cerebral palsy ( cp ) is a chronic neurologic disorder caused by a static lesion in the 
 immature brain and is characterized by deficits in movements and postural control . because 
 of various muscle function impairments such as weakness , spasticity , incoordination , and 
 reduced selective motor control , many children with cp have difficulties with activities 
 such as propelling their wheelchairs , walking independently , negotiating steps on uneven 
 terrain and running1
. an important 
 treatment goal of therapeutic interventions for children with cp is to improve their ability 
 to walk or perform other functional activities .
most interventions aiming to improve 
 movement abilities in children with cp focus on muscle strength or skeletal alignment which 
 is only a secondary impairment2 .
strength 
 training used to be avoided in children with cp because it could lead to increased 
 spasticity and reduced range of motion3 , 4 . however
, systematic reviews provide 
 reasonable and sufficient evidences that muscle strength training improves functional motor 
 activity as well as strength in children with cp without adversely affecting spasticity or 
 range of motion1 , 5 .
however , in recent years , rehabilitation interventions have focused on promoting muscle 
 strength6,7,8 .
several studies provide 
 evidences supporting the benefits of strengthening programs in children with cp4 , 9 , 10 .
found that children with 
 cp exhibit significantly improved quadriceps and knee extensor strength as a result of 
 muscle strength training .
they also observed an improved gait pattern in children with cp , 
 such as decreased knee flexion during the stance phase and increased stride length during 
 gait11 .
report that a 6-week strengthening program in adolescents with cp increased distance walked 
 in 3 minutes , gait velocity , step length , and cadence9 .
the deviation of pelvic alignment in the standing position is a common problem in children 
 with cp .
such children retain an anterior pelvic tilt due to the contracture of the 
 iliopsoas muscle as well as weakness in the trunk flexors and hip extensors .
problems 
 associated with anterior pelvic tilt include femoral antetorsion and medial shift of the 
 patella to the sagittal plane bisection of the knee joint .
therefore , a major goal of 
 movement training is reciprocal control of the pelvis by improving interplay among the 
 abdominal obliques , rectus abdominalis , quadrates lumborum and lumbar extensor muscles12 . on the basis of previous studies
, we hypothesized that strengthening the trunk and hip 
 muscles increases the muscle activation of the trunk and hips , and decreases the exaggerated 
 anterior pelvic tilt during quiet standing in children with spastic diplegia .
accordingly , 
 we designed modified trunk - hip strengthening exercises based on the core strength exercise 
 for adults and tailored to children13 . 

the muscle activation patterns of the four exercises used in this study were analyzed from 
 the electromyography signal , which have been reported previously8 , 9 , 11 , 13 .
thus , this 
 study evaluated the effects of trunk - hip strengthening exercise on trunk - hip activation and 
 pelvic tilt motion during standing in children with spastic diplegia and compared the 
 modified trunk - hip strengthening exercise with the conventional exercise with respect to the 
 improvement of pelvic tilt .
ten ambulatory children with spastic diplegia were recruited from bobath children s 
 hospital in south korea and pre - selected by a pediatric physical therapist .
the inclusion 
 criteria were as follows : spastic cp diagnosis , gross motor function classification system 
 ( gmfcs ) level i , age between 6 and 13  years , able to understand and follow verbal 
 instructions , and able to participate in a group training program .
the exclusion criteria 
 were as follows : unstable seizures , any treatment for spasticity or surgical procedures up 
 to 3 months ( for botulinum toxin injections ) or up to 6 months ( for orthopedic surgery ) 
 prior to the study , and any change in spasmolytic medication expected during the study 
 period .
the physical characteristics of the subjects are presented in table 1table 1.physical characteristics of the participants ( n = 10)variableconventional groupmodified groupage ( years)8.2  0.8 ( 79)8.2  1.6 ( 610)height ( cm)119.4  9.7 ( 110133)119.8  11.4 ( 109134)weight ( kg)21.2  3.5 ( 1726)21.4  5.6 ( 1831)gender ( females / males)3/23/2data are mean  sd ( range ) . all the participants understood the purpose of this study and provided 
 written informed consent prior to participation in accordance with the ethical standards of 
 the declaration of helsinki .
data are mean  sd ( range ) each child participated three 30-minutes one - on - one sessions with a physical therapist per 
 week for 6 weeks .
the conventional trunk - hip strengthening exercise group received routine 
 physiotherapy for 15 minutes and conventional trunk - hip strengthening exercise for 15 
 minutes .
the exercise consisted of a bridge exercise and a modified quadruped position with 
 lower extremity lift .
meanwhile , the modified trunk - hip strengthening exercise group 
 received routine physiotherapy for 15 minutes and modified trunk - hip strengthening exercise 
 for 15 minutes . the newly designed exercise consisted of modified unilateral bridge exercise 
 and modified prone bridge exercise ( fig .
1.schematics and descriptions of the conventional ( 1 , 2 ) and modified ( 3 , 4 ) trunk - hip strengthening exercises ) .
schematics and descriptions of the conventional ( 1 , 2 ) and modified ( 3 , 4 ) trunk - hip strengthening exercises to measure the participants muscle activation , bipolar surface emg ( wemg-8 , laxtha , south 
 korea ) data from 5 muscles ( listed below ) were used . before attaching the electrodes ,
the 5 sites on the dominant 
 side were as follows : ( 1 ) the rectus abdominis ( ra ) muscle at the level of the anterior 
 superior iliac spine , 12  cm lateral to the midline ; ( 2 ) the erector spinae ( es ) muscles , 
 12 finger widths lateral from the l1 spinous process ; ( 3 ) the gluteus maximus ( gm ) muscle , 
 50% of the distance from sacral vertebrae to the greater trochanter at the greatest 
 prominence of the middle buttocks parallel to a line from the posterior superior iliac spine 
 to the middle posterior thigh ; ( 4 ) the rectus femoris ( rf ) muscle , 50% of the distance from 
 the anterior superior iliac spine to the superior patella ; and ( 5 ) the semitendinosus ( st ) 
 muscle , 50% of the distance from the ischial tuberosity to the medial tibial epicondyle .
the emg signals were 
 preamplified , filtered ( input impedance , 10  ; common mode rejection ratio , 110 
 db ; bandpass digital filter , 50300  hz ) and sampled at 1,024  hz .
the raw emg data were 
 converted into root mean square data using telescan version 3.3 ( laxtha , daejeon , south 
 korea ) .
pelvic tilt angle was evaluated by using a dualer iq inclinometer ( jtech medical , midvale , 
 usa ) .
the primary sensor was placed on t12 and the secondary sensor was placed over the 
 sacral midpoint in the sagittal plane ; we recorded the angle with the participant standing 
 in the neutral position , with knees straight , and weight equally on both feet .
the 
 wilcoxon signed rank test was used to analyze the differences in emg data and pelvic tilt 
 motion before and after the intervention .
the significance of differences between the 
 conventional and modified groups was evaluated by the mann - whitney u - test ( table 2table 2.changes in pelvic tilt angle and muscle activation over 6 weeksvariablesconventional strengthening groupmodified strengthening groupprepostchangeprepostchangeangle ( )24.2  5.819.0  7.25.2  3.926.8  5.518.8  3.58.0  4.0ra5.8  1.46.1  3.40.3  2.57.9  3.74.9  1.63.0  3.6es13.6  8.113.9  6.90.2  8.025.0  15.115.0  7.810.0  7.7gm7.3  5.87.8  7.50.5  2.54.2  1.44.6  2.30.4  1.9rf15.6  8.512.9  6.42.7  4.67.8  4.35.3  3.62.5  1.4st15.0  10.37 .
pre : pre - intervention , post : 
 post - intervention , ra : rectus abdominis , es : extensor spinae , gm : gluteus maximus , rf : 
 rectus femoris , st : semitendinosus ) .
pre : pre - intervention , post : 
 post - intervention , ra : rectus abdominis , es : extensor spinae , gm : gluteus maximus , rf : 
 rectus femoris , st : semitendinosus
the anterior pelvic tilt angle during standing decreased significantly in the modified 
 group after 6 weeks of training ( p < 0.05 ) .
there was no significant difference in the anterior pelvic tilt 
 angle between groups ( p < 0.05 ) .
es , rf , and st activation during standing decreased significantly in the modified group 
 after 6 weeks of training ( p < 0.05 ) , but no significant changes were observed in ra or 
 gm activation . furthermore , there were no significant changes in the activation of any 
 muscle in the conventional group after 6 weeks of training .
meanwhile , only the activation of the es differed significantly between groups ( p < 
 0.05 ) .
this study evaluated the effects of modified trunk - hip strengthening exercise on trunk - hip 
 muscle activation and pelvic tilt motion during standing in children with spastic diplegia 
 and compared the modified trunk - hip strengthening exercise with conventional exercise with 
 respect to the improvement of pelvic tilt .
the results show that pelvic anterior tilt during 
 standing decreased after 6-week interventions in both the modified and conventional exercise 
 groups , but only the modified exercise group decreased significantly .
pelvic position during activities performed in a closed kinematic chain depends on the 
 integrity of the osteoligamental system , the adequate interaction between muscles and 
 fascia , appropriate neuromuscular control , and anatomically remote factors such as the 
 alignment of the lower - limbs joints14,15,16 . 

