children with cerebral palsy ( cp ) have neurodevelopment disorders , such as spasticity , 
 contracture , reduced coordination , selective voluntary motor control , and muscle 
 weakness1 . among these
, muscle weakness 
 is a major motor problem for children with cerebral palsy2,3,4,5,6,7 . as with muscle weakness , 

poor selective voluntary motor control ( svmc ) is also a prominent characteristic of children 
 with cp .
svmc is defined as the performance of isolated movement while performing a 
 functional task such as walking8 , and the 
 ability to activate muscles independently in response to voluntary motor requirements in 
 amounts appropriate for recruitment and activation of muscles .
compared with normal 
 children , children with cp have various muscle recruitment patterns and magnitudes9 , and these differences can affect voluntary 
 muscle recruitment leading to impairments in motor ability .
although children with spastic cp can walk independently , they have 52% or less maximum 
 contractile force in the main lower extremity muscles compared to same - aged normally 
 developing children in ankle flexion and extension5 . in particular
, the plantarflexor , which is the weakest muscle in 
 children with spastic cp , has 36% of the muscle strength of normal children10 . muscle strength and resistance training have been widely used as a therapeutic 
 interventions for increasing muscle strength and functional improvement3 , 11,12,13 . in the past , 

muscle strength training for children with cp was not considered viable because it required 
 much effort by the children and led to increased muscle spasticity14 .
however , some studies have reported that children with 
 spastic cp do not show an increase in muscle spasticity after they performing muscle 
 strength training15 , 16 .
a study 
 of 10 children with spastic cp who performed knee extensor , ankle extensor , and closed chain 
 exercises showed that the positive effect was maintained for six weeks13 .
the same study also reported functional improvements in 
 walking , running , and jumping as assessed by the gross motor function measure ( gmfm)13 . in another study of ankle plantarflexor 
 muscle strengthening exercises for children with cp , stride length and gait velocity 
 increased11 .
in spastic cp , the distal muscles of the lower limbs are weaker and may be proportionally 
 smaller than the proximal muscles .
the plantarflexor is one of the key muscles of the lower 
 extremities in children with cp10 . in 
 normal gait ,
the plantarflexors provide much of the force required to support the body and 
 advance the lower limb , particularly in midstance and late stance17 .
the purpose of this investigation was to determine whether increasing ankle strength 
 improves the gait parameters and gross motor function of children with cp .
we also 
 investigated its effect on the electromyogram ( emg ) activities of the ankle plantarflexor 
 and dorsiflexor muscles .
the subjects were a convenience sample of six children diagnosed with spastic cp ( 1 boy and 
 5 girls ) who were attending a cp clinic in south korea .
they were aged between 4 and 
 10  years ( mean age : 5.8  2.5 years ) , 110.7  11.5  cm tall , and weighed 20.4  4.3  kg .
this 
 study complied with the ethical standards 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 the subjects were assessed by gross motor function 
 classification scale ( gmfcs ) as level i. they could follow verbal commands and walk 
 independently without orthotics or assistive devices .
they had not received nerve block 
 injections or orthopedic surgery , and they had hypertonicity lower than grade + 1 of the 
 plantarflexors as evaluated by the modified ashworth scale .
potential subjects were excluded if they had ankle plantarflexion contracture greater than 
 15 degrees , or had knee or hip fixed flexion deformity greater than 10 degrees .
two normally developing children ( 1 boy and 1 girl with a mean age of 5.6  2.1  years , a 
 mean height of 113.5  0.7  cm , and a mean weight of 21.5  0.7  kg ) served as the control 
 group , providing comparative strength , muscle activity , and gait parameter data .
the 
 subjects and control children showed no significant differences in age , height , or 
 weight .
ankle dorsiflexor selective control was graded on a 3-point scale using the trost smc test 
 protocol ( a higher score indicates greater strength ) . in the test ,
a score of 0 = no ability 
 to isolate movement , a score of 1 = partially isolated movement , and a score of 2 = complete 
 isolation of movement18 .
electromyograms 
 of the ankle plantarflexor and tibialis anterior muscles were obtained using surface emg 
 ( qemg-4 , laxtha inc . , korea ) .
the quantification of the collected signals during the contraction of 
 each muscle was achieved by the root mean square method .
the degree of muscle vitalization 
 was analyzed by measuring the muscle activity in the smc test ( ankle dorsiflexion ) and in 
 the heel raise .
gait parameters were measured using an electrical walkway system ( gaitrite , cir system 
 inc .
the system captures temporal and spatial gait parameters through the serial port 
 of a personal computer .
it consists of an 810  89  0.625  cm ( length  width  height ) 
 instrumented mat with 27,648 embedded pressure - sensitive sensors , which are spaced at 
 1.27  cm and arranged in a 48  576 grid .
the sampling rate was 80  hz , and the obtained data 
 were analyzed using gait analysis software ( gaitrite gold , version 3.2b ) .
the subjects 
 walked at a gait speed with which they were comfortable in three trials .
the subjects 
 initiated and terminated walking a minimum of 3  m from the start and end of the walkway to 
 maintain the gait speed on the mat .
the gait velocity , cadence , and step length for both 
 legs were measured .
the gmfm is a standardized , criterion - referenced test designed to assess changes in gross 
 motor function in children with cp19 . 

gmfm-88 has been shown to have high levels of validity , reliability , and responsiveness in 
 evaluations of motor function and intervention effects in children with cp19 , 20 .
dimension d ( 13 items ) , which measures motor activities while 
 standing on the gmfm-88 , and dimension e ( 24 items ) , which measures motor activities while 
 walking , running , and jumping , were chosen as the outcome measures .
these represent areas 
 with which many children with mild spastic diplegia have difficulty21 , and they are activities that are more likely to be 
 improved by a lower limb functional strength training program .
maximal voluntary isometric contraction ( mvic ) was measured using a handheld dynamometer 
 ( power track ii , jtech medical , uas ) .
the handheld dynamometer has been shown to have good 
 reliability in the assessment of isometric strength of children with cp22 , 23 .
the ankle 
 plantarflexor muscles were tested bilaterally in a random order in the standardized 
 positions described in table 15 .
the dynamometer was positioned against a 
 solid , immovable object for measurement of the ankle plantarflexor strength to ensure that 
 there was no measureable force exerted by the examiner .
the dynamometer was held 
 perpendicular to the long axis of the body segment , and force was applied at right angles . 

the subject was instructed to hold the appropriate position for 5  s while pushing maximally 
 against the plate of the handheld dynamometer .
each muscle was tested three times , with a 
 rest period of 30  s between each test .
the subjects in the intervention group did a heel raise exercise , which included 
 progressive resistance ankle plantarflexor training for 6 weeks , 3 times a week , with each 
 session lasting 30  min .
it involves 
 stretching the hip adductor , ankle plantarflexor , and hamstring muscles for 35  min as a 
 warm - up to increase excitation of the motor unit and activate the range of motion before the 
 training .
the main exercise , the heel raise , was performed by applying a load with a 
 weighted vest of 20% of 1 repetition maximum ( rm ) for the first and second sets .
when the 
 child was able to perform the complete set of the exercises , the exercise was performed 
 iteratively by applying a load with a weighted vest of 50% of 1rm24 .
the exercise was finished with a cool - down period of 
 35  min to reduce damage and increase relaxation and flexibility of the body .
the subjects 
 were allowed to rest for 1  min between the sets to maintain the exercise performance .
they 
 repeated the exercise 8 to 12 times , with three to five sets performed per session .
the 1rm 
 of the heel raise exercise started at 30% of the child 's weight .
it was then increased up to 
 a weight where the child could still perform one set completely without losing balance24 .
weight was added or removed by using a 
 weighted vest in which a 0.5  kg weight can be placed in the pocket .
the wilcoxon signed - rank test was used to identify differences between the 
 pre- and post - test data for each of the dependent measures .
cp : cerebral palsy , nd : normally - developing children , mas : modified ashworth scale , 
 gmfcs : gross motor functional classification scale cp : cerebral palsy , nd : normally - developing children , mvic : maximal voluntary isometric 
 contraction ( n ) , * = significant difference , p < 0.05 cp : cerebral palsy , gmfm : gross motor function measure ( % ) , d : standing , e : walking , 
 running , and jumping cp : cerebral palsy , nd : normally - developing children , * = significant difference , p 
 < 0.05 the characteristics of the subjects are presented in table 2 .
the results show that the muscle strength of the ankle plantarflexor 
 significantly increased ( p < 0.05 ) ( table 3 ) 
 in all six children .
the subjects showed no statistically significant electromyogram changes 
 while performing the ankle dorsiflexion and heel raise exercises .
the average scores of the standing , walking , running , and jumping dimensions of the gmfm 
 showed changes , but they were not statistically significant ( table 4 ) .
the analysis of the spatiotemporal gait parameters 
 showed that the velocity , cadence , and step length of all six children with cp were 
 significantly increased ( p < 0.05 ) ( table 
 5 ) .
this study aimed to determine the effect of ankle plantarflexor training for children with 
 cp on muscle strength , muscle activation , gait parameters , and gross motor function .
the 
 results show that the muscle strength of the ankle plantarflexor showed a significant 
 improvement and that the subjects ' gait velocity , cadence , and step length increased .
engsberg et al.11 reported that the 
 muscle strengths of the ankle dorsiflexors and plantarflexors of children with cp were about 
 50% and 35% , respectively , compared with the strength of these muscles in children with 
 typical development , suggesting that children with cp require muscle strength training .
the results of the ankle plantarflexor strength exercise in this study are similar to 
 findings reported by engsberg et al11 . 

their subjects showed muscle strength increases after ankle muscle strength training using 
 an isokinetic dynamometer for 12 weeks .
engsberg et al.11 also conducted ankle dorsiflexor as well as plantarflexor training 
 using an isokinetic dynamometer .
however only ankle plantarflexor training was performed in 
 the present study using a protocol , which was familiar to the children .
crompton et al.22 reported that results obtained with an 
 isokinetic dynamometer or a similar machine are not reliable when used for children with cp 
 and that training using an isokinetic machine can be difficult for children with cp . based on our review of strength training programs
, it appears that a training program for a 
 minimum of six weeks may be sufficient to improve lower extremity muscle performance .
dodd 
 et al . have demonstrated that a six week strengthening program can increase the ability to 
 generate muscle force in children with cp13 , 25 .
our present study also demonstrated a 
 change in the muscle strength after six weeks of training .
the results of the gmfm showed that 4 of the 6 children had increased scores in the 
 standing dimension although this result was not statistically significant .
three children 
 had increased scores in the walking , running , and jumping dimension , and this was also not 
 statistically significant .
wiley and damiano5 investigated lower extremity muscle training for 6 weeks with 11 
 children with cp .
six of the children with cp were diagnosed with spastic diplegia , and five 
 with hemiplegia .
one child who performed only ankle plantarflexor exercise showed an 
 increase in muscle strength , as well as an increase in scores of the gmfm e dimension . 

another study reported that the gmfm e dimension score of children with cp increased to 4.4 , 
 on average , after lower extremity muscle strength training for 6 weeks13 .
the present study also showed increased in the average 
 scores of 2.3 of the gmfm e dimension .
the results of the spatiotemporal gait analysis showed that gait velocity increased by an 
 average of 7.3  cm / s .
although this speed was still slower than that of two children with 
 normal development , this result is similar to that of another study , which reported an 
 increase of about 6  cm / s after knee extensor strength training for six weeks4 . in our present study , an increase of about 
 11 steps / min in cadence and increases of about 2  cm for the right and left sides in step 
 length were realized . in comparison ,
engsberg et al.11 reported a 8.0  cm / s increase in gait velocity and a 2.4 steps / min 
 increase in cadence following ankle plantarflexor strength training , similar to the results 
 of this study .
the 
 study by engsberg et al.11 included 
 subjects categorized as level i , ii and iii , which is relatively wide .
measurement of the activity pattern of the plantarflexor using emg revealed a variety of 
 patterns , and no significant results were found .
the activity of the motor unit , muscle 
 fiber type , muscle length , and physiological state of the muscles influence the magnitude of 
 emg signals26 .
although the children with 
 cp in the present study had the same functional level , the length and physiological state of 
 their muscles were different due to individual gait patterns .
thus , the children with cp 
 showed various patterns of muscle activity compared to children with normal development . in 
 particular ,
if the prime movement involves a distal muscle , accurate activity is more 
 difficult due to antagonist muscle co - contraction .
tedroff et al.9 found that children with cp experienced greater difficulty 
 in recruiting the lateral gastrocnemius , which is an agonist muscle , during ankle 
 plantarflexion .
a limitation of this study is that only a small number of subjects participated in this 
 study .
further studies are required with larger sample numbers , and with the inclusion of 
 children aged more than 10  years old , and subjects with gmfcs levels of i , ii , and iii who 
 have mobility , with and without limitation . in conclusion ,
preservation of function and mobility is one of the primary aims in the 
 management of children with cp , and intervention is often directed at the 
 plantarflexors11 , 27 .
the heel raise exercise is a valid training method for children 
 with cp because it improves the strength of the plantarflexor , thereby increasing their 
 mobility .
this exercise can be performed without any equipment , which might be difficult to 
 handle , and children with cp can perform it themselves as part of a muscle strength training 
 program . increases in muscle strength resulted in maintenance of function in the present cp group . 

plantarflexor strengthening may turn out to be one of the most important interventions 
 available for ambulant children with cp .
   [ purpose ] the purpose of this study was to investigate the effect of ankle plantarflexor 
 strength training on selective voluntary motor control , gait parameters , and gross motor 
 function of children with cerebral palsy ( cp ) , focusing on changes in the strength and 
 muscle activity of the ankle plantarflexors . 
 [ methods ] six children aged between 4 and 
 10  years with cp participated in a 6 week strengthening program . the subjects were 
 evaluated before and after the intervention in terms of ankle plantarflexor strength , 
 muscle activity , gait velocity , cadence , step length , and d ( standing ) and e ( walking , 
 running , and jumping ) dimensions of the gross motor function measure ( gmfm ) . the data were 
 analyzed using the non - parametric wilcoxon signed - rank test . [ results ] the strength of the 
 plantarflexors increased in the majority of subjects . 
 significant and clinically 
 meaningful post - intervention improvements in subject 's gait velocity , cadence , and step 
 length were found . 
 [ conclusion ] the controlled ankle plantarflexor strengthening program 
 may lead to improvements in strength and spatiotemporal gait parameters of children with 
 cp . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION