the structure of the knee joint provides a high level of resistance that enables weight 
 support , activity control , and the bearing of heavy loads , so the knee joint is in charge of 
 weight - bearing and has a wide range of motion ( rom)1 . from a biomechanical perspective ,
the quadriceps femoris group , 
 iliotibial band , adductor magnus , adductor longus , pes anserine group , and biceps femoris 
 work as knee joint stabilizers for the patellofemoral joint2 .
patellar alignment and tracking are determined by the amount of 
 force and the direction of soft tissues around the patellofemoral joint .
in particular , the 
 vastus medialis oblique ( vmo ) muscle works as a medial patellar stabilizer3 .
an increase in the q - angle increases the pressure on the patellofemoral joint4 and can give rise to anterior knee pain5 .
an excessive q - angle can result from 
 imbalance between the vmo and the vastus lateralis ( vl ) muscles6 .
this imbalance leads to lateral gliding and incorrect 
 tracking of the patella , thereby causing pain by increasing the pressure on the 
 patellofemoral contact area7 .
weakening of 
 the vmo is especially regarded as an important cause of knee imbalance8 .
women showed a greater increase in the q - angle than in men 
 due to their wider pelvises , which can cause malalignment of the genu valgum9 .
patellofemoral pain is also reported to be 
 about twice as common in women than in men10 .
therefore , selective strength training for the vmo is of great 
 importance to secure balance and stability in the vmo and vl11 .
one study suggested their application as 
 a safe and effective exercise method that minimizes stress in the patellofemoral joint 
 within its functional range13 .
mcclelland 
 et al . stated that exercises using a visual feedback device are effective for symmetrical 
 pattern reeducation training of knee joint exercises14 .
mcconnell also reported that this type of real - time information 
 delivery induced selective strengthening of the vmo15 .
comparison and analysis of the action potentials of different muscles during muscle 
 strengthening exercises in the knee joint are also important elements in identifying the 
 effects of these exercises .
evaluation of exercises using an electromyogram ( emg ) provides 
 information on bioelectric activities related to the start of muscle contraction and muscle 
 control actions , so the use of emg is effective in these kinds of studies16 .
several previous studies reported that 
 emg - based visual feedback exercises positively affect the alignment of lower extremities in 
 young women with patellofemoral pain syndrome ( pfps ) , but their application has not been 
 generalized .
the aim of the present study was to compare and analyze the muscle activation of the vmo 
 and vl due to performance of visual feedback exercises in young adults with a large q - angle , 
 thereby verifying the extent of active improvement of control ability .
the overall goal was 
 to suggest a more general exercise method that can prevent pain occurring in the knee .
this study used a motion analysis program ( dartfish , switzerland ) to select 20 young adults 
 with an increased static q - angle , who were then divided into two groups .
one group underwent 
 squat exercises with visual feedback ( visual feedback squat group ; vsg , n=10 ) , and the other 
 group performed squat exercises with no visual feedback ( squat group ; sg , n=10 ) .
the average 
 age , height , weight , static q - angle , and kujala patellaofemoral score ( kps ) in the vsg were 
 22.601.83  years , 167.007.45  cm , 63.8012.01  kg , 17.030.54 , and 83.202.83 , respectively . 

the average age , height , weight , static q - angle , and kps in the sg were 23.202.14  years , 
 168.809.37  cm , 64.6011.86  kg , 16.860.60 , and 84.702.86 , respectively ( table 1table 1.general characteristics of the subjects ( meansd)groupvsg ( n=10)sg ( n=10)gendermale : 4male : 4female : 6female : 6age ( years)22.601.8323.202.14height ( cm)167.007.45168.809.37weight ( kg)63.8012.0164.6011.86static q - angle ( )17.030.5416.860.60kps ( score)83.202.8384.702.86meansd , meanstandard deviation ; vsg : visual feedback squat group ; sg : squat group , 
 kps : kujala patellofemoral pain score ) .
meansd , meanstandard deviation ; vsg : visual feedback squat group ; sg : squat group , 
 kps : kujala patellofemoral pain score the study s purpose and exercise methods were explained before the experiment to all 
 subjects , who then agreed to participate .
they also signed a written consent form according 
 to the ethical principles of the declaration of helsinki .
the subjects were young adults 
 with a larger static q - angle than normal as determined using a motion analysis program 
 ( dartfish , switzerland ) .
in addition , they had to score at least 80 points , but below 90 
 points , for the kps , and they had to have no medical history of undergoing orthopedic 
 surgery or treatment in the lower extremities including the knee joint , no visual field 
 defects nor abnormalities in vestibular organs , and no deformities in the knee joint , hip 
 joint , and foot . before the experiment , the tester demonstrated the designed exercises to help the subjects 
 understand the experiment s progression and procedures , and then all subjects were 
 instructed to practice for five minutes to become familiar with the squat positions . the 
 exercise program consisted of a warm - up , main exercises , and a cooldown .
the warm - up and 
 cool - down exercises were identical in the vsg and sg groups .
for the main exercises , the vsg 
 performed squat exercises with visual feedback , whereas the sg performed squat exercises 
 without visual feedback .
the intensity of the exercises in this progressive exercise program 
 was increased every two weeks the course of a six - week period .
visual feedback in the vsg consisted of marks attached to a mirror that provided a visual 
 route that guided the ideal alignment of the lower extremities .
in addition , while each 
 subject s knee joint was extended in the sagittal plane , a visual marker was attached to the 
 upper side of the patella .
the distance between the visual marker on the subject s knee 
 joint and the lines guiding the visual route on the mirror was set as 1  m. within the lines 
 guiding the visual route , the subject performed squat exercises while gradually increasing 
 the level of knee flexion , with the maximum being 90. in the sg , each subject performed squat exercises without wearing a visual feedback device 
 and also gradually increased the level of knee flexion , with the maximum being 90. for the 
 warm - up , all subjects performed walking in the functional exercise system while maintaining 
 a balance in the lower extremities and stretching exercises for shortened muscles related to 
 increases in the q - angle .
for the main exercises , the vsg performed squat exercises with 
 visual feedback , and the sg performed squat exercises without visual feedback . during weeks 
 1 and 2 , the subjects performed one set of 20 squat exercises , which consisted of 20 squats , 
 at 90of knee flexion . during weeks 3 and 4 , they performed two sets of squat exercises . 
 during weeks 5 and 6
the muscle activation of the vmo and vl was measured with each subject in a 90 squat 
 position using a surface emg ( noraxon myosystem dts , usa ) .
the emg signals were standardized 
 by measuring the muscle activation of the vmo and vl during maximal voluntary isometric 
 contraction by conducting a manual muscle test .
the data values underwent rms processing for 
 five seconds , and the average emg signal for three seconds , excluding the first and last 
 second , was used as 100% mvc . for statistical analyses , comparisons of the vmo and vl within 
 each group before and after the experiment were verified using paired t - tests .
differences 
 between the two groups in values before and after the experiment were compared by 
 independent t - tests .
fisher s least significant difference ( lsd ) was employed as a post hoc 
 test .
data were statistically processed using spss 17.0 for windows , and the statistical 
 significance level was set at 0.05 .
analysis of the muscle activation due to 90 squat exercises indicated that both groups had 
 statistically significant increases in activation of the vl ( p<0.05 ) .
the vsg exhibited 
 statistically significant increases in activation of the vmo ( p>0.05 ) ( table 2 
 table 2.comparison of the vmo and vl within and between groups ( unit : ratio ) ) .
this study identified the effects of the muscle activation of the vmo and vl in young 
 adults with an increased q - angle by dividing the subjects into a squat exercise group that 
 was provided with visual feedback ( vsg ) and a squat exercise group that received no visual 
 feedback ( sg ) .
the effects of visual feedback exercises that are easily accessible in daily 
 life are meaningful in terms of preventive medicine .
therefore , this study was undertaken to 
 verify the effects of new , easily accessible visual feedback exercises .
recent relevant studies have focused on how to improve the control of the vmo , strengthen 
 muscles functionally , and improve muscle performance with regard to the patella , rather than 
 solely focusing on muscle strengthening17 .
fehr et al . reported increases in the kps following application of 
 ckc exercises in a group of patients with pfps18 .
jae - yeong kang reported that the measurement of the q - angle at 60 
 of knee flexion resulted in statistically significant decreases in a ckc exercise group that 
 used emg biofeedback11 .
surface emg analysis is a useful tool for evaluating the results of treatment during 
 treatment processes19 .
hyeon - hee lee 
 reported that patients with patellofemoral pain showed statistically significant declines in 
 muscle activation of the vmo based on surface emg readings20 . in the present study ,
the q - angle measurements were 17.032.01 in 
 the vsg and 16.862.41 in the sg , which confirmed increases in the q - angle compared with 
 the average levels of normal adults .
reported that the average 
 measurement values for the q - angle in normal adult women were larger than those in men21 .
another study noted that an increase in 
 the q - angle over normal levels led to genu valgum and could cause pfps due to excessive 
 pressure22 . in the present study , 
 analysis of muscle activation following 90 squat exercises showed statistically significant 
 increases in the vmo activation in the vsg .
grossi et al . reported statistically significant increases in muscle activation in both an 
 pfps group and the general groups during 60 squatting23 .
seo - yi park also reported that , among ckc exercises , squat and 
 step - up / down exercises yielded statistically significant increases in activation24 .
gi - cheol kim analyzed the muscle 
 activation ratios of the vmo and vl when subjects performed squat exercises with different 
 angle variations , and found statistically greater effects in the group that performed 
 biofeedback squat exercises25 .
they also 
 compared the average differences between the biofeedback and general squat exercise groups 
 and reported greater effects with biofeedback squat exercises than with general squat 
 exercises at all tested angles ( 30 , 60 , and 90 ) . in the present study , measurement of 
 muscle activation before the experiment showed that the vmo had a higher level of muscle 
 activation than the vl .
both the vsg and sg exhibited statistically significant increases in 
 muscle activation of the vl after the treatments ; however , only the vsg showed a 
 statistically significant increase in activity of the vmo .
these findings suggest that squat 
 exercises with visual feedback are more effective in activating the vmo than squat exercises 
 without visual feedback .
squat exercises with visual feedback are also effective in 
 activating both the vmo and vl .
the limitation of this study is its focus on young adults with an increased q - angle , which 
 precluded the identification of pain reduction effects in patients who have pain .
however , 
 this study is considered meaningful in terms of helping to prevent potential patellofemoral 
 pain using visual feedback squat exercises that activate the vmo , a primary cause of 
 patellofemoral pain .
therefore , this study provides basic data regarding the muscle 
 activation of the vmo and vl , but additional systematic studies should be conducted in the 
 future using more diverse subjects and variables .
 [ purpose ] the purpose of this study was to identify the effects of performing squat 
 exercises with visual feedback on the activation of the vastus medialis oblique ( vmo ) and 
 vastus lateralis ( vl ) muscles in young adults with an increased quadriceps angle 
 ( q - angle ) . 
 [ subjects ] this study used a motion analysis program ( dartfish , switzerland ) to 
 select 20 young adults with an increased q - angle , who were then divided into a squat group 
 that received visual feedback ( vsg , n=10 ) and a squat group that received no visual 
 feedback ( sg , n=10 ) . [ methods ] the intensity of exercises 
 was increased every two weeks 
 over a six - week exercise period in both groups . 
 a visual marker was attached to the 
 patella of the subjects in the vsg , and they then performed squat exercises with a maximum 
 of 90 of knee flexion within a route marked on a mirror . 
 the sg performed squat exercises 
 with a maximum 90 of knee flexion without attaching a visual feedback device . 
 [ results ] 
 analysis of the muscle activation due to 90 squat exercises indicated that both groups 
 had statistically significant increases in activation of the vl . 
 the vsg exhibited 
 statistically significant increases in activation of the vmo . 
 [ conclusion ] this study 
 confirmed that squat exercises with visual feedback are effective in activation of the vmo 
 and vl muscles . 
 the findings are meaningful in terms of preventing the occurrence of 
 patellofemoral pain . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION