patellofemoral joint pain syndrome ( pfps ) is one of the most common pathologic conditions 
 of the knee in sports medicine1 .
it is 
 well documented that female athletes are more likely than male athletes to suffer with 
 pfps2 .
pfps can be caused by a variety 
 of factors , including quadriceps weakness , increased q - angle , loss of lower extremity 
 function , hypermobile patella , ligamentous laxity , and lateral retinaculum tightness3,4,5 .
specific activities , such as prolonged sitting , stair descent and 
 squatting often aggravate the pain6 .
also , 
 one of the most commonly accepted etiologies of pfps is abnormal tracking of the patella 
 within the femoral trochlea7 .
a cause of 
 this abnormal tracking may be delayed muscle activity onset time of the vastus medialis 
 oblique ( vmo ) relative to the vastus lateralis ( vl)8 . in the past , the patellofemoral joint has been regarded as the main problem of pfps . 

however , a recent study demonstrated that poor hip adduction and internal rotation control 
 during weight - bearing activities were related to pfps in athletes due to weakness of the hip 
 abductor and external rotator muscles9 . 

these reports suggest that improving pain and hip lateral rotator and abductor 
 muscle strength improves the function of patients with patellofemoral pain9 , 10 .
many therapeutic exercises emphasize the importance of the vmo muscle because of its medial 
 pull on the patella1 , 11 , 12 .
a previous study 
 investigated the effect of a rehabilitation program on the activity timing of the vmo 
 relative to the vl using a mcconnell - based rehabilitation program13 . also , boling et al .
demonstrated effects of a 
 weight - bearing rehabilitation program on pain , electromyographic activity , and function in 
 subjects with pfps14 .
weight - bearing exercises are more functional than non - weight - bearing exercises because they 
 need multi - joint movement , facilitate functional movement of muscle recruitment , and 
 stimulate proprioceptors15 . in addition , 
 evidence has been provided that during weight - bearing activities , altered patellofemoral 
 tracking may be the result of the femur rotating medially beneath the patella , rather than 
 the patella moving laterally on the femur16 .
because of these advantages , weight - bearing exercises are 
 recommended for the rehabilitation of pfps14 .
however , the actual study of weight - bearing exercises performed by 
 elite athletes with pfps is insufficient . therefore , the purpose of this study was to 
 investigate the effects of a weight - bearing rehabilitation program for elite athletes with 
 pfps through changes in the visual analogue scale , static and dynamic q - angles , and the 
 electromyographic onset timing of the vmo and vl muscles .
we hypothesized that after 8 
 weeks , the weight - bearing rehabilitation program groups would demonstrate greater 
 improvement in static and dynamic q - angles , and electromyographic onset timing of the vmo 
 and vl muscles than the control group .
the subjects were 34 ( 21 men , 13 women ) track and field hockey elite athletes from seoul t 
 center . the criteria used for the diagnosis of pfps were based on those used in other pfps 
 studies : diagnosis of pfps by a medical doctor17 ; and at least two of the following activities exacerbated their 
 symptoms : prolonged sitting , ascending or descending stairs , squatting , and kneeling . 

exclusion criteria were unregulated neurological impairment , knee surgery in the past 
 2  years , or acquired structural or functional lower limb failures , such as systemic 
 arthritis ligamentous knee injury .
this study used a randomized pre- and post - test , three 
 group design .
subjects randomly allocated to a sling exercise group ( n=11 , seg ) , elastic 
 band exercise group ( n=13 , ebg ) , or control group ( n=10 , cg ) .
prior to subjects participation , all the procedures were explained 
 to them and each subject provided his / her written informed consent to participation .
this 
 study was approved by the sahmyook university institutional review board . in the training course
, the therapeutic exercises of seg and ebg were performed 3 times a 
 week ( 30  min ) for 8 weeks .
each therapeutic exercise program included a warm - up ( stationary 
 bike , 10  min ) , exercise program ( seg or ebg with weight - bearing , 20  min ) , and cool - down 
 ( hamstring self - stretching , 5  min ) .
therapeutic exercise programs were performed one - on - one 
 with a physical therapist .
weight - bearing therapeutic exercise programexercise typeexercise program time ( sets / duration)ebgsegwarm - upstationary bike10 minweight - bearing therapeutic exerciseknee extensionwb ( affected side ) + ebbridge  with knee extensionprone position on 
 sling20 min ( 310 seconds repeat 4 times / 35 times)hip flexionwb ( affected side ) + ebbridge  with hip flexionprone position on slinghip extensionwb ( affected side ) + ebbridgesupine position on slinghip abductionwb ( affected side ) + ebbridgeside - lying position on sling ( below affected 
 side)hip adductionwb ( affected side ) + ebbridgeside - lying position on sling ( above affected 
 side)cool - downhamstring self - stretching5 minebg , elastic band group ; seg , sling exercise group ; cg , control group ; eb , elastic 
 band .
ebg , elastic band group ; seg , sling exercise group ; cg , control group ; eb , elastic 
 band prior to the intervention , a physical characteristics analyzer ( inbody 520 , biospace , 
 korea ) was used to measure the body weight and body mass index ( bmi ) . a 10  cm visual 
 analogue scale ( 10  cm  vas )
was used pre- and post - test to assess pain and discomfort 
 during stair - climbing , descending stairs , squatting , and long sitting .
the static q - angle of 
 the standing position and dynamic q - angle of coming down the stairs were also measured .
all 
 participants had their anterior superior iliac spines ( asis ) , tibial tubercles and midpoint 
 of their patella marked bilaterally by the same examiner16 .
static and dynamic q - angles for the standing position were 
 measured on digital images of the subjects captured by a digital video camera ( sony , 
 dcr - sr300 , japan ) .
the camera was positioned on a tripod 2  m away from the subjects , with 
 the camera height set to each individual s patella height .
the muscle activity onset time of the vmo and 
 vl muscles while subjects descended stairs was measured by surface emg ( pocket emg , bts , 
 italy ) .
the electrode ( norotrode , 20tm bipolar , usa ) for the vmo was placed approximately 
 4  cm superior to and 3  cm medial to the superomedial border of the patella and oriented 55 
 to the long axis of the femur14 .
the 
 electrode for vl was placed approximately 10  cm superior and 7  cm lateral to the superior 
 border of the patella and oriented 15 to the long axis of the femur14 .
descriptive statistics were 
 used to describe patient characteristics after confirming the data was normally distributed . 

comparisons of all groups general characteristics were performed using the independent 
 t - test or the  test .
pre- and post - data were analyzed using the paired t - test 
 the within to test differences groups and one - way anova to test differences among the 
 groups .
scheffe s post hoc test was used to test the significance of differences between the 
 groups .
general characteristics of the participantsparametersebg ( n=13)seg ( n=11)cg ( n=10)gender male / female ( % ) 7/6 ( 53.8/46.2)8/3 ( 72.7/27.3)6/4 ( 60.0/40.0)affected side right / left ( % ) 7/6 ( 53.8/46.2)6/5 ( 54.5/45.5)4/6 ( 40.0/60.0)height , ( cm)170.1 ( 7.8)168.2 ( 7.8)168.3 ( 9.1)age , years23.2 ( 3.8)22.6 ( 3.7)22.6 ( 2.8)bmi , ( kg / m)22.2 ( 2.2)22.4 ( 2.0)21.9 ( 2.1)values are n ( % ) or mean ( sd ) .
ebg , elastic band group ; seg , sling exercise group ; 
 cg , control group ; bmi , body mass index .
no significant differences in general characteristics were observed between 
 ebg , seg and cg ( age , 23.15  years vs. 22.55  years vs. 22.60  years ; height , 170.10  cm vs. 
 168.17  cm vs. 168.30  cm ; body mass index , 22.18  kg / m vs. 22.39  kg / m 
 vs. 21.90  kg / m ) .
ebg , elastic band group ; seg , sling exercise group ; 
 cg , control group ; bmi , body mass index differences in pre- and post - test values within groups and between groups are summarized in 
 table 3table 3 .
comparison of vas , q - angle and muscle activity onset times of vl and vmo within 
 groups and between groupsparametersvaluesebg ( n=13)seg ( n=11)cg ( n=10)prepostprepostprepostvas ( cm)3.9 ( 1.5 ) 2.3 ( 1.3)4.4 ( 1.4)3.8 ( 1.2)3.8 ( 1.2)3.8 ( 1.8)static q - angle ( )14.9 ( 7.3)12.8 ( 5.3 ) 16.1 ( 4.0)12.0 ( 4.7)17.0 ( 4.0)17.5 ( 4.8)dynamic q - angle ( )22.2 ( 8.2)17.1 ( 8.7)21.7 ( 7.5)21.7 ( 7.5)22.2 ( 5.2)23.5 ( 3.2)onset time of vl ( ms)455.0 ( 182.3)469.1 ( 189.0)420.0 ( 169.3)434.6 ( 144.3)390.0 ( 99.8)381.0 ( 77.0)onset time of vmo ( ms)546.4 ( 186.0)453.9 ( 202.6)506.6 ( 127.9)422.8 ( 153.8)438.1 ( 151.3)438.1 ( 151.3)differences of onset time vl & vmo ( ms)91.3 ( 65.8 ) 11.15 ( 86.0)86.7 ( 132.7)57.4 ( 168.5)53.0 ( 98.7)57.1 ( 93.4)values are mean ( sd ) . within group differences * p<0.05 , * * p<0.01 , 
 * * * p<0.001 .
. ebg , elastic band 
 group ; seg , sling exercise group ; cg , control group ; vas , visual analogue scale ( range 
 010  cm ) ; vl , vastus lateralis ; vmo , vastus medialis oblique .
specifically , ebg showed a significant decrease in the dynamic q - angle and 
 the difference was significantly greater than that of cg .
also , seg showed a significant 
 decrease in vas ( p < 0.01 ) and the difference was significantly greater than that of cg . 

in addition , the muscle activity onset time of vl in seg was significantly different between 
 pre- and post - test and the differences in muscle activity onset times between vmo and vl in 
 ebg were significantly different between pre- and post - test ( p < 0.001 ) .
ebg , elastic band 
 group ; seg , sling exercise group ; cg , control group ; vas , visual analogue scale ( range 
 010  cm ) ; vl , vastus lateralis ; vmo , vastus medialis oblique
the study results demonstrate that participants with pfps had decreased pain and dynamic 
 q - angle , and altered vl and vmo onset timing differences after the weight - bearing 
 therapeutic exercise program which lasted for 8 weeks .
the results of this study indicate that the elite athletes with pfps had decreased pain in 
 ebg and seg .
a 
 previous study demonstrated that a weight - bearing rehabilitation program effectively 
 decreased pain and increased the function of subjects with pfps14 .
another study showed that when osteoarthritic patients 
 with tolerable pain perform a weight - bearing training , it might be better to begin with 
 non - weight - bearing exercise , and progressively shift to partial weight - bearing , followed by 
 full weight - bearing exercise18 .
the q - angle is frequently cited as a possible predictor of knee problems and lower limb 
 injuries .
abnormally high q - angles ( more than 15 for males and 20 for females ) are 
 regarded as an anatomical risk factor in the etiology of overuse injuries of the knee19 .
reported that 
 increased knee abduction impulses should be deemed as risk factors that play a role in the 
 development of pfps in track athletes .
similarly , decreased strength of the hip abductors 
 has been associated with increased knee joint medial displacement , which may be associated 
 with an increased q - angle in a unilateral stance20 . in this study ,
weight - bearing exercise with an elastic band 
 significantly decreased the q - angle compared to cg .
a previous study demonstrated that 
 exercise with an elastic band was an effective tool for performing weight - bearing exercise 
 closed kinetic chain ( ckc ) exercise15 . 

our results suggest that weight - bearing elastic band ckc increased muscle strength , and 
 improved muscle alignment and motor control of the knee during functional activities . in this study , electromyography ( emg ) was used to determine the change of muscle activity 
 onset time of vl and differences of muscle activity onset time between vmo and vl due to the 
 performance of weight - bearing exercises .
the muscle activity onset times of vmo and vl in 
 ebg and seg were not significantly different from cg .
however , the post - test muscle activity 
 onset time of vl in seg was significantly different from its pre - test value ( p < 0.01 ) , 
 and the differences in the muscle activity onset times of vmo and vl in ebg and seg were 
 significantly different between pre- and post - test ( ebg ; p < 0.01 , seg ; p < 0.05 ) . 

researchers have stated that vmo should activate earlier than , or at the same time as , the 
 vl because a delay in vmo activation may laterally move the patella and result in pfps21 .
a previous study demonstrated that as 
 little as a 5  ms delay in vmo activation may cause a lateral increase in the compressive 
 forces on the patella - femoral joint22 . 
 one study conducting
a weight - bearing rehabilitation program reported that patients with 
 pfps had altered vl and vmo onset timing differences after a mcconnell - based rehabilitation 
 program .
showed that weight - bearing exercises performed by subjects with pfps 
 ( squatting , descent or ascent phase of the stair - stepping task , elastic band exercise ) 
 resulted in significant differences in vl and vmo onset times14 . however , the present study had some differences from these 
 previous studies .
the results of the present study show that the vl onset time of the elite 
 athletes was shorter than that of normal adults . despite demonstrating of the effectiveness of weight - bearing therapeutic exercise on the 
 q - angle and muscle activity of the elite athletes with pfps
first , the statistical power was not calculated and only a small number of 
 subjects were recruited .
second , because participants consisted of only track and field 
 hockey athletes , the results of this study can not be generalized to all elite athletes with 
 pfps .
therefore , we suggest that further studies include a variety of athletes with 
 pfps .
   [ purpose ] the purpose of this study was to determine the effect of a weight - bearing 
 therapeutic exercise program for elite athletes diagnosed as having patellofemoral pain 
 syndrome ( pfps ) . 
 [ subjects ] the subjects were 34 elite athletes from the seoul t center . 
 
 they were randomly allocated to three groups : an elastic band exercise group ( ebg ) , a 
 sling exercise group ( seg ) , or a control group ( cg ) . 
 [ methods ] therapeutic exercises were 
 performed 3 times a week for 8 weeks . the visual analogue scale ( vas ) hamstring length , 
 and static and dynamic q angles 
 were used to test the exercise effect of the exercises , as 
 well as the onset time of electromyographic activity of vastus medialis oblique ( vmo ) and 
 vastus lateralis ( vl ) . 
 [ results ] decrease of the dynamic q - angle in ebg was significant 
 and significantly greater than that in cg . the decrease in vas in seg was significant and 
 significantly greater than that in cg . 
 there were significant differences in the vl and 
 vmo activity onset times in seg between pre- and post - test , and their differences between 
 pre- and post - test were also significantly different . 
 [ conclusion ] weight - bearing 
 therapeutic exercise is hoped that clinicians will use this information for better 
 implementation of effective exercise methods for elite athletes with pfps . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION