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Paper text:
the lumbar multifidus ( lm ) muscle is an important local stabilizer of the spinal 
 segments1 .
its main function involves 
 stabilizing the  neutral zone  of the lumbar spine2 and controlling the extension moment of the lumbar spine3 .
a previous study showed that the lm was 
 atrophied on the side of pain in patients with acute4 and chronic unilateral low back pain ( lbp)5 . on the other hand , the lumbar erector spinae ( les ) muscles 
 are global stabilizers of trunk stability ; high les activity is associated with increased 
 spinal loading6 and may induce pain or 
 even be harmful in patients with lbp .
lumbar extensor strengthening or stabilization 
 exercises that focus on the lumbar paraspinal muscles are frequently used by physical 
 therapists for the treatment of lbp entailing dysfunction of the lumbar paraspinal 
 muscles7 , 8 .
in contrast to lumbar extensor strengthening exercises , which 
 involve activation of the paraspinal musculature at high levels of contraction , lumbar 
 stabilization exercises involve low - load , low - intensity isometric or restricted 
 range - of - motion techniques9 .
various 
 exercises have been evaluated to determine whether or not high electromyographic ( emg ) 
 activity of the lumbar paraspinal muscles influences lbp treatment outcomes . in particular , 
 recent research has shown high emg activity of the lm during prone trunk extension ( pte ) and 
 four - point kneeling contralateral arm and leg lift ( fpkal ) exercises .
mayer et al.10 recommended trunk extension exercises with 
 gradually increasing load and intensity to improve lumbar extensor strength and endurance . 

imai et al.11 reported higher emg 
 activity of the lm than of the les during contralateral arm and leg lift , but their study 
 did not focus on selective activation of the lumbar paraspinal muscles . although recent 
 research has suggested that the lumbar paraspinal muscles play a significant role in 
 stabilizing the lumbar spine during exercise12 , and previous studies have focused on the effect of lumbar extensor 
 exercises on the lumbar paraspinal muscles , no studies have evaluated the selective 
 activation of the lm muscles during pte and fpkal exercises .
moreover , in the clinical 
 field , because lumbar extensor exercises have been frequently utilized in therapeutic 
 approaches for the recovery of lbp by many physical therapists , an experimental study for 
 baseline data with healthy individuals is needed to assess the efficacy of lumbar extensor 
 exercises aimed at selective activation of the lumbar paraspinal muscles .
because 
 experimental data from patients with lbp may show different emg activity patterns of the 
 lumbar paraspinal muscles , this study examined the selective emg activity of the superficial 
 lm during pte and fpkal exercises in healthy male and female subjects .
twenty healthy individuals ( nine male and 11 female subjects ) aged 20 to 22  years were 
 recruited for this study . the average age of the subjects was 20.14  0.24  years , and their 
 mean height and weight were 168.90  7.27  cm and 63.29  8.08  kg , respectively .
the subjects 
 were healthy individuals without lbp who had not participated in lumbar strengthening or 
 stabilization exercises in the past 6 months .
all subjects signed an informed consent form 
 approved by the inje university ethics committee for human investigations prior to 
 participation .
the emg data were collected and analyzed using a surface emg system ( mp150 ; biopac systems , 
 inc .
, santa barbara , ca , usa ) . after rubbing the skin at the electrode sites with alcohol 
 swabs , pairs of disposable surface electrodes
were unilaterally attached over the left les 
 ( 2  cm lateral to the l2 spinous process and aligned parallel to the spine)13 and lm ( 2  cm lateral to the midline on a 
 line through the l5 spinal process and parallel to the muscle fibers)13 , and left - side surface emg data were recorded from the les 
 and lm . the raw emg signals were amplified , sampled at a rate of 1,000  hz , band - pass 
 filtered between at 20 to 500  hz , and the root mean square value was calculated .
maximum 
 voluntary isometric contractions ( mvics ) were performed against manual resistance for all 
 muscles14 .
mvic of the lumbar paraspinal 
 muscles were performed three times for 5  s each .
the average muscle activity of the middle 
 3  s of each of the three trials was used for normalization . the lm / les ratio was calculated 
 to examine selective activation of the lumbar paraspinal muscles during pte and fpkal 
 exercises .
the subjects were asked to lie in the prone 
 position while resting their arms on a plinth with the head at the midline .
they were then 
 instructed to extend the trunk as far as possible with their hands across the chest and legs 
 resting flat on the plinth . for fpkal ,
the subjects started from a four - point kneeling 
 posture with their hands on push - up handles shoulder - width apart and knees positioned at hip 
 width and maintained at 90 flexion .
they were then asked to lift their right arm and left 
 leg simultaneously as far as possible until both were approximately parallel to the floor 
 while maintaining normal lumbar lordosis .
the subjects were asked to maintain this exercise 
 position with isometric contraction for 5  s , and the exercise was performed five times .
emg 
 data of the lumbar paraspinal muscles during the two exercises were compared using the 
 paired t - test .
the % mvic of the activity levels of the left les and lm were greater during pte ( les , 87.2 
  11.7 ; lm , 83.3  15.8 ) than during fpkal ( les , 31.3  14.9 ; lm , 41.9  20.0 ; p < 0.05 ) , 
 whereas the lm / les ratio was significantly higher during fpkal ( mean  sd , 1.61  0.51 ) than 
 during pte ( 0.96  0.18 ; p < 0.05 ) .
the % mvic as determined from the emg activity levels 
 of the left les and lm during the pte and fpkal exercises is shown in table 1table 1.%mvic and the lm / les ratio of the emg activity levels of the les and lm during 
 pte and fpkal exercisesptefpkalleslmleslm%mvic ( mean  sd)87.2  11.783.3  15.831.3  14.941.9  20.0lm / les ratio0.96
 0.181.61  0.51pte : prone trunk extension ; fpkal : four - point kneeling contralateral arm and leg 
 lift ; les : lumbar erector spinae ; lm : lumbar multifidus ; % mvic : percentage of maximal 
 voluntary contraction . pte : prone trunk extension ; fpkal : four - point kneeling contralateral arm and leg 
 lift ; les : lumbar erector spinae ; lm : lumbar multifidus ; % mvic : percentage of maximal 
 voluntary contraction
this study investigated the selective activation of the lumbar paraspinal muscles during 
 pte and fpkal exercises in healthy male and female subjects performing two lumbar extensor 
 exercise programs .
the emg activity level of the les and lm was higher during pte than during the fpkal 
 exercise . on the other hand ,
the lm / les ratio during the fpkal exercise was significantly 
 higher than that during pte .
these findings indicate that fpkal is more beneficial for the 
 selective activation of the lm muscle than pte , although higher les and lm muscle activation 
 was observed during pte than during fpkal .
this outcome indicates the need for higher les 
 activation to lift the trunk , a high load , during pte , and the lower requirement for les 
 activation , about half the activity level observed during pte , given the lower load during 
 fpkal .
many researchers have emphasized the safety of exercises for treatment of lbp , with a 
 particular focus on lm and les function .
richardson et al.15 suggested that the multifidus must contract independently of the 
 global muscles , and mcgill et al.16 
 suggested that excessive spine loading related to high activation of global muscles should 
 be avoided in patients with back pain to prevent structural damage .
the lm is a lumbar 
 stabilizing muscle that mainly comprises type i fibers17 , and relatively low loads requiring only approximately 3040% of 
 mvic are needed to improve lm muscle performance15 .
additionally , in one study that evaluated joint compression and 
 shear force using an emg - driven model during different exercises , the mean compression 
 values of the lumbar joint ( l4/l5 ) were lower during contralateral arm and leg lift 
 exercises than during trunk extension exercises , 2500 and 4000 n , respectively18 .
another study noted negative l4/l5 
 anteroposterior joint shear force values on the lumbar spine during contralateral arm and 
 leg lift ( values of approximately 200 n ) compared with trunk extension exercises ( values of 
 approximately 250 n)19 .
thus , the fpkal 
 exercise of our study ( appropriate emg amplitude of approximately 40% of mvc ) is suitable 
 for exercising the lm muscle function with selective activation of the lumbar paraspinal 
 muscles and is recommended as a safe and effective simple therapeutic exercise for treatment 
 of lbp .
an emg recording 
 method that targets the emg site in the lm could be used for intramuscular emg .
second , the 
 measurement of mvic for emg normalization was performed in prone trunk extension , like the 
 biering - sorenson endurance test , and this may have led to the recruitment of other muscles . 

third , because we examined healthy young individuals , the results of this study can not be 
 generalized to older adults or patients with lbp .
we may assess the effects of exercise on 
 selective activation of the lumbar paraspinal muscles in older adults or patients with lbp 
 in a further study .
[ purpose ] this study examined the selective electromyographic activity of the lumbar 
 paraspinal muscles in healthy male and female subjects in the prone trunk extension ( pte ) 
 and four - point kneeling arm and leg lift ( fpkal ) exercises to determine the most 
 beneficial exercise for selective activation of the lumbar multifidus ( lm ) . [ subjects and 
 methods ] twenty healthy male and female subjects participated in this study . 
 surface 
 electromyographic data were collected from the left - side lumbar erector spinae ( les ) and 
 lm muscles during pte and fpkal exercises . [ results ] 
 the lm / les ratio related to selective 
 activation of the lumbar paraspinal muscles during the fpkal exercise was higher than that 
 during pte . 
 [ conclusion ] fpkal exercise is safe and effective for the selective activation 
 of the lm muscle .