in particular , anterior pelvic tilt is performed by active force - coupling between the hip 
 flexors and low - back extensors .
in contrast , children with cp exhibit passive anterior 
 pelvic tilt owing to contracture of the iliopsoas muscle and weakness of the trunk flexors 
 and hip extensors12 . therefore , pelvic 
 tilt exercises for children with cp should enhance the strength of these muscles , especially 
 the force - coupling generation between the trunk flexors ( i.e. , ra and obliquus externus 
 abdominis ) and hip extensors ( i.e. , gm and hamstrings)17 . the significant decrease in pelvic anterior tilt during standing 
 after the 6-week intervention could be due to increased activation of the hip extensors and 
 diminished activation of the hip flexors .
the emg results showed significant decreases in 
 the activations of the es , rf , and st muscles and a significant increase in gm activation in 
 the modified exercise group .
therefore , the modified trunk - hip strengthening exercise 
 appeared diminish excessive the hip flexor activation and increase hip extensor activation , 
 albeit in a limited manner
. decreased es activation is another reason for the significant change in pelvic tilt in the 
 modified exercise group .
this result is consistent with previous studies showing lower es 
 activation after a modified trunk - hip strengthening exercise ( i.e. , modified unilateral 
 bridging and modified prone bridging ) compared to conventional exercise ( i.e. , bridging and 
 modified crawling position)18 .
it is 
 hypothesized that anterior pelvic tilt is linearly associated with a force - coupling between 
 the hip flexors and low - back extensor muscles .
the present results suggest the modified 
 trunk - hip strengthening exercise would produce a greater improvement in pelvic tilt motion 
 during standing with diminished activation of the hip flexors and back extensors as well as 
 increased activation of the hip extensors and trunk flexors .
in general , the contraction of  antigravity  muscles is primarily responsible for 
 maintaining the body in an upright position both in both static and dynamic postures .
the 
 hip , knee , trunk , and neck extensors are considered major antigravity muscles .
other related 
 muscles include the neck flexors and lateral benders , trunk flexors and lateral benders , hip 
 abductors and adductors , and ankle pronators and supinators17 .
therefore , the present results indicate our exercise program is 
 effective for strengthening the muscles required for standing .
even highly functional children with spastic cp are likely to have considerable weakness in 
 their involved extremities compared to age - related peers , with the degree of weakness 
 increasing with the level of neurologic involvement .
such weakness limits functional 
 performance in children with cp but can be improved through training . in addition , 
 therapists should be more proactively involved in the prevention of secondary impairments as 
 well as the promotion of wellness and fitness in their patients .
strength and endurance 
 training are important components of fitness , and may improve health throughout life and 
 increase participation in recreational , social , and occupational activities in children and 
 adults with cp19 .
several recent studies 
 of a more specific group of children with reported standing ability problems suggest more 
 individually tailored exercises could be improved by emphasizing the training of the weakest 
 muscle groups4 , 8 . on the basis of the present results
, the modified trunk - hip 
 strengthening exercise could be used for specific muscles or muscle groups to improve the 
 standing posture of children with cp .
six weeks is reported to be the 
 minimum time required to observe increases in the strength of adults .
however , eagleton et 
 al.9 suggest a similar or greater period 
 is required for children or adolescents with cp .
another limitation of the present study is 
 its small sample size . finally , the participants were from a specific region around bobath 
 children s hospital in south korea
. in conclusion , our modified trunk - hip strengthening exercise is more effective for 
 improving trunk - hip activation and decreasing anterior pelvic tilt motion during standing in 
 children with spastic diplegia than the conventional trunk - hip strengthening exercise . 

therefore , we suggest using individually tailored modified trunk - hip strengthening exercise 
 programs like the one described herein to strengthen the weakest muscle groups of children 
 with reported standing ability problems .
 [ purpose ] this study evaluated the effects of trunk - hip strengthening exercise on 
 trunk - hip activation and pelvic tilt motion during standing in children with spastic 
 diplegia and compared the improvement of pelvic tilt between the modified trunk - hip 
 strengthening exercise and conventional exercise . [ subjects and methods ] ten ambulant 
 children with spastic diplegia were randomized to the modified trunk - hip strengthening 
 exercise ( n = 5 ) or conventional exercise ( n = 5 ) group . 
 
 the intervention consisted of a 6-week modified trunk - hip strengthening exercise 3 times 
 per week . 
 the children were tested for trunk - hip muscles activation and pelvic tilt motion 
 during standing by surface electromyography and an inclinometer before and after the 
 intervention . [ results ] 
 the anterior pelvic tilt angle and activation of the extensor 
 spinae , rectus femoris , and semitendinosus during standing decreased significantly in the 
 modified exercise group . 
 the activation of extensor spinae differed significantly between 
 groups . 
 [ conclusion ] compared to the conventional exercise , the modified exercise was more 
 effective for trunk - hip activation improvement and anterior pelvic tilt motion decrease 
 during standing in children with spastic diplegia . 
 we suggest clinicians use an 
 individually tailored modified trunk - hip strengthening exercise for strengthening the 
 weakest muscle groups in children with standing ability problems . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION