neck pain is a common musculoskeletal disorder that leads to significant disability in the 
 general population . in a 6-month period , 54% of adults suffer from neck pain , and 4.6% 
 experience limitations of important activities because of neck problems1 . reported that 30% of men and 43% of women 
 were affected by neck pain at some time in their lives , and that the symptoms became chronic 
 among 10% of men and 17% of women2 . the 
 prevalence of this condition increases with age and is greater in women than men1 . various factors 
 have been identified as predisposing to neck pain , such as the duration of computer use , 
 sustained awkward posture , and prolonged working with a visual display unit ( vdu)3 , 4 . a 
 prolonged forward head posture is commonly adopted by this occupational group , and it may be 
 associated with musculoskeletal disorders5 . biomechanically , sustained forward flexion of the neck results in 
 increased compressive loading on the cervical spine and a creep response in the surrounding 
 soft tissues . also the source of pain is excessive loading of the cervical and shoulder 
 girdle muscles , especially in low - load repetitive work which promotes over - activity of low 
 threshold motor units6 . other mechanisms , 
 such as nociceptor sensitization due to intra - muscular shear forces are also considered to 
 play a role7 . these phenomena may 
 concurrently increase electromyographic activity of the cervical musculature , such as neck 
 extensor muscles and the levator scapulae . in addition , the superficial muscles of the 
 neck - shoulder region , i.e. , the sternocleidomastoid , anterior scalene and upper trapezius 
 muscles , demonstrate increased activities compared to deeper postural stabilizers like the 
 deep cervical flexors8 . moreover , several 
 studies have reported significantly lower maximal isometric strength of both the cervical 
 flexors and extensors in patients with chronic neck pain compared to healthy controls9,10,11 and one study also found weakness of the 
 neck rotator muscles12 . recent studies have shown that the activities of the deep cervical flexor muscles , such as 
 the longus colli and longus capitis , are impaired in persons with neck pain13 . furthermore , the findings of a 
 significant deficit in the ability to maintain low or moderate load by the ccf muscles 
 suggests that head and neck postural orientation is challenged under prolonged or repetitive 
 circumstances in neck pain patients . the ccf muscles may fatigue prematurely and be 
 incapable of controlling cranio - cervical orientation . indeed , evidence is emerging that persons with neck pain tend to 
 adopt a more forward head position when distracted15 . this has been observed despite a lack of postural differences in 
 erect sitting16 , 17 . moreover , retraining the deep cervical flexor muscles has been 
 shown to decrease neck symptoms and increase the activation of the deep cervical flexor 
 muscles during performance of a cranio - cervical flexion test18 . this may improve the capacity of the cervical spine to sustain an 
 upright posture . physical exercise has been recommended as a treatment for musculoskeletal neck 
 disorders19 , 20 . while several studies have demonstrated that pain can to some 
 extent be reduced by strength training19,20,21,22 or endurance training21 , 22 , one study 
 found no effect of physical training on nonspecific pain in the neck area21 . a recent review showed limited evidence 
 for the efficacy of physical exercise in the treatment of symptoms of the neck and/or 
 shoulder due to the lack of high - quality research23 . one meta - analysis concluded that there was unclear and 
 insufficient evidence in support of the benefit of strengthening exercises for neck 
 pain24 and the relative benefit of 
 different exercise approaches , such as cranio - cervical flexion of the deep cervical flexor 
 muscles . although there is some evidence of pain reduction occurring following 
 strengthening , endurance or cranio - cervical flexion exercise19 , 20 , 22 , it is not known how the training influences the muscle activities 
 of persons with chronic neck pain during working with a computer . a randomized control trial compared outcomes among 3 neck muscle exercise programs and a 
 control group . subjects who participated in this study were females , aged between 20 and 35 with a history 
 of intermittent work - related neck pain lasting for more than 6 months . they worked with a 
 computer at least 4 hours each working day . the pain level at the time of examination 
 exceeded 30  mm on a visual analogue scale of 0100  mm . subjects were excluded if they had 
 neck or shoulder pain from non - musculoskeletal causes , demonstrated neurological signs , or 
 had a history of malignancy , pregnancy , or menstruation at the time of examination . this study received approval from the mahidol university institutional review board and is 
 in full compliance with international guidelines for human research protection , the 
 declaration of helsinki , the belmont report , cioms guidelines and the international 
 conference on harmonization in good clinical practice . all subjects received verbal and 
 written information about the study and signed a consent form . the extremes were  no pain  and  pain 
 as bad as it could be  . the neck disability index ( ndi ) used in this study was the thai 
 version of ndi developed by luckumnueporn et al25 . surface electromyography ( semg ) was used to obtain 
 electromyograms of the : upper trapezius ( ut)26 , cervical erector spinae ( ce)26 , sternal head of the sternocleidomastoid ( scm)27 and anterior scalenes ( as)27 using pairs of standard adhesive surface electrodes . emg data were collected during standardized maneuvers to normalize of the emg amplitude to 
 maximum voluntary contraction ( mvc ) . each mvc task was performed for 10 seconds and repeated 
 3 times with 30 seconds rest between each repetition . mvc tasks for the normalization of scm 
 and as were performed in supine lying . the subjects flexed the chin and lifted the head so 
 that it just cleared the bed and held this position13 . for the ce muscles , the subject raised 
 and held her head 20  mm above the bed in prone lying4 . neck muscle activities were measured by an 8-channel surface emg device ( myresearch xp 
 master edition 1.06.64 program , naroxon inc , usa 2006 ) at a frequency of 
 1,000  hz . the emg signals were recorded using bipolar ag - agcl surface electrodes . subjects 
 were asked to sit on a chair with their backs supported in a comfortable position . the emg 
 electrodes were attached to the skin with hypoallergenic tape at an inter - electrode distance 
 of 1  cm ; the inter - electrode impedance was kept below 2  k26 . subjects who met the criteria were invited to participate in the study and were randomized 
 by the slot - drawing method into 4 groups : a strength - endurance exercise group ( group 1 ) , a 
 cranio - cervical flexion exercise group ( group 2 ) , a combined exercise group ( group 3 ) , and a 
 control group ( group 4 ) . the strength - endurance exercise consisted of a progressive resistance exercise program for 
 the neck muscles , especially the superficial neck flexor and extensor muscles ( scm , as and 
 ce ) . neck flexion and extension were performed in the supine and prone positions , 
 respectively , with the head supported in a comfortable resting position . subjects slowly 
 moved the head and neck through the total range of motion avoiding discomfort or symptom 
 reproduction . the first phase of 4 weeks and the 
 second of 8 weeks were recommended for initiating a weight program in untrained 
 individuals28 . in phase one , each 
 subject performed 1215 repetitions with a weight that they could lift 12 times on the first 
 training session ( 12 repetitions maximum ) and progress to 15 repetitions . , subjects performed 3 sets of 15 
 repetitions of the initial 12 repetitions at maximum load with one minute rest interval 
 between sets . the craniocervical flexion exercise consisted of a low load exercise for the 
 cranio - cervical flexor muscles . subjects lay supine and slowly moved the head to the inner 
 range of cranio - cervical flexion , guided by feedback from an air filled pressure sensor 
 placed suboccipitally behind the neck and inflated to a baseline pressure of 20 mmhg . subjects moved the head to increase the pressure to between 22 to 30 mmhg ; and maintained 
 this position for 10 seconds in 15 repetitions . the targets 
 of this exercise are the deep flexors of the upper cervical region , the longus capitis and 
 colli , rather than the superficial flexors , which flex the neck but not the head . the combined exercise group performed both strength - endurance and cranio - cervical flexion 
 exercises . a 
 five minute rest was then taken before performing the strength - endurance exercise . subjects in each group performed exercise every day for 12 weeks and kept a log book for 
 monitoring . exercise compliance in this study was over 80% in all groups . the semg were recorded in two sessions 
 during a copy - typing task lasting 5 minutes . after exercise training of 12 weeks , vas , ndi 
 and semg were recorded again for all subjects . for the copy - typing task , subjects sat at a 
 standard office desk on an adjustable office chair . they could adjust the chair and desk 
 before the test to obtain the most comfortable position , but they were not allowed to move 
 between tasks . the visual display monitor and keyboard were positioned directly in front of 
 the subjects for the typing tasks . a copy - typing task was chosen over typing from a document 
 holder to eliminate movement of the head or the need to change head position from document 
 to screen as needed for eye - hand coordination activities . the copy - typing task was performed 
 continuously for 5 minutes . after finishing data collection , subjects in the control group were advised to perform both 
 the strength - endurance and cranio - cervical exercises . in the strength - endurance exercise 
 group , subjects were trained in how to perform deep cervical flexor muscle ( ccf exercise ) 
 and subjects in the ccf exercise group were trained in how to perform strength - endurance 
 exercise . the vas , ndi 
 scores and the averages of root mean square ( rms ) semg values were used in the analyses . one - way anova was used to 
 identify differences in the characteristics of subjects using vas , emg and ndi values before 
 the exercise interventions among the 4 groups . two - way anova was used to evaluate the 
 effects of group ( exercise groups ) and time ( pre - and post - intervention ) on the outcomes . a 
 post hoc multiple comparisons test with bonferroni correction data are expressed in means ( sd ) group 1 = strength - endurance exercise , group 2 
 = craniocervical flexion exercise , group 3 = combination of endurance - strength and 
 craniocervical flexion exercise , and group 4 = control data are expressed in means ( sd ) group 1 = strength - endurance exercise , group 2 
 = craniocervical flexion exercise , group 3 = combination of endurance - strength and 
 craniocervical flexion exercise , and group 4 = control data are expressed in means ( sd ) group 1 = strength - endurance exercise , group 2 
 = craniocervical flexion exercise , group 3 = combination of endurance - strength and 
 craniocervical flexion exercise , and group 4 = control subjects in this study were 100 females who had a history of intermittent work - related neck 
 pain . data are expressed in means ( sd ) group 1 = strength - endurance exercise , group 2 
 = craniocervical flexion exercise , group 3 = combination of endurance - strength and 
 craniocervical flexion exercise , and group 4 = control the neck pain and disability scores showed that there was a significant interaction of 
 group by time ( p<0.001 ) , and significant main effects of group ( p<0.001 ) and time 
 ( p<0.001 ) in the vas and ndi scores . main effects analysis showed that there were 
 significant differences in vas between before and after in groups 1 , 2 and 3 ( p = 0.002 ) , 
 but there were no differences between before and after in the control group ( p = 0.575 ) . this showed that 
 vas of all groups after the intervention were significantly different except the vas scores 
 between group 1 and group 2 . similarly , there were significant main effects of group 
 ( p<0.001 ) and time ( p<0.001 ) . for ndi scores , main effects analysis of time ( before 
 and after 12 week ) showed that there were significant differences group 1 , 2 and 3 ( p = 
 0.001 ) , but there was no difference in the control group ( p = 0.091 ) . the post hoc multiple 
 comparison with bonferroni correction revealed that the control group after the intervention 
 was significantly different from all the other groups , and that there were no differences 
 among the ndi scores of group 1 , 2 and 3 . vas and ndi scores of each group before and after 
 exercise are presented in tables 2 and 3 . the results of normalized rms semg values of the cervical erector spinae , 
 sternocleidomastoid , anterior scalenes and upper trapezius muscle during the copy - typing 
 task reveal that there were significant interactions of group with time ( p<0.001 ) for all 
 muscles except the left as muscle ( p=0.158 ) . the main effect of group ( p<0.001 ) and time 
 ( p<0.001 ) was also significant for all muscles . rms values of each group before and after 
 exercise are presented in table 4 . main effects 
 analysis showed that there were significant differences in rms between before and after the 
 exercise interventions in groups 1 , 2 and 3 for the cervical erector spinae and anterior 
 scalenes , sternocleidomastoid ( p<0.05 ) ; ( both right and left sides ) and in all groups for 
 both the right and left of upper trapezius muscles ( p<0.05 ) . however , there were no other 
 significant differences between before and after in the control group ( p = 0.332 , p = 0.261 
 for right and left cervical erector spinae ; p = 0.524 , p = 0.775 for right and left 
 sternocleidomastoid ; p = 0.72 , p = 0.985 for right and left anterior scalenes ) . the analysis showed that group 
 4 had significantly different rms semg in all muscles from the other groups , except the left 
 cervical erector spinae . however , there were no differences among the rms semg values of 
 groups 1 , 2 and 3 . the results of this study support the recommendation to use strength - endurance and the 
 cranio - cervical flexion ( ccf ) exercises for the cervical muscles as treatment interventions 
 for patients with chronic neck pain19 , 20 . the results were also in agreement with 
 previous studies that demonstrated that pain can be reduced by strength training19,20,21,22 
 and endurance training21 , 22 . moreover , general exercises like strength and endurance 
 training , as well as specific exercises such as cranio - cervical flexion of deep cervical 
 flexor muscles have been shown to decrease neck symptoms18 . in the present study , the neck pain and disability index significantly improved after 12 
 weeks of exercise intervention in all the exercise groups . this indicates that exercise 
 caused the changes in vas and ndi score of females who had chronic neck pain . this result 
 was in agreement with previous studies29 , 30 which showed the same trend of decrease in 
 ndi score and vas after exercise interventions . the improvement in pain and disability in 
 the three exercise groups were not only statistically , but also clinically significant . the 
 decrease in vas was 16.32  mm in the strength - endurance exercise group , 13  mm in the ccf 
 exercise group and 44.6  mm in the combined exercise group . the decreases in ndi score were 
 13.51 in the strength - endurance exercise group , 15.55 in the ccf exercise group and 13.52 in 
 the combined exercise group . the reductions in pain and neck disability were significantly 
 different among the control and all three exercise groups . there was a tendency of greater 
 reduction in neck pain in the combined exercise group compared to the strength - endurance 
 exercise and ccf exercise groups . the muscle activities during the typing task showed differences between before and after in 
 all the exercise groups , but there was no significant difference between before and after 
 the intervention in the control group in both the right and left cervical erector spinae , 
 sternocleidomastoid , and anterior scalenes . this result indicates that the exercise 
 interventions caused changes in muscle recruitment during the typing task . the upper 
 trapezius muscle on both the right and left sides showed a significant reduction in muscle 
 activity after the interventions in all the exercise groups . there was a trend of increased 
 in rms in the control group , which performed no exercise intervention , and there were no 
 significant differences among the rms values of the three exercise groups . the subjects in 
 the control group had rms values that were greater than those of the other groups . this 
 indicates that the exercise interventions of groups 1 , 2 and 3 had the effect of decreasing 
 the rms value , whereas , the control group showed no change in rms values during the typing 
 task . the mechanisms involved in the improvement in the strength - endurance exercise group might 
 have been improved coordination , increased motor unit recruitment , an increased firing rate 
 in each unit31 , and an increase in the 
 number of capillaries in the muscle within 10 weeks32 , all of which would have contributed to improvement of muscular 
 fatigue in chronic neck pain . in the ccf exercise group , the benefits might have accrued 
 from a combination of improvement in neuromuscular efficiency and cervical motor control 
 strategies improving the deep cervical flexor muscle . therefore , the decrease in of cervical 
 muscle activation seen in this study might have been effected by these combined mechanisms 
 operating on the neck extensor , superficial flexor and deep cervical flexor muscles . moreover , several studies have shown that people with neck pain demonstrate decreased 
 ability to relax the anterior scalene and sternocleidomastiod muscles following 
 activation9 . the upper trapezius has 
 also been shown to have a reduced ability to relax following repetitive arm movements and 
 has reduced muscle rest periods during repetitive tasks33 . the present study revealed decreases in rms of the cervical 
 erector spinae , upper trapezius , anterior scalene and sternocleidomastoid muscles which 
 might have improved the ability to relax the muscles and changed the motor control strategy 
 during the typing task . this study provided evidence of an exercise effect on the pain levels , ndi scores and rms 
 values of subjects who performed exercise for 12 weeks . the results of this study indicate 
 that pain levels and ndi scores decreased after exercise intervention . the reduction of rms 
 after 12 weeks exercise intervention suggests that strength - endurance exercise and the 
 combined exercise are effective at decreasing the muscle activities of the upper trapezius , 
 cervical erector spinae ( ce ) , sternal head of the sternocleidomastoid ( scm ) and anterior 
 scalenes ( as ) when performing tasks . the results should encourage therapists to prescribe 
 strength - endurance exercise , craniocervical flexion exercise and combined exercise for 
 patients with chronic neck pain . a limitation of this study is that it is not possible to generalize the results to the 
 general population because the subjects were females with chronic neck pain . therefore , it 
 might not be possible to extrapolate the results to subjects with neck pain disorders of 
 other etiologies such as whiplash injuries . further study is necessary to investigate the effect of longer durations of training , such 
 as 6 months or more , because the muscle activities seen in this study showed no significant 
 difference among the exercise intervention groups . the effects might be varied in other neck 
 pain conditions , or in men . moreover , the severity of neck pain such as mild , moderate or 
 severe pain may influence the muscle activities after exercise intervention .
[ purpose ] to compare muscle activities and pain levels of females with chronic neck pain 
 receiving different exercise programs . 
 [ subjects and methods ] one hundred females with 
 chronic neck pain participated in this study . 
 they were randomly allocated into 4 groups 
 ( n = 25 ) on the basis of the exercises performed as follows : strength - endurance exercise , 
 craniocervical flexion exercise , combination of strength - endurance and craniocervical 
 flexion exercise and control groups . 
 pain , disability levels and changes in the muscle 
 activities of the cervical erector spinae ( ce ) , sternocleidomastoid ( scm ) , anterior 
 scalenes ( as ) and upper trapezius ( ut ) muscles were evaluated before and after the 
 interventions . 
 [ results ] after 12 weeks of exercise intervention , all three exercise 
 groups showed improvements in pain and disability . 
 the muscle activities during the typing 
 task were significantly different from the control group in all three exercise groups for 
 all muscles except those of the extensor muscles in the craniocervical flexion exercise 
 group . 
 [ conclusion ] the results of this study indicate that exercises for the cervical 
 muscles improve pain and disability . 
 the exercise programs reduced the activities of 
 almost all cervical muscles .