lbp is a complex disorder with multifactorial causes and much 
 research has focused on clarifying certain aspects of the condition while others still 
 remain unclear .
greater knowledge of lbp might help to improve its negative impacts , such as 
 patient pain , functional disability and work absenteeism2,3,4,5 .
the natural history of lbp 
 tends towards spontaneous resolution either with or without treatment .
however , in a subset 
 of patients , the development of chronic low back pain ( clbp ) is debilitating and 
 unpredictable6 . the determination of 
 which patients will progress to a prolonged and disabling course is currently unknown .
clbp patients display reduced endurance and strength of the muscles of the spine ( e.g. , the 
 lumbar erector spinae ) and the hip ( e.g. , the gluteus maximus ) , and decreased flexibility of 
 the back as a result of prolonged inadequate posture , which may be responsible for the 
 pain7 .
a variety of clbp treatment 
 programs have addressed the musculoskeletal alterations responsible for the pain with 
 protocols that address strengthening8 and 
 flexibility9 of trunk muscles , 
 electrotherapy with low laser therapy10 , 
 or alternative therapy as yoga11 or 
 acupuncture12 . in general ,
good 
 outcomes for self - reported pain , disability and improved quality of life have been 
 reported .
a common alteration is 
 delay in the activation of deep muscles ( e.g. , the transversus abdominis and the obliquus 
 internus abdominis ) during voluntary limb movements18,19,20 .
clbp subjects also exhibit higher and constant activation of the 
 lumbar erector spinae muscle during tasks such as walking21 . in clbp patients ,
the change in motor planning activity might be 
 associated with other levels of the neurologic system .
correlated the 
 alterations in the pattern of transversus abdominis activity to the cortical map 
 reorganization of the motor cortex in clbp subjects . later ,
tsao et al . showed that the deep 
 and superficial fascicles of the erector lumbar spinae muscles had increased overlap of 
 motor cortical representation , suggesting that it might reduce the selection of activation 
 between deep and superficial fascicles . in support of this theory , reeducation of the 
 transversus abdominis delayed pattern of contraction showed shifting of the muscle cortical 
 representation and improvement in the level of pain24
therefore , in clbp patients it is crucial to understand the 
 movement pattern and muscle activation during the performance of a specific task .
tasks involving asymmetrical lower limb movements , e.g. , running or climbing steps or 
 stairs , primarily require lumbopelvic control for balance25 , motor coordination , and adequate synergy of the trunk and hip 
 muscles26 . in the clinical setting ,
the 
 kneeling to half - kneeling task has been a useful tool for assessing lumbopelvic control in 
 balance , due to minimum interference of the lower limbs , and it is commonly used in the 
 treatment of neurologic patients27 .
the 
 task starts from the kneeling position , and the patient supports the body on one side ( knee ) 
 while flexing the contralateral hip until reaching the ground with his / her foot to the final 
 half - kneeling position . the purpose of this study was to compare the activity of the trunk and hip muscles in clbp 
 patients and asymptomatic subjects during the kneeling to half - kneeling task .
we chose the 
 obliquus internus abdominis and lumbar erector spinae ( trunk muscles ) , due to the function 
 of the obliquus internus abdominis in stabilizing the pelvis and the spine during voluntary 
 lower limb movement28 , 29 , and the function of the lumbar erector spinae in 
 controling the excessive movements of the trunk in the sagittal and frontal plane30 , 31 .
the gluteus medius muscle ( hip muscle ) plays an important role in 
 stabilizing the hip during unipedal dynamic tasks32,33,34 .
we hypothesized that the clbp patients would have different 
 lumbopelvic control , tested during the asymmetrical movement of the lower limbs , showing 
 different utilization of the trunk and hip muscles compared to asymptomatic subjects .
twenty - nine women with a history of non - specific chronic low back pain [ clbp , 
 age=45.85  years ; body mass index ( bmi)=23.91.7  kg / m ] and thirty healthy , 
 pain - free women ( c , age=44.55  years ; bmi=23.71.5  kg / m ) were the subjects of 
 this study .
the clbp subjects were recruited from the orthopedic and traumatology 
 department of the hospital das clnicas , the university of so paulo , and were included if 
 they were diagnosed with non - specific low back pain ( e.g. , low back pain not attributable 
 to a recognizable known specific pathology ) , and had experienced low back pain for at 
 least 3 months with intensity sufficient to limit daily activity .
the exclusion criteria 
 for both groups were pregnancy , neurological conditions , obesity ( body mass index : 
 bmi>30 ) , previous spine or abdominal surgery or any rheumatological disease .
the ethics committee of the 
 clinics hospital in so paulo , brazil approved the study ( 1174/09 ) .
electromyography activity ( emg ) was recorded using an 8-channel emg system ( emg810c , emg 
 system do brasil ltda , so jos dos campos sp / brazil ) and surface electrodes 
 with 10-mm diameter ag / agcl discs set at an inter - electrode distance of 20  mm ( emg system 
 do brasil ltda , so jos dos campos sp / brazil ) . following skin preparation 
 ( shaved and cleaned with 70% alcohol ) to reduce electrode impedance
, surface electrodes 
 were placed bilaterally ( right , r , and left , l ) over the obliquus internus abdominis ( roi , 
 loi ) 2  cm inferior to the anterior superior iliac spine ( asis ) , and midway between asis 
 and the symphysis pubis35 .
electrodes 
 were also placed on the lumbar erector spine ( rles , lles ) , 30  mm directly lateral to the 
 l2 spinous process36 , 37 , and the gluteus medius ( rgm , lgm ) , midway between the 
 iliac crest and the greater trochanter38 .
the 
 emg signals were converted to a digital format using a 12-bit analog - to - digital converter 
 ( emg system do brasil ltda , so jos dos campos sp / brazil ) .
each electrode was 
 connected to a preamplifier ( 20x ) and further amplified ( 50x ) for a total gain of 1000 . 

the raw emg signals were recorded within a bandwidth of 20 to 500  hz at a sampling 
 frequency of 2 khz . a force platform ( biomec400 ,
sp / brazil ) was synchronized with the emg system to determine the onset 
 and the end of movement .
all subjects were instructed to wear adapted gymnastics clothing 
 to facilitate the attachment of the electrodes and to allow them to perform the movement 
 as naturally as possible .
the participants were instructed to initiate the task by kneeling on the force platform 
 with their knees apart ( at pelvis width ) while maintaining the trunk in the upright 
 position and keeping the arms free beside the body .
the instructor asked each participant to perform the task : move 
 to a half - kneeling position by flexing the right hip and then bringing the right foot 
 forward at a comfortable pace while maintaining the left knee on the force platform to 
 support the body weight .
task and data acquisition were completed when a stable 
 half - kneeling position was reached and the body weight was supported on the right knee and 
 left foot . before the data collection commenced ,
the task was explained to the patients , 
 and they were allowed to perform one attempt to familiarize themselves with the movement . 

the clbp subjects were pain - free on the day of data collection , and the task did not 
 provoke any pain .
postural reactions for balance , e.g. , abduction of the arms during the 
 task , were allowed ; however , the trials in which the participants needed hand support on 
 the ground for any moment during the task or trials in which the participant was not able 
 to bring the right foot straight forward to the final position without interrupting the 
 movement to support the right foot on the ground were excluded .
raw emg data were first converted to ascii format with emg system software ( emg system do 
 brasil ltda , so jos dos campos sp / brazil ) and then transferred to origin 8 
 software ( originlab corporation , northampton , ma , usa ) .
the raw emg signals were full - wave 
 rectified and low - pass filtered using a fourth - order butterworth filter with a cutoff 
 frequency of 5  hz . the emg amplitudes were normalized with the average of the filtered 
 values of the activity of the muscles during the task39 , 40 .
the onset and end of the task were identified using the force platform data , and the time 
 of the execution of the task was normalized as a percentage so that the data could be 
 compared between the groups .
the normalized emg data were processed , and the emg 
 parameters used in the analysis were the averages of peak amplitude , time of peak , and the 
 integrated linear envelope emg . the age , weight , height , and bmi were compared between the groups using student s t - test . 
 the distribution of each variable was compared between the groups using the mann - whitney 
 u - test ( minitab 15 , state college , pa , usa ) . the alpha - level was chosen as 0.05 for all of 
 the analyses .
twenty - nine women with a history of non - specific chronic low back pain [ clbp , 
 age=45.85  years ; body mass index ( bmi)=23.91.7  kg / m ] and thirty healthy , 
 pain - free women ( c , age=44.55  years ; bmi=23.71.5  kg / m ) were the subjects of 
 this study .
the clbp subjects were recruited from the orthopedic and traumatology 
 department of the hospital das clnicas , the university of so paulo , and were included if 
 they were diagnosed with non - specific low back pain ( e.g. , low back pain not attributable 
 to a recognizable known specific pathology ) , and had experienced low back pain for at 
 least 3 months with intensity sufficient to limit daily activity .
the exclusion criteria 
 for both groups were pregnancy , neurological conditions , obesity ( body mass index : 
 bmi>30 ) , previous spine or abdominal surgery or any rheumatological disease .
the ethics committee of the 
 clinics hospital in so paulo , brazil approved the study ( 1174/09 ) .
electromyography activity ( emg ) was recorded using an 8-channel emg system ( emg810c , emg 
 system do brasil ltda , so jos dos campos sp / brazil ) and surface electrodes 
 with 10-mm diameter ag / agcl discs set at an inter - electrode distance of 20  mm ( emg system 
 do brasil ltda , so jos dos campos sp / brazil ) . following skin preparation 
 ( shaved and cleaned with 70% alcohol ) to reduce electrode impedance ,
surface electrodes 
 were placed bilaterally ( right , r , and left , l ) over the obliquus internus abdominis ( roi , 
 loi ) 2  cm inferior to the anterior superior iliac spine ( asis ) , and midway between asis 
 and the symphysis pubis35 .
electrodes 
 were also placed on the lumbar erector spine ( rles , lles ) , 30  mm directly lateral to the 
 l2 spinous process36 , 37 , and the gluteus medius ( rgm , lgm ) , midway between the 
 iliac crest and the greater trochanter38 .
the 
 emg signals were converted to a digital format using a 12-bit analog - to - digital converter 
 ( emg system do brasil ltda , so jos dos campos sp / brazil ) .
each electrode was 
 connected to a preamplifier ( 20x ) and further amplified ( 50x ) for a total gain of 1000 . 

the raw emg signals were recorded within a bandwidth of 20 to 500  hz at a sampling 
 frequency of 2 khz . a force platform ( biomec400 , emg system do brasil ltda , 
 so jos dos campos
sp / brazil ) was synchronized with the emg system to determine the onset 
 and the end of movement .
all subjects were instructed to wear adapted gymnastics clothing 
 to facilitate the attachment of the electrodes and to allow them to perform the movement 
 as naturally as possible .
the participants were instructed to initiate the task by kneeling on the force platform 
 with their knees apart ( at pelvis width ) while maintaining the trunk in the upright 
 position and keeping the arms free beside the body .
the instructor asked each participant to perform the task : move 
 to a half - kneeling position by flexing the right hip and then bringing the right foot 
 forward at a comfortable pace while maintaining the left knee on the force platform to 
 support the body weight .
task and data acquisition were completed when a stable 
 half - kneeling position was reached and the body weight was supported on the right knee and 
 left foot . before the data collection commenced ,
the task was explained to the patients , 
 and they were allowed to perform one attempt to familiarize themselves with the movement . 

the clbp subjects were pain - free on the day of data collection , and the task did not 
 provoke any pain .
postural reactions for balance , e.g. , abduction of the arms during the 
 task , were allowed ; however , the trials in which the participants needed hand support on 
 the ground for any moment during the task or trials in which the participant was not able 
 to bring the right foot straight forward to the final position without interrupting the 
 movement to support the right foot on the ground were excluded .
raw emg data were first converted to ascii format with emg system software ( emg system do 
 brasil ltda , so jos dos campos sp / brazil ) and then transferred to origin 8 
 software ( originlab corporation , northampton , ma , usa ) .
the raw emg signals were full - wave 
 rectified and low - pass filtered using a fourth - order butterworth filter with a cutoff 
 frequency of 5  hz . the emg amplitudes were normalized with the average of the filtered 
 values of the activity of the muscles during the task39 , 40 .
the onset and end of the task were identified using the force platform data , and the time 
 of the execution of the task was normalized as a percentage so that the data could be 
 compared between the groups .
the normalized emg data were processed , and the emg 
 parameters used in the analysis were the averages of peak amplitude , time of peak , and the 
 integrated linear envelope emg . the age , weight , height , and bmi were compared between the groups using student s t - test . 
 the distribution of each variable was compared between the groups using the mann - whitney 
 u - test ( minitab 15 , state college , pa , usa ) . the alpha - level was chosen as 0.05 for all of 
 the analyses .
the mean  standard deviation of the anthropometric characteristics of the 
 participantsc group * * ( n=30)clbp group * * ( n=29)age ( y)44.5713.645.814.3weight ( kg)61.277.164.7210.8height ( cm)1.600.071.640.07bmi ( kg / cm)23.772.124.153.9**c group= asymptomatic subjects , clbp group= chronic low back pain patients . 

