wheelchair propulsion is essential for ambulation in people with paraplegia . in particular , 
 people with paraplegia due to spinal cord injuries have many upper - limb problems owing to 
 trunk instability and repetitive wheelchair propulsion . trunk impairments due to manual 
 wheelchair propulsion cause an unstable sitting posture , which decreases the person s 
 abilities to perform wheelchair activities during daily living1 . manual wheelchair users must repetitively use limited upper - limb 
 muscles against a high mechanical load2 . manual wheelchair users have many opportunities to overload the trunk , neck , and upper 
 extremities during wheelchair propulsion , which incur a risk of overuse disease and chronic 
 pain in contrast with normal people3 , 4 . therefore , it is important to understand 
 the differences in the muscle activities between normal and paraplegic people during 
 wheelchair propulsion in order to help prevent overuse disease . however , previous studies mainly involved subjects who were all normal individuals5 or all paraplegia patients6 and investigated the muscle activities of 
 the upper - limb and trunk muscles7 . thus , 
 there is a deficiency of studies comparing able - bodied individuals and people with 
 paraplegia with respect to the muscle activities of the neck and upper limbs during 
 wheelchair propulsion . therefore , this study compared the muscle activities of the neck and upper - limb muscles 
 between able - bodied individuals and people with paraplegia during wheelchair propulsion on 
 the ground . the subjects were 
 informed of the purpose and methods of the study before the experiment . the subjects 
 provided informed consent before participating in the study . the 8 able - bodied individuals 
 had never used a wheelchair and had not experienced any upper - limb disorders during the past 
 year . meanwhile , the 8 people with paraplegia were full - time wheelchair users , had thoracic 
 spinal cord ( i.e. , t1t12 ) injuries , and had no history of persistent joint pain or 
 musculoskeletal deformities in their upper limbs . to create homogeneity in the wheelchair propulsion skills between the people with 
 paraplegia and able - bodied individuals , we trained all subjects to perform ground wheelchair 
 propulsion such that it took from 1.5 to 3 minutes to cover 200 m8 . the people with paraplegia used their own wheelchairs , 
 while able - bodied individuals used the activity wheelchair as model ( nissin , kitanagoya , 
 aichi , japan ) , which is usually used for individuals with paraplegia . all subjects performed wheelchair propulsion three times at a comfortable speed on the 
 ground . the wheelchair propulsion tasks were intended to measure muscle activity during the 
 mid - point of the push phase of a stroke on the ground . a surface electromyograph ( telemyo 
 2400 t g2 , noraxon , scottsdale , az , usa ) we collected 
 electromyogram signals during the push phase of wheelchair propulsion and processed the root 
 mean square and normalization by maximum voluntary isometric contraction . the activity of 
 the latissimus dorsi ( lsd ) , pectoralis major ( pcm ) , anterior / posterior deltoids ( ad / pd ) , 
 triceps brachii ( trb ) , extensor carpi radialis ( ecr ) , and sternocleidomastoid ( scm ) muscles 
 were measured . the kolmogorov - smirnov test and shapiro - wilk test were performed first to confirm data 
 normality . an independent t - test was performed to test for significant differences in muscle 
 activation between the two groups . a total of 16 male subjects were enrolled . the normal group , which comprised normal 
 able - bodied individuals , had a mean  sd age , weight , and height of 22.75  1.04  years , 
 68.00  4.11  kg , and 175.38  3.11  cm , respectively ; these values for those in the 
 paraplegic group were 37.00  8.47  years , 71.25  8.05  kg , and 170.75  1.04  cm , 
 respectively . respect to weight and height , there were no significant differences between 
 two groups ( p > 0.05 ) but there was a significant difference between two groups in age 
 variable ( p < 0.05 ) . scm activity was higher in the paraplegic group than the normal group ( p < 0.05 ) . 
 likewise , lsd activity was higher in the paraplegic group than the normal group , but the 
 difference was not significant ( p = 0.07 ) . there were no significant differences in the 
 other activities of other muscles between groups ( p > 0.05 ) ( table 1table 1.percentage of maximum voluntary isometric contraction of the upper - limb and neck 
 muscles between normal and paraplegic groupsnormal groupparaplegic groupmeansdmeansdlsd4.36  0.87%10.44  7.98%pcm23.65  13.08%25.67  15.41%scm3.14  1.35%5.82  2.27%ad16.41  6.20%22.39  17.71%pd6.02  1.84%6.60  3.02%trb8.71  5.23%17.42  14.13%ecr23.70  9.09%23.82  9.84%*p lsd : latissimus dorsi ; 
 pcm : pectoralis major ; scm : sternocleidomastoid ; ad : anterior deltoids ; pd : posterior 
 deltoids ; trb : triceps brachii ; ecr : extensor carpi radialis ) . * lsd : latissimus dorsi ; 
 pcm : pectoralis major ; scm : sternocleidomastoid ; ad : anterior deltoids ; pd : posterior 
 deltoids ; trb : triceps brachii ; ecr : extensor carpi radialis this study compared the upper - limb and neck muscle activities during wheelchair propulsion 
 between healthy people and people with paraplegia . recent 
 increases in sitting time as a result of work in front of computer monitors have increased 
 the tendency of the scm to be overloaded , which causes many pathologies collectively termed 
  visual display terminal syndrome10 . muscles can influence the brachial plexus nerve , internal and external carotid arteries , and 
 cervical lymph nodes below them11 . 
 therefore , dysfunction of the scm muscle can cause head and face pain , nausea , dizziness , 
 coryza , and lacrimation12 . in people with 
 paraplegia complaining of shortness of breath , , people 
 with paraplegia can overactivate the scm during wheelchair propulsion , which may lead to 
 visual display terminal syndrome as mentioned above . therefore , physical therapy should 
 include posture education such as maintaining a chin - in position when the trunk or neck is 
 in flexion in order to prevent excessive use of the scm as well as provide treatment to 
 stretch the scm for people with paraplegia who use a manual wheelchair14 . the lsd muscle tended to exhibit relatively higher muscle activity in the paraplegia group 
 than the normal group , although the difference was not significant . the lsd plays many roles 
 including extension , adduction , flexion from an extended position , and internal rotation of 
 the shoulder joint15 . future studies 
 should aim to clarify the shoulder motion angle during wheelchair propulsion in order to 
 explain why the lsd muscle exhibits higher activity in paraplegia . the major limitations of this study are the lack of motion analysis of the shoulder and 
 neck joints for explicating the muscle activity pattern and the small sample size . in conclusion , during wheelchair propulsion , patients with paraplegia tend to use the scm 
 and lsd muscles more than normal subjects . therefore , physiotherapists should not overlook 
 the treatment of these muscles for patients with paraplegia who are long - term wheelchair 
 users .
[ purpose ] this study compared the muscle activities of the neck and upper - limb muscles 
 between able - bodied individuals and persons with paraplegia during wheelchair propulsion 
 on the ground . [ subjects and methods ] the muscle activities of the neck and upper - limb 
 muscles of 8 normal individuals and 8 individuals with paraplegia were analyzed during 
 wheelchair propulsion . 
 the activities of the latissimus dorsi , pectoralis major , 
 anterior / posterior deltoids , triceps brachii , extensor carpi radialis , and 
 sternocleidomastoid muscles were assessed . 
 [ results ] the paraplegic group showed 
 significantly higher sternocleidomastoid activity than the normal group . 
 latissimus dorsi 
 activity was also higher in the paraplegia group than in the normal group , but the 
 difference was not significant . 
 there were no significant differences in the other muscle 
 activities between groups . 
 [ conclusion ] paraplegic patients tend to use the 
 sternocleidomastoid and latissimus dorsi muscles with greater degrees of activity . 
 therefore , physiotherapists should not overlook the treatment of these muscles for 
 paraplegic patients who are long - term wheelchair users .