cerebral palsy ( cp ) , defined as a nonprogressive injury to the brain , covers numerous 
 neurological conditions , which result in abnormal development of movement and postural 
 control .
injury to the brain typically results in impairments in motor function , such as 
 muscle weakness , spasticity , and decreased selective motor control , which are primary causes 
 of children with cp limitations in the performance of activities of daily living and 
 participation1 .
children with cp have a 
 decreased level of daily physical activity in comparison to their healthy peers .
they do not 
 use their physical reserves sufficiently during the day to achieve optimal levels of daily 
 physical activity2 .
children with cp need 
 to maintain a higher level of physical fitness than healthy children in order to maintain 
 the natural growth process as they grow older3 .
the peak oxygen uptake ( vo2 peak ) , typically used as a measure of aerobic 
 fitness , is lower in children with cp , as has been shown through exercise tests using cycle 
 ergometry or a treadmill4 , 5 .
the maximum aerobic physical fitness , vo2 peak , 
 is an internationally acknowledged measure of the fitness of the cardiorespiratory system . 

three studies4,5,6 have studied vo2 
 peak in children and adolescents with cp during a maximal exercise test .
these studies 
 compared vo2 peak to the values observed in normally developing ( nd ) children and 
 adolesents5 , 6 . the most functional and appropriate way to assess
vo2 
 peak in children with cp who are able to walk independently is a progressive walking or 
 running - based maximal exercise test4 , 7 .
various researchers have developed 
 treadmill walking maximal exercise tests to assess individuals with cp and to investigate 
 the effectiveness of rehabilitation programs4,5,6 , 8,9,10,11 .
however , these methods limit the generalization of the results to actual daily walking , 
 because a variety of comfortable walking speeds are exhibited by children with different 
 types of cp5 . therefore , it is important 
 to test children under general conditions that are comparable to daily living conditions . 
 for estimating the maximal aerobic capacity , an adapted cycle ergometer test specifically 
 developed for cp can be used12 , 13 .
this aerobic test has the advantage of reducing errors 
 that are produced when walking with diverse patterns .
currently , studies of ergometer 
 aerobic tests14 have provided 
 insufficient evidence of their effect12 , 15 ; furthermore , no direct cardiorespiratory 
 results have been considered in the aerobic measurements16 .
although unnitan et al.17 studied the effect of uphill walking on children with diplegic cp , 
 and measured the of physical fitness of adult male cp subjects18 , their evaluations were performed using an arm ergometer . 

therefore , their score does not reflect changes in fitness resulting from a mainly leg - based 
 training program . timed
walking tests may offer a less expensive , simpler , and safer alternative to 
 laboratory testing of children with cp10 , 19 . among such tests ,
the 6-min walk test 
 ( 6mwt ) has been shown to predict cardiorespiratory fitness in both healthy and severely 
 disabled children , whether used with or without gas collection20 , 21 .
novac et al.22 systematically discussed 
 the most effective and applicable interventions for children with cp . in their reports of 
 the literature ,
the most recommended and applicable intervention was green light 
 intervention , and they emphasized the importance of fitness training for aerobic fitness . 
 before children with cp perform aerobic fitness tests , their aerobic ability should be 
 measured .
however , previous studies have reported in lacked consistent results and utilized 
 various measurement methods and environments .
thus , it is necessary to provide a precise 
 method and measurement for base data to obtain accurate reference values .
accordingly , this 
 preliminary study aimed to determine the cardiorespiratory endurance of children with cp 
 using a case series study in order to provide the reference data required for interventions 
 appropriate for south korean cp sufferers , since aerobic ability evaluation and 
 interventions for it for children with cp are not well recognized in south korea .
six children participated in this study . four subjects ( 3 boys , 1 girl ) had a diagnosis of 
 bilateral or unilateral spastic cp , and 2 subjects ( 1 boy , 1 girl ) were children with normal 
 development .
four children with cp gmfcs ( gross motor function classification system ) level 
 i and ii and two normally developing children ( age : 715  years ) were studied ( table 1table 1.general characteristics of subjectssubjectstypegmfcs levelgender ( boys : 0 , girls : 1)age ( years)height ( cm)weight ( kg)nda--01215148b--1711522cpcspastic bilateral101214031dspastic bilateral2015155.446espastic unilateral21711632fspastic unilateral201013838cp : cerebral palsy ; nd ; normally developing children ; gmfcs : gross motor function 
 classification scale ) .
subjects with cp were recruited from a medical center in gyeonggi - do south . 