* p<0.05 shows the descriptive analysis of the clbp and c groups of age , weight , height 
 and bmi . * * c group= asymptomatic subjects , clbp group= chronic low back pain patients . 

* p<0.05 there were significant differences between the groups for all of the emg parameters 
 analyzed , except for the integrated linear envelope of loi .
the c group right and left oi 
 and gm muscles displayed higher peak amplitudes ( rloi , p=0.001 ; loi , p=0.014 ; rgm , p=0.007 ; 
 lgm , p<0.001 ) ( table 2table 2 .
the median and interquartile intervals ( q1q3 ) and peak amplitudes of the 
 muscles analyzedmusclesc group**clbp group**roi1.84 ( 0.782.18)1.23 ( 1.002.44)*loi1.53 ( 1.002.08)1.28 ( 1.051.80)*rles1.11 ( 0.991.32)1.52 ( 1.058.07)*lles1.13 ( 0.642.00)1.36 ( 1.095.28)*rgm1.60 ( 1.002.10)1.25 ( 1.002.16)*lgm1.81 ( 1.022.11)1.19 ( 1.042.31)*right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients . * p<0.05 ) and earlier times of peak amplitude ( rloi , p=0.002 ; loi , p=0.026 ; rgm , 
 p=0.001 ; lgm , p<0.001 ) ( table 3table 3 .
the median and interquartile time ( % ) intervals ( q1q3 ) of the peak emg 
 amplitudes of the muscles analyzedmusclesc group**clbp group**roi0.42 ( 0.070.88)0.69 ( 0.100.97)*loi0.42 ( 0.030.97)0.59 ( 0.080.90)*rles0.59 ( 0.111.00)0.36 ( 0.030.89)*lles0.77 ( 0.131.00)0.24 ( 0.010.97)*rgm0.44 ( 0.070.74)0.68 ( 0.110.94)*lgm0.21 ( 0.050.83)0.86 ( 0.131.00)*right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients .
the clbp group right and left les 
 muscles showed higher peak amplitudes ( rles , p=0.003 ; lles , p<0.001 ) ( table 2 ) and earlier times of peak amplitude ( rles , p=0.003 ; lles , 
 p<0.001 ) ( table 3 ) than the c group .
the 
 integrated linear envelope emg was higher in the c group for the right oi ( p<0.021 ) and 
 the bilateral gm muscles ( rgm , p=0.004 ; lgm , p=0.001 ) ( table 4table 4 .
the median and interquartile intervals ( q1q3 ) of the integrated linear envelope 
 emg of the muscles analyzedmusclesc group**clbp group**roi0.96 ( 0.122.00)0.68 ( 0.201.00)*loi1.00 ( 0.532.00)1.00 ( 0.181.00)rles1.00 ( 0.101.00)1.00 ( 0.792.00)*lles0.94 ( 0.111.00)1,00 ( 1.002.28)*rgm1.00 ( 0.351.48)0.66 ( 0.171.00)*lgm1.00 ( 0.872.00)1.00 ( 0.571.00)*right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients . *
p<0.05 ) , while the clbp group showed increased integrated linear envelope emg for the 
 bilateral les muscles ( rles , p<0.001 ; lles , p<0.001 ) ( table 4 ) .
right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients . * p<0.05 right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients . * p<0.05 right and left ( r , l ) obliquus internus abdominis ( oi ) , the lumbar 
 erector spinae ( les ) and the gluteus medius ( gm ) . * * c group= asymptomatic subjects , 
 clbp group= chronic low back pain patients . *
this study was conducted to test the hypothesis that compared to asymptomatic subjects ; 
 clbp women would have poorer lumbopelvic control , as tested during asymmetric movement of 
 the lower limbs .
the results reveal that the lumbopelvic control of an asymmetrical lower 
 limb task is different in clbp women compared to asymptomatic subjects .
clbp women recruit 
 the les muscles , while the execution of this task in pain - free women is based on the 
 recruitment of the abdominal and hip muscles .
the kneeling to half - kneeling task involves 
 load transfer from double to single support and requires adequate motor control of the trunk 
 and the hip .
this task is not as functional as stair or step climbing , which might better 
 represent daily living activities of trunk and hip motor control ; however , it was chosen to 
 minimize interference of the distal lower limbs joints .
the alteration of the activity 
 pattern of the trunk and hip muscles has been described during internal perturbation evoked 
 by voluntary movement and external perturbation elicited by unexpected environmental 
 perturbation in clbp subjects41 , 42 .
the kneeling to half - kneeling task 
 combines internal perturbation ( voluntary movement of lower limb ) with hip instability 
 ( asymmetric lower limb movement ) .
the main finding of our study was that clbp women mainly activate the back muscles , while 
 asymptomatic subjects displayed activation of the abdominal and hip muscles to accomplish 
 the kneeling to half - kneeling task .
this finding is evidenced by the higher and faster peak 
 amplitudes ( time of peak ) , with higher muscular activity ( integrated linear envelope emg ) of 
 the les muscles in clbp patients , and of the oi and gm muscles in the asymptomatic subjects . 

this finding suggests that the core stabilization of the clbp group is anchored in the back 
 muscles , and in the asymptomatic subjects it is distributed between the trunk ( abdomen ) and 
 the hip muscles .
similar muscular behavior has been reported in the literature for tasks with asymmetrical 
 demands of the lower limbs : the oi and gm muscles reportedly play an important role in 
 stabilizing the lumbar spine and the hip in the stance phase during the gait of asymptomatic 
 subjects43 . increased activity of the 
 les muscles was reported during walking and running by clbp subjects44 , 45 .
it seems that 
 the clbp subjects adopt the strategy of increased activation of the les muscles to maintain 
 the stiffness and stability of the spine46,47,48 . 

however , the increased activity of the les muscles seems to be an improper strategy that 
 reduces endurance and alters the proper function of the lower limbs after an external 
 perturbation49 , 50 . in our study
, the clbp patients did not acknowledge pain during the task , which shows that 
 they adopted an improper strategy of muscular recruitment , activating the back muscles even 
 in the absence of symptoms .
the elevated activity of the back muscles might produce 
 compressive forces in the spine and predispose clbp patients to be vulnerable to injury and 
 the recurrence of pain51 .
the alteration 
 of the back muscle activity ( les and multifidus ) and the abdominal muscles ( tra ) has been 
 previously associated with changes in how the cortical map of these muscles is organized in 
 the motor cortex22 , 23 .
also , there is a change in inputs of corticomotor excitability in 
 the trunk muscles52 .
therefore , in 
 agreement with tsao and hodges and macdonald et al . , we recommend that intervention for clbp 
 subjects should include symptom control or musculoskeletal alterations such as strength or 
 flexibility , and it should also emphasize the motor control recovery of the trunk and the 
 hip in different dynamic activities .
a limitation of this study was that subjects kept their arms free beside the body during 
 the kneeling to half - kneeling task .
perhaps the subjects should have kept their arms crossed 
 to control their movements , since the oi muscle activates during arm movements18 .
this study revealed important findings 
 about the activities of muscles of the abdomen and hip during a task with minimum 
 interference of the lower limbs in chronic low back pain population .
future studies are 
 needed to verify the activities of the abdominal and hip muscles during asymmetrical lower 
 limb tasks , such as climbing stairs .
 [ purpose ] the aim of this study was to compare the activities of the trunk and hip 
 muscles in chronic low back pain ( clbp ) women and asymptomatic subjects during the 
 kneeling to half - kneeling task . [ subjects ] twenty - nine clbp women and thirty asymptomatic 
 subjects ( c ) participated in this study . 
 [ methods ] electromyography activity ( emg ) of the 
 obliquus internus abdominis ( oi ) , the lumbar erector spinae ( les ) and the gluteus medius 
 ( gm ) muscles was recorded bilaterally . 
 the peak amplitude , the time of peak amplitude and 
 the integrated linear envelope emg for each muscle were obtained . 
 [ results ] the c group 
 bilateral oi and gm muscles displayed higher peak amplitudes and earlier times of peak 
 amplitude . 
 they also had higher integrated linear envelope emg values . 
 the clbp group 
 bilateral les muscles had higher peak amplitudes and earlier times of peak amplitude . 
 they 
 also showed an increased integrated linear envelope emg values . 
 [ conclusion ] the clbp 
 women activate the les muscles in the kneeling to half - kneeling task , showing different 
 patterns of motor planning activity . 
INTRODUCTION
SUBJECTS AND METHODS
Participants
Electromyographic Recordings
Procedure
Data Process and Statistical Analysis
RESULTS
DISCUSSION