handgrip strength ( hgs ) is an objective measure of muscular function in the upper extremity 
 and has been used as a marker of frailty in older adults1,2,3 . in general , measurement of hgs this is because several studies have observed that 
 hgs is 10% higher with the dominant hand compared with the nondominant hand4 , 5 . in 
 contrast , petersen et al.6 reported that 
 for approximately 20% of participants ( 61 of 310 subjects ) , the hgs of the nondominant hand 
 was equal to or greater than that of the dominant hand ; however , the reasons for this 
 phenomenon are unknown . recently , a study investigated the relationship between ultrasound - measured forearm muscle 
 thickness ( mt ) and hgs in old men and women7 . the authors found that the forearm - ulna mt and forearm - radius mt 
 was significantly correlated with hgs in women . we hypothesized that the hgs dominance may 
 be closely associated with the difference in muscle size in the forearm . thus , the purpose 
 of this study was to investigate the relationship between side - by - side differences in hgs 
 and forearm mt . thirty - one young women between the ages of 20 and 33  years were recruited from the 
 university of mississippi campus through a printed advertisement and by word of mouth . all 
 subjects were free of overt chronic disease ( e.g. , angina , myocardial infarction , arthritic 
 and neuromuscular disorders , etc . ) and were not taking any medications known to affect 
 muscle size and function as assessed by self - report . prior to testing , study approval was 
 granted by the institutional review board of the university of mississippi , and written 
 informed consent was obtained from all subjects . hand dominance was ascertained by asking each subject which hand they used to perform 
 well - learned skills such as writing . twenty - six of the 31 subjects reported right - hand 
 dominancy , while the remaining 5 subjects reported left - hand dominancy . all right - handed 
 subjects used their right hand preferentially for not only writing but also for throwing a 
 ball and grasping a racket . on the other hand , three left - handed subjects used their left 
 hand preferentially for writing , but they used their right mainly for throwing and grasping . thus , only two left - handed subjects used their left hand preferentially for all 
 activities . mt was measured using b - mode ultrasound ( aloka ssd-500 , tokyo , japan ) at the anterior 
 forearm [ at 30% proximal between the styloid process and the head of the ulna ] on both sides 
 of the body as described previously8 . measurement sites were marked 
 with a marker pen and then limb girth was measured . the measurements for forearm mt were 
 taken while the subjects stood quietly with their elbow extended and relaxed . a linear 
 transducer with a 7.5-mhz scanning head was coated with water - soluble transmission gel to 
 provide acoustic contact and reduce the pressure applied by the scanning head to achieve a 
 clear image . the scanning head was placed on the skin surface at the measurement site using 
 the minimum pressure required , and cross sections of each muscle were imaged . three images 
 from each site were printed ( up-897md , sony , tokyo , japan ) , and mean values of each site 
 were used for data analysis . two mts were measured , that is , the perpendicular distances 
 between the subcutaneous adipose tissue - muscle interface and muscle - bone interface of the 
 radius ( forearm - radius mt ) and ulna ( forearm - ulna mt ) , as shown in the study of abe et 
 al7 . the precision and linearity of the image reconstruction have been 
 described and confirmed elsewhere9 . test - retest reliability of forearm - radius and forearm - ulna mt measurements was determined 
 using the intra - class correlation coefficient ( icc3,1 ) , standard error of 
 measurement ( sem ) , and minimal difference from 11 young subjects ( 5 males and 6 females ) 
 scanned twice with a 24 hours interval ( 0.928 , 0.10  cm , and 0.27  cm and 0.992 , 0.05  cm , and 
 0.15  cm , respectively ) . handgrip strength was measured using a factory - calibrated hydraulic hand dynamometer 
 ( fabrication enterprises inc . , elmsford , ny , usa ) . all subjects were instructed to maintain 
 an upright standing position to keep their arms at their sides , and to hold the dynamometer 
 in the right hand with the elbow flexed at 90 degrees without squeezing the arm against 
 their body . the size of the dynamometer s handle was set to that which the subjects felt 
 comfortable whilst squeezing the grip . subjects were allowed to perform one test trial , 
 followed by two maximum trials , and the best value of the trials was used for analysis . test - retest reliability of handgrip strength measurements was previously determined using 
 the icc3,1 , sem , and minimal difference from the same 11 young subjects described 
 earlier tested twice with an interval of 24 hours ( 0.967 , 2.4  kg and 6.6  kg , 
 respectively ) . side - by - side 
 differences in forearm girth , mt , and hgs were tested using paired student t - test in 
 right - handed ( n=26 ) and left - handed ( n=5 ) groups . using overall data ( n=31 ) , pearson product 
 correlations were performed to assess the relationship between side - by - side differences 
 ( right minus left ) in hgs and forearm - ulna mt or forearm - radius mt . in the right - handed group , forearm girth , forearm - ulna and forearm - radius mt and hgs were 
 greater ( p<0.001 ) in the right hand than the left hand ( table 1table 1.forearm girth , handgrip strength and ultrasound - measured forearm muscle 
 thicknesses in young womenright - handerleft - handeroverall(n=26)(n=5)(n=31)age , yr23 ( 3)22 ( 1)23 ( 3)height , m1.63 ( 0.06)1.65 ( 0.08)1.63 ( 0.06)body mass , kg63.4 ( 10.4)68.9 ( 16.0)64.3 ( 11.3)body mass index , kg / m23.8 ( 3.3)25.1 ( 3.4)24.0 ( 3.3)forearm girth ( right ) , cm24.2 ( 2.0)*25.0 ( 3.5)24.3 ( 2.3)forearm girth ( left ) , cm23.6 ( 1.9)25.1 ( 3.5)23.8 ( 2.2)muscle thickness , cmforearm - radius ( right)1.95 ( 0.22)*1.94 ( 0.29)1.95 ( 0.22)forearm - radius ( left)1.87 ( 0.22)2.00 ( 0.35)1.89 ( 0.25)forearm - ulna ( right)3.51 ( 0.26)*3.60 ( 0.45)3.53 ( 0.29)forearm - ulna ( left)3.34 ( 0.23)3.70 ( 0.51)3.40 ( 0.31)hgs ( right ) , kg26.8 ( 4.2)*28.0 ( 9.4)27.0 ( 5.2)hgs ( left ) , kg24.0 ( 4.3)29.8 ( 10.6)24.9 ( 5.9)hgs : handgrip strength . * significant difference from contralateral hand , 
 p<0.001 ) . in the left - handed group , there were no significant ( p>0.05 ) differences 
 in any of the variables between the two hands . the side - by - side difference in hgs expressed 
 as a percentage was 10.2% for the right - handed group , meaning the right hand was stronger . however , the left hand in the left - handed group was 7.8% stronger compared with the right 
 hand . * significant difference from contralateral hand , 
 p<0.001 there was a significant positive correlation between side - by - side differences in hgs and 
 forearm - ulna mt ( r=0.765 , p<0.001 ) and side - by - side differences in hgs and forearm - radius 
 mt ( r=0.622 , p<0.001 ) . it is well known that the dominant hand has approximately 10% , on average , greater hgs 
 compared with the nondominant hand . however , it was unknown whether hgs dominance was 
 related to the size of the forearm flexor muscles . to the best of our knowledge , this is the 
 first study that has investigated the side - by - side relationship between forearm mt and hgs 
 in young women . the increased muscle size in the dominant hand may occur due to muscle 
 contractions during asymmetric hand motion activities such as carrying a weight with one 
 hand , throwing a ball , or grasping a racket during a sports activity . a previous study 
 investigated the influence of years of work experience on hgs dominance in factory workers 
 with the samples being categorized into five subgroups based on years of employment in 
 factory work10 . they reported that 
 workers with 02 years of experience had a greater side - by - side percent difference in hgs 
 compared with workers with 1020 years of experience , which may be due to their simultaneous 
 use of both hands to complete a task . in addition , our recent studies indicated that forearm 
 mt is correlated with hgs in old women7 
 and is strongly correlated with hgs in young women11 . the regression lines between hgs and mt from the aforementioned 
 study11 revealed that 1  cm differences 
 in forearm - ulna and forearm - radius mts are comparable to approximately 13  kg and 16  kg 
 differences in hgs , respectively . in the present study , our results support previous studies 
 showing that 1  cm differences in forearm - ulna and forearm - radius mts corresponds to 14.9  kg 
 and 17.1  kg differences in hgs , respectively . our results showed that the side - by - side difference in hgs was 10.2% in right - handed women 
 with the right hand being stronger . although the sample size was very small , the 
 side - by - side difference in hgs was 7.8% in left - handed women with the left hand being 
 stronger . petersen et al.6 reported that 
 right - handers showed a 12.7% greater right - hand hgs in young and middle - aged men and women , 
 while there was no difference in hgs ( 0.08% ) in left - handers . cornwell et al.5 reported that right - handers displayed 10.4% 
 greater right - hand hgs in young and middle - aged adults ; the left - handers exhibited 5.5% 
 greater left - hand hgs . the results of this study support the 10% rule for right - handed 
 women . in conclusion , our results suggest that side - by - side differences in forearm - ulna and 
 forearm - radius mts were positively correlated with hgs dominance . for young women , forearm 
 muscle size may be a major determinant for evaluating hgs dominance .
[ purpose ] it is unknown whether handgrip strength dominance is related to the size of the 
 forearm flexor muscles . the purpose of the present study was to investigate the 
 relationship between side - by - side differences in handgrip strength and forearm muscle 
 thickness . 
 [ subjects ] thirty - one young women ( 26 right handed and 5 left handed ) between 
 the ages of 20 and 33  years volunteered to participate . [ methods ] two muscle thicknesses 
 ( forearm - ulna and forearm - radius muscle thicknesses ) were measured using b - mode ultrasound 
 at the anterior forearm on both sides of the body . 
 handgrip strength was also measured on 
 both sides . 
 [ results ] the side - by - side difference in handgrip strength was 10.2% for the 
 right - handed group , meaning the right hand was stronger 
 . however , the left hand of the 
 left - handed group was 7.8% stronger compared with their right hand . 
 there was a 
 significant positive correlation between side - by - side differences in handgrip strength and 
 forearm - ulna muscle thickness ( r = 0.765 ) and between handgrip strength and forearm - radius 
 muscle thickness ( r = 0.622 ) . 
 [ conclusion ] our results indicate that side - by - side 
 differences in forearm muscle size may strongly contribute to handgrip strength 
 dominance .