this study complied with the ethical prinsiples of the declaration of helsinki , and all the 
 subjects and parents received explanations regarding the purpose and procedure of the study 
 before voluntarily agreeing to take part .
all parents signed an informed consent statement 
 before the start of the measurements . before testing , a medical examination was completed 
 and anthropometric data were collected .
the inclusion criteria were gmfcs levels i to ii , 
 uni- or bilateral spastic cp , age of 516  years , ability to walk continuously for 6  min , and 
 ability to provide informed consent .
potential subjects were excluded if they had received 
 orthopedic surgery or neurosurgery and/or botulinum toxin injection within the previous 6 
 months , or had cardiac or respiratory conditions that could have been negatively affected by 
 the proposed training .
all the selected subjects were also free of intellectual problems 
 that could have influenced their participation and/or motivation .
cycle ergometer testing 
 was performed with calf supports ( motomed viva cycle , reek medizinterchnik gm bh , 
 betzenweiler , germany ) .
the cycle ergometer test served to familiarize and habituate the 
 subjects , and it also allowed us to check whether a given subject needed to have his / her 
 feet attached to the pedals by velcro strapping23 . the concentration and volume of oxygen consumed ( vo2 ) , 
 peak respiratory exchange ratio ( rer peak ) , and minute ventilation ( ve ) were measured 
 simultaneously by portable metabolic measurement systems with prevent 
 pneumotachs ( medgraphics vo2000-medical graphics , st .
the ergometer 
 test began with a 5-min warm up followed by 612  min of exercise with increasing intensity 
 at a pedaling rate of 50  rpm as paced by a metronome .
verbal encouragement was provided 
 throughout the test to help each child achieve maximal effort .
the subjects were also fitted 
 with a neoprene face mask that could be used with the vo2000 .
a polar hr strap was also 
 fitted around the chest of the subjects ( polar electro oy , kempele , finland ) .
gas exchange 
 and pulmonary ventilation values were recorded using the breathbreath mode with 20-s 
 average values printed during testing .
cp : cerebral palsy ; nd ; normally developing children ; gmfcs : gross motor function 
 classification scale the 6-min walk test was performed in the laboratory corridor between two lines set 20  m 
 apart according to a standard procedure24 
 under the supervision of the same physiotherapist .
the subjects were instructed to walk as 
 far as possible in 6  min .
the subjects received standardized and vigorous verbal 
 encouragement , and they were advised of the distance covered and time remaining every 30 s. 
 all subjects performed , the cycle - ergometer test first , and the 6-min walking test was 
 conducted on the next day to avoid fatigue effects .
the ages of the subjects were distributed as follows : two were aged 7  years , two were aged 
 12  years , one was aged 10  years , and one was aged 15  years ; i.e , the youngest and oldest 
 subjects were 7 and 15  years of age . regarding the subjects gmfcs assessment , three were 
 level ii , and one was level i. two normal children of 7 and 12  years age participated in 
 this experiment to serve as controls for comparison with the children with cp .
the vo2 peak ( ml / kg / min ) of child f ( cp ) was 57.4 , which was the 
 highest , and that of child d was 22.6 , which was the lowest .
the two normal children , a and 
 b , had vo2 peaks ( ml / kg / min ) of 22.9 and 56.5 , respectively .
in the 6mwt , 
 child c ( cp ) walked 578 m , which was the longest distance , and child e walked 390  m , which 
 was the shortest distance ( table 2table 2.subjects peak cardiorespiratory responses to ergometrytypesubjectsvo2 peakrer peakve peakhr peak6mwtnda22.90.8218.5105580b56.50.9723.8135450cpc25.91.3625.3145578d22.61.0222.9131527e44.50.8732.5129390f57.40.9759.5147560vo2 peak ( ml / kg / min ) : peak oxygen uptake ; rer peak : peak respiratory 
 exchange ratio ; ve peak ( l / min ) : maximum ventilation per minute ; hr peak ( beats / min ) : 
 peak heart rate ; 6mwt ( m ) : 6-min walk test ) .
furthermore , the comparison of vo2 peak between normal child a 
 and child c ( cp ) showed that the former had a value of 22.9 , which was lower than that of 
 the latter .
the comparison of vo2 peak between normal child b and child e ( cp ) 
 showed that the latter had a value of 44.5 , which was lower than that of the former .
the 
 comparison of 6mwt between normal child a and child c ( cp ) and between normal child b and 
 child e ( cp ) showed that the normal children walked further than the children with cp . vo2 peak ( ml / kg / min ) : peak oxygen uptake ; rer peak : peak respiratory 
 exchange ratio ; ve peak ( l / min ) : maximum ventilation per minute ; hr peak ( beats / min ) : 
 peak heart rate ; 6mwt ( m ) : 6-min walk test
this preliminary study aimed to determine the cardiorespiratory endurance of children with 
 cp using a case series study to provide the reference data required for interventions 
 appropriate for south korean cp sufferers , since aerobic ability evaluation and 
 interventions for it for children with cp are not well recognized in south korea .
children with cp have lower vo2 peak values ( ml / kg / min ) as well as shorter 
 walking distances in set times than normal children .
numerous studies have reported the 
 lower physical activities of children with cp in terms of aerobic abilities4 , 5 , 1725 , 
 and some studies have reported that children and adolescents with cp have lower physical 
 activity abilities than normal peers26 . 

verschuren et al.6 reported that 
 comparisons with normative data sets suggest that adolescents with cp tend to participate in 
 less structured and lower intensity physical activities than healthy adolescents .
durstine et al.27 described a vicious 
 circle in which persons with a chronic disease or disability experience less physical 
 activity , which then leads to a cycle of deconditioning and further physical deterioration 
 and reduction in activity .
however , as seen in this study , the child with cp aged 7 ( subject 
 e ) had a lower vo2 peak value than the normally developing child ( subject b ) , and 
 the child with cp aged 12 ( subject c ) had a higher vo2 peak value than the 
 normally developing child ( subject a ) .
subject b ( nd ) had a lower vo2 peak than 
 subject e ( cp ) , consistent with the results of previous studies6 , 13 .
one study6 reported that a child with cp had a 
 vo2 peak value of 42  ml / kg / min , which was close to our study result of 
 44.5  ml / kg / min ; however , the interpretation of the results of this previous are limited , 
 because the subjects were aged from 7 to 17  years . with regard to the comparison of the 
 results of subjects
a and c , it is necessary to determine the reason for the higher 
 vo2 peak value in children with cp than in normal children , considering of 
 various possibilities . a child with gmfcs level
i can perform gross motor skills such as 
 running and jumping and participate in physical and dynamic activities .
in contrast , a child 
 with cp at gmfcs level ii can not participate in physical and dynamic activities such as 
 playground activities owing to his / her limited abilities .
despite examining only one case in 
 this study , our results suggest children with cp who have small body mass and high 
 functional level have even higher vo2 peak values than normal children .
nsenga et 
 al.13 reported that children with cp at 
 gmfcs levels i and ii can have cardiorespiratory endurance similar to that of normal 
 children of similar ages .
the former showed higher values ( 41.4 ) than 
 the latter ( 33.6 ) .
this result was used as an explanation for the lower vo2 of 
 children with cp .
the present study found comparable values for children and adolescents 
 with cp and normally developing subjects .
the ventilation peak ( vepeak ) value for child c 
 ( cp ) was higher ( 25.3 ) than that ( 18.5 ) of child a ( nd ) .
similarly , the child e ( cp ) showed 
 a higher value ( 32.5 ) than that ( 23.8 ) of child b ( nd ) .
the distance walked strongly correlated with the 6mwt 
 vo2 peak ( r = .948 ) and was related more modestly to the 
 cycle - ergometer vo2 peak ( r = 0.625)19 . in this study
, vo2 was not collected while 
 performing the 6mwt . however , the results of the present study show that children with cp ( c 
 and e ) walked shorter distances than normal children ( a and b ) .
nsenga et al.19 reported that the 6mwt distance increased 
 after aerobic training , showing a correlation between the cardiorespiratory capacity and 
 6mwt distance .
although a previous study suggested there is no significant correlation 
 between the ergometer vo2 peak and 6mwt distance , maanum et al.28 reported that the 6mwt distance was a 
 significant predictor of cardiorespiratory capacity for children with spastic cp .
peak rer is generally used as a secondary criterion for 
 maximal effort ; however , large individual variations may be present depending on the test 
 modes and protocols29 .
the average peak 
 rer values in the present study ( 0.871.36 ) were comparable to the average values reported 
 in previous studies of children with cp ( 0.91.15 ) , and most studies have reported a peak hr 
 of 190 bpm4 , 30 .
these results does not support the finding that the children did 
 not produce their maximal effort because of the lower peak hr values .
however , the present 
 study conducted ergometer tests and not treadmill tests ; furthermore , there was an age 
 difference among the subjects . thus far , most studies of children with cp have focused on cycle ergometer or treadmill 
 walking tests6 , 8,9,10 , seeking to verified the effectiveness of these tests12 , 
 13,14,15 , 17 . however , the available literature on the cardio - respiratory capacity of 
 children with cp focuses on treadmill walking rather than cycle ergometry .
verschuren et al.7 noted that treadmill protocols such as the bruce and balke tests are 
 not appropriate for children with cp .
furthermore , treadmill testing is difficult for many 
 children with cp because they suffer from severe balance issues31 .
it is difficult to compare the children from all studies 
 that have provided information about vo2 peak for children and adolescents with 
 cp .
although many studies have recognized the importance of fitness for maintaining aerobic 
 capacity , it is not easy to conduct aerobic tests with children with cp owing to the 
 limitations described in the studies cited above . among studies with a high evidence level , 
 the accuracy of the results may not be that high owing to the use of arm ergometry rather 
 than a test of the lower extremities .
other studies include a case study15 with a low evidence level and studies with 
 a small number of subjects12,13,14 .
accordingly , 
 more evidence and data that can be used as a reference to provide fitness programs for 
 school children with cp are needed in the future .
this study aimed to determine the 
 cardiorespiratory endurance of children with cp using a case series study in order to 
 provide the reference data required for interventions appropriate for south korean cp 
 sufferers , since aerobic ability evaluation and interventions for it for children with cp 
 are not well recognized in south korea . despite success in the study aims , the results 
 should be interpreted with care , owing to the small number of participating subjects . in conclusion , this case report reports cardiorespiratory parameter values that are similar 
 to those that have been reported previously .
fitness training for aerobic fitness is an 
 important intervention method for children with cp .
accordingly , it is necessary to provide 
 evidence of cardiorespiratory fitness levels for children with cp when such fitness programs 
 are conducted .
furthermore , it is necessary to provide precise methods and measurements for 
 base data in every assessment to obtain accurate reference values . in this
regard , our study 
 will provide information about vo2 peak values for an aerobic - fitness - related 
 study conducted with children with cp in the future .
 [ purpose ] this preliminary study aimed to determine the cardiorespiratory endurance of 
 children with cerebral palsy ( cp ) using a case series study in order to provide the 
 reference data required for interventions appropriate for south korean cp sufferers , since 
 aerobic ability evaluation and interventions for children with cp are not well recognized 
 in south korea . 
 [ subjects and methods ] four children and adolescents with cp gmfcs ( gross 
 motor function classification system ) level i and ii and two normally developing children 
 ( nd ) ( age : 715  years ) were studied . 
 cycle ergometer testing was performed to determine 
 their vo2 peak and rer peak concentrations as well as ve peak and 6mwt 
 distance . 
 [ results ] the vo2 peak was lower in subject e ( cp ) at 44.5 than in 
 subject b ( nd ) , and it was lower in subject a ( nd ) at 22.9 than in subject c ( cp ) . 
 the 
 6mwt distance was longer in subjects a and b ( nd ) than in age - matched cp subjects . 
 
 [ conclusion ] this case report demonstrates that the cardiorespiratory parameters values of 
 cp children were similar to those reported previously . 
 further research is required to 
 evaluate the normative values of cp and the optimal cardiorespiratory parameters . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION