recent developments in aircraft technology have significantly contributed to the 
 development of high performance fighter aircraft , and fighter pilots are placed under a lot 
 of stress in extreme gravity acceleration when performing a lot of tasks1 . continuous stress on pilots can result in a 
 decreased sense of the static organ and spatial disorientation due to a maladjusted 
 condition of the vestibular organ , caused by an illusion phenomenon . furthermore , a 
 situation of rapidly increasing gravity ( + 69 g ) causes excessive inflammation in the human 
 body , which lacks immediate reactions and coping mechanisms against psychological and 
 emotional situations2 . exposure to a high 
 gravity condition can lead to a decreased blood flow and g - induced loss of consciousness 
 ( g - loc ) , causing temporary loss of brain function , due to declined peripheral vision . even 
 though the timing of exposure in 3-dimensional space movement and positive or negative 
 acceleration stress during flight varies according to each person , the role of physical 
 strength in preventing g - loc during flight is very significant . in general , pilots perform the l1 maneuver , which maximizes the human response , to tolerate 
 temporary disruption of cerebral blood flow3 . moreover , as a method for maximizing the l1 maneuver , pilots always 
 perform weight training to improve their muscle strength4 , 5 . it is known that using isokinetic equipment is the most effective method of measuring 
 maximum strength to determine the efficiency of training with respect to muscular function 
 within the 60240/sec or 30300/sec range6 , 7 . that is , with use of isokinetic movement 
 devices , peak torque , muscle power , and muscular endurance can be measured and improved at 
 60/sec , 180/sec , and 240/sec angular velocity , respectively . however , when trainers do nt 
 consider the muscular ratio between the antagonistic muscle and the agonist muscle and only 
 focus on improvement in muscle power and endurance , it can cause an injury . especially , when 
 the muscular ratio of knee extension and flexion is lower than 60% , there is the possibility 
 of causing pain or rupturing nearby ligaments and cartilage . in general , athletes can 
 achieve approximately 80% of the muscular ratio , which is necessary for peak torque , muscle 
 power , and muscular endurance8 . an 
 appropriate and well - balanced muscular ratio of the right and left sides for pilots 
 experiencing extreme gravity is considered to be a muscle ratio of 80% . in particular , exerting maximum muscular strength can be a factor that reduces g - loc in 
 situations of rapidly increasing acceleration . therefore , this research examined muscular 
 ratios of the knee and trunk and explored the influence on the success of korea air force 
 academy students in gravity acceleration ( + 6g/30 sec ) tolerance tests . in this study , through a muscular function test , the muscular ratio between flexion and 
 extension was examined , after obtaining the informed consent and voluntary participation of 
 80 korea air force academy male students who were preparing for air missions . all subjects 
 underwent an acceleration test ( + 6g/30 sec ) and were classified as the passing and fail 
 groups . the fail group was further divided into 3 groups according to the failure time : 
 within 10 seconds ( a group ) , 20 seconds ( b group ) , and 30 seconds ( c group ) . three out of 
 the 80 subjects were excluded from the study because of personal issues and incomplete 
 consent ; ultimately , 77 subjects participated in this study . all experimental procedures 
 were explained in detail to all of the subjects , who then signed a written informed consent 
 statement . the study was approved by the korea air force medical center institutional review 
 board , and it was conducted in accordance with the declaration of helsinki . height and weight were measured % fat , bmi , and body composition of the left and right leg 
 muscle amounts were determined using a body composition analyzer inbody 729 ( bio space , 
 korea ) . for muscle function evaluation , the subjects were tightly fastened in a humac , and 
 isokinetic testing of left and right knee flexion and extension was performed at angular 
 velocities of 60 and 240/sec . the test items were peak torque , body weight to peak torque 
 ratio and body weight to total work ratio . a g - tolerance test is performed as one of the eligibility criteria for entry into the 
 flight training program at the air force aerospace medical center . the subjects were exposed 
 to + 6 g at a rapid acceleration of + 1 g per second , for a maximum of 30 seconds . while they 
 were exposed to the acceleration , the subjects performed the l1 maneuver , a tolerance 
 promotion method of positive acceleration and they were fully skilled at a certain level of 
 the l1 maneuver . when they were exposed to the acceleration , the subjects were not wearing 
 an anti - g suit . subjects were classified into the failed group and the successful group 
 based on whether they had loss of consciousness or not while they were exposed to 
 acceleration . in the case of the failed group , once the subjects failed the test , the time 
 ( sec ) of their failure was recorded . the mean and sd ( standard deviation ) of all the outcome measures one - way anova was conducted on the body composition , muscle function test , and 
 acceleration test results , and duncan s post - hoc test was also conducted . all physical characteristics of the subjects in this study are listed in table 1table 1.characteristics of the participantsvariablefg ( n=40)pg ( n=37)post hoca ( n=18)b ( n=10)c ( n=12)age ( years)21.6  0.721.5  1.021.8  0.821.7  0.9height ( cm)176.3  5.2175.1  4.5176.4  6.0174.1  4.5weight ( kg)67.3  9.471.3  8.573.5  8.470.7  8.1muscle mass ( kg)33.1  4.234.6  4.136.0  3.734.3  3.6a < cfat mass ( kg)9.0  3.410.6  3.110.5  4.010.7  3.8bmi ( kg / m)21.2  2.423.2  2.423.6 1.923.3  2.2a < c , d%fat ( % ) 13.2  3.514.8  3.214.0  4.114.9 3.9%fat visceral ( % ) 0.8  0.00.8  0.00.8  0.00.8  0.0a < c , dmean  sd , fg : fail group , pg : pass group . p<0.05 . a ; 10 sec , b ; 20 sec , c ; 30 
 sec , d ; pg . the muscle mass and fat percentage of the failed c group and passing group 
 were significantly higher than those of the failed a group ( p<0.05 ) . moreover , the failed 
 c group and the passing group had higher bmi values than the failed a group ( p<0.05 ) . knee 60/sec peak torque is displayed in table 
 2table 2.change of knee 60/sec peak torquevariableextensorsflexorsleftrightleftrightpt ( n / m)fga159.4  38.0175.0  34.1114.2  21.6119.8  24.9b160.3  19.5168.8  25.2109.5  17.8115.9  15.1c180.3  37.4180.9  34.5128.3  25.5128.8  19.7pg169.2  26.5176.8  23.7122.4  21.8124.7  19.0post hocnsnsb < cnsptbw ( % ) fga235.2  30.9259.0  27.5169.3  21.3177.8  25.3b226.8  32.4237.8  32.6155.9  32.2164.0  23.7c248.1  42.4248.6  28.5176.4  27.0177.5  16.9pg240.8  34.4251.2  29.0193.9  26.7176.9  20.4post hocnsnsnsnswr ( n / m)fga157.7  44.2174.1  37.7126.3  24.0133.9  27.3b162.7  17.0173.1  30.2121.8  20.5130.2  15.0c185.7  38.9186.7  29.2140.3  27.0144.4  22.8pg173.0  28.7180.2  27.1133.2  23.8138.9  21.2post hoca < cnsnsnswrbw ( % ) fga231.9  38.2257.2  31.3187.8  26.2198.6  29.8b230.3  30.8244.1  40.5173.3  37.2184.4  26.6c256.3  45.4256.3  27.6192.3  28.4198.8  22.6pg245.8  35.7255.7  31.0189.1 27.7197.0  22.1post hocnsnsnsnsmean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; wr : work per 
 repetition ; wrbw : work per repetition body weight . post hoc test : p<0.05 a , 10sec ; 
 b , 20sec ; c , 30sec ; d ; pg . knee 60/sec left flexion peak torque of the failed c group was significantly 
 higher than that of the failed b group ( p<0.05 ) . p<0.05 . a ; 10 sec , b ; 20 sec , c ; 30 
 sec , d ; pg mean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; wr : work per 
 repetition ; wrbw : work per repetition body weight . post hoc test : p<0.05 a , 10sec ; 
 b , 20sec ; c , 30sec ; d ; pg the results of knee 240/sec peak torque of the subjects are presented in table 3table 3.change of knee 240/sec peak torquevariableextensorsflexorsleftrightleftrightpt ( n / m)fga88.2  18.194.1  20.079.6  13.480.4  16.3b96.8  17.697.7  12.576.8  8.977.3  7.4c103.8  22.1105.0  23.484.4  12.587.4  11.8pg100.2  16.198.2  18.581.2  15.383.1 15.3post hoca < c , dptbw ( % ) fga130.7  20.1139.3  18.5118.7  17.7119.2  17.6b136.4  28.3138.2  23.2109.4  20.3109.4  19.1c143.5  29.3145.0  31.3116.8  16.3121.0  15.6pg141.9  17.1139.0  20.9115.1  16.8117.8  17.6post hoctwd ( n / m)fga1,961.1  349.02,053.5  331.61,881.9  310.31,834.9  354.4b2,216.0  340.92,220.7  257.41,852.7  132.11,831.5  223.6c2,259.5  375.42,299.6  302.52,096.4  251.52,083.2  240.2pg2,192.0  318.42,241.3  363.21,971.5  353.51,974.9 305.4post hoca < c , da < ctwdbw ( % ) fga2,913.8  371.33,017.0  411.12,807.9  433.52,724.8  410.0b3,129.5  491.43,134.5  357.52,634.9  385.72,614.2  525.4c3,126.4  498.03,183.2  424.42,903.2  358.12,895.3  433.7pg3,111.1  337.33,176.4  370.92,795.2 397.42,800.8  318.2post hocmean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight . post hoc test : p<0.05 ; a , 10sec ; b , 20sec ; 
 c , 30sec ; d , pg . the failed c group and the passing group showed higher 240/sec left knee 
 extension peak torque values than the failed a group ( p<0.05 ) . the total work of left 
 knee extension in the failed c group and the passing group was significantly higher than 
 that of the failed a group ( p<0.05 ) , and the total work of right knee flexion of the 
 failed c group was significantly higher than that of the failed a group ( p<0.05 ) . mean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight . post hoc test : p<0.05 ; a , 10sec ; b , 20sec ; 
 c , 30sec ; d , pg the knee 240/sec left flexor / extensor ratio of the passing group was significantly lower 
 than that of the failed a group ( p<0.05 ) , and the right extensor / flexor ratio of the 
 failed b group was significantly lower than that of the failed a group ( p<0.05 ) in table 4table 4.change of knee left / right for extensor / flexors ratiovariableleftrightextensor / flexors 60/secfga72.3  7.168.4  8.0b68.5  9.569.1  6.6c71.8  9.871.7  8.0pg72.8  9.470.7  7.5post hocextensor / flexors 240/secfga92.1  15.397.1  15.3b81.5  14.385.1  11.6c83.2  12.994.5  15.6pg81.7  12.890.5  13.6post hoca > da > bmean  sd , fg : fail group ; post hoc test : p<0.05 ; a , 10sec ; b , 
 20sec ; c , 30sec ; d , pg . mean  sd , fg : fail group ; pg : passing group . post hoc test : p<0.05 ; a , 10sec ; b , 
 20sec ; c , 30sec ; d , pg the passing group showed a significantly higher trunk 60/sec extensor / flexor ratio than 
 the failed a group ( p<0.05 ) , and the total work extensor / flexor ratio of the failed b 
 group was significantly higher than that of the failed a group . the trunk 120/sec 
 extensor / flexor ratio of the failed c group and the passing group was significantly higher 
 than that of the failed a group , and the total work extensor / flexor ratio of the failed c 
 group was significantly higher than that of the failed a group ( tables 5table 5.change of trunk 60/sec peak torquevariableextensorsflexorspt ( n / m)fga286.3  58.9253.2  58.3b284.9  36.9247.5  29.8c297.9  43.3270.7  43.0pg286.7  52.5256.7  50.3post hocptbw ( % ) fga425.2  68.9374.4  65.2b400.8  38.9347.7  22.8c413.8  64.8375.9  64.2pg406.8  61.5362.8  52.4post hoctwd ( n / m)fga268.8  58.9222.1  56.9b265.4  39.8222.8  36.6c276.7  62.6243.2  44.1pg268.0  46.3229.2  45.4post hoctwdbw ( % ) fga398.7  66.8327.1  58.0b373.9  54.5312.4  35.6c383.8  85.0338.1  60.4pg380.7 57.9324.2  47.6post hocmean  sd ; pt : peak torque , ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight , 6table 6.change of trunk 120/sec peak torquevariableextensorsflexorspt ( n / m)fga321.3  83.1270.0  73.5b317.0  78.3270.0  58.3c331.4  56.1318.9  65.6pg308.4  76.7285.9  70.6post hocptbw ( % ) fga473.3  84.9399.7  84.3b444.7  101.9380.3  79.4c464.5  106.4445.8  108.6pg435.6  86.8402.7 72.5post hoctwd ( n / m)fga3,017.0  724.12,854.7  768.8b2,968.8  732.02,858.6  439.1c3,158.5  803.93,131.0  507.1pg3,065.7  562.62,927.2  608.2post hoctwdbw ( % ) fga4,468.4  842.44,208.6  752.0b4,163.0  884.44,009.4  418.6c4,368.5  1059.84,337.6  682.5pg4,348.0 662.24,135.4  639.0post hocmean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight , 7table 7.change of trunk for extensor / flexors ratiovariablepttwdextensor / flexors 60/secfga92.1  15.397.1  15.3b81.5  14.385.1  11.6c83.17  12.994.5  15.6pg81.7  12.890.5  13.6post hoca > da > bextensor / flexors 120/secfga85.5  17.482.6  11.3b87.2  12.484.6  14.0c96.7  16.489.3  8.3pg94.7 19.586.7  16.7post hoca < c , da < cmean  sd ; pt , peak torque ; twd , total work done . a , 10sec ; 
 b , 20sec ; c , 30sec ; d , pg ) . mean  sd ; pt : peak torque , ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight mean  sd ; pt : peak torque ; ptbw : peak torque per body weight ; twd : total work done ; 
 twdbw : total work done per body weight mean  sd ; pt , peak torque ; twd , total work done . post hoc test : p<0.05 ; a , 10sec ; 
 b , 20sec ; c , 30sec ; d , pg this research studied the effect of body composition and muscular function ( knee 
 extensor / flexor ratio ) on the g - tolerance ( + 6g/30 sec ) of 77 male students of the korea air 
 force academy . when the endurance time against gravity was prolonged or subjects 
 successfully endured high gravity , lean body mass - related factors of body composition were 
 significantly high . moreover , in the muscular function test , the right and left difference 
 between the knees at 240/sec , one of the factors of muscle endurance was low , and the 
 maximum muscular ratio of the trunk was high and significant . high acceleration of gravity can cause negative effects on the human body , not only on the 
 cardiovascular and central nervous system , but also on the functioning of the pulmonary 
 circulation . fundamentally , fighter pilots perform 
 anti - g straining l1 maneuvers , which is one of the methods of anti - g straining maneuvers 
 ( agsm ) . this method is known to be optimal , and using it , pilots can endure acceleration of 
 gravity without loss of consciousness10 . gravity acceleration training is particularly difficult because pilots can experience g - loc 
 due to inexperience with the l1 maneuver against instantaneously increasing gravity . therefore , for successful gravity acceleration training ( + 6g/30 sec ) , the role of agsm is 
 highlighted more than the physical ability . however , other studies have emphasized that 
 physical features and strength are very important and even essential . epperson et al . 
