neuromuscular control can be defined as an interaction between the nervous and 
 musculoskeletal systems to produce a desired effect or response to a stimulus3 .
enhancements of several factors such as 
 muscular strength , power , and endurance are directly related to the improvement in an 
 athletes exercise performance .
recently , various kinds of training methods have been 
 implemented in order to improve the muscular power of sports players ; plyometric training 
 has been a typical intervention for enhancing the muscular function4 , power5 , 
 and running performance ability6 .
however , 
 it might cause musculoskeletal injuries at landing phase7 , 8 . in this sense ,
whole - body 
 vibration exercise ( wbve ) , regarded as a neuromuscular training method utilizing a moderate 
 vibration stimulus to improve muscular strength and power9,10,11,12 , has become a practical 
 exercise intervention for athletes .
the potential factors expected from wbve are vibration 
 type , frequency , body position , and additional load13 . among these
, a change in the body position through different knee 
 bending angles14 , 15 might be one of the most crucial factors that can augment muscular 
 function with wbve .
however , previous studies have not suggested the optimal squatting 
 position that can maximize the effect of wbve , and explained the interrelationship between 
 the optimum knee angle during a squat and wbve .
accordingly , the primary objective of this 
 study was to validate the optimal squatting position that maximizes muscular function when 
 wbve is performed with a certain vibration frequency , and for a certain time duration .
12 subjects ( men , aged 26  1.9  years , height 175.91  7.3  cm , weight 74.4  10.88  kg ) who 
 did not exercise regularly participated in this study .
the participants were explained the 
 procedures and the purpose of the study , and were requested to submit a written consent 
 form .
this study was approved by the university of sunmoon research ethics review committee 
 ( syuirb 2010 - 007 , 27 february 2015 ) according to the declaration of helsinki .
the protocol of this study for assessing the vibration frequency and time is based on a 
 previous study conducted by bosco14 , and 
 interventions for the different squatting positions are adopted from studies conducted by 
 deleclus15 and jacobs16 . in addition , this study defined the 
 squatting position according to the knee and hip angle as lower squatting position ( ls ) 
 ( 90 ) , middle squatting position ( ms ) ( 140 ) , and high squatting position ( hs ) ( 170 ) .
wbve was performed at 26  hz frequency with 5 sets of exercise in one minute . after resting 
 for 6 minutes , another session of 5 sets
all participants 
 implemented the exercise program without wearing shoes and socks in order to eliminate 
 additional effects like cushion of the shoes .
moreover , all measurements in this study were 
 performed by the same tester , and the measurement schedules were planned with at least 
 one - week interval after a certain session to minimize the learning effect .
data from knee isokinetic muscular function test were evaluated with an isokinetic 
 dynamometer , bte primusrs system ( bte technologies inc . ,
usa ) , and jump performance 
 variables were measured with g - jump ( bts bioengineering , italy ) .
wbve equipment ( galileo 
 2000 , novotec medical , germany ) was used to determine the effects of the exercise 
 program .
statistical analysis was performed using spss / pc 18.0 statistical program for mean and 
 standard deviations .
analysis of variance ( anova ) was performed for repeated measurements to 
 analyze the differences in knee isokinetic muscular function and jump performance depending 
 on the squatting position . moreover , the post - hoc test with least significance difference 
 ( lsd ) was used in this study . statistical significance level (  ) for data analysis was set 
 at p < 0.05 .
in table 1table 1.differences in isokinetic muscular function of the knee and jump performance 
 according to the squatting positionpre - interventionhs ( 170)ms ( 125)ls ( 90)comparison60/sec ( nm)extension518.3  68.9542.2  56.3537.0  5.5550.3  67.8a < dflexion339.0  50.5392.2  49.9387.8  47.8412.3  61.9a < b , c , d180/s total work(j)2,188.7  346.62,728.0  478.22,787.0  444.02,685.9  432.9a < b , c , djump height(cm)49.16  2.850.59  3.451.04  3.7651.32  3.6a
s : second . * a significant difference between the interventions ( p < 0.05 ) .
a : pre - intervention , b : hs , c : ms , d : ls , the difference in isokinetic muscular sunction of the knee and jump 
 performance depending on the squatting position , and the knee angles for each squatting 
 position ( hs , ms , and ls ) are represented .
significant difference was seen in the knee 
 flexor strength at 60/s and knee muscle endurance at 180/s after wbve intervention in all 
 squatting positions ( p < 0.05 ) . for the knee extensor strength at 60/sec , among the 
 squatting positions significant difference
in addition , jump height 
 was significantly increased in all squatting positions ( p < 0.05 ) .
all variables are mean  standard deviaion . s : second . * a significant difference between the interventions ( p < 0.05 ) . a : pre - intervention , b : hs , c : ms , d : ls
in this study , it can be said that wbve might have provided an external stimulus for 
 improving muscular strength , power , and performance for sports players during the time 
 period .
the present study shows that isokinetic muscular functions such as muscular strength 
 and endurance had significantly increased in all squatting positions with wbve when compared 
 to pre - exercise state .
this implies that primary endings of the muscle spindle are 
 stimulated by the vibrations , which excites the motor neurons causing contraction of motor 
 units , resulting in tonic contraction of the muscle known as tonic vibration reflex15 , 17 , and greater training effects are stimulated by increased motor unit 
 recruitment as an effect of the tonic vibration reflex18 .
it is thought that the results of this study demonstrate the 
 improvement in muscular functions by increasing the co - contraction ability of the synergist 
 muscles .
in addition , it is noteworthy that the muscular function in ls ( 90 knee angle ) was 
 significantly better than the pre - intervention state .
although no significant difference was 
 found among the squatting positions , ls with wbve might be able to maximize the 
 neuromuscular exercise effect in terms of amplifying the sensitivity of the muscle spindle . 

it can be said that the stimulated spindle of vastus medialis and lateralis and its muscular 
 power are the optimum results of wbve with ls .
these aspects could increase the tonic 
 vibration reflex , and , as a result , the exercise ability such as jump performance was better 
 in ls in comparison with other squatting positions ( ms and hs ) .
in other words , when 
 applying wbve with squatting position , the knee angle is one of the most important factors 
 when it comes to considering the optimal exercise effect .
more importantly , wbve might be 
 able to offer positive training effects to the sports players hoping to improve their 
 muscular power and endurance within a short period , as shown in this study , when time or 
 exercise methods are lacking . in conclusion
, this study suggests that wbve at 26  hz 
 vibration frequency with 90 angle of hip and knee might be a feasible exercise intervention 
 for sports players ; however , other combinations between the knee angle and vibration 
 frequency for an optimal exercise effect should be considered in future studies .
 [ purpose ] the purpose of this study was to investigate the effects of whole - body 
 vibration exercise ( wbve ) on isokinetic muscular function of the knee and jump performance 
 depending on different squatting positions . 
 [ subjects ] the subjects were 12 healthy adult 
 men who did not exercise regularly between the ages of 27 and 34 . [ methods ] wbve was 
 performed with high squat position ( sp ) , middle sp , and low sp . before and after the 
 intervention , isokinetic muscular function of the knees and jump performance were 
 measured . 
 [ results ] knee flexion peak torque at 60/s and total work at 180/s were 
 significantly increased after implementing wbve . 
 jump height also significantly increased 
 after completing the exercise at all positions in comparison with the pre - exercise 
 programs . 
 [ conclusion ] the results of this study suggest that sp during wbve is an 
 important factor stimulating positive effects on muscular function . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION