one of the hands is more skilled and characteristically is used to 
 carry out more skilled work2 . the dominant 
 hand is clearly utilized in local muscle activities such as writing , eating , drawing , and 
 throwing3 . most studies on left - handers have dealt with 
 genetic causes or relations between the dominant hand and language , and there are 
 insufficient numbers of studies on other themes . for example , left - handers have risk factors 
 for accidents at work in various areas , as evidenced by the fact that the frequency of 
 accidents among left - handers is reported to be higher than that of right - handers6 . while right - handers place the hand below the area in which they are 
 writing , left - handers invert the writing posture by placing the hand above the area in which 
 they are writing8 . when writing letters , 
 they place the right side of the paper to the left of the very middle line of the body . therefore , when left - handers write letters , they sit to the left side of the desk so that 
 their arm movement is not restricted . in addition , easing tension by ensuring that the wrist 
 or shoulder does not excessively flex when writing letters would prevent any unnatural 
 change of posture9 . the purpose of this study was to investigate if there is any difference in muscle 
 activation ( % mvic ) according to the dominant side in writing . through this research , the 
 study is intended to prevent musculoskeletal disorders in left - handers by identifying the 
 risks for musculoskeletal disorders and restricted work performance for left - handers , and to 
 further suggest the need for work performance enhancement through an ergonomics 
 approach . among the subjects who participated in the research , there were 16 left - handers and 20 
 right- handers . of the left - handers , there were 4 male subjects ( 25.00% ) and 12 female 
 subjects ( 75.00% ) , and the average age was 23.37 ( 3.34 ) . of the 20 right handers , there 
 were 13 male subjects ( 65.00% ) and seven female subjects ( 35.00% ) , and the average age was 
 24.42 ( 4.04 ) ( table 1table 1 . general characteristic n=36left - hander ( n=16)right - hander ( n=20)gendermale4 ( 25.00%)13 ( 65.00%)female12 ( 75.00%)7 ( 35.00%)age23.37 ( 3.34)24.42 ( 4.04 ) ) . the subjects did not have any diseases related to the hands , fractures , or 
 past histories of diseases or fractures , and they were normally healthy persons without 
 neurologic disorders . before the study , the principal investigator explained all procedures 
 to the subjects in detail . all subjects signed an informed consent form , which was approved 
 by the inje university college of human health science studies committee . emg data for measuring muscle activation was collected through the use of a bagnoli emg 
 system ( delsys inc , boston , ma , usa ) to analyze writing performed by the dominant hand . 
 before the experiments , the skin of each subject was cleaned using an alcohol cotton ball to 
 remove foreign substances at the electrode adherence point , after which markers were 
 attached . six electrodes were attached to the fcu ( flexor carpi ulnaris ) , fcr ( flexor carpi 
 radialis ) , ecu ( extensor carpi ulnaris ) , ecr ( extensor carpi radialis ) , and both ut ( upper 
 trapezius ) muscles . to measure muscle activation , the sampling frequency for electromyography signals electromyography signals entering through the six channels were collected , root 
 mean square ( rms ) values were calculated , and the values were then normalized as ratio 
 maximal voluntary isometric contraction ( mvic and % mvic . for each muscle , mvic was measured 
 three times , and the average was calculated . each task was performed three times , and the 
 measured values were used to calculate the mvic and % mvic . the writing items were the 7 subtests of the jebsen - taylor hand function test10 , 11 . the collected data were analyzed using spss for windows for 
 frequency , and the differences were examined using an independent t - test . when conducting the writing activity , the fcu muscle activation was 16.779.12% in 
 left - handers and 10.294.13% ( % mvic ) in right - handers . fcr muscle activation was 19.099.43% in left - handers and 10.645.03% in 
 right - handers . in addition , the ut muscle 
 activation on the writing hand side was 11.915.79% in left - handers and 1.661.19% in 
 right - handers . there were no significant 
 differences in ecu , ecr , or nondominant side ut muscle activation ( table 2table 2 . % mvic depending on dominant handleft ( n=16)right ( n=20)m  sdm  sdfcu16.77  9.12 * 10.29  4.13*fcr19.09  9.43 * 10.64  5.03*ecu27.98  9.6521.77  7.88ecr17.47  7.3010.82  5.75nondominant ut3.43  2.837.32  4.14dominant ut11.91  5.79 * 1.66  1.19*fcu ( flexor carpi ulnaris ) , fcr ( flexor carpi radialis ) , ecu ( extensor carpi 
 ulnaris ) , ecr ( extensor carpi radialis ) , nondominant ut ( nondomianant hand side upper 
 trapezius ) , dominant ut ( dominant hand side upper trapezius ) . fcu ( flexor carpi ulnaris ) , fcr ( flexor carpi radialis ) , ecu ( extensor carpi 
 ulnaris ) , ecr ( extensor carpi radialis ) , nondominant ut ( nondomianant hand side upper 
 trapezius ) , dominant ut ( dominant hand side upper trapezius ) . ninety percent of the population is right - handed , and most living environments are designed 
 for the right - handed12 . designs focused 
 on the righted - handed cause many difficulties for left - handed persons , but studies of this 
 issue are rare13 . this study is intended 
 to lay a scientific foundation for left - hander intervention through quantified analysis of 
 the function of the dominant upper extremity of left - handers when conducting work - related 
 tasks . the results suggest that in the writing activity , left - handers flexed the wrist more than 
 right - handers . in addition , the muscle activations of the fcu and fcr , as well as that of 
 the ut on the writing hand side , were higher among left - handers than right - handers . the 
 results are meaningful in that they scientifically identify the function of the upper 
 extremity based on the dominant hand , as there has previously been insufficient empirical 
 data on the subject . in addition , it is thought that accumulation of with regard to 
 left - handers will expand understanding in this area . based on the results of this study , there is a need to more realistically consider stress in left - handers resulting from the 
 left hand in a world where right - handers task the lead . this study was conducted on people with normal use of the left hand . in left - handers , therefore , left - handers with musculoskeletal disorders would have even bigger risk factors . 
 among them there is a need to examine whether there 
 are differences in work performance between cases in which stroke patients began to use the 
 right hand because of hemiparalysis on the left side and cases in which stroke patients 
 began to use the left hand because of hemiparalysis on the right side . this would provide 
 importance evidence for proving the lowered work performance of left - handers . this study 
 could be expanded to examine schizophrenia and other developmental disorders with a high 
 occurrence rate among left - handers . this study is meaningful in that it offers scientific data in consideration of 
 left - handers , given that there is insufficient ergonomic research based on dominant hand . in 
 addition , this study is meaningful in that it confirmed the need for an occupational therapy 
 approach aimed at enhancing work performance and maximizing independence .
[ purpose ] this study investigated the difference in muscle activation of the dominant 
 upper extremity in right - handed and left - handed persons during writing . 
 [ subjects ] there 
 were 36 subjects ( 16 left- handers/ 20 right- handers ) , and the study was conducted from 
 03/01/2012 to 30/3/2012 . 
 [ methods ] six electrodes were attached to the fcu ( flexor carpi 
 ulnaris ) , fcr ( flexor carpi radialis ) , ecu ( extensor carpi ulnaris ) , ecr ( extensor carpi 
 radialis ) , and both ut ( upper trapezius ) muscles . 
 [ results ] fcu muscle activation was 
 16.779.12% in left - handers and 10.294.13% ( % mvic ) in right - handers . 
 fcr muscle 
 activation was 19.099.43% in left - handers and 10.645.03% in right - handers . 
 in addition , 
 the ut muscle activation on the writing hand side was 11.915.79% in left - handers and 
 1.661.19% in right - handers . 
 [ conclusion ] as a result of this study , it was discovered 
 that left - handers used more wrist flexion in performance of the writing task with the 
 dominant upper extremity than right - handers , and that the left - handers activated the wrist 
 and shoulder muscles more than the right - handers . 
 these results indicate a potential 
 danger of musculoskeletal disease in left - hander .