hamstring muscle injury is one of the commonest sports injuries among athletes1 , 2 . based on the literature , risks of hamstring muscle injury include previous injury , strength 
 imbalance , older age , inadequate warm - up , poor quadriceps flexibility and muscle 
 fatigue1,2,3,4,5 . this factor remains inconclusive , as studies have 
 shown conflicting results6,7,8,9,10 . despite this , hamstring 
 flexibility is recommended during routine pre - participation examinations and in deciding 
 athlete readiness to return - to - play following injury11,12,13 . methods to assess hamstring flexibility include the straight - leg - raising ( slr ) test , sit 
 and reach ( sr ) test , and active knee extension ( ake ) test14,15,16 . the slr test specificity has been questioned , as it is also widely 
 used as a neurological test17 . further , 
 cinematographic study showed that pelvic rotation may influence the validity of slr angle 
 measurements18 . even though hamstring 
 flexibility assessment is easy using the sit and reach ( sr ) test , the validity of this test 
 is considered poor19 . the ake test is an 
 active test that involves movement at the knee joint , and most considers it safe , as the 
 patient dictates the end point of movement . further , the ake test aided by a metal rig and 
 straps to limit pelvic and leg motion ( as a stabilizing apparatus ) showed a high intrarater 
 correlation coefficient when conducted within 30 minutes16 , 20 . others though , question 
 the practicality of such method , as the apparatus used by researchers are complicated , 
 rarely available in a clinical setting , and require more than one assessor to conduct the 
 test21 , 22 . therefore , a simple and reliable method of hamstring flexibility 
 assessment that ensures pelvic and leg stability during measurement is needed . we designed and made a simple , portable and easy - to - use stabilizing apparatus for use in 
 performance of the ake test . pvc tubes were selected because they are light , easily cut , commonly available in 
 hardware stores , and inexpensive . when used with a universal goniometer , this apparatus 
 allows measurement in the ake test to be conducted by a single assessor without 
 assistance . the objective of this study was to determine the interrater and intrarater reliability of 
 the ake test using a pvc stabilizing apparatus for hamstring flexibility assessment in 
 healthy subjects . the university of malaya medical centre ethics committee approved the study ( mec ref no . a convenient sample of 16 healthy participants ( 10 men and 6 women ) with ages 
 ranging from 28 to 39  years was used in this study . participants were sports medicine 
 postgraduates and staff at the faculty of medicine , university of malaya . all participants 
 were free from any orthopaedic or neurological disorders . flexion of the knee until the thigh touches the horizontal pvc bar   knee position during the ake test we designed a simple , portable apparatus made up of pvc tubes ( total cost of usd 6.00 ) to 
 aid in performance of the ake test . it consisted of a single 
 horizontal bar anchored ( removable ) by two vertical poles on either side of the plinth . assessments were conducted at the sports medicine clinic , university of malaya medical 
 centre . to ensure that all participants would be assessed in the standard manner , both 
 assessors attended a half - day workshop on the ake test using the pvc stabilizing apparatus . the ake testing procedure was described to all participants , and each provided informed 
 consent . the dominant knee was determined 
 based on the participant 's preferred leg when kicking a ball or when performing a single - leg 
 jump , while the other knee was considered the nondominant knee ; a previous researcher used a 
 similar definition23 . a sports physician ( sah ) and a physiotherapist ( lpc ) performed all the ake tests 
 independently . all assessments were conducted at the sports medicine clinic of the 
 university of malaya medical centre between 9.00 and 11.00 am at room temperature . as 
 previous study demonstrated changes in biomechanical characteristics of collagen and muscle 
 viscoelastic properties , no warming up activities were allowed24 . participants were assessed on a plinth in the supine 
 position with both lower extremities extended . both anterior superior iliac spines were 
 positioned by aligning them with the vertical bars of the apparatus . the lower extremity not 
 being measured was secured to the plinth using a strap across the lower third of the thigh . the first was drawn to the greater trochanter , and another to other was drawn to 
 the apex of the lateral malleolus . the participants were told to flex the hip until the 
 thigh touched the horizontal pvc bar ( fig . 1 ) . 
 while maintaining the contact between the thigh and horizontal pvc bar , the participants 
 were asked to extend the leg as much as possible while keeping their foot relaxed and to 
 hold the position for about 5 seconds . a standard universal goniometer was placed over the 
 previously marked joint axis , and the goniometer arms were aligned along the femur and 
 fibula ( fig . the ake measurement was defined as the degree of knee flexion from terminal knee extension . each knee was measured twice , and the mean angle of the ake test was used for analysis . all 
 participants attended two testing sessions one week apart to allow for establishment of 
 test - retest reliability of the method . the order in which the rater assessed the 
 participants was randomly assigned in the first session and maintained thereafter . all data were analyzed using the statistical package for the social sciences ( spss ) version 
 20.0 software . data were described descriptively , and a normality test was performed using 
 the shapiro - wilks test . paired t - tests were performed to compare differences between tests 
 and retest measurements within and between raters . two different types of measures of reproducibility were assessed : measures of agreement and 
 measures of reliability . the interrater agreement was quantified by calculating the mean 
 difference between the two raters ( rater 1  rater 2 ) and the standard deviation ( sd ) of 
 this difference . further , the 95% limits of agreement were calculated according to the 
 method of bland and altman25 . these 
 limits represent the range in which 95% of the differences between the two raters fall . plots of differences between raters against the corresponding mean of the two raters for 
 each participant were produced to examine homoscedasticity as proposed by bland - altman25 . further , the frequency of agreement of 
 the raters within 5 and 10 was calculated . differences exceeding 10 were determined as 
 being unacceptable , as a previous study suggested they are likely to affect decisions on 
 patient management26 . the reliability was evaluated by computing intraclass correlation coefficients ( iccs ) , 
 which analyzed the consistency of quantitative measures . an icc based on a two - way random 
 model was used to establish test - retest reliability , while an icc based on a two - way mixed 
 model was chosen for intrarater reliability27 . the icc value of the standard error of measurement ( sem ) was 
 calculated to express the magnitude of disparity between measurements28 . sem was calculated using the formula , sem = 
 sdavg ( 1icc ) where sd corresponds to the pooled standard deviation and icc is 
 the reliability coefficient29 . a smaller 
 sem value suggests greater agreement between measurements30 . the minimum detectable change ( mdc ) sd , standard deviation fourteen ( 8 men and 6 women ) participants completed the test and retest sessions . two 
 participants were excluded from the final analysis , as one suffered a hamstring injury and 
 the other was involved in a road traffic accident . a significant difference in body weight 
 between male ( mean=77.69 , sd=12.86 ) and female ( mean=63.42 , sd=10.27 ) participants there was no 
 significant difference in ake measurements between the dominant and nondominant knees . in 
 addition , no significant difference was observed between test and retest sessions for both 
 dominant ( t=0.77 , p=0.46 ) and nondominant ( t=1.01 , p=0.33 ) knees . bland - altman plot of the differences versus means of the dominant knee ake 
 measurements   bland - altman plot of the differences versus means of the nondominant knee ake 
 measurements a summary of the interrater agreement observed in this study is displayed in table 2 . both raters had similar ake measurements , 
 with the limits of agreement being 0.1  12.9 ( sd ) for the dominant knee and 1.1  15.7 for 
 the nondominant knee . the percentages of agreement within 10 for these measurements were 
 93% and 79% for the dominant and nondominant knees respectively . sem , standard error measurement the ake measurement differences between raters were plotted against the mean value of both 
 raters for both the dominant and nondominant knees ( fig . 
 3 and 4 ) . errors of measurement for both knees were independent of the magnitude of 
 the range of measurements ( homoscedasticity ) the ake measurements of raters 1 and 2 from the first testing session were compared ( table 3 ) . the ake test interrater reliability was excellent , with 
 icc2,1 values of 0.87 ( 0.580.97 ; 95%ci ) for the dominant knee and 0.81 
 ( 0.410.94 ; 95%ci ) for the nondominant knee and standard error of measurement ( sem ) values 
 of 3.5 ( 18.031.7 ; 95%ci ) and 3.8 ( 16.931.7 ; 95%ci ) respectively . minimal detectable 
 change was between 9.7 and 10.5. no significant difference in mean ake measurements was 
 noted between the first and second testing sessions for both raters ( table 4 ) . despite conflicting findings concerning the association of poor hamstring flexibility and 
 the risk of hamstring muscle injury , assessment of hamstring flexibility is routinely 
 conducted . hamstring flexibility assessment is useful , especially in deciding an athlete 's 
 readiness to return - to - play following injury11,12,13 . the ake test is considered by some to be the gold standard for hamstring flexibility 
 assessment32 . with the aid of a simple stabilizing apparatus and a universal goniometer interrater reliability icc2,1 
 values of 0.87 and 0.81 were found for the dominant and nondominant knees respectively . further , the device also produced a standard error of measurement of 3.5 for the dominant 
 knee and 3.8 for the nondominant knee . the test - retest reliability in this study was excellent , with icc3,1 values 
 ranging from 0.78 to 0.92 for both raters . gajdosik reported a pearson product - moment correlation coefficient for the ake test of 0.99 
 for both lower extremities33 . the higher 
 reliability coefficient value could be explained by the different statistical analysis used . further , the interval between the first ake test and the retest session was very short . both 
 ake tests were conducted on the same day 30 minutes apart , and this may have introduced 
 systematic bias and affected reliability2 . we chose an interval of one week between the test and retest ake assessment because it 
 reflects our clinical practice , as majority of cases are reviewed a week apart . using the mean value of ake measurements from both knees , in contrast to gabbe et al . , the current study evaluated 
 each knee separately to explore any potential differences between the dominant and 
 nondominant knees , and such differences in method may explain the wider icc3,1 
 values noted in this study . further , the current study found no significant difference in 
 ake measurement between the dominant and nondominant knees of healthy individuals . similarly , a pilot study conducted by davis reported excellent intrarater reliability of 
 the knee extension angle ( kea ) test , with an icc3,1 of 0.9432 . the method of hamstring flexibility assessment employed 
 by the previous author differs from that in the current study . in the former study , measurements were taken from two gravity inclinometers placed immediately superior to 
 patella , and another was placed on the distal anterior tibia of the patient 's lower 
 extremity . in addition , the examiners performed hip flexion and knee extension passively , 
 whereas participants actively performed all movements in the current study . our finding concerning interrater reliability was consistent with those reported by earlier 
 studies29 , 34 . gabbe reported an interrater reliability icc2,1 of 0.93 
 and 4 sem for the ake test in 15 healthy participants of comparable age group ( mean age : 
 31.6  years)29 . similarly , in a study to 
 determine the effect of pelvic positioning and stretching method on hamstring flexibility , 
 sullivan reported an interrater reliability icc1,1 and sem of 0.93 and 4.81 
 respectively for the ake test among 12 healthy subjects34 . on the other hand , rakos et al . performed the ake test with aid of 
 an intricate stabilizing apparatus and demonstrated a good interrater reliability with an 
 icc2,1 of 0.79 among children age 10 to 13  years old22 . despite demonstrating excellent interrater and test - retest reliability , a wide range of cis such findings , suggests that further research 
 with larger samples may be necessary to determine the reliability estimates with greater 
 precision35 . second , the reliability 
 displayed in this study was based on assessment in healthy and uninjured volunteers . whether 
 the ake test would be as reliable in a population of injured athletes the ake test might still be useful , especially during the preseason assessment , as most 
 athletes are free from injury at the beginning of the season . the current study demonstrated that the ake test can be performed easily by a single 
 assessor with a simple , portable , and inexpensive stabilizing apparatus and have excellent 
 interrater and intrarater reliability .
[ purpose ] the purpose of this study was to determine the reliability of the active knee 
 extension ( ake ) test among healthy adults . [ subjects ] 
 fourteen healthy participants ( 10 
 men and 4 women ) volunteered and gave informed consent . 
 [ methods ] two raters conducted ake 
 tests independently with the aid of a simple and inexpensive stabilizing apparatus . 
 each 
 knee was measured twice , and the ake test was repeated one week later . [ results ] the 
 interrater reliability intraclass correlation coefficients ( icc2,1 ) were 0.87 
 for the dominant knee and 0.81 for the nondominant knee . 
 in addition , the intrarater 
 ( test - retest ) reliability icc3,1 values range between 0.780.97 and 0.750.84 
 for raters 1 and 2 respectively . 
 the percentages of agreement within 10 for ake 
 measurements were 93% for the dominant knee and 79% for the nondominant knee . 
 [ conclusion ] 
 the finding suggests the current ake test showed excellent interrater and intrarater 
 reliability for assessing hamstring flexibility in healthy adults .