***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Background Female athletes have a higher risk of anterior cruciate ligament injury than their male counterparts who play at similar levels in sports involving pivoting and l and ing . Hypothesis The competitive female basketball players who participated in a sports injury prevention training program  would show better muscle strength and flexibility and improved biomechanical properties associated with anterior cruciate ligament injury than during the pretraining period and than posttraining parameters in a control group . Study Design Controlled laboratory study . Methods A total of 22 high school female basketball players were recruited and r and omly divided into 2 groups ( the experimental group and the control group , 11 participants each ) . The experimental group was instructed in the 6 parts of the sports injury prevention training program and performed it during the first 20 minutes of team practice for the next 8 weeks , while the control group performed their regular training program . Both groups were tested with a rebound-jump task before and after the 8-week period . A total of 21 reflective markers were placed in preassigned positions . In this controlled laboratory study , a 2-way analysis of variance ( 2 × 2 ) experimental design was used for the statistical analysis ( P < .05 ) using the experimental group and a testing session as within and between factors , respectively . Post hoc tests with Sidak correction were used when significant factor effects and /or interactions were observed . Results A comparison of the experimental group 's pretraining and posttraining results identified training effects on all strength parameters ( P = .004 to .043 ) and on knee flexion , which reflects increased flexibility ( P = .022 ) . The experimental group showed higher knee flexion angles ( P = .024 ) , greater interknee distances ( P = .004 ) , lower hamstring-quadriceps ratios ( P = .023 ) , and lower maximum knee extension torques ( P = .043 ) after training . In the control group , no statistical differences were observed between pretraining and posttraining findings ( P = .084 to .873 ) . At pretraining , no significant differences were observed between the 2 groups for any parameter ( P = .067 to .784 ) . However , a comparison of the 2 groups after training revealed that the experimental group had significantly higher knee flexion angles ( P = .023 ) , greater knee distances ( P = .005 ) , lower hamstring-quadriceps ratios ( P = .021 ) , lower maximum knee extension torques ( P = .124 ) , and higher maximum knee abduction torques ( P = .043 ) than the control group . Conclusion The sports injury prevention training program improved the strength and flexibility of the competitive female basketball players tested and biomechanical properties associated with anterior cruciate ligament injury as compared with pretraining parameters and with posttraining parameters in the control group . Clinical Relevance This injury prevention program could potentially modify the flexibility , strength , and biomechanical properties associated with ACL injury and lower the athlete 's risk for injury Background : The causes of noncontact anterior cruciate ligament injury remain an enigma . Purpose : To prospect ively evaluate risk factors for noncontact anterior cruciate ligament injuries in a large population of young athletic people . Study Design : Prospect i ve cohort study . Methods : In 1995 , 1198 new United States Military Academy cadets underwent detailed testing and many parameters were documented . During their 4-year tenure , all anterior cruciate ligament injuries that occurred were identified . Statistical analyses were used to identify the factors that may have predisposed the cadets to noncontact anterior cruciate ligament injuries . Results : Among the 895 cadets who completed the entire 4-year study , there were 24 noncontact anterior cruciate ligament tears ( 16 in men , 8 in women ) . Significant risk factors included small femoral notch width , generalized joint laxity , and , in women , higher than normal body mass index and KT-2000 arthrometer values that were 1 st and ard deviation or more above the mean . The presence of more than one of these risk factors greatly increased the relative risk of injury . All female cadets who had some combination of risk factors sustained noncontact anterior cruciate ligament injuries , indicating that some combinations of factors are especially perilous to the female knee . Conclusion : Several risk factors may predispose young athletes to noncontact anterior cruciate ligament injury CONTEXT Improving neuromuscular control of hamstrings muscles might have implication s for decreasing anterior cruciate ligament injuries in females . OBJECTIVE To examine the effects of a 6-week agility training program on quadriceps and hamstrings muscle activation , knee flexion angles , and peak vertical ground reaction force . DESIGN Prospect i ve , r and omized clinical research trial . SETTING Sports medicine research laboratory . PATIENTS OR OTHER PARTICIPANTS Thirty female intramural basketball players with no history of knee injury ( age = 21.07 + /- 2.82 years , height = 171.27 + /- 4.66 cm , mass = 66.36 + /- 7.41 kg ) . INTERVENTION(S ) Participants were assigned to an agility training group or a control group that did not participate in agility training . Participants in the agility training group trained 4 times per week for 6 weeks . MAIN OUTCOME MEASURE(S ) We used  surface electromyography to assess muscle activation for the rectus femoris , vastus medialis oblique , medial hamstrings , and lateral hamstrings for 50 milliseconds before initial ground contact and while the foot was in contact with the ground during a side-step pivot maneuver . Knee flexion angles ( at initial ground contact , maximum knee flexion , knee flexion displacement ) and peak vertical ground reaction force also were assessed during this maneuver . RESULTS Participants in the training group increased medial hamstrings activation during ground contact after the 6-week agility training program . Both groups decreased their vastus medialis oblique muscle activation during ground contact . Knee flexion angles and peak vertical ground reaction force did not change for either group . CONCLUSIONS Agility training improved medial hamstrings activity in female intramural basketball players during a side-step pivot maneuver . Agility training that improves hamstrings activity might have implication s for reducing anterior cruciate ligament sprain injury associated with side-step pivots Background : Anterior cruciate ligament ( ACL ) injuries are immediately disabling , costly , take a significant amount of time to rehabilitate , and are associated with an increased risk of developing posttraumatic osteoarthritis of the knee . Specific multiplanar movement patterns of the lower extremity , such as those associated with the drop vertical jump ( DVJ ) test , have been shown to be associated with an increased risk of suffering noncontact ACL injuries . The  L and ing Error Scoring System ( LESS )  has been developed as a tool that can be applied to identify individuals who display at-risk movement patterns during the DVJ . Hypothesis : An increase in LESS score  is associated with an increased risk of noncontact ACL injury . Study Design : Case-control study ; Level of evidence , 3 . Methods : Over a 3-year interval , 5047 high school and college participants performed preseason DVJ tests that were recorded using commercial video cameras .  All participants were followed for ACL injury during their sports season , and video data from injured participants and matched controls were then assessed with the LESS . Conditional logistic regression analysis was used to examine the association between  LESS score and ACL injury risk in all participants as well as subgroups of female , male , high school , and college participants . Results : There was no relationship between the risk of suffering ACL injury and LESS score  whether measured as a continuous or a categorical variable . This was the case for all participants combined ( odds ratio , 1.04 per unit increase in LESS score ; 95 % confidence interval , 0.80 - 1.35 ) as well as within each subgroup ( odds ratio range , 0.99 - 1.14 ) . Conclusion : The LESS did not predict ACL injury in our cohort of high school and college athletes CONTEXT Anterior tibial shear force and knee valgus moment increase anterior cruciate ligament ( ACL ) loading . Muscle coactivation of the quadriceps and hamstrings influences anterior tibial shear force and knee valgus moment , thus potentially influencing ACL loading and injury risk . Therefore , identifying exercises that facilitate balanced activation of the quadriceps and hamstrings might be beneficial in ACL injury rehabilitation and prevention . OBJECTIVE To quantify and compare quadriceps with hamstrings coactivation electromyographic ( EMG ) ratios during commonly used closed kinetic chain exercises . DESIGN Cross-sectional study . SETTING Research laboratory . PATIENTS OR OTHER PARTICIPANTS Twenty-seven healthy , physically active volunteers ( 12 men , 15 women ; age = 22.1 ± 3.1 years , height = 171.4 ± 10 cm , mass = 72.4 ± 16.7 kg ) . INTERVENTION(S ) Participants completed 9 separate closed chain therapeutic exercises in a r and omized order . MAIN OUTCOME MEASURE(S ) Surface electromyography quantified the activity level of the vastus medialis ( VM ) , vastus lateralis ( VL ) , medial hamstrings ( MH ) , and biceps femoris ( BF ) muscles . The quadriceps-to-hamstrings ( Q : H ) coactivation ratio was computed as the sum of average quadriceps ( VM , VL ) EMG amplitude divided by the sum of average hamstrings ( MH , BF ) EMG amplitude for each trial . We used repeated- measures analyses of variance to compare Q : H ratios and individual muscle contributions across exercises ( α = .05 ) , then used post hoc Tukey analyses . RESULTS We observed a main effect for exercise ( F(3,79 ) = 22.6 , P < .001 ) . The post hoc Tukey analyses revealed smaller Q : H ratios during the single-limb dead lift ( 2.87 ± 1.77 ) than the single-limb squat ( 5.52 ± 2.89 ) exercise . The largest Q : H ratios were observed during the transverse-lunge ( 7.78 ± 5.51 , P < .001 ) , lateral-lunge ( 9.30 ± 5.53 , P < .001 ) , and forward-lunge ( 9.70 ± 5.90 , P < .001 ) exercises . CONCLUSIONS The most balanced ( smallest ) coactivation ratios were observed during the single-limb dead-lift , lateral-hop , transverse-hop , and lateral b and -walk exercises . These exercises potentially could facilitate balanced activation in ACL rehabilitation and injury-prevention programs . They also could be used in postinjury rehabilitation programs in a safe and progressive manner BACKGROUND The purpose of this study was to determine whether current post-operative rehabilitation protocol s return the strength of the contralateral uninjured limb knee flexors and extensors after an  anterior cruciate ligament ( ACL ) reconstruction to those of an uninjured control group . METHODS Subjects with a hamstring tendon ACL reconstruction ( n=12 ) were compared to an  active control group ( n=30 ) . Comprehensive bilateral knee flexor and extensor isovelocity strength testing was performed ( five speeds , 5 - 95 degrees , concentric and eccentric contractions ) . FINDINGS After hamstring tendon ACL reconstruction and rehabilitation , bilateral strength normalization ( within 10 % of the contralateral limb ) is achieved by the knee extensors but not the knee flexors . When compared to the uninjured control group , large and statistically significant strength deficits were demonstrated in the knee extensors and knee flexors of both the anterior cruciate ligament reconstructed ( extensors 24.8 % ; flexors 26.8 % ) and the contralateral uninjured ( extensors 21 % ; flexors 13.5 % ) limbs . INTERPRETATION These findings suggest that improvement can be made in knee flexor rehabilitation after ACL reconstruction and limit the validity of the use of a contralateral leg as a rehabilitation endpoint or as a control in the ACL reconstructed population Objective : To determine the association of quadriceps and hamstrings strength to anterior cruciate ligament ( ACL ) injury risk in female athletes . The primary hypothesis was that there would be decreased knee flexor and increased knee extensor strength in female athletes who went on to ACL injured status ( FACL ) compared to uninjured female ( FC ) and male ( MC ) control subjects . Study Design : Matched case control . Setting : Institutional Biomechanics Laboratory . Participants : Prospect ively measured FACL ( n = 22 ) female athletes who subsequently suffered confirmed noncontact ACL ruptures ( 16 during soccer and 6 during basketball play ) were matched ( 1:4 ratio ) to female controls ( FC ; n = 88 ) using limb ( dominant or nondominant ) , pubertal status , sport , and nearest height and mass . In addition , male controls ( MC ) were matched ( 1:1 ratio ) to FACL to serve as a secondary comparative control . Assessment of Risk Factors : Isokinetic ( concentric ) knee extension/flexion strength ( 300 degrees/s ) . Results : FACL subjects had decreased hamstrings strength compared to MC ( 15 % ; 95 % CI , 1 to 27 % ; P = 0.04 ) . FC were not different from MC in hamstrings strength . Conversely , FACL subjects did not differ compared to the MC in quadriceps strength , and the FC demonstrated decreased quadriceps strength relative to MC ( 10 % ; 95 % CI , 3 to 18 % ; P = 0.01 ) . Conclusions : The results of this investigation indicate that female athletes who suffered ACL injury subsequent to strength testing had a combination of decreased hamstrings strength but not quadriceps strength compared to males . In direct contrast , female athletes who did not go on 
    Output:
    
Three of which looked into muscular capacity and one looked into muscular activation patterns but none of the studies found strong evidence of how muscular capacity or muscular activation deficits are a risk factor for a primary non-contact ACL injury .