patients with spinal cord injuries ( sci ) have motor and sensory disorders , resulting in 
 disabilities in daily activities1 . 
 although they should receive intensive care and rehabilitation treatment after injury , most 
 patients experience disorders ( e.g. , impingement syndrome , osteoarthritis , bursitis , 
 paralysis , parasthesia ) in their upper extremities , trunk , or lower extremities due to 
 physiological and physical changes .
they experience functional disorders in ambulation , 
 particularly with respect to activities of daily living ( adl)2 , 3 . due to these ambulatory 
 disorders ,
spinal cord injury patients often use wheelchairs and learn to perform basic adl 
 ( e.g. propulsion , lifting , transfer ) in relation to the use of a wheelchair .
these patients often suffer upper extremity pain due to performance of adl almost 
 exclusively by the upper extremities ( overall upper extremity pain prevalence rates : 58.5% ; 
 shoulder : 71% , elbow : 35% , wrist : 53% , hand : 43%)4 , and such pain impedes the performance of adl5 . among the basic adl
, transfer is a task that is performed 
 by each patient 1520 times per day , on average .
this is the most burdensome task for the 
 musculoskeletal system , the nervous system , and the cardiovascular system among wheelchair 
 related adl . in particular
sitting pivot transfer ( spt ) is the most frequently used transfer method using the upper 
 extremities . using this method ,
the hip is moved from the initial seat ( iseat ) to the target 
 seat ( tseat ) using the trailing hand ( th ) and the leading hand ( lh ) while both lower 
 extremities maintain contact with the floor as an axis6 .
one is a translational 
 strategy in which the head and the hip move horizontally in the same direction , and the 
 other is a rotational strategy in which the head and the hip move while rotating in 
 different directions using both feet as a pivot2 . during spt movements , the shoulder is in a position of internal 
 rotation and abduction , which will invariably cause shoulder impingement unless other aids 
 are used6 .
although there are many 
 shoulder pain treatment methods , the shoulder can not take any rest because of transfer 
 movements , which are essential for patients adl .
recently , some studies have been conducted of methods for minimizing shoulder injuries 
 through dynamic analyses of transfer movements . according to a recent study
, spt is the most 
 efficient and imposes the lowest loads on individual joints when the wheelchair moves 
 horizontally without any variation in floor height compared to when there are differences in 
 height between the position of the wheelchair and the floor on which the wheelchair 
 moves8 .
a previous study using kinematic analysis of spt movements reported that , in an experiment 
 conducted to measure loads on the shoulder joint in three different positions , anterior 
 trunk positions mobilized large muscles around the shoulder and the mobilization of muscles 
 reduced the risk of rotator cuff impingement2 .
the maximum flexor momentum at the shoulder joint during spt 
 movements is known to be approximately 1.45 nm / kg at the th and approximately 1.36 nm / kg at 
 the lh of patients and approximately 1.56 nm / kg in healthy adults9 .
joint reaction force is known to be always higher at th 
 than at lh , and joint loads are known to be higher during transfer to higher seats10 . in a recent study of human movement , it was reported that the destabilizing force ( df ) , 
 which tends to make movements , was determined by the height of the center of mass ( com ) , 
 center of pressure ( cop ) , base of support ( bos ) , and the reaction force and shear force 
 acting on the floor11 . in a study of the 
 df and stabilizing force ( sf ) occurring in spt movements , it was reported that low df and 
 high sf were shown , and that the low df and high sf were related to the securing of 
 stability against the risk of falls12 , 13 .
nevertheless , no study to date has been conducted on changes in loads on the lower 
 extremities during actual spt in relation to decreases in bos and increases in the height of 
 the com .
studies of 
 transfer methods that will reduce the burden on the upper extremity will contribute to the 
 relief of shoulder pain eventually leading to the prevention of paraplegic patients 
 shoulder pain .
therefore , the purpose of the present study was to examine the effects of 
 different heights of the hands of the supporting arms on the loads on the shoulder joint 
 during transfer movements in order to seek effective and safe transfer methods .
the subjects of the present study were recruited from among students , who voluntarily 
 wanted to participate in the study , attending in hallym college located in chuncheon - si . 
 based on the principles of the declaration of helsinki , research ethics , the purpose and 
 contents of the study
were sufficiently explained to the subjects before they participated 
 in the experiment , and they were required to submit their written informed consent .
the 
 subjects had no history of musculoskeletal system disease of their upper extremity . among 
 the recruited subjects , only 18 adult males participated in the experiment : excluding those 
 who could not lift their trunk because their upper extremity muscle strength was not 
 sufficient to perform spt movements and those who could not wear the tight suit for motion 
 analysis were excluded .
the iseat and tseat of the device specially designed for spt were made from 30  
 50  cm sized 3.2  mm thick steel plates , and the plates for th and lh were made 
 using 60  50  cm sized steel plates of the same thickness as the seats . for 
 height adjustment ,
hand jerks that could endure at least 2,000 kgf were fixed by welding 
 between the steel plates .
thereafter , 1  cm diameter holes were drilled at the four corners 
 of the welded steel plated using a laser .
long steel bolts were inserted through the holes 
 to fix the upper and lower steel plates of the iseat and tseat .
the th and lh plates were 
 fixed with bolts in order to minimize vibration or shaking caused by loads during transfer 
 movements .
then , 20  cm high aluminum profiles were fastened to the two fixed steel plates 
 using bolts so that the final height could be adjusted to between 35  cm and 65  cm .
prior 
 to the experiment , audio - visual education on the rotational strategy among spt method was 
 conducted along with a verbal explanation .
the subjects moved from the iseat at a height of 50  cm to the tseat 
 at the same height at an angle of 90. the subjects adopted a posture with the th located as 
 close as possible to the hip on the iseat and the lh located as close as possible to the 
 tseat . to keep the same hand positions for all subjects , the shape of a hand was printed and 
 attached to the positions of the th and the lh on the force plates ( fig .
the trailing hand and the leading hand were 
 placed on the hand shaped marks attached to the force plates and the initial seat and 
 the target seat were placed immediately next to the two hand positions .
the leading hand were 
 placed on the hand shaped marks attached to the force plates and the initial seat and 
 the target seat were placed immediately next to the two hand positions .
the angle 
 between the two tables was set to 90 after the verbal order 
start  , the subjects moved from the iseat to the tseat by lifting 
 their hips solely using the strength of their arms . at this time
, the subjects were 
 instructed to limit the activity of their lower extremities maximally .
then , the subjects 
 performed the same movement after reducing the height of the th and the lh plates by 10  cm . 

the height of 50 or 40  cm was randomly selected to eliminate order effects .
the subjects took a sufficient rest 
 of one minute between each movement . during the spt movements ,
if a subject complained of 
 pain in any part of the upper extremity , the experiment was immediately stopped . in the present study ,
the time labeled at which loading occurred on the force plate below the lh after the 
 verbal order 
start  was labeled event1 , and the time at which the loading became 0 at the 
 th plate , when the transfer to the tseat had been completed , was labeled event2 .
the angles of the movements of the upper extremity and the trunk were measured using a 
 motion analyzer ( oqus100 , qualisys , sweden ) . before the experiment
, the study subjects wore 
 upper and lower body stockings that clung to their body shapes , and 15  mm diameter 
 reflective markers , that could be recognized by infrared cameras , were attached to the c7 
 and t10 vertebrae , jugular notch , xiphoid process of the sternum , head ( left / right forehead 
 and rear head ) , acromion , upper arms , humeral lateral epicondyles , wrist lateral / medial 
 epicondyles of the wrists , 2nd metacarpal heads , and asis and psis .
the light signals 
 reflected individual markers were recorded using six cameras and qtm ( qualisys , sweden ) at a 
 rate of 100 frames per second . the body joints and segments in the obtained data
were 
 labeled , and the kinematics of individual joints and segments were quantitatively analyzed 
 using visual 3d software ( c - motion , usa ) . to reduce measurement errors , the markers for 
 motion analysis
force plates ( 9260aa6 , kistler , switzerland ) were used to measure the external force 
 generated by the upper extremities while spt movements were being performed .
the voltages 
 measured at different loads were amplified through an amplifier ( 5233a2 , kistler , 
 switzerland ) and transmitted to the computer through an a / d board ( usb-2533 , measurement 
 computing corporation , usa ) .
then , the values of the force applied to the force plates by 
 external loads were calculated using qtm motion analysis software program .
kinetic data were 
 sampled at 1,000  hz to align with the kinematic data .
the kinematic data measured between 
 event1 and event2 of each subjects were evenly divided into 101 frames ( 0 to 100 frames ) and 
 normalized to each subject s height and weight values .
each subject s spt movements were 
 measured five times and the average was used in the analysis .
statistical analysis was conducted using pasw ver . 18.0 ( spss , ibm , usa ) .
the paired t - test 
 was used to compare kinetic and kinematic data between the two heights of the th and lh .
the group means ( standard deviation ) of age , height , weight of the participants were 21.11 
 ( 1.71 ) years , 1.78 ( 0.04 ) meters , 74.28 ( 9.40 ) kilograms , respectively .
the maximum 
 flexion of the trunk was significantly larger when the hand position was low 75.14 ( 7.95) 
 than when the hand position was normal 53.12 ( 13.50) ( p=0.000 ) .
the maximum ranges of 
 lateral flexion when the hand positions were low and normal were 48.04 ( 9.37) and 42.82 
 ( 9.74) , respectively , and the difference was significant ( p=0.022 ) .
the maximum ranges of 
 rotation when the hand positions were low and normal were 0.26 ( 9.72) and 17.89 ( 11.24) , 
 respectively , and the difference was significant ( p=0.000 ; table 1table 1.means (  sd ) of the peak trunk angles of each hand heightcomponenttrunkhlhnpeak angle ( degree)flexion75.1 ( 8.0)53.1 ( 13.5)lateral flexion ( left)48.0 ( 9.4)42.8 ( 9.7)rotation ( left)0.3 ( 9.7)17.9 ( 11.2)hl : low hand height ( 40  cm ) , hn : normal hand height ( 50  cm ) , * p<0.05 ) .
hl : low hand height ( 40  cm ) , hn : normal hand height ( 50  cm ) , * p<0.05 the maximum flexion angles of the shoulder joint when the hand positions were low and 
 normal were 51.55 ( 10.25) and 40.89 ( 11.35) , respectively , at the th ( p=0.000 ) and 32.03 
 ( 8.87) and 18.68 ( 7.29) , respectively , at the lh ( p=0.000 ) .
the differences in the angles 
 between the two hand heights were significant at both the th and at the lh .
the maximum 
 abduction angles were not significantly different between the two hand heights at the th , 
 but showed significant differences at the lh , with values of 15.60 ( 10.53) and 13.51 
 ( 8.04) when the hand positions were low and normal , respectively ( p=0.027 ) .
the maximum 
 rotation angles were not different between the two hand heights at the th , but they showed 
 significant differences at the lh , with values of 74.79 ( 14.22 )  and 64.90 ( 11.20 )  when 
 the hand positions were low and normal , respectively ( p=0.000 ; table 2table 2.means (  sd ) of the peak shoulder angles of each hand heightcomponenttrailing handleading handhlhnhlhnpeak angle ( degree)flexion51.6 ( 10.3)53.1 ( 13.5)32.0 ( 8.9)18.7 ( 7.3)abduction16.6 ( 8.6)42.8 ( 9.7)15.6 ( 10.5)13.51 ( 8.0)rotation ( internal)37.5 ( 19.3)17.9 ( 11.2)74.8 ( 14.2)64.9 ( 11.2)hl : low hand height ( 40  cm ) , hn : normal hand height ( 50  cm ) , * p<0.05 ) .
hl : low hand height ( 40  cm ) , hn : normal hand height ( 50  cm ) , * p<0.05 the values of anterior / posterior force measured at the force plates below the th and lh 
 when the hand positions were low and normal were 8.98 ( 1.96)% ( bw ) and 7.89 ( 1.96)% ( bw ) , 
 respectively , at the th , and the difference was significant ( p<0.05 ) , but there was no 
 significant difference at the lh .
the values of lateral / medial force showed significant 
 differences between the two hand heights at the th with values of 7.96 ( 2.33)% ( bw ) and 8.92 
 ( 2.92)% ( bw ) , respectively ( p<0.05 ) , but did not show any significant difference at the 
 lh .
the values of vertical force did not show statistically significant difference between 
 the two hand heights at the th or the lh ( table 
 3table 3.means (  sd ) of the peak forces of each hand heightcomponenttrailing handleading handhlhnhlhnpeak force ( % bw)posterior9.0 ( 2.0)7.9 ( 1.7)0.1 ( 0.5)0.1 ( 0.3)lateral8.0 ( 2.3)8.9 ( 2.9 ) 1.4 ( 1.8)1.3 ( 0.8)vertical44.7 ( 6.0)45.4 ( 4.9)43.2 ( 7.2)45.2 ( 6.5)bw : body weight , * p<0.05 ) .
the purpose of the present study was to analyze the movements of the shoulder joint and the 
 trunk at different heights of the th and the lh in spt movements to provide reference data 
 for effective and safe transfer methods for spinal cord injury , paraplegia , and lower 
 extremity amputation patients .
reported that during transfer to seats of 
 different heights , trunk flexion of 6871 appeared at the initial hip lifting , that trunk 
 flexion facilitated spt movements during which the hip was lifted and moved , and that trunk 
 flexion affected balance and stability in spinal cord injury patients with weakened erector 
 spinae muscle or neurological disorders with upper extremity muscle strength8 .
advised that the degree of 
 trunk flexion increased the time of hip lifting for the entire spt movement14 .
finley noted that patients who complained 
 of shoulder impingement showed smaller trunk flexion angles , and that smaller angles were 
 associated with the formation of small trunk flexion moments at the beginning of the initial 
 phase of hip lifting after injury6 . in the 
 present study , when the hand height was in the lower position ( 40  cm ) , trunk flexion 
 essentially increased to use the lower hand position as the weight - bearing surface .
positive 
 effects could be expected from this in that trunk flexion generally acts as propulsion 
 during hip lifting at the beginning of transfer movements . another movement that indispensably appears along with trunk flexion in spt movements is 
 rotation .
trunk rotation occurs in the opposite direction to the seat that would move around 
 the th . according to a study conducted by forslund et al.15 ,
trunk rotation of 41 can occur at the maximum in females , and 32 
 can occur at the maximum in males .
the difference was assumed to be attributable to 
 differences in shoulder widths and pelvis sizes between the genders . in the present study , 

rotation was shown to be smaller by 17.73 on average when the hand height was lower .
this 
 is assumed to be associated with the increase in trunk flexion appearing when the hand 
 height is low .
in addition , increases in trunk rotation are thought to affect shoulder joint 
 angles and the strength of the surrounding muscles directly . in previous spt
movement analysis studies , maximum shoulder joint flexion was 36 , 
 abduction was 50 , and internal rotation was 15306 , 
 16 , 17 .
it is known that during transfer movements , complicated upper 
 extremity movement combinations reduce the subacromial space and eventually affect the 
 rotator - cuff muscle and soft tissues ( e.g. bursae ) around the shoulder joint resulting in 
 shoulder impingement .
the angles of flexion and abduction at low hand positions in the 
 present study were different from those reported by previous studies .
flexion should 
 increase when the bearing surface is low , and larger flexion and abduction angles should 
 occurs to compensate for the bent trunk ( fig . 

 : 
 trunk flexion angle at hn ,  : trunk flexion angle at hl ) .
 : 
 trunk flexion angle at hn ,  : trunk flexion angle at hl since trunk rotation movements occur around the axis of the th at the beginning , of spt 
 movements , internal rotation of the th shoulder is inevitable . in a study conducted by 
 finely et al . , patients with shoulder impingement were identified as utilizing more internal 
 rotation than other patients during spt movements6 .
also , a study conducted by riek et al . reported that internal 
 rotation of 49 occurred at the th of spinal cord injury patients . in the present study , 

internal rotation at the th occurred more frequently when the hand was low , and this seems 
 to increase the risk of shoulder impingement17 .
however , gagnon et al.8 advised that the maximum angle of internal rotation might vary with 
 hand position when spt movements began .
therefore , this problem might be resolved by studies 
 seeking the hand position that can minimize internal rotation of the shoulder .
forslund et al.15 reported that when sci 
 patients transferred to a seat that was 7  cm higher , the maximum vertical reaction force at 
 the th was always higher than that at the lh , and that this seemed to be a natural 
 phenomenon because the th is closer to the body to initiate movements at the beginning of 
 the movement .
they reported that the average vertical reaction force at the th was 32% ( bw ) , 
 and that it was 24.5% ( bw ) at the lh . in a study conducted by gagnon et al.18 ,
the values were 44.5% ( bw ) at the th and 
 39.6% ( bw ) at the lh , similar to the values of the present study , 43.2% ( bw ) at the th and 
 41.3% ( bw ) at the lh .
advised that the maximum vertical reaction force was 
 different between male and female spinal cord injury patients because in the case of males , 
 force was delivered from the th to the lh while in the case of females , force was exerted on 
 both hands almost simultaneously because males were stronger than females18 . in the present study , since all of the 
 subjects were males , the subjects exerted more force at the th when they transferred and a 
 relatively smaller vertical reaction force was observed at the lh .
when the hand positions 
 were low , the movement accordingly began with the trunk more bent , and this seems to have 
 acted as a dynamic advantage for vertical reaction force in the phase of hip lifting during 
 transfer movements . with regard to the shearing force ( anterior / posterior , medial / lateral ) measured at the 
 force plates ,
the anterior shearing force was found to be higher when the hand position was 
 lower than the seat position , and the lateral shear force was found to be higher when the 
 hand height was the same as the height of the seat .
when the hand position is low , greater 
 movement to bend the trunk forward occurs . in reaction to the forward
bending of the trunk , 
 relatively more anterior and relatively smaller lateral forces act .
this is associated with 
 the destabilizing force that decreases when the hand height decreases due to the com 
 becoming farther from the bos as the hand height decreases .
duclos et al.11 advised that if the destabilizing force is 
 large , the movement of the center of pressure ( cop ) to the outside of the bos would become 
 more difficult , and that if the com is high , the destabilizing force would be reduced 
 allowing movements to be made with a smaller force . given that when the hand is lower , the 
 vertical reaction forces at the th and the lh as well as the lateral force are smaller , it 
 is our opinion that when the bearing surface for the arm is lower , transfer movements can be 
 made with smaller force , and , in particular , the vertical loads and lateral loads on the 
 shoulder joint can be reduced .
limitations of the present study include the fact that the experiment was not conducted 
 with spinal cord injury patients with shoulder pain , and that data were not obtained through 
 measurements in actual transfer environments , but were obtained in a laboratory setting . 

furthermore , since the experiment was conducted with only healthy male , the results can not 
 be generalized to both sexes , and even though the subjects were educated not to use their 
 lower extremity , they might not have been able to control their lower extremities as 
 completely as actual patients . taken together , our results indicate that as the hand position becomes lower , trunk flexion 
 increases .
this would act as a dynamic advantage ( propulsion ) for the movement to lift the 
 hip , thereby reducing the vertical reaction force and shear force acting on the shoulder 
 joint , thereby reducing the load on the shoulder joint . through the present study ,
the position of the supporting arms during spt movements lower 
 than the seat position was identified to have biomechanical advantages over the position of 
 the supporting arms at the same height as the seat position .
the results of the present 
 study can be applied as guidelines for effective and safe methods for quadriplegia or spinal 
 cord injury patients spt , and can be utilized as reference data when considering the 
 appropriate heights of aids for wheelchairs .
 [ purpose ] the purpose of this study was to compare the changes in trunk and shoulder 
 angles , and reaction forces under the two hands elicited by different hand base of support 
 positions during sitting pivot transfer . 
 [ subjects and methods ] eighteen unimpaired 
 subjects performed independent sitting pivot transfer . 
 subjects performed sitting pivot 
 transfer between an initial seat to a target seat by only using their hands positioned at 
 the same height as and lower than the seat position . trunk and shoulder kinematics , and 
 reaction forces on the trailing and 
 leading hands were calculated . mean 
 peak joint angles 
 and forces were compared between the hand positions using the pared t - test for the lift 
 phase of the transfer . 
 [ results ] there were significant increases in the trunk angles of 
 forward and lateral flexion , even though rotation decreased while transferring in the 
 lower hand position . increased shoulder flexion , anterior / posterior forces and reduced 
 lateral forces were also shown . 
 [ conclusion ] placing the hands of the supporting arms 
 lower than the seat position during sitting pivot transfer was identified as having 
 biomechanical advantages . 
 therefore , the lower hand position can be recommended as an 
 effective and safe method for sitting pivot transfer by patients with spinal cord injury 
 and can be utilized as a reference data for considering the appropriate height of aids for 
 a wheelchair . 