previous studies of test - retest reliability of muscle strength measurement using a handheld 
 dynamometer ( hhd ) have shown low reliability in measuring the lower limbs and high 
 reliability in measuring the upper limbs1 , 2 .
wikholm et al.1 conducted an investigation with 3 examiners and healthy 
 subjects and reported that , while the intraclass correlation coefficient ( icc ) values for 
 measurements of elbow flexor and shoulder external rotator muscles , which have low muscle 
 strength , were 0.768 and 0.932 , respectively , that of measurements of knee extensor muscles , 
 which have high muscle strength , was 0.226 .
agre et al.2 conducted an investigation with three examiners and healthy subjects 
 and reported that pearson s product - moment correlation values ranged from 0.19 to 0.96 for 
 the lower extremities , but from 0.88 to 0.94 for the upper extremities .
katoh et al.3 developed a method of 
 measurement with an hhd and a belt in order to increase the reliability of lower extremity 
 muscle strength measurement .
the icc ( 2 , 1 ) values for measurements of hip adduction , 
 external rotation , and internal rotation , the average strength of which was less than 20 
 kgf , ranged from 0.70 to 0.83 without a belt and from 0.97 to 0.99 with a belt , suggesting 
 that using a belt increases reliability even if muscle strength is lower than 30 kgf4 ( 300 n5 ) , which was believed to be the hhd measurement limit .
the purpose of this study was to develop a method of measuring shoulder joint muscle 
 strength with an hhd and a belt and to investigate its test - retest reliability .
the subjects comprised 40 right - handed healthy adults ( 20 male , 20 female ) with an average , 
 height , and weight of 20 ( range 20 to 22 ) years , 164.5  cm ( sd=7.8  cm ) , and 60.8  kg 
 ( sd=13.4  kg ) , respectively , and no history of orthopedic disease or shoulder injury , from 
 whom informed written consent was obtained .
the study was conducted in accordance with the 
 principles of the declaration of helsinki ( 1975 , revised 1983 ) .
explanations of the methods 
 and the purpose of the study were provided by the assessor to the subjects in writing , and 
 consent to participation was obtained in the form of signed consent forms .
the study was 
 approved by the institutional review board of ryotokuji university ( approval number 
 2376 ) .
isometric shoulder joint muscle strengths ( flexion , extension , abduction , external 
 rotation , internal rotation , horizontal extension ) were measured twice with an hhd ( tas 
 f-1 , anima corp . ,
prior to measurement , subjects 
 performed exercises using 50% , 75% , and 100% of maximum muscle strength to both warm - up and 
 practice .
measurements were taken as subjects performed isometric exercises with 3 seconds 
 of maximum effort , once before and once after a 30-second break .
subjects were instructed 
 not to strongly contract muscle groups of the elbow , hand joints , or digits when performing 
 exercises .
measurement conditions are described in table 1table 1.conditions for measuring shoulder joint muscle strength using a handheld 
 dynanometer with a beltexertion taskposturelimb positionsdynanometer positionbelt fixationflexionsupine0 shoulder flexion , 0 abduction , elbow slightly 
 bent , forearm in pronationhumerus lateral supracondylar ridgebed leg below armextensionseated ( a)0 shoulder flexion , 0 abduction , 0 elbow flexion , 
 forearm in pronationolecranon stairs baluster parallel to armabductionseated ( a)90 shoulder abduction , elbow slightly bent , forearm 
 in pronationhumerus lateral supracondylar ridgebed leg below armexternal rotationseated ( b)45 shoulder flexion , 135 elbow flexionstyloid process of the ulnastairs baluster parallel to forearminternal rotationseated ( b)45 shoulder flexion , 135 elbow flexionstyloid process of the ulnastairs baluster parallel to forearmhorizontal extensionprone90 shoulder abduction , 90 elbow flexionolecranon bed leg below arm(a ) the examiner held the subject s shoulder on the measured side .
( b ) to prevent 
 abduction - adduction , a 5  kg bag of sand was fixed between the elbow and the 
 baluster .. a silicon cover was placed on the hhd sensor , and the lower edge of the hdd 
 was fixed at the measuring position on the subject using a hook - and - loop fastener .
then the 
 limb being measured , to which the hhd had been attached , and a fixture such as bed leg or 
 frame , selected according to the measurement being taken , were linked with a belt so that 
 when the subject performed the exercise , force was applied to the hhd .
the belt length was 
 adjusted slightly shorter so that the joint angle defined during exercise .
angle of the belt 
 was adjusted to body part for fixing the hhd and the belt at right angles . while subjects 
 performed the exercise , one physiotherapist ( male , height 180  cm , weight 53  kg ) with over 
 10  years of experience performing muscle strength measurement with an hhd and a belt held 
 both sides of the hhd sensor so it remained relative to the direction of movement ( table 1 ) .
measurements were taken while subjects lay 
 on a training bench ( bed , l 200  cm  w 60  cm  h 42  cm ) with a metal frame and steel legs or 
 sat on a 40-cm high stool with the soles of their feet touching the floor or a platform .
( b ) to prevent 
 abduction - adduction , a 5  kg bag of sand was fixed between the elbow and the 
 baluster . in measuring shoulder flexion
, subjects lay supine on a bed with a bed leg , which was 
 distal to the upper arm on the measurement side , directly under them .
subjects placed their 
 bilateral upper extremities along their sides with their elbow joints in mild flexion and 
 forearms in pronation so that their thumbs were by their sides and their palms were facing 
 down .
the hhd was fixed 
 distal to the upper arm bone with its lower edge at the lateral supracondylar ridge , and the 
 extremity to be measured was linked by the belt to the bed leg . in measuring shoulder joint extension , subjects sat on the stool facing some training 
 stairs with a steel baluster in front of the upper extremity on the measurement side . 

subjects held their trunk vertical with the upper extremity to be measured descending with 
 the forearm in pronation parallel to the baluster .
the hhd was fixed to the posterior 
 surface distal to the humerus with its lower edge at the olecranon fossa , and the extremity 
 to be measured was linked by the belt to the baluster . in measuring shoulder joint abduction ,
subjects sat on a stool by a bed with a bed leg , 
 which was parallel to their anteroposterior axis directly underneath distal to the upper arm 
 when the measurement side was abducted 90 to the shoulder joint , directly underneath them . 

subjects held their trunk vertical with the upper extremity on the measurement side abducted 
 90 at the shoulder joint , elbow joints in mild flexion , and forearms in pronation . in order 
 to prevent the trunk from tilting to compensate for the strain during measurement , the hand 
 on the non - measurement side
was placed on a surface with the palm facing down lateral to the 
 limb being measured .
the hhd was fixed distal to the humerus with its lower edge placed at 
 the lateral supracondylar ridge , and then the extremity to be measured was linked by a belt 
 to the bed leg . in measuring shoulder joint internal and external rotation ,
they placed their elbows on the bed in the middle 
 position of shoulder joint abduction - adduction with the baluster of the training stairs and 
 the forearms parallel .
the extremity to be measured was placed in flexion at an angle at 45 
 of the shoulder joint , and the elbow was placed in flexion at 135 with the forearm 
 perpendicular to the bed . in order to prevent shoulder joint abduction and adduction during 
 measurement , a 5  kg sandbag was positioned between the baluster and the forearm to fix the 
 position of the elbow . for internal rotation ,
the hhd was fixed to the anterior side distal 
 to the forearm ( to the plam of the hand ) , and for external rotation , it was fixed to the 
 posterior side distal to the forearm ( the hand dorsal side ) with is upper edge at the 
 styloid process of the radius ; the extremity to be measured was linked by a belt to the 
 baluster .
in shoulder horizontal extension , subjects lay prone on a bed with their arms extended 
 beyond the edge of the bed up to the distal part of humerus and their shoulder joint 
 abducted to 90 and elbow joint flexed ( the forearm was descending ) . in this position ,
the 
 elbow , bed leg , and shoulder were aligned when viewed from above .
the hhd sensor was fixed 
 to the posterior surface distal to the humerus and the extremity to be measured was linked 
 by a belt to the bed leg . the intraclass correlation coefficient ( icc ) was used to assess relative reliability , and 
 bland - altman analysis was used to assess absolute reliability . when a proportional bias was 
 observed , regression analysis was used to obtain the primary regression equation .
table 2table 2.isometric shoulder muscle strength measurements of young healthy adults made by 
 one tester using a handheld dynamometer with a beltshoulder exertion task1st
time2nd timeflexion16.2 ( 7.9)16.1 ( 7.5)extension14.6 ( 5.2)14.9 ( 4.7)abduction13.9 ( 5.7)13.3 ( 5.5)external rotation8.4 ( 3.4)7.9 ( 3.0)internal rotation15.3 ( 5.8)15.0 ( 5.6)horizontal extension11.0 ( 5.1)10.7 ( 4.2)values are shown as the mean ( sd ) .
the average values for the first and second measurements of shoulder joint muscle strength 
 were as follows : flexion , 16.2 and 16.1 kgf ; extension , 14.6 and 14.9 kgf ; abduction , 13.9 
 and 13.3 kgf ; external rotation , 8.4 and 7.9 kgf ; internal rotation , 15.3 and 15.0 kgf , and 
 horizontal extension , 11.0 and 10.7 kgf .
unit : kgf table 3table 3.reliability of isometric shoulder muscle strength measurements of young healthy 
 adults made by one tester using a handheld dynamometer with a beltshoulder exertion taskicc ( 1,1)bland - altman analysispoint estimation ( 95% ci)loasemfixed biasproportional biasrandom error95% cibias*slope**bias*mdcflexion0.957(0.9210.977)0.60.8 n - exi0.062 p=0.202n - exi4.5extension0.951(0.9100.974)0.80.2 n - exi0.102 p=0.042existabduction0.976(0.9560.987)0.92.10.20.20.9 exist0.040 p= 0.207n - exiexternal rotation0.902(0.8230.947)1.42.40.20.10.9 exist0.111 p=0.107n - exiinternal rotation0.963(0.9320.981)0.20.8 n - exi0.044 p= 0.318n - exi3.0 horizontal extension0.917(0.8500.955)0.30.9 n - exi0.191 p=0.002existreliability : reliability of the 1st value and the 2nd value ; icc , intraclass 
 correlation coefficient ; 95% ci , 95% coefficient interval ; loa , limit of agreement ; 
 sem , standard error of measurements .
* presence of bias : exist , present ; n - exi , not 
 present . *
* slope of regression : mdc , line minimal detectable change shows the reliability of measures of isometric shoulder joint muscle strength 
 measurements . in terms of relative reliability ,
the icc ( 1 , 1 ) values ranged from 0.976 to 
 0.902 ( p<0.05 ) . in terms of absolute reliability ,
fixed biases were observed for 
 abduction and external rotation , and proportional biases were observed for extension and 
 horizontal extension .
the limit of agreement ( loa ) for extension ranged from 16.0% to 
 10.6% .
no systematic biases 
 were observed for flexion and internal rotation , and only random errors were observed .
reliability : reliability of the 1st value and the 2nd value ; icc , intraclass 
 correlation coefficient ; 95% ci , 95% coefficient interval ; loa , limit of agreement ; 
 sem , standard error of measurements .
* presence of bias : exist , present ; n - exi , not 
 present . *
since the icc values for all six types of exercise were > 0.9 , relative test - retest 
 reliability was considered high . however , absolute reliability by bland - altman analysis 
 revealed random errors at 4.5 kgf for flexion and 3.0 kgf for internal rotation .
the average 
 value of flexion and internal rotation was 15 kgf , whereas the random errors relative to the 
 average value were 28% in flexion and 37% in internal rotation , which may impact patient 
 performance .
therefore , it was considered appropriate to adopt the larger of two 
 measurements rather than assuming errors within the random error range when performing 
 measurement once .
proportional biases were observed for extension and horizontal extension . based on the loa , 
 biases from 16.0% to 10.6% for extension and from 18.6% to 20.6% for horizontal extension 
 were expected .
since the range of bias was wide , we considered it appropriate to adopt the 
 larger of two measurements rather than assuming biases within the loa range .
since fixed biases observed in abduction and external rotation mostly showed smaller values 
 in the second measurement for both muscle strengths , we considered it appropriate to adopt 
 the first measurement .
however , as some subjects showed larger values in the second 
 measurement , we considered it acceptable to adopt the larger value of two measurements in 
 line with the other exercise items .
in lower extremity muscle strength measurement with an hhd with a belt in 40 young healthy 
 subjects , katoh et al.3 reported that 
 measurement values when a belt was used were higher than measurement values when the hhd was 
 held by the examiner .
the present study measured the strength of shoulder joint muscles 
 which included many items considered to be below the limit of value that can be measured to 
 have to hand the hhd .
it is necessary to compare measurements obtained with an hhd and a 
 belt with those obtained with an hhd but without a belt , i.e. , with the hhd held by the 
 examiner , when measuring should joint muscle strength in the future .
since the present study measured young adult healthy subjects , the results may differ from 
 those of elderly subjects and those suffering from a disease .
moreover , while the present 
 study performed two measurements taking into account the time required for measurements in 
 the clinic , the results may be different in an investigation in which measurements are 
 performed three times or more .
the relative reliability of isometric shoulder joint muscle strength measurements with an 
 hhd and a belt in young healthy adults was high ; however , as absolute reliability analysis 
 revealed random errors , it was considered appropriate to perform two measurements of 
 isometric shoulder muscle strength and to adopt the larger value of the two .
 [ purpose ] the aim of this study was to develop a method of measuring isometric shoulder 
 joint muscle strength using a handheld dynamometer with a belt and investigate its 
 test - retest reliability . 
 [ subjects ] the subjects comprised 40 healthy adults . [ methods ] 
 
 six types of isometric shoulder muscle strength were measured twice , and reliability was 
 assessed . 
 [ results ] the intraclass correlation coefficient ( 1 , 1 ) values ranged from 0.976 
 to 0.902 . 
 the result of a bland - altman analysis showed differences in the types of errors 
 between measurement items . 
 [ conclusion ] the relative reliability of isometric shoulder 
 muscle measurement using a handheld dynamometer with a belt was high . 
 however , analysis of 
 absolute reliability revealed errors that may affect interpretation of values ; therefore , 
 it was considered that adapting the greater of two measurement values is appropriate . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION