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Paper text:
owing to the multi - directional movement of the cervical spine , it must be mechanically 
 stable under both static and dynamic conditions1 . to accomplish cervical stability , deep and segmental cervical 
 muscles , such as the longus colli , are important for the control and support of cervical 
 alignment and postural maintenance2,3,4 . 
 longus colli muscle dysfunction , including a lack of strength and endurance , has been 
 demonstrated in patients with neck pain and whiplash injury5,6,7 . to measure the longus colli muscle strength , the cranio - cervical flexion test using 
 bio - feedback pressure ,
magnetic resonance imaging ( mri ) , electromyography , and 
 ultrasonography ( us ) have been used8,9,10,11 . of these measurement techniques ,
us is 
 the most cost - effective and feasible method for tissue measurement , which is visualized in 
 real - time .
measurements can be obtained when muscle are relaxed or contracting as well as 
 during movement12 . on us
measurement , 
 cross - sectional area ( csa ) and muscle thickness ( mt ) are commonly used to quantify longus 
 colli muscle strength13 , 14 . the us measurement must be reliable and sensitive to provide accurate and relevant 
 information15 .
previous studies found 
 moderate reliability and questionable validity in longus colli muscle measurement using us 
 and mri12 .
therefore , greater accuracy 
 may be required when measuring the csa and mt . to ensure an accurate measurement , steady 
 probe position , orientation , and inward pressure
previous studies reported that the examiner should 
 attempt to maintain consistent inward pressure of the probe to quantify the minimal change 
 in mt on us measurements17 , 18 . to our knowledge , no study has investigated the effects of different inward us probe 
 pressure on the longus colli muscle ( csa and mt ) . therefore , the purpose of this study was 
 to investigate the intra- and inter - rater reliability of measurements of the csa and mt of 
 the longus colli according to the inward us probe ( 0.5 and 1  kg ) .
thirteen subjects ( 11 males and 2 females ) were recruited via convenience sampling of among 
 a university student population .
the subjects characteristics are presented in table 1table 1.descriptive data ( n = 13)mean  sdrangeage ( years)23.12.92028height ( cm)169.89.9153187weight ( kg)64.912.74688sd : standard deviation .
the exclusion criteria were : 1 ) neuromuscular or musculoskeletal disorder ; 2 ) 
 history of clavicle fracture , metal implant , or surgery ; and 3 ) current neck pain .
the 
 principal investigator explained the procedure to the subjects prior to the experiment using 
 detailed written and verbal information , and all subjects signed an informed consent form . 

sd : standard deviation real - time us ( sonoace x8 , medison , inc . ,
seoul , south korea ) was used to measure the csa 
 and mt of the right longus colli in the m - mode with a 4.5  cm , 512  mhz linear probe head 
 ( l5 - 12ec ) .
this was connected to a screen that showed an image of the consistent inward 
 pressure of the us probe at 0.5 and 1.0  kg .
the spring gauge had a force - measuring 
 capacity 0.030.0  kg in 0.1  kg increments .
the probe was secured to the end of the spring 
 gauge using non - elastic sports tape ( bsn medical , hamburg , germany ) between the fixed bar 
 and the spring gauge .
a hands - free probe holder ( high - density foam cube ) was used to improve 
 the accuracy of us .
the subjects were placed in a neutral supine position with their knees and hips bent and 
 arms along the sides of the body . to make cervical lordosis ,
the inward pressure was set at 0  kg in contact with the skin 
 during the application of the probe while a height - adjustable table was used to precisely 
 apply the two different inward pressures ( 0.5 and 1.0  kg ) using a spring gauge to produce 
 consistent pressure . for the cross - sectional area ,
the bottom of the laryngeal prominence of the thyroid cartilage , which 
 corresponds to the c5 level , served as a reference point . to measure the thickness of the 
 longus colli muscle ,
the probe was positioned longitudinally on the anterior of the neck 
 parallel with the trachea and approximately 5  cm from its mid - line .
the us image of the 
 longus colli muscle was captured , stored , and measured by two experienced examiners , who 
 were both therapists with clinical orthopedic physical therapy experience of 5 and 2  years , 
 respectively . to minimize bias , the examiners collected the measurements in a separate room 
 and were blinded to each subject s information and each other s results .
examiner training 
 sessions were conducted by the principal investigator to ensure familiarization with and 
 standardization of the us measurements , including the precise location of the landmarks to 
 reduce measurement errors .
the study protocol was explained simultaneously in the 1-hour 
 training session prior to the testing .
repeated us measurements using the same protocol were performed to assess intra- and 
 inter - rater reliability on the same day with an 1-hour break between them .
each examiner 
 measured the us image ( i.e. , csa and mt ) under both the 0.5 and 1.0  kg conditions once for 
 each subject in a given session .
the examiners were blinded to their own previous findings 
 as well as the us measurement results .
the order of the measurements and examiners was 
 randomized using a random number generator ( excel , microsoft corp . ,
calipers were used to measure the csa and mt in centimeters . the mean and standard deviation ( sd ) of each subject s characteristics and us image ( csa 
 and mt ) data were calculated .
intra - class correlation coefficients ( icc 2 , 1 ) were used to 
 determine the intra- and inter - rater reliability of the csa and mt measurements .
excellent  , 0.400.75 was  fair to good  , and 0.000.40 was  poor19 .
the standard error of measurement ( sem ) 
 was calculated for each measurement to assess absolute consistency [ sem = sd1  icc ] . the 
 minimum detectable difference ( 95% confidence interval ; mdd ) scores were 
 calculated [ mdd = sem  2  1.96]20 .
the longus colli muscle measurement data ( icc , sem , and mdd ) are shown in 
 tables 2table 2.intra-rater reliability of the csa and mt of the longus colli according to inward 
 probe pressure of usexaminer 1csamt0.5  kg1.0  kg0.5  kg1.0  kgicc0.990.990.980.96sem0.010.020.000.05mdd0.040.050.010.14csa : cross - sectional area ; mt : muscle thickness ; icc : intra - class correlation 
 coefficient ( 95% confidence interval ) ; sem : standard error of measurement ; 
 mdd : minimum detectable differences ( 95% confidence interval ) and 3table 3.inter-rater reliability of the csa and mt of the longus colli according to inward 
 probe pressure of ustest session 1csamt0.5  kg1.0  kg0.5  kg1.0  kgicc0.980.990.970.96sem0.020.020.010.05mdd0.060.050.020.15csa : cross - sectional area ; mt : muscle thickness ; icc : intra - class correlation 
 coefficient ( 95% confidence interval ) ; sem : standard error of measurement ; 
 mdd : minimum detectable differences ( 95% confidence interval ) .
csa : cross - sectional area ; mt : muscle thickness ; icc : intra - class correlation 
 coefficient ( 95% confidence interval ) ; sem : standard error of measurement ; 
 mdd : minimum detectable differences ( 95% confidence interval ) csa : cross - sectional area ; mt : muscle thickness ; icc : intra - class correlation 
 coefficient ( 95% confidence interval ) ; sem : standard error of measurement ; 
 mdd : minimum detectable differences ( 95% confidence interval )
the purpose of the present study was to determine intra- and inter - rater reliability of 
 measurements of the csa and mt of the longus colli according to the inward pressure of the 
 us probe ( 0.5 and 1  kg ) .
we believe that this study is the first to investigate these 
 parameters in this manner .
concerning the intra- and inter - rater reliability , the present study demonstrates that us 
 measurements ( 0.5 and 1  kg ) of the csa and mt of the longus colli have excellent reliability 
 due to the experimental protocol used .
first , the spring gauge provided consistent inward 
 probe pressure that enabled precise and consistent measurements . additionally , a 
 height - adjustable perpendicular fixed bar was helpful in the adjustment of the precise probe 
 height , with respect to its contact with the surface of the skin over the longus colli in 
 response to different degrees of inward pressure .
a previous study suggested that us 
 requires a strict measurement protocol because slight angulations of the probe and 
 variations in the probe pressure exerted on the underlying muscle greatly influenced the 
 images produced10 .
ishida and 
 watanabe18 reported that maintenance of 
 a consistent inward probe pressure is required to enhance the reliability of us measurements 
 of the lateral abdominal muscle .
jeon et al.17 suggested that maintaining a consistent inward pressure is 
 essential to ensuring the reliability of the results when the mt of the psoas major is 
 measured by different examiners .
second , the hands - free probe holder can also affect 
 reliability : to steady the position , orientation , and inward pressure of the us probe , a 
 hands - free probe holder is required during us measurements16,17,18 .
hands - free probe holders may be better able to prevent us 
 measurement errors than hand - held probes .
first , our results are not widely generalizable 
 because all of the participants were healthy students .
thus , additional research is needed 
 to establish whether our findings apply to participants with neck pain .
the present study demonstrated that us measurement of the csa and mt of the longus colli 
 has excellent intra- and inter - rater reliability when a consistent inward pressure is 
 maintained .
based on these results , a consistent inward probe pressure must be maintained to 
 enable precise us measurement of the longus colli muscle .
[ purpose ] to investigate the intra- and inter - rater reliability of the cross - sectional 
 area ( csa ) and muscle thickness ( mt ) of the longus colli according to the inward pressure 
 of an ultrasonography ( us ) probe ( 0.5 and 1  kg ) . 
 [ subjects ] thirteen subjects ( 11 males 
 and 2 females ; age , 23.1  2.9  years ) were recruited via convenience sampling of 
 university students . 
 [ methods ] real - time us measurements of the csa and mt of the longus 
 colli were recorded 
 . repeated us measurements using a standard protocol were performed on 
 the same day 1 hour apart to assess intra- and inter - rater reliability . 
 intra - class 
 correlation coefficients ( icc ; 2 , 1 ) were used to determine the intra- and inter - rater 
 reliability of the csa and mt measurements . [ results ] 
 this study demonstrated that the us 
 measurements ( 0.5 and 1  kg ) of the csa and mt of the longus colli give reliable and 
 consistent results . 
 [ conclusion ] based on these results , a consistent inward pressure of 
 the probe is needed to ensure precise us measurement of the longus colli muscle .