quiet standing postural balance is an indispensable factor for performing routine 
 activities of daily living1 .
the 
 maintenance of a quiet stance is a complicated task that requires the integration of 
 vestibular , visual and somatosensory inputs from the whole body , for the assessment of the 
 motion and position of the body in space , and the ability to generate forces to adjust body 
 position2 .
disorders in these postural 
 control systems often result in falls , and falls are a potential risk , limiting activities 
 of daily living of patients with parkinson s disease3 .
patients with parkinson s disease have problems maintaining balance 
 and coordinating goal directed movements4 . 

in particular , the contributions of proprioceptive feedback information to static position 
 and movement perception processing are decreased in patients with parkinson s disease5 .
therefore , parkinsonian patients have 
 smaller than normal limits of stability when asked to perform quiet standing6 .
since the center of pressure ( cop ) and 
 ground reaction force ( grf ) are very important variables for the maintenance of postural 
 control , we need to evaluate the cop sway and grf as a clinical method of functional 
 assessment7 , 8 . also , because movement disability is the main symptom of patients with parkinson s disease , 
 exercise training is very important , and a recommended intervention in terms of exercise 
 that helps functional rehabilitation and decreases the side - effects of medications for 
 parkinson s disease9 , 10 .
however , it is difficult to develop a specific 
 therapeutic exercise for these symptoms which include hypokinesia , tremor , and muscular 
 rigidity11 .
recently , various devices and exercise interventions have been developed to replace the 
 loss of self - motion information due to disease , injury or aging . among these
, the 
 application of vibration has been widely used to improve the function of proprioception12 .
however , ross et al.14 reported that vibration applied to young healthy individuals did 
 not affect their static balance . some studies
have reported that vibration improved the 
 postural balance of patients with neurological injury , whereas the others have reported no 
 difference .
the purpose of this study was to investigate if the application of vibration to the lower 
 extremities affects the quiet standing postural balance of patients with parkinson s 
 disease .
the subjects had an 
 average age of 61.82  5.57 , an average height of 155.36  3.71 cm , and an average weight of 
 60.15  4.38 kg .
approval for the study was received from the institutional review board of 
 national evidence - based healthcare collaborating agency ( pirb11 - 015 - 1 ) , and written informed 
 consent was obtained from each patient before the start of the study .
eight vibrators ( 10 g , diameter of 1 cm ) were made especially for this study .
they were 
 attached to the muscle bellies of the tibialis anterior , gastrocnemius , biceps femoris , and 
 rectus femoris on both sides of the lower extremities of the subjects .
the subjects wore 
 short pants to minimize external stimuli , and were barefoot . to identify the effects of 
 vibration stimuli on static postural balance ,
subjects asked to stand on a force platform 
 and measurement were made with and without vibration applied to both of the lower 
 extremities .
the force platform ( amti , newton , ma , usa ) measured the center of pressure 
 ( cop ) sway and ground reaction forces ( grf ) during quiet standing .
the amplified force 
 platform signals were sampled on - line at a rate of 1,000  hz for 1 second and cop data ( path 
 length , path area ) and grf ( fx , fy , fz ) were calculated using bioanalysis ( amti , watertown , 
 ma , usa ) .
the independent t - test was used to identify the significance of differences in the 
 length and area of cop sway and grf ( medial / lateral , anterior / posterior , vertical force ) 
 between with and without vibration stimuli .
the length of cop sway of the parkinson s disease patients was not significantly different 
 between with and without vibration ( p>0.05 ) , but the area of cop sway with vibration was 
 significantly smaller than that without vibration ( p<0.05 ) ( table 1table 1 . comparison of center of pressure sway between with and without vibrationvariablewithout vibrationwith vibrationpath length ( mm)1,419.36 ( 276.04)1,425.31 ( 262.08)path area ( m)266.66 ( 139.71)122.19 ( 60.14)**significant difference between with and without vibration ( p<0.05 ) ) .
for grf , the medial - lateral maximum force ( fy ) with vibration was 
 significantly higher than that with no vibration ( p<0.05 ) , but the antero - posterior force 
 ( fx ) and vertical force ( fz ) showed no significant differences ( table 2table 2 .
comparison of ground reaction forces between with and without vibrationvariablewithout vibrationwith vibrationanterior - posterior ( % bm)0.00290 ( 0.00207)0.00391 ( 0.00215)medial - lateral ( % bm)0.00338 ( 0.00257)0.00604 ( 0.00234)*vertical ( % bm)1.03674 ( 0.07680)1.03694 ( 0.07649)*significant difference between with and without vibration ( p<0.05 ) ) .
* significant difference between with and without vibration ( p<0.05 ) * significant difference between with and without vibration ( p<0.05 )
parkinson s disease is characterized by tremor , postural reflex disorder , and rigidity , 
 which increase the risk of falls15 .
the 
 symptoms of parkinson s disease have been implicated in several aspects of the postural 
 control and locomotor systems including the integration of sensory information relevant for 
 balance16 .
this study demonstrated the effects of vibration on the postural balance of parkinson s 
 disease patients in quiet standing .
patients with parkinson s disease often have larger than 
 normal center of mass displacements in response to external perturbations17 , and they have problems integrating 
 proprioceptive information for posture - movement coordination4 .
vibratory stimulation increases the afferent signals generated by 
 the muscle spindles creating a proprioceptive illusion18 .
vibration can also evoke postural adaptation enhancing postural 
 performance and reducing the likelihood of imbalance19 . in our study of parkinson
s disease patients , the area of cop sway with vibration was 
 significantly smaller and the medial - lateral force ( fy ) with vibration was significantly 
 higher than that of the no vibration condition .
these results are similar to those of 
 previous studies which have reported that vibration can affect postural reactions and creat 
 postural kinesthetic illusions in standing subjects20 , 21 .
we believe that the 
 decrease of the area of cop sway and the increase of medial - lateral force induced by 
 vibration indicates a more rapid reaction to posture perturbation . in conclusion
, our results suggest that the application of vibration stimuli to the lower 
 extremities can help parkinson s disease patients to control postural balance during quiet 
 standing .
   [ purpose ] the purpose of this study was to investigate the effect of muscle vibration 
 applied to the lower extremities on static postural balance of patients with parkinson s 
 disease ( pd ) . 
 [ subjects ] seven subjects with parkinson s disease participated in this 
 study . [ methods ] 
 the oscillators of vibration were attached to the muscle bellies of the 
 tibialis anterior , gastrocnemius , biceps femoris , and rectus femoris on both sides of the 
 lower extremities with adhesive tape . a vibration frequency of 60  hz was used to induce 
 static postural reactions . 
 subjects center of pressure ( cop ) sway and peak ground 
 reaction force ( grf ) were measured with their eyes open with and without vibration . 
 cop 
 sway and peak grf ( fx , fy , fz ) were measured using a force plate ( amti , newton , usa ) , 
 which provides x , y and z coordinates of body movement . 
 [ results ] the area of cop sway 
 with vibration was significantly smaller than that with no vibration , but the length of 
 cop sway showed no difference between two conditions . 
 peak medial - lateral maximum force 
 ( fy ) with vibration was significantly higher than that with no vibration , but peak 
 anterior - posterior force ( fx ) and peak vertical force ( fz ) showed no differences . 
 
 [ conclusion ] these results suggest that vibration applied to the lower extremities can 
 help pd patients control postural balance during quiet standing . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION