volleyball is recognized as one of the most popular sports in the world amongst men and 
 women .
, volleyball has witnessed remarkable technical 
 progress , particularly in women s volleyball , with faster performance and evolving 
 techniques accompanied by changes in the type2 .
most sports require various kinds of high and low muscle strength with fast or slow speed . 

plyometric training is widely used as a method to develop explosive power capacity in sports 
 that require jumping ability3 .
plyometric 
 training is a type of muscle strength exercise that can improve basic physical strength .
it uses 
 muscles stretch reflexes and stretch - shortening cycles to develop lower extremity 
 muscles4 .
therefore , plyometric training 
 has been used a typical intervention method to enhance muscular function , and power5 .
, various kinds of training methods have been implemented in order to improve the 
 muscular power of sports players .
have reported that whole - body vibration 
 exercise is an effective method for improving muscular strength instead of resistance 
 movements .
in addition , it is a safe and effective exercise method for improving muscle 
 strength7 .
whole - body vibration exercise 
 provides an external stimulus for improving muscular strength , power , and performance in 
 sports players8 .
have 
 reported that whole - body vibration exercise offers a good chance of improving the jumping 
 ability and the muscle strength of lower limbs in 56 healthy adults9 .
therefore , it is expected that whole - body vibration 
 exercise can enhance exercise capacity not only in athletes but also in the general 
 population .
however , previous studies have not yet applied whole - body vibration exercises in female 
 volleyball players .
therefore , in the present study , female volleyball players were divided 
 into two groups : the whole - body vibration exercise ( wbve ) group and the plyometric exercise 
 ( pme ) group .
the objective of this study was to examine the effects of the two exercises on 
 isokinetic muscular strength , jumping performance , and balance ability of female volleyball 
 players .
the present study was conducted among players who were registered and who played for female 
 professional teams that belonged to the korea female volleyball federation .
study subjects 
 were selected from those who had no orthopedic disease as disease could make it difficult 
 for them to participate in regular games or training for regular games , and those who 
 sufficiently understood the purpose and intent of this study .
the subjects agreed to participate in the 
 study after receiving explanations regarding its purpose and procedures .
the study protocol was approved by the 
 local ethics committee of yongin university ( 2 - 1040966-ab - n-01 - 20 - 1603-hsr-046 ) .
thirty subjects were initially selected and randomly divided into the whole - body vibration 
 exercise group ( wbve group ) or the plyometric exercise group ( pme group ) .
a total of 28 players were considered as final study 
 subjects , after excluding two players who dropped out due to injuries .
general 
 characteristics of these subjects are summarized in ( table 1table 1.general characteristics of subjectswbve grouppme groupage ( years)23.2  2.423.5  4.2height ( cm)176.7  6.5178.3  6.5weight ( kg)70.3  8.270.2  8.2body fat ( % ) 22.9 
3.8323.2  4.5wbve group : whole - body vibration exercise group ; pme group : plyometric exercise 
 group .
wbve group : whole - body vibration exercise group ; pme group : plyometric exercise 
 group .
mean  sd in the present study , subjects were divided into the wbve group and pme group .
the exercise 
 was conducted for 50  min , three times per week , for a total of 8 weeks .
the exercise program 
 consisted of warm - up exercises for 10 minutes , main exercises for 30 minutes , and cool - down 
 exercises for 10 minutes .
three sets of exercises were performed . during the 3rd and the 4th weeks , four sets 
 of exercise were performed . from the 5th week to the 8th week , four sets of exercise were 
 performed with an increasing frequency of vibrations .
the vibration frequency was set at 
 26  hz during the 1st and 2nd week . from the 3rd week to the 8th week , the vibration 
 frequency was set at 8  hz .
details of the whole body vibration exercise program is 
 summarized in ( table 2table 2.whole-body vibration exercise program12 week34 week58 weektraining program positionstretching stretching stretching squatsquatsquatlunge ( front , side)lunge ( front , side)lunge ( front , side)one leggedone leggedone leggedstandingstandingstandingstretchingstretchingstretchingfrequency ( hz)2688time ( min)505050 ) .
the plyometric exercise was designed according to the method described by jastrzebski et 
 al10 . before the intervention
, subjects 
 performed warm - up exercises for 20 minutes . after the exercise program began , each motion 
 was limited to 10 times until the 2nd week so that the subjects could adapt to the program . 

the height of the box was 
 increased from 20  cm to 30  cm after the fifth week .
details of the plyometric exercise 
 program is summarized in ( table 3table 3.plyometric exercise programexercise type12 week34 week58 weekrep .
 seriessum of jumpsheight ( cm)double - legs leap on the spot10  220 - ------forward single - leg leap10  440 - ------double - leg vertical jump on the spot1  440 - 1  448 - 12  448-double - leg jump over a hurdle1  440201  4482012  44830squat leap ( frog leap)4  416 - 7  428 - 7  428-double - leg vertical jump from the squat jumps---6  530 - 6  530-approach run followed by a single - leg and vertical jump---6  424206  42430rep : repetition ) . to assess muscular strength , isokinetic muscle strengths of the lumbar and knee joints
each subject practiced the exercises three times and took rest for 
 three minutes before the measurement . jumping performance
the vertical jump height with simultaneous explosive power in both 
 legs was measured in units of 0.1  cm using measuring sensors .
each subject was instructed to stand with the hip 
 joint and knee joint flexed to 90 with eyes closed and both hands placed on the waist .
analysis of 
 variance ( anova ) was used to evaluate the changes in muscle strength , jumping ability , and 
 balance .
female volleyball players were divided into the wbve group and the pme group . with respect 
 to measurements of isokinetic muscular strength , the wbve group showed significant increase 
 in isokinetic muscular strength ( p<0.05 ) .
the pme group showed no significant increase in 
 the lumbar flexion and extension and knee flexion ( p>0.05 ) .
however , muscle strength of 
 the knee extension was significantly increased in the pme group ( p<0.05 ) ( table 4table 4.measurement of isokinetic muscular strengthpre - testpost - testwbve grouplumbar flex ( nm)112.0  17.2129.4  15.1*lumbar ext ( nm)197.6  41.8225.1  31.4*right knee flex ( nm)72.3  21.881.5  17.9*right knee ext ( nm)142.3  32.2184.2  39.7*left knee flex ( nm)73.6  22.584.7  19.7*left knee ext ( nm)153.1  32.0189.8  36.7*pme grouplumbar flex ( nm)101.9  15.3102.1  18.7lumbar ext ( nm)191.3  38.9185.2  36.8right knee flex ( nm)64.0  8.765.6  10.3right knee ext ( nm)137.0  22.4148.5  16.5*left knee flex ( nm)61.3  8.162.8  13.4left knee ext ( nm)134.9 
wbve group : whole - body vibration exercise group ; pme group : 
 plyometric exercise group ; flex : flexion ; ext : extension .
wbve group : whole - body vibration exercise group ; pme group : 
 plyometric exercise group ; flex : flexion ; ext : extension
. * significant difference 
 between before and after the intervention with respect to the measurement of vertical jumping , the wbve group showed no significant 
 increased in vertical jump ( p>0.05 ) .
however , the pme group showed a significant increase 
 in vertical jump ( p<0.05 ) .
with respect to the measurement of romberg s test , the wbve 
 group showed a significant increase in the score of the romberg s test ( p<0.05 ) .
however , 
 the pme group showed no significant increase in the score of the romberg s test ( p>0.05 ) 
 ( table 5table 5.measurement of vertical jump and romberg testpre - testpost - testwbve groupvertical jump ( cm)35.0  4.537.9  6.4right rom test ( sec)23.8  9.135.4  18.8*left rom test ( sec)22.4  15.938.1  16.7**pme groupvertical jump ( cm)36.0  3.941.2  43.9*right rom test
( sec)24.5  11.729.5  18.0left rom test ( sec)25.3  15.131.0  17.8values are mean  sd .
wbve group : whole - body vibration exercise group ; pme group : 
 plyometric exercise group . * significant difference between before and after the 
 intervention ) .
wbve group : whole - body vibration exercise group ; pme group : 
 plyometric exercise group .
the purpose of all sports training is to maximize the physical and mental elements required 
 to perform exercise or play games4 . 

however , plyometric training 
 requires careful attention because it requires high level of physical strength .
whole - body vibration exercise is a stable 
 exercise method as it reduces physical stimulation while mechanical stimuli are applied to 
 the muscles12 .
therefore , the present 
 study examined the effect of whole - body vibration exercise versus plyometric exercise on 
 female volleyball players .
with respect to the measurement of isokinetic muscular strength , the wbve group showed 
 significant increase in lumbar flexion and extension , and knee flexion and extension 
 ( p<0.05 ) .
have reported that vibration training is effective in improving the 
 muscle strength of lower extremities13 . 

kim et al . have also reported that vibration exercises can stimulate the muscle spindles to 
 recruit more motor units , thereby exerting greater power8 .
this study also found that whole - body vibration activated 
 proprioceptor ( muscle spindle ) and positively affected muscle strength ability .
in contrast , the pme group only had significant increase in knee extension ( p<0.05 ) , but 
 not in lumbar flexion and extension , or knee flexion ( p>0.05 ) .
plyometric exercises are 
 considered to have positive effects on the muscular strength of the extensor muscles of the 
 lower limb rather than on the flexor muscles .
the strengthening of the extensor muscles of the lower limb is considered to 
 have positive effect on jumping ability .
park has reported that plyometric exercises can 
 improve jumping ability through instantaneous exertion of elastic energy and stretch reflex 
 of the lower limb with increased muscular strength14 .
the reason for this occurrence might be due to the fact that 
 plyometric exercise can increase the jumping performance . the scores of romberg s test were significantly increased in the wbve group ( p<0.05 ) . 

courtine et al . have reported that vibration exercise can improve the proprioceptive 
 function15 .
proprioception maintains 
 the stability and orientation of the body during static and dynamic movements16 .
therefore , whole - body vibration in this 
 study appears to have stimulated the proprioceptors , resulting in a positive effect on 
 balance .
however , the pme group showed no significant increase in the scores of romberg s 
 test ( p>0.05 ) , indicating that plyometric exercise alone does not have a positive effect 
 on balance ability . in the present study ,
the whole - body vibration exercise had positive effects on isokinetic 
 muscular strength , and balance ability .
therefore , we conclude 
 that , although both whole - body vibration exercise and plyometric exercise are effective 
 interventions for female volleyball players , there is a difference in improvement of 
 isokinetic muscular strength , jumping performance , and balance between the two types of 
 exercise . this study included a limited number of subjects .
nevertheless , our study demonstrated the 
 importance of whole - body vibration exercise and plyometric exercise in female volleyball 
 players .
we hope that diverse training methods will be used to train female volleyball 
 players based on the findings of this study .
 [ purpose ] the purpose of this study was to assess the effect of whole - body vibration 
 exercise and plyometric exercise on female volleyball players . [ subjects and methods ] 
 subjects 
 were randomly allocated to two exercise groups ( whole - body vibration exercise 
 group and plyometric exercise group ) . 
 the exercise was conducted three times each week for 
 8 weeks . 
 isokinetic muscular strength , jumping performance , and balance were measured 
 before starting the exercise and after finishing the 8 weeks of exercise . 
 [ results ] 
 measurements of isokinetic muscular strength revealed that the whole - body vibration 
 exercise group showed significant increase after the exercise . however , the plyometric 
 exercise group had no significant increase in lumbar flexion , extension , and knee flexion . 
 measurements of vertical jumping revealed that , the whole - body vibration exercise group 
 had no significant increase after the exercise . 
 however , the plyometric exercise group 
 showed significant increase . measurements of balance revealed that , the whole - body 
 vibration exercise group showed significant increase 
 . however , the plyometric exercise 
 group showed no significant increase . [ conclusion ] 
 although both whole - body vibration and 
 plyometric exercises are effective intervention methods , the two methods have different 
 effects on the improvement of isokinetic muscular strength , jumping performance , and 
 balance of female volleyball players . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION