INTRODUCTION {#s1}
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Active cervical range of motion (ROM) is frequently used to assess pain, and cervical ROM is reportedly one of the best estimators of cervical disability[@r1]^)^. Previous reports have suggested that early changes in cervical ROM and muscle endurance could be interpreted as risk factors for the development of neck discomfort[@r2], [@r3]^)^. In modern society, neck discomfort is regarded as one of the most prevalent types of pain among computer workers[@r4]^)^. Sustained computer work requires constant tension of the musculature of the rear neck region and can easily result in adoption of a forward-head posture[@r3], [@r4]^)^. Previous work has suggested that cervical ROM during neck flexion could be a predictive factor for changes in neck posture and muscular dysfunction after sustained computer work[@r5], [@r6]^)^. When assessing ROM of the cervical region, however, cervical flexion should be differentiated into total neck flexion and upper cervical flexion, because a forward-head posture is defined as the posture that adopts upper cervical extension and lower cervical flexion[@r7]^)^. Therefore, the purpose of the present study was to identify changes in cervical ROM after sustained computer work, especially with respect to upper cervical flexion, total neck flexion, and the ratio between these parameters. 

SUBJECTS AND METHODS {#s2}
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Nine male office workers were recruited for the present study.  They were aged 24 to 29 years (26±3.2), and their mean height and weight were 174.5±6.2 cm, and 75.3±4.1 kg, respectively.  The inclusion criterion was regular office workers who used a computer at least four hours per day.  Exclusion criterion was a history of upper or lower extremity injury or disease that might have affected computer work.  All subjects provided their informed consent before participating in this study.  This study was approved by the Inje University Faculty of Health Sciences Human Ethics Committee.  The total and upper cervical flexion angles were measured using a CROM instrument (Performance Attainment Associates, St. Paul, MN) before and after computer work.  The instrument can measure the movements performed by the cervical spine, using inclinometers and a compass goniometer.  A pressure biofeedback unit was placed at the lower cervical region, between the back rest and participant's head, below the C4 level, which is used for regulating lower cervical flexion, to provide pressure information.  Each participant was asked to sit on a standard chair with a high backrest and maintain a neutral spinal alignment as perceived by an experienced physiotherapist.  For measuring total cervical flexion, each subject was asked to flex the head until a feeling of muscle tightness or pain was occurred.  For measuring upper cervical flexion, each subject was asked to flex the head until the pressure biofeedback unit showed a decrease in pressure.  Three measurement trials were conducted at 60-s intervals, pre-and post-computer work.  All participants performed selected computer work for 1-hour.  Each participant was allowed 5-min of adjustment time to regulate the work circumstances to those most comfortable for them.  The mean values of both measured values of the total cervical flexion and upper cervical flexion angles, and their ratios in the three trials, pre-and post-test, were calculated for statistical analysis.  The paired t-test was conducted to examine differences.  Significance was accepted for values of p\<0.05, and SPSS version 18.0 was used for statistical analyses. 

RESULTS {#s3}
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The upper cervical flexion, and the ratio between the upper cervical flexion and total cervical flexion were significantly reduced after computer work, compared to pre-measurement (p\<0.05) ([Table 1](#tbl_001){ref-type="table"}Table 1.Comparison of the angles of the total and upper cervical flexion, and ratioMeasurementsMean ± SDBefore workAfter workTotal cervical flexion (°)60.6±4.859.4±3.4Upper cervical flexion (°)17.7±2.211.8±2.9\*Ratio0.29±0.020.19±0.04\*\* significant difference, p\<0.05).  The total cervical flexion angle was not significantly different between pre-and post-measurement (p\>0.05) ([Table 1](#tbl_001){ref-type="table"}). 

DISCUSSION {#s4}
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Reduced ROM in the cervical region can disturb functional activities and elicit protective responses, affecting changes in the muscular responses and passive structures of the cervical spine[@r1], [@r2]^)^. The present results show that upper cervical flexion and its relationship to total cervical flexion were significantly reduced.  Yoo et al.[@r6]^)^ reported a positive correlation between the magnitude of neck flexion and dysfunction of the cervical erector spinae.  A previous work suggested that a prolonged abnormal posture results in impaired proprioception of "good posture" and repositioning sense[@r8], [@r9]^)^. Although posture during computer work was not evaluated in the present study, the nine subjects usually performed computer work with a forward-head posture, which might have influenced our results.  The forward-head posture is defined as extension of the upper cervical region and flexion of the lower cervical region, which requires sustained activation of the cervical erector spinae at the C4 level[@r2], [@r6]^)^. This manifests as muscular dysfunction of the cervical erector spinae in the rear neck, especially the upper cervical region. 

This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No.  2012R1A1B4001058).