the lumbar paraspinal muscles play a key role in providing stability during dynamic 
 exercises1 . the lumbar multifidus ( lm ) 
 is a significant local stabilizer of the lumbar spinal segment , and therapeutic exercises in 
 patients with low - back pain ( lbp ) emphasize strengthening the lm2 . on the other hand , the lumbar erector spinae ( les ) muscles 
 form a global stabilizing system for trunk stability , and high les activity is associated 
 with increased spinal loading3 , which may 
 aggravate pain or even be harmful in lbp patients . in a recent study , selective activation 
 of the lm , independent of the other lumbar paraspinal muscles , was stressed as the target of 
 exercise interventions2 . many researchers 
 have reported high activity in the lumbar paraspinal muscles , which are responsible for 
 lumbar stabilization during various exercises , and lumbar extensor exercises in a prone 
 position have been recommended for lumbar paraspinal muscle strengthening 4 . jari et al.5 reported high activation of the lm during trunk extension and hip 
 extension in a prone position , and jeffrey et al.6 suggested the arm lift exercise in a prone position as a means of 
 activating lm function . although many exercises have been suggested as exercises for 
 strengthening the lumbar paraspinal muscles , no study has examined selective activation of 
 the lumbar paraspinal muscles in a prone position , such by as trunk extension , hip 
 extension , and the arm lift , in healthy males . therefore , this study investigated selective 
 activation of the lumbar paraspinal muscles during various exercises in a prone position in 
 healthy males . the inclusion 
 criteria were no chronic lbp and the ability to participate in the exercises safely . the 
 subjects mean age was 21.82  2.22  years , and their mean height and weight were 174.91  
 5.96  cm and 68.11  8.96  kg , respectively . all individuals reported that they were 
 right - hand and right - leg dominant . all subjects read and signed an informed consent form 
 approved by the inje university ethics committee for human investigations prior to 
 participation . the emg data were recorded and analyzed using a surface emg system ( mp150 , biopac systems , 
 inc . , santa barbara , ca , usa ) . after the skin at the electrode sites was shaved and cleaned 
 with alcohol swabs , right - side surface emg data were collected from the les ( 2  cm lateral to 
 the spinous process of the l2 level and aligned parallel to the spine ; criswell , 2010 ) and 
 lm ( 2  cm lateral to the midline running through the l5 spinal process and aligned parallel 
 to the muscle fibers ; cram et al . , 1998 ) . the signals were amplified and band - pass filtered 
 ( 20500  hz ) before being recorded digitally at 1,000  hz , and then the root mean square ( rms ) 
 was calculated . maximum voluntary isometric contractions ( mvics ) were performed against 
 manual resistance for all muscles7 . each 
 mvic maneuver was performed twice for 5  s , and the average muscle activity for the middle 
 3  s of each of the two trials was used for normalization . the lm / les ratio was calculated to 
 assess selective activation of the lumbar paraspinal muscles during each exercise . the subjects were asked to lie prone with their arms at their sides and their head in the 
 midline . the three exercises in the prone position were performed as follows . for trunk 
 extension , subjects were instructed to extend the trunk as far as possible ; for hip 
 extension , they were asked to extend the right hip as far as possible , while maintaining 
 normal lumbar lordosis ; and for the arm lift , they were asked to lift the right arm as far 
 as possible , with the upper arm abducted 120 and the elbow flexed 90. the subjects were 
 asked to perform the three exercises for 5  s each . emg data of the lumbar paraspinal muscles during the 
 three exercises were compared using repeated - measures one - way analysis of variance ( anova ) . 20.0 ; spss , ibm corp . , armonk , ny , 
 usa ) . post hoc comparison ( bonferroni test ) was conducted to examine differences among 
 exercises . the lm / les ratio was significantly higher in hip extension ( mean  sd , 1.35  0.39 ) 
 compared with those in trunk extension ( 0.95  0.13 ; p < 0.05 ) and during the arm lift 
 ( 1.01  0.49 ; p < 0.05 ) . the activity level of the right les during trunk extension 
 ( 52.53  16.71 ) was greater than those during hip extension ( 32.51  10.91 ; p < 0.05 ) and 
 the arm lift ( 14.37  11.24 ; p < 0.05 ) , and it was greater during hip extension than 
 during the arm lift ( p < 0.05 ) . the % mvic of the right lm during trunk extension ( 49.13  
 16.27 ) and hip extension ( 41.87 10.94 ) resulted in greater activation than the % mvic during 
 the arm lift ( 13.60  9.62 ; p < 0.05 ) . this study examined selective activation of the lumbar paraspinal muscles in healthy males 
 during various exercises in a prone position . we observed that the lm / les ratio during hip extension was higher than that during trunk 
 extension and the arm lift , indicating that hip extension was more effective for selective 
 activation of lm muscles than trunk extension or the arm lift . additionally , the highest 
 levels of activation in the lm and les were recorded during trunk extension . this result is 
 thought to reflect increased activation of the les during trunk extension in a prone 
 position , as this exercise requires greater activation of the les to lift the trunk . for 
 stabilization of the lumbar region jeseph et al.8 indicated that the les and lm are capable of 
 various roles , such as prime movers or synergists working against the weight of the trunk 
 and upper limbs , with the two muscles functioning to stabilize the pelvis with leg holding . moreover , during the hip extension exercise , contraction of the gluteus maximus muscles 
 generates pelvic posterior tilt torque9 , 
 and pelvic anterior tilt torque generated by contraction of the les to counteract the former 
 torque would , in turn , require greater activation of the lm . during hip extension , the lm 
 muscles function to stabilize the pelvis via their attachments to the ilia and sacrum , and 
 this provides a stable base for the work of the gluteus maximus and hamstring , which are 
 responsible for hip extension in the prone position . we found that hip extension resulted in 
 the highest lm / les ratio , indicating selective activation of the lumbar paraspinal muscles 
 in healthy males . the results of this study indicate that , although the trunk extension 
 exercise is recommended for activation of the les , the hip extension exercise should be 
 emphasized for selective activation of the lm . first , because we used surface emg , we were unable to 
 consider anatomical factors in lm . an intramuscular emg recording system could be used to 
 target the emg site in the lm . further studies are 
 needed to assess the effects of exercises intended for selective activation of the lumbar 
 paraspinal muscles in healthy females .
[ purpose ] this study compared the effects of three exercises performed in a prone 
 position on the selective activation of the lumbar erector spinae ( les ) and lumbar 
 multifidus ( lm ) muscles in healthy males to investigate the effective method for selective 
 activation of the lm . [ subjects ] twenty - two healthy males were recruited . 
 surface emg data 
 were collected from the right les and lm muscles during three exercises : 1 ) trunk 
 extension , 2 ) hip extension , and 3 ) the arm lift . [ results ] 
 the ratio of lm to les emg 
 activity during hip extension was higher than those during trunk extension and the arm 
 lift . 
 [ conclusion ] hip extension in a prone position may be effective for selective 
 activation of the lumbar multifidus muscles in healthy males .