stretching is helpful for injury prevention , flexibility of periarticular connective 
 tissues , strengthening of exercise performance , and rehabilitation of the musculoskeletal 
 system1,2,3,4,5,6,7 .
the american college of 
 sports medicine8 advises that stretching 
 is effective in warm - up and cooldown before and after aerobic exercise , and that it should 
 be included in rehabilitation exercise programs in terms of musculoskeletal injury 
 prevention . in static stretching ,
the most commonly used among the different types of 
 stretching , a static is maintained for 1045 seconds up to the maximum range of motion ( rom ) 
 centered on the agonist muscle required during exercise
. this practice increases body 
 temperature , is effective for injury prevention , and is used by most athletes in the 
 field9 .
conventionally , studies showing 
 that static stretching improves exercise performance and flexibility and is effective for 
 injury prevention are dominant10 . however , despite the fact that stretching is broadly used in such a way , putting together 
 previous studies associated with this , it is considered that pre - exercise stretching 
 temporarily decreases muscle strength , power , and sports performance11,12,13,14,15,16,17,18,19,20 . in this
regard , 
 nelson et al.16 reported that pregame 
 stretching inhibited the exertion of maximum muscle strength , vertical jumping ability , and 
 muscle endurance .
however , perrier et al.18 reported that no significant difference in the sargent jump was 
 observed between their static stretching group and their control group .
likewise , even if there is a possibility that static stretching might adversely affect 
 exercise performance and athletic performance , it is recognized as a partial element of 
 warm - up , and warm - up including static stretching is performed in most fields of recreational 
 sports . because of this , further studies on temporary effects of flexibility exercise in 
 performance of activities related to physical strength are needed .
thus this study was 
 conducted in order to verify the effect of pre - exercise static stretching on muscle strength 
 and muscle power by evaluating the muscular function of the knee joint using an isokinetic 
 machine by type of warm - up .
the subjects of this study were 10 students who were attending s university in seoul , 
 republic of korea , had no medical problem , and consented to participate in the experiment 
 after the purpose of the study was fully explained to them .
their physical characteristics 
 are as shown in table 1table 1.characteristics of the subjectsgendernage ( yrs)height ( cm)weight ( kg)body fat ( % ) male1022.03.4175.65.570.59.018.07.2 below .
this study was approved by the ethics committee of the institutional 
 review board of sahmyook university . to achieve the purpose of this study ,
subjects were asked to avoid drinking and smoking one 
 day before the experiment , not to participate in excessive physical activity and nonroutine 
 social activity , and to maintain normal sleeping hours in order to secure proper test data . 
 on the day of the experiment ,
they were asked to consume a light meal , arrive at the 
 measurement room by 09:00 a.m. , and take a rest . for comparison of muscle strength and muscle power according to the presence or absence of 
 warm - up with stretching , the same subjects were classified into a control group that did not 
 perform warm - up , a warm - up group that performed simple running and joint exercise , and a 
 warm - up with stretching group .
the control group directly underwent isokinetic muscle 
 testing without warm - up , while the warm - up group started power walking at a strength of 
 4060% of the predicted maximum heart rate , performed light running for 10 minutes , and then 
 underwent isokinetic muscle testing . the warm - up with stretching group performed light 
 running for 5 minutes , performed static stretching , and then underwent isokinetic muscle 
 testing . the stretching program consisted of 12 types stretching of the global muscles of 
 the whole body .
two repetitions of each stretching motion were performed , each taking 20 
 seconds , and the entire stretching program took 10 minutes to perform .
all subjects rested 
 for one minute after warming up and then underwent isokinetic muscle testing of the knee 
 joint .
the sequence of performance of each warm - up was individually randomized . in 
 successive weeks
, each group was tested according to the type of warm - up being utilized . 

this occurred over a period of three weeks , with the control group , warm - up group , and 
 warm - up and stretching group allowed a week to rest in between tests .
a knee extension / flexion isokinetic dynamometer ( humac norm testing & rehabilitation 
 system ; csmi ) was used for this study .
first , the subjects were asked to have a seat on the 
 humac norm stand , which was made to allow the hip joint to bend at 90 degrees , and then the 
 anatomical axis of rotation of the knee joint was adjusted in accordance with the 
 dynamometer axis of the dynamical system .
the upper body , pelvis , and femoral region were 
 fixed using a three - point safety belt and thigh strap , and the axis of the foot and 
 dynamometer was fixed to the direct upper part of the medial ankle bone using a velcro 
 strap .
the opposite lower extremity was fixed with a limb stabilization bar . to prevent the 
 influence of the weight of the axis of motion of the tested lower leg and isokinetic machine 
 on the torque of the knee joint ,
gravity effect torque was measured and entered in a 
 computer , and range of motion ( rom ) was limited to between 0 of extension and 90 of 
 flexion .
they were asked to extend 
 and flex the knee by exerting their maximum strength as soon as possible , to keep their 
 trunk up against the back rest during the test , and to hold onto the handle of the machine 
 with their hands .
each maximal 
 test was conducted with an angular speed of 60/sec ( velocity of 60/sec ) for measurement of 
 isokinetic muscle strength and with an angular speed of 180/sec ( velocity of 180/sec ) for 
 measurement of isokinetic muscle power .
the exercise was conducted twice prior to testing so 
 that adaptability to the test was improved for subjects and optimal results were achieved . 

also , for motivation during testing of maximal isokinetic strength and isokinetic power , 
 subjects were verbally encouraged , and were allowed to view their torque graphs during 
 testing as a form of visual feedback . in this study , for analysis of muscle strength and muscle power , measurements of the left 
 and right knee joints were divided into each independent variable , and data processing was 
 performed . for data analysis , the mean and standard error were calculated per variable using 
 the spss for windows , version 12.0 , software .
in addition , one - way anova was performed using 
 a randomized block design for analysis of differences in the isokinetic muscle strength and 
 muscle power of the extensor muscle and flexor muscle of the knee joint between groups .
when 
 there was a significant difference between groups , the least significant difference post hoc 
 test was used . the significance level for statistical verification
in this study , prior to evaluation of muscle strength ( 60/sec ) and muscle power ( 180/sec ) 
 of the knee joint , warm - up and warm - up with stretching were conducted .
one - way anova was 
 performed by randomized block design for each variable , and the following results were 
 obtained table 2table 2.maximal isokinetic muscle strength and muscle power of the knee jointangular speed groupcontrolwarm - upwarm - up with stretchingpost hocflexion60/sec99.3  4.296.4  4.495.6  5.4180/sec * 75.3  3.678.2  3.582.2  3.61,2<3extension60/sec173.7  7.0172.4  8.0165.7  10.3180/sec121.8  4.8125.6  5.2124.4  5.9mean  se ( nm ) . 1=control ; 2=warm - up ; 3=warm - up with stretching . *
mean  se ( nm ) . 1=control ; 2=warm - up ; 3=warm - up with stretching .
* p<0.05 comparative analysis of the differences in flexor peak torque among the control group ( 99.3 
  4.2 ) , warm - up group ( 96.4  4.4 ) , and warm - up with stretching group ( 95.6  5.4 ) with an 
 angular speed of 60/sec showed no significant difference among the groups ( f = 0.26 , p = 
 0.77 ) .
comparative analysis of the differences in flexor peak power among the control group ( 75.3 
  3.6 ) , warm - up group ( 78.2  3.5 ) , and warm - up with stretching group ( 82.2  3.6 ) at 
 180/sec showed significant differences among the groups ( f = 4.63 , p = 0.02 ) , and the post 
 hoc test showed that the warm - up with stretching group had higher muscle power than the 
 control group and warm - up group .
comparative analysis of the difference in extensor peak torque between the control group 
 ( 173.7  7.0 ) , warm - up group ( 172.4  8.0 ) , and warm - up group with stretching group ( 165.7  
 10.3 ) at 60/sec showed no significant difference among the groups ( f = 0.89 , p = 0.42 ) .
comparative analysis of the differences in extensor peak power among the control group 
 ( 121.8  4.8 ) , warm - up group ( 125.6  5.2 ) , and warm - up group with stretching group ( 124.4  
 5.9 ) at 180/sec showed that no significant difference among the groups ( f = 1.19 , p = 
 0.32 ) .
it enhances 
 flexibility , reduces the possibility of injury , and contributes to the performance of 
 advanced techniques .
in particular , static stretching maintains a performed posture without 
 bound , and studies on such stretching effects5 , 21,22,23 have reported that it can improve muscle 
 strength .
young and elliott22 reported 
 that flexibility training to prevent stiffness of upper limbs was improved exercise 
 performance of the bench press , and wilson et al.21 and worrell et al.5 reported that peak torque increased in the hamstring muscle . 

however , many recent studies have expressed skepticism with regard to results indicating 
 that stretching has a positive effect on improvement of exercise performance or injury 
 prevention11 , 13 , 14 , 16,17,18 , 24,25,26,27 . in a study targeting 22 university students ,
nelson et al.24 reported that after static stretching , knee flexor peak torque 
 showed a significant decrease , approximately 7.5% , and knee extensor peak torque decreased 
 by 5.6% , compared with the control group .
cramer et al.11 and marek et al.13 , who conducted stretching in women in their twenties and healthy 
 university students , reported that it had a negative effect on isokinetic peak power .
causes 
 for reduced muscle strength after stretching include decreased motor unit activation or 
 neural factors , such as changes in reflex sensitivity , and mechanical factors including 
 changes in muscular elasticity affected by the length - tension relationship28 .
in addition , behm and chaouachi29 and fowles et al.28 reported that static stretching would decrease the 
 autonomy of the reactive nerve of the muscle spindle and the sensitivity of the receptor , 
 and that stretching continued for more than tens of seconds would extend muscles and 
 decrease pressure on the joint , leading to impaired the requirement of type ii muscle at 
 need to muscle power and speed expression .
cramer et al.12 , who measured peak torque and performed electromyography after 
 acute stretching , found that force production and muscle activation decreased both in the 
 stretched leg and unstretched leg , arguing that the reason why peak torque decreased in the 
 unstretched leg was that the inhibitory mechanism of the central nervous system acted as a 
 result of stretching of the opposite leg . on the other hand
, according to the study of unick et al.26 , performance of the vertical jump test in female basketball players 
 after static stretching and dynamic stretching , revealed that neither stretching types 
 influenced jumping ability .
also , according to the study of little and williams14 , performance of static stretching and 
 dynamic stretching in soccer players , showed that neither of the stretching types influenced 
 jumping ability , but dynamic stretching improved high - speed performance . in this study ,
changes in the flexor peak torque and extensor peak torque of the knee joint 
 were compared after static stretching in relatively active university students .
this study 
 tended to decrease in the warm - up with stretching group at 60/sec compared with the control 
 group and warm - up group , but without statistical significance .
in addition , extensor peak 
 power at 180/sec was not found to be statistically significant .
however , flexor peak power 
 at 180/sec was shown to increase significantly in the warm - up with stretching group 
 compared with the control and warm - up groups . therefore , the results of this study show that 
 performance of the two sets of pre - exercise stretching for 20 seconds by muscle group did 
 not decrease isokinetic torque and muscle power during exercise .
it is considered that causes for differences in results after stretching include the 
 specificity of the subjects and their exercise capacity in addition to methodological 
 differences , that is , type , level , time , and frequency of stretching .
therefore , it is 
 concluded that further studies are required to verify the type , time , and frequency of the 
 most proper stretching method according to the level of exercise .
 [ purpose ] the purpose of this study was to clarify the influence of static stretching at 
 warm - up on the isokinetic muscle torque ( at 60/sec ) and muscle power ( at 180/sec ) of the 
 flexor muscle and extensor muscle of the knee joint . 
 [ subjects and methods ] the subjects 
 of this study were 10 healthy students with no medically specific findings . 
 the warm - up 
 group and warm - up with stretching group performed their respective warm - up prior to the 
 isokinetic muscle torque evaluation of the knee joint . 
 one - way anova was performed by 
 randomized block design for each variable . 
 [ results ] the results were as follows : first , 
 the flexor peak torque and extensor peak torque of the knee joint tended to decrease at 
 60/sec in the warm - up with stretching group compared with the control group and warm - up 
 group , but without statistical significance . 
 second , extensor power at 180/sec was also 
 not statistically significant . however , it was found that flexor power increased 
 significantly in the warm - up with stretching group at 180/sec compared with the control 
 group and warm - up group in which stretching was not performed . 
 [ conclusion ] therefore , it 
 is considered that in healthy adults , warm - up including two sets of stretching for 20 
 seconds per muscle group does not decrease muscle strength and muscle power . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION