the supraspinatus is one of the rotator cuff muscles ; it is positioned at the supraspinous 
 fossa and under the trapezius and it abducts the shoulder joints to rotate externally1 , 2 . 
 the rotator cuff muscles are highly important for dynamic stability of the shoulders , but it 
 is the supraspinatus that plays an important role in dynamic stability during shoulder 
 abduction . the supraspinatus is also the most frequently injured area when the rotator cuff 
 muscles are injured3 .
thus , strengthening 
 the supraspinatus is essential to prevent damage to the rotator cuff .
generally , the full can and empty can positions are recommended as exercises that 
 strengthen the supraspinatus4 , 5 .
boettcher et al.6 indicated that there was no distinctive difference in muscle 
 activity between the full can and empty can positions .
however , few studies have been 
 conducted to determine changes in the cross - sectional areas of the supraspinatus according 
 to abduction angles , suggesting no definite answers concerning which posture and abduct 
 angles are the best for strengthening the supraspinatus . jobe and
moyne7 suggested an abduction 
 angle of approximately 90 for the supraspinatus strengthening exercise , while escamilla et 
 al.8 suggested that muscle activity of 
 the supraspinatus was highest at an abduction angle of 60. however , in clinical practice , 
 no recommendation for the abduction angle has been made for the supraspinatus strengthening 
 exercise , so various angles have been applied by physiotherapists .
it would be much easier 
 for physiotherapists to determine the criteria for strengthening exercises if they knew 
 which abduction angle of the shoulders incurs the largest cross - sectional area of the 
 supraspinatus .
therefore , the objective of this study was to determine by ultrasonography 
 the changes in the supraspinatus cross - sectional areas according to shoulder abduction 
 angles .
forty subjects at d college participated in the present study ( 20 males and 20 females ) . 

the average ages , heights , and weights of the subjects were 21.32.3  years , 165.24.2  cm , 
 and 57.64.8  kg , respectively .
we excluded individuals who had shoulder pain ; had cervical , 
 shoulder , or elbow operations ; had experienced sprains or strains ; or had neurological 
 problems or blood vessel disorders .
all included patients understood the purpose of this 
 study and provided written informed consent prior to participation in the study in 
 accordance with the ethical standards of the declaration of helsinki . in order to measure
the thickness of the supraspinatus muscle during shoulder abduction , we 
 seated the subjects in chairs without elbow and back rests , and all subjects wore clothes 
 that exposed the right shoulder and scapula .
while subjects were sitting comfortably , their 
 waists and backs remained straight , their eyes faced the horizontal plane in front of them , 
 and their foreheads and chins were positioned vertically .
shoulder abduction was conducted 
 in the frontal plane , the elbows of the subjects were extended , and the palms faced the 
 front with the thumbs up . during abduction , we set four abduction angle levels 
level i ( 0 to 30 ) , level ii ( 30 to 
 60 ) , level iii ( 60 to 90 ) , and level iv ( 90 to 120)to measure the thickness of the 
 supraspinatus muscle with a newly manufactured angle plate ( 100  cm width100  cm length ) 
 designed for that purpose .
the center point of the angle plate was positioned at the axis of 
 the movement of the shoulder joint . in order for the subject to be able to position their 
 abduction at five different angles ,
one research assistant adjusted the arm of the subject 
 so that it was positioned at the appropriate angle , and the subject maintained the position 
 while the other research assistant monitored the subject s response . in each abduction step , 

subjects maintained positions for 10 seconds to permit the recording of ultrasonography 
 images and took a rest for 10 seconds between steps .
all subjects practiced three times 
 before the measurement . while the subjects conducted each level exercise , an ultrasound imaging system ( mysono , 
 seoul , south korea ) and a 7.5-mhz transducer were used to measure muscle thickness .
two 
 experienced researchers with ultrasonography experience participated in the experiment to 
 measure the ultrasonographic image . before ultrasonography
, the shoulder areas of all subjects were wiped with alcohol gauze , 
 and gels were applied to the supraspinatus region .
one researcher positioned the transducer 
 to give the optimized image of the supraspinatus , while the other researcher operated the 
 computer to capture the optimized supraspinatus image .
a line was drawn between the 
 acromioclavicular joint and the superior angle to move the transducer in the longitudinal 
 direction , and the transducer was positioned to see the starting point at the left side of 
 the image .
the right side of the supraspinatus muscle of all subjects was measured two times 
 for each level , and the best quality image was selected . during measurement , the mysono u6 

was positioned behind the back of the subject so that the subject could not see the 
 ultrasonographic image .
the images obtained from ultrasonography were used to measure the supraspinatus muscle 
 thickness by using the national institutes of health image j software ( version 1.44 for 
 windows ) . for measurement of supraspinatus muscle thickness
, a reference line was drawn at 
 the starting point of the muscle at the left side of the image , while vertical lines were 
 drawn 0.5  cm , 1  cm , and 1.5  cm from the reference line .
the distance from the boundary 
 between the trapezius and the supraspinatus muscle and between the supraspinatus muscle and 
 the scapular fossa were measured .
average values of the measured muscle thickness were used , 
 and the change rate of muscle thickness was calculated by the formula ( muscle thickness at 
 the time of contraction  muscle thickness at the time of rest)/muscle thickness at the time 
 of rest .
all measurements were conducted three times , and averages were used as the final 
 result values9 . based on this protocol ,
a 
 test  retest reliability study was conducted to determine the degree of reliability between 
 the pre- and post - tests of ultrasound measurements of supraspinatus muscle size in normal 
 young adults .
intra - class correlation coefficient ( icc ) statistical analysis revealed good 
 to excellent iccs ranging from 0.74 to 0.93 .
the data collected from this study were analyzed using spss 17.0 , and the average and 
 standard deviation are presented .
in addition , repeated measures of analysis of variance was 
 conducted to determine the rate of change in the thickness of the muscle according to 
 abduction angle .
using ultrasonography , the changes in the cross - sectional area of the supraspinatus 
 according to the shoulder abduction angles were measured .
the average rate of change in the 
 thickness of the supraspinatus showed that level iii ( 60 to 90 ) exhibited the most 
 statistically significant change ( p<0.05 ) ( table 
 1table 1.comparison of changes in supraspinatus thickness according to abduction angle 
 ( unit : cm)level ilevel iilevel iiilevel ivmeansd*0.360.320.670.410.850.500.650.39*p < 0.05 .
the shoulder joints consist of ball and socket joints with insufficient stability but very 
 high mobility . because of their wide movement range
, it is important for the shoulder joints 
 to ensure stability and mobility between many ligaments and muscles .
the rotator cuff muscle 
 is important for maintaining stability within the range of most movements of the shoulder 
 joint10 . in addition
, the rotator cuff 
 muscle always moves with movement of the shoulder joints , thus playing the role of a dynamic 
 ligament . because of this , it frequently experiences damage and is one of the main causes of 
 shoulder pain11 .
the supraspinatus is the most frequent area of damage in the rotator cuff muscle3 ; thus , the supraspinatus strengthening 
 exercise is highly important for the dynamic stability of this muscle .
the full can and 
 empty can positions are both recommended as examination methods for the supraspinatus4 , but we conducted abduction based on the 
 suggestion that the full can position should be used to avoid conflicts in the subacromial 
 space12 . while different recommended positions and angles have been reported for the supraspinatus 
 strengthening exercises , the most commonly used angle is 90 abduction and 30 horizontal 
 adduction .
abduction at 90 is reported to result in the highest muscle activity of the 
 supraspinatus7 ; however , escamilla et 
 al.8 suggested that 60 of abduction 
 result in the highest muscle activity in the supraspinatus .
furthemore forbush et al.13 reported that both the full can and empty 
 can positions at 60 of abduction result in a significant increase in cross - sectional area 
 compared with that at the time of stabilization .
another study recommended less than 60 of 
 abduction for the empty can position to avoid conflict in the subacromial space , but it also 
 recommended consideration of the full can position11 .
the measurement results in this study comparing abduction angles of 0 , 30 , 60 , 90 , and 
 120 showed that the largest cross - sectional area of the supraspinatus was found between 60 
 and 90. this result is consistent with previous results showing that the muscle activity 
 and cross - sectional area of the supraspinatus were greatest at a 60 abduction angle12 .
we suggest the reason for our results is 
 that the movement of the shoulder joint is minimized at abduction angles between 60 and 
 90 , so abduction under the stable condition creates stronger torque in the supraspinatus . 
 therefore
, performance of abduction exercises that strengthen the supraspinatus , which is 
 essential to improve the functions of the rotator cuff muscle , is suggested at abduction 
 angles between 60 and 90. while previous studies have suggested only one angle for 
 abduction , we set a range of angles instead of a single angle to suggest an effective range 
 of movement .
 [ purpose ] the purpose of this study was to determine the changes in the supraspinatus 
 cross - sectional areas according to shoulder abduction angles , using ultrasonography . 
 
 [ subjects and methods ] the subjects consisted of 40 individuals ( 20 males and 20 females ) . 
 
 the cross - sectional areas of the supraspinatus of all subjects were measured with 
 ultrasonography at abduction angle of 0 , 30 , 60 , 90 , and 120. we set four abduction 
 angle levels ( i , ii , iii , and iv ) , 0 to 30 , 30 to 60 , 60 to 90 , and 90 to 120 , 
 respectively , when determining the largest change in cross - sectional area . [ results ] 
 the 
 results revealed that cross - sectional areas of the supraspinatus increased at all levels , 
 but the abduction angle level with the largest increase in cross - sectional area of the 
 supraspinatus was level iii . 
 [ conclusion ] the above results indicate that performing 
 exercises at an abduction angle between 60 and 90 will be the most effective for 
 supraspinatus strengthening in clinical practice . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION