although anterior cruciate ligament ( acl ) damage occurs most frequently in populations aged 
 1525 years participating in pivoting sports , it can occur in people of any age1 . at least 80,000250,000 cases of acl damage 
 occur annually in the usa , and acl ruptures occur annually at a ratio of approximately one 
 per every 3,000 people2 . since acl damage 
 frequently occurs , incurs large treatment expenses , and can cause various complications even 
 after surgical treatment , many studies have been conducted on acl damage - related surgery and 
 rehabilitation exercises . although recent methods of rehabilitation after acl reconstruction 
 are faster and more diverse , the purpose of rehabilitation exercises is invariably to reduce 
 knee joint instability to enable activities without damage . an important objective of 
 rehabilitation exercise after acl reconstruction is the recovery of the normal muscle 
 strength of the femoral muscles3 . since 
 the recovery of the original muscle strength after atrophy of the femoral muscles takes a 
 long time , disuse atrophy of the femoral muscles is considered very important in knee joint 
 surgery . although experts in exercise prescriptions have recently been examining the effects 
 of accelerated rehabilitation exercises after acl reconstruction , no study has been 
 conducted on differences in the effects of accelerated rehabilitation exercises between 
 males and females . therefore , research is needed into muscle functions with changes in 
 muscle strength and muscle power , which are the core of rehabilitation exercises , after the 
 performance of accelerated rehabilitation exercises after acl reconstruction . the purpose of 
 the present study was to examine changes in the knee joint s isokinetic muscle functions 
 after systematic and gradual rehabilitation exercises lasting for 12 weeks for male and 
 female patients who underwent acl reconstruction . differences in muscle functions between 
 the uninvolved side ( us ) and the involved side ( is ) before surgery , differences in muscle 
 functions between us and is after rehabilitation exercises for 12 weeks , and changes in 
 muscle functions on us and is between before and after surgery were analyzed to examine the 
 effects of accelerated rehabilitation exercises after acl reconstruction . the study subjects were 10 patients , five females and five males , who underwent acl 
 reconstruction performed by the same surgeon . the male group was ( meansd ) 25.801.92  years 
 old , 173.005.83  cm tall , and 67.007.28  kg in weight . the female group was 26.603.44  years 
 old , 167.404.77  cm tall , and 63.207.73  kg in weight . to ensure the safety and validity of rehabilitation exercises , a rehabilitation exercise 
 program was prepared as follows . based on a review of the literature related to 
 rehabilitation exercises after acl reconstruction , wilk s accelerated rehabilitation 
 exercise program after acl reconstruction was modified for the content of the rehabilitation 
 exercise program ( table 1table 1 . objectives of rehabilitation exercise programs after acl reconstruction by stage 
 and rehabilitation exercises ) . as a measuring tool , a biodex multi - joint system 3pro ( usa ) , which is an isokinetic 
 measuring device , was used to examine the flexion and extension forces of the knee joint . for accurate measurement during tests , test motions 
 were practiced three times with maximum muscle strength before measurements were taken , and 
 the measurements were conducted after a rest had been taken . to prevent the force of the 
 other parts of the body from acting during repeated knee joint extension and flexion 
 exercises , the subject was instructed to sit on the chair , and the subject s shoulder , 
 chest , and pelvis were fixed using a belt connected to the chair . then , the thigh of the 
 subject was fixed using the thigh stabilization belt . the length of the belt of the 
 dynamometer was adjusted so that the shin pad was placed approximately 1  cm above the 
 lateral malleolus of the ankle joint , the force point , and the shin pad was fixed using a 
 velcro strap . the axis of the dynamometer was aligned with the axis of exercise , and the 
 subjects were verbally encouraged to exert maximum muscle strength during the test . the entire work done is a variable 
 that can provide information useful for determining the degree of injury rehabilitation , 
 because this value is affected by the rom . therefore , in the present study , during 
 isokinetic muscle strength evaluation , the rom of us was the same as that of is for 
 consistency of measurement . the study data were statistically processed using the spss 15.0 
 statistics program for windows . preoperative differences in isokinetic muscle functions 
 between us and is , postoperative differences in isokinetic muscle functions between us and 
 is , and differences in isokinetic muscle functions between before and after surgery on each 
 of us and is were analyzed using the paired t - test with a significance level of =0.05 . all the subjects understood the purpose of this study and provided their written informed 
 consent prior to their participation in the study in accordance with the ethical standards 
 of the declaration of helsinki . at 60/s , the isokinetic muscle functions of the females did not show any significant 
 change between before and after surgery in any of variables on both us and is ( table 2table 2 . changes in females isokinetic muscle functions between before and after surgery 
 at an angular velocity of 60/s ) . at 60/s , the isokinetic muscle functions of the males did not show any 
 significant change between before and after surgery in peak torque , average power , and 
 entire work done on us ( table 3table 3 . changes in males isokinetic muscle functions between before and after surgery 
 at an angular velocity of 60/s ) . in extension , however , in extension , the average power and entire work done on is significantly increased 
 ( p<0.05 ) . in flexion , whereas the peak torque and average power on us significantly 
 increased ( p<0.05 ) , the entire work done on the same side did not show any significant 
 change . in flexion , the peak torque , average power , and entire work done on is significantly 
 increased ( p<0.01 ) . rehabilitation exercises after acl reconstruction are receiving attention from many experts 
 in sports medicine . traditional rehabilitation exercise methods restrict the range of 
 motion , do not apply weight bearing at the beginning , and are composed of only low intensity 
 exercises . therefore , however , accelerated rehabilitation programs are composed of immediate and 
 active rehabilitation exercises after surgery , and have been reported to enable a return to 
 sport activities in approximately six months after acl reconstruction4 . studies related to the evaluation of acl reconstruction 
 patients muscle strength report that an analysis of the deficit ratio of is to us is more 
 valuable than the evaluation of individual muscle strengths5 , 6 . clinical specialists , 
 referring to empirical evidence , point out that applying the same accelerated rehabilitation 
 exercises is somewhat impractical . therefore , in the present study , the discussion focuses 
 on the results of the application of a modified wilk s accelerated rehabilitation exercise 
 program lasting for 12 weeks after acl reconstruction surgery7 . at 60/s , the isokinetic muscle functions of the females did not show any significant 
 change between before and after surgery in any variable on both us and is . at 60/s , the 
 isokinetic muscle functions of the males did not show any significant change between before 
 and after surgery , except that in extension , the average power and entire work done on is 
 significantly increased ( p<0.05 ) . therefore , we consider 12-week duration rehabilitation 
 exercises are incapable of improving knee joint extension muscle functions in females , but 
 are capable of partially recovering extensor muscle functions on is in males . evidence in 
 support of this conclusion includes a study on gender differences regarding the effects of 
 rehabilitation exercises after acl reconstruction conducted by an8 , who found that when the same rehabilitation exercises were 
 performed by both males and females , subjective knee evaluation scores ( 2000 international 
 knee document committee subjective knee evaluation : 2000 ikdc ) of males had improved at 12 
 weeks after surgery , whereas ikdc scores of females had decreased . this result is consistent 
 with the present study results that show different responses of males and females after 12 
 weeks of rehabilitation exercises after acl reconstruction . male and female patients exhibited different effects after a 12-week course of 
 rehabilitation exercises for the recovery of knee joint muscle functions after acl 
 reconstruction . for full recovery of knee joint muscle functions after surgery , 
 rehabilitation exercises of longer duration are necessary .