalgia.

Also, based on the EMG measurements we ound thatwomen with trapezius myalgia and healthy controls hadsimilar ability to relax the muscles, that is, the same levelo EMG amplitude, between repeated contractions, whichcontrast the EMG ndings by Elert and coworkers [].However, there are methodological differences between the

studies which make direct comparison difficult. Elert andcoworkers used dynamic contractions and dened the abilityto relax the trapezius as the ratio between EMG amplitude othe eccentric (relaxation phase) and concentric phase (con-traction phase) o the contractions. As a ratio dependsboth on the numerator and denominator it can increasesimply by decreased maximal EMG during each concentriccontraction, which makes the results by Elert and coworkersdifficult to interpret.

Different types o normalization o the EMG signal aretypically perormed to avoid the inherent variance associatedwith EMG amplitude. By contrast, we did not normalize theEMG amplitude to a maximal voluntary contraction (MVC)

as neck/shoulder pain inhibits central drive and therebythe EMG signal during maximal contraction [, , ].Tus, normalizing the EMG signal to a maximal contractionwould give erroneous normalized values when comparingindividuals with and without pain and also when comparingdata beore and afer an intervention that decreases pain. Onthe other hand, comparing nonnormalized EMG amplitudesbetween groups is also associated with limitations, suchas variance due to electrode placement and thickness osubcutaneous at. Tereore we careully placed the EMGelectrodes at thesame part o the musclebetween participantsand test sessions by using the seventh cervical vertebrae andthe acromion as reerence points in accordance with SENIAMguidelines []. Further, we have previously reported thatthere was no difference between MYA and CON in thicknesso the subcutaneous layer o at above the trapezius muscle,and neither did this change signicantly during the -week intervention period []. Tus, our results indicate thatwomen with trapezius myalgia have the same ability to relaxbetween muscle contractions.

In spite o similar resting EMG between contractions,the orce measurements showed that relaxation rom max-imal to zero muscle contraction was slower, that is, lowerrate o orce relaxation, in women with trapezius myalgiathan healthy controls. Tus, although women with trapeziusmyalgia have the ability to ully relax the muscles, it takeslonger than in healthy controls. Although speculatively, this

may be related to altered Ca2+ kinetics o myalgic muscles.Interestingly, Green and coworkers ound a compromised

sarcoplasmic reticulum Ca2+-APase activity, Ca2+-uptake,

and Ca2+-release in a case-series study involving women withmyalgia []. A slower relaxation o myalgic muscles mayhave negative implications or high pace work tasks where thetime or recovery between contractions is minimal.

Te intervention study showed that high-intensitystrength training improves both maximal and rapid orcecapacity as well as the ability to rapidly relaxthat is,rate o orce relaxationafer each contraction. We havepreviously reported a marked reduction (%) o pain along

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with increased maximal and rapid orce capacity o singlemaximal voluntary contractions in response to the -weekhigh-intensity strength training intervention [, , ].Te present study elaborates on these ndings by showingthat muscle unction is improved during repetitive maximalmuscle contractions. Tis may have important practical

implications as many job tasks require repetitive muscle con-tractions, such as keyboard typing or repetitive arm move-ments during assembly line work. Further, previous analyseshave shown increased carbohydrate oxidative capacity aferspecic strength training in women with trapezius myalgia[], which may also help to explain the ability to sustain ahigh orce development during repetitive contractions. Apartrom improved muscle unction during repetitive job tasks,the present study also demonstrated signicant myoberhypertrophy and increased capillarization in response to weeks o specic strength training. Tus, these muscularadaptations may partly explain the present ndings, althoughwe cannot exclude the existence o neural adaptations mech-anisms. Despite the act that neither o the EMG parameterschanged signicantly between the intervention groups, thestrength training group had the numerically highest EMGamplitude values at -week ollow-up. Post hoc power anal-ysis showed that subjects in each group would be requiredto detect a %difference in peak EMG between groups rombaseline to ollow-up. Tereore,the present study was under-powered to detectsignicant changes dueto theinherenthigh

variability o the EMG measurements, making signicantresults more difficult to obtain with a small sample size.

Median power requency o the EMG signal decreased asexpected during atiguing contractions (Figure). Tis wasevident both in healthy controls and women with trapeziusmyalgia at baseline and ollow-up. Tis validates that theendurance test induces muscle atigue both among healthyindividuals and individuals with pain.

We also included a general tness training group whoperormed leg cycling while relaxing the shoulders. Previ-ous research in other populations has shown physiologicaladaptations in sites distant rom the trained muscles [,].Increased blood ow to the orearms [] and nonworkinglimb [] has also been shown in response to leg exercise.Our hypothesis was that both specic strength trainingand general tness training would improve muscle unctioncompared with the reerence intervention. However, in thepresent study leg cycling did not improve muscle bercapillarization or muscle endurance o the trapezius muscle.

Tus, o the three present interventions specic strengthtraining remains the most effective or improving muscleunction in women with trapezius myalgia.

In conclusion, the case-control study showed that womenwith trapezius myalgia have lower strength-endurancecapac-ity during repetitive maximal contractions o the trapeziusmuscle compared with healthy controls, along with lowermuscle activity (EMG amplitude). Moreover, relaxation oorcemeasured as the rate o orce relaxationoccurredmore slowly in women with trapezius myalgia, althoughthe ability to ully relax the muscles between contractionswas not lower than that in healthy controls. Moreover, theintervention study demonstrated that high-intensity strength

training effectively improves strength capacity during repet-itive contractions o the painul trapezius muscle attainingunctional levels comparable to the healthy control grouptogether with their decrease in pain. Tis nding wasaccompanied with muscle ber hypertrophy and increasedcapillarization per muscle ber, which may at least partly

explain the unctional improvements. By contrast, leg cyclingdid not improve trapezius muscle unction. Collectively, thepresent ndings emphasize the importance o implementingspecic resistance exercises in rehabilitation programmes oradults with trapezius myalgia.

Conflict of Interests

Te authors declare that there is no conict o interestsregarding the publication o this paper.

Acknowledgments

Te authors thank all the researchers, assistants, and studentso the RAMIN study group. Tis study was supported byGrants rom the Danish Medical Research Council -- and the Danish Rheumatism Association --...

References

[] L. L. Andersen, O. S. Mortensen, J. V. Hansen, and H. Burr,A prospective cohort study on severe pain as a risk actor orlong-term sickness absence in blue- and white-collar workers,Occupational and Environmental Medicine, vol. , no. , pp., .

[] B. Larsson, K. Sgaard, and L. Rosendal, Work related neck-shoulder pain: a review on magnitude, risk actors, biochemicalcharacteristics, clinical picture and preventive interventions,Best Practice and Research: Clinical Rheumatology, vol. , no., pp. , .

[] B. Juul-Kristensen, R. Kadeors, K. Hansen, P. Bystrom, L.Sandsjo, and G. Sjgaard, Clinical signs and physical unctionin neck and upper extremities among elderly emale computerusers: the NEW study,European Journal o Applied Physiology,vol. , no. , pp. , .

[] L. L. Andersen, K. Hansen, O. S. Mortensen, and M. K. Zebis,Prevalence and anatomical location o muscle tenderness inadults with nonspecic neck/shoulder pain, BMC Muscu-loskeletal Disorders, vol. , article , .

[] B. Visser and J. H. Van Dieen, Pathophysiology o upperextremity muscle disorders,Journal o Electromyography andKinesiology, vol. , no. , pp. , .

[] G. M. Hagg, Human muscle bre abnormalities related tooccupational load,European Journal o Applied Physiology, vol., no. -, pp. , .

[] B. Ghaouri, B. K. Larsson, A. Sjors, P. Leandersson, and B. U.C. Gerdle, Interstitial concentration o serotonin is increasedin myalgic human trapezius muscle during rest, repetitive workand mental stress an in vivo microdialysis study,ScandinavianJournal o Clinical and Laboratory Investigation, vol. , no. ,pp. , .

[] P. Olausson, B. Gerdle, N. Ghaouri,B. Larsson, and B. Ghaouri,Identication o proteinsrom interstitium o trapezius muscle

7/27/2019 187324

10/12


in women with chronic myalgia using microdialysis in combi-nation with proteomics,PLoS ONE, vol. , no. , Article IDe, .

[] J. Hadrevi, B. Ghaouri, B. Larsson, B. Gerdle, and F. Hellstrom,Multivariate modeling o proteins related to trapezius myalgia,a comparative study o emale cleaners with or without pain,PLoS ONE, vol. , no. , Article ID e, .

[] B. Larsson, J. Bjork, F. Kadi, R. Lindman, and B. Gerdle, Bloodsupply and oxidative metabolism in muscle biopsies o emalecleaners with and without myalgia, Clinical Journal o Pain, vol., no. , pp. , .

[] L. L. Andersen, C. Suetta, J. L. Andersen, M. Kjr, and G.Sjgaard, Increased proportion o megabers in chronicallypainul muscles,Pain, vol. , no. , pp. , .

[] L. L. Andersen, A. K. Blangsted, P. K. Nielsen et al., Effecto cycling on oxygenation o relaxed neck/shoulder muscles inwomen with and without chronic pain, European Journal oApplied Physiology, vol. , no. , pp. , .

[] R. Larsson, P. A. Oberg, and S.-E. Larsson, Changes o trape-zius muscle blood ow and electromyography in chronic neck

pain due to trapezius myalgia,Pain, vol. , no. , pp. ,.

[] G. Sjgaard, L. Rosendal, J. Kristiansen et al., Muscle oxygena-tion and glycolysis in emales with trapezius myalgia duringstress and repetitive work using microdialysis and NIRS,European Journal o Applied Physiology, vol. , no. , pp. , .

[] G. Sjogaard, M. K. Zebis, K. Kiilerich, B. Saltin, and H.Pilegaard, Exercise training and work task induced metabolicand stress-related mRNA and protein responses in myalgicmuscles,BioMed Research International, vol. , Article ID, pages, .

[] L. Rosendal, A. K. Blangsted, J. Kristiansen et al., Intersti-tial muscle lactate, pyruvate and potassium dynamics in thetrapezius muscle during repetitive low-orce arm movements,measured with microdialysis,Acta Physiologica Scandinavica,vol. , no. , pp. , .

[] L. Rosendal, B. Larsson, J. Kristiansen et al., Increase inmuscle nociceptive substances and anaerobic metabolism inpatientswith trapezius myalgia: microdialysis in restand duringexercise,Pain, vol. , no. , pp. , .

[] O. A. Steingrmsdottir, S. Knardahl, and N. K. Vllestad, Pro-spective study o the relationship between musculoskeletal andpsychological complaints and electromyographic activity dur-ing isometric muscular contractions in a working population,Scandinavian Journal o Work, Environment and Health , vol.,no. , pp. , .

[] G. Sjgaard, K. Sgaard, H. J. Hermens et al., Neuromuscularassessment in elderly workers with and without work relatedshoulder/neck trouble: the NEW-study design and physiolog-ical ndings,European Journal o Applied Physiology, vol. ,no. , pp. , .

[] B. R. Jensen, B. Schibye, K. Sogaard, E. B. Simonsen, and G.Sjogaard, Shoulder muscle load and muscle atigue amongindustrial sewing-machine operators, European Journal oApplied Physiology and Occupational Physiology, vol. , no. ,pp. , .

[] L. L. Andersen, A. Holtermann, M. B. Jrgensen, and G.Sjgaard, Rapid muscle activation and orce capacity in con-ditions o chronic musculoskeletal pain, Clinical Biomechanics,vol. , no. , pp. , .

[] L. L. Andersen, P. K. Nielsen, K. Sgaard, C. H. Andersen, J.Skotte, and G. Sjgaard, orque-EMG-velocity relationship inemale workers with chronic neck muscle pain,Journal o Bio-mechanics, vol. , no. , pp. , .

[] J. E. Elert, S. B. Rantapaa-Dahlqvist, K. Henriksson-Larsen, R.Lorentzon, and B. U. C. Gerdle, Muscle perormance, elec-tromyography and bre type composition in bromyalgia andwork-related myalgia,Scandinavian Journal o Rheumatology,vol. , no. , pp. , .

[] L. Dellve, L. Ahlstrom, A. Jonsson et al., Myoeedback trainingand intensive muscular strength training to decrease pain andimprove work ability among emale workers on long-term sickleave with neck pain: a randomized controlled trial, Interna-tional Archives o Occupational and Environmental Health, vol., no. , pp. , .

[] A. Holtermann, K. Roeleveld, P. J. Mork et al., Selectiveactivation o neuromuscular compartments within the humantrapezius muscle,Journal o Electromyography and Kinesiology,vol. , no. , pp. , .

[] C. Ahlgren, K. Waling, F. Kadi,M. Djupsjobacka, L.-E. Tornell,and G. Sundelin, Effects on physical perormance and painrom three dynamic training programs or women with work-related trapezius myalgia, Journal o Rehabilitation Medicine,vol. , no. , pp. , .

[] J. Ylinen, E. P. akala, M. Nykanen et al., Active neck muscletraining or treatment o women with chronic neck pain: arandomized controlled study,Manuelle Medizin, vol. , no. ,pp. , .

[] L. L. Andersen, M. Kjr, K. Sgaard, L. Hansen, A. I. Kryger,and G. Sjgaard, Effect o two contrasting types o physicalexercise on chronic neck muscle pain, Arthritis Care andResearch, vol. , no. , pp. , .

[] A. K. Blangsted, K. Sgaard, E. A. Hansen, H. Hannerz,and G. Sjgaard, One-year randomized controlled trial with

different physical-activity programs to reduce musculoskeletalsymptoms in the neck and shoulders among office workers,Scandinavian Journal o Work, Environment and Health, vol.,no. , pp. , .

[] P. K. Lunde, I. Sjaastad, H.-M. Schitz Torud, and O. M.Sejersted, Skeletal muscle disorders in heart ailure, ActaPhysiologica Scandinavica, vol. , no. , pp. , .

[] N. Yuza, K. Ishida, and M. Miyamura, Cross transer effects omuscular endurance during training and detraining,Journal oSports Medicine and Physical Fitness, vol. , no. , pp. ,.

[] D. Silber, D. McLaughlin, and L. Sinoway, Leg exercise condi-tioning increases peak orearm blood ow,Journal o AppliedPhysiology, vol. , no. , pp. , .

[] H. anaka, S. Shimizu, F. Ohmori et al., Increase in bloodow and shear stress to nonworking limbs during incrementalexercise,Medicine and Science in Sports and Exercise, vol. ,no. , pp. , .

[] L. L. Andersen, M. B. Jrgensen, A. K. Blangsted, M. . Peder-sen, E. A. Hansen, and G. Sjgaard, A randomized controlledintervention trial to relieve and prevent neck/shoulder pain,Medicine and Science in Sports and Exercise, vol. , no. , pp., .

[] H. J. Hermens and B. Freriks, Te State o the Art on Sensorsand Sensor Placement Procedures or Surace Electomyography:A Proposal or Sensor Placement Prodedures. SENIAM Project,Roessingh Research and Development, Enschede, Te Nether-lands, .

7/27/2019 187324

11/12


[] H. J. Hermens, B. Freriks, C. Disselhorst-Klug, and G. Rau,Development o recommendations or SEMG sensors andsensor placement procedures,Journal o Electromyography andKinesiology, vol. , no. , pp. , .

[] D. A. Winter, Biomechanics and Motor Control o HumanMovement, John Wiley & Sons, New York, NY, USA, ndedition, .

[] M. H. Brooke and K. K. Kaiser, Muscle ber types: how manyand what kind?Archives o Neurology, vol. , no. , pp. , .

[] L. L. Andersen, J. L. Andersen, C. Suetta, M. Kjr, K. Sgaard,and G. Sjgaard, Effect o contrasting physical exercise inter-ventions on rapid orce capacity o chronically painul muscles,Journal o Applied Physiology, vol. , no. , pp. , .

[] L. L. Andersen, M. Kjr, C. H. Andersen et al., Muscle activa-tion during selected strength exercises in women with chronicneck muscle pain,Physical Terapy, vol. , no. , pp. ,.

[] W. J. Kraemer, K. Adams, E. Caarelli et al., Progression modelsin resistance training or healthy adults, Medicine and Science

in Sports and Exercise, vol. , no. , pp. , .[] P. O. Astrand and K. Rodahl, extbook o Work Physiology:

Physiological Bases o Exercise, McGraw-Hill, New York, NY,USA, rd edition, .

[] J. Cohen,Statistical Power Analysis or the Behavioral Sciences,Lawrence Erlbaum Associates, nd edition, .

[] A. Ben-Yishay, J. D. Zuckerman, M. Gallagher, and F. Cuomo,Pain inhibition o shoulder strength in patients with impinge-ment syndrome,Orthopedics, vol. , no. , pp. , .

[] P. K. Nielsen, L. L. Andersen, H. B. Olsen, L. Rosendal,G. Sjgaard, and K. Sgaard, Effect o physical training onpain sensitivity and trapezius muscle morphology,Muscle andNerve, vol. , no. , pp. , .

[] H. J. Green, P. Galvin, D. A. Ranney, H. ick, and J. Ouyang,Are abnormalities in sarcoplasmic reticulum calcium cyclingproperties involved in trapezius myalgia? Case studies onthree emales, American Journal o Physical Medicine andRehabilitation, vol. , no. , pp. , .

[] L. L. Andersen, C. H. Andersen, M. K. Zebis, P. K. Nielsen, K.Sgaard, and G. Sjgaard, Effect o physical training on unc-tion o chronically painul muscles: a randomized controlledtrial,Journalo Applied Physiology, vol. , no. , pp. ,.

7/27/2019 187324

12/12

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