 reported that 12 weeks of weight training could intensify endurance of gravity acceleration , 
 but until now , there has been little research on this issue11 . in particular , as agsm is performed , based on the basic physical 
 strength , physical and muscular strength are necessary for people working in the air . the 
 results of the present research show that the subjects withstanding prolonged gravity 
 acceleration , or those belonging to the passing group , had relatively higher muscle mass and 
 bmi than the other subjects . these results indicate that pilots need a relatively higher 
 muscle mass and bmi to endure rapidly increasing acceleration of gravity ( an increase of + 1 g 
 per second ) . the isokinetic muscular function exercise test can accurately assess the muscle strength of 
 diverse joints . the knee and trunk are most commonly used for maximum muscular measurement 
 of the lower extremity and lumbar muscles12 , and these muscles are most commonly used when enduring high 
 gravity acceleration . in order to measure the muscular strength , isokinetic strength evaluation of the knee using 
 an isokinetic strength evaluation device is important12 . this is because while demonstrating great power , as one of the 
 pivotal muscles for all movements , knees are surrounded by the largest muscle . moreover , 
 when experiencing gravity acceleration , the femoral muscle s isometric muscle power and l1 
 maneuver play a pivotal role . according to the results of the present study the imbalance 
 between the left and right sides in the failed c group and the passing group was the lowest 
 and the muscular ratio was the most stable . furthermore , the differences between the left 
 and right sides and changes in the muscular ratio , an indicator of muscle endurance at 
 240/sec in the passing group indicated that this group had the best balance between the 
 left and right sides and the most stable muscular ratio . these results indicate that the 
 left and right femoral balance and an adequate ratio of flexion and extension are required 
 to endure rapidly increasing gravity in the early stage . after that , an improvement in 
 muscle endurance , which the pilots can maintain for a long time , is needed to tolerate high 
 acceleration of gravity for 30 seconds . this is because 
 acceleration of gravity occurring from head to toe rapidly transfers the blood flow into the 
 chest , abdomen , and legs . therefore , the blood flow decreases in the direction of the chest 
 and upper body , circumferential orbital blood pressure significantly reduces and blood 
 supply to the brain and optic nerves fail . in the end , pilots experience g - loc13 . it is believed that lumbar and femoral 
 muscle strength and a high level of muscular endurance are needed in order to endure a high 
 acceleration of gravity , provide blood supply to the upper body through the l-1 maneuver , 
 and prevent transfer of blood flow to the legs . lumbar joints including the waist area and 
 abdominal muscles are quite important for creating the ideal power needed for all physical 
 activities , and to show performance in all items of sports . the results of this study did nt 
 show significant differences among the lumbar joints of the groups . in the case of the 
 muscular ratio , there was no statistically significant difference , but the failed c group 
 and the passing group tended to show higher values than the other groups . thus , when the 
 muscular ratio was high after exposure to high acceleration , it was considered to be more 
 effective . this is because the failed group showed lack of power in maintaining muscle 
 strength and an inaccurate l-1 maneuver in the early stage when a relatively lower muscle 
 ratio can rapidly increase the acceleration with passage of time . therefore , it is necessary 
 for korean air force academy students to endure situations of high acceleration not only for 
 balanced muscles and improvement of muscular endurance , but also for improvement of the 
 maximum muscular strength . in this study , the body composition and muscular function tests of 77 male students of the 
 korea air force academy was investigated and the effects of muscular ratios on the success 
 or failure of a gravity acceleration test ( + 6g/30 sec ) were investigated . the amount of 
 muscle and bmi in the passing group were significantly higher than those in the failed 
 group . in the muscle function test , the passing group showed that knee joint maximum muscle 
 strength and balance of the muscular ratio are more effective indices of g tolerance than 
 other parameters . considering these results , it is necessary to have balance between the left and right knee 
 joints , muscular ratio , and raise the muscular ratio of the lumbar joints to successfully 
 endure a high gravity acceleration test ( + 6g/30 sec ) . furthermore , improving the maximum 
 muscle strength is necessary to tolerate a rapidly increasing acceleration situation in the 
 early stage ; hence , training for improving the muscle strength is also needed .
[ purpose ] the aim of this study was to examine the flexor / extensor ratio of the knee 
 joints and compare it with the results of korean air force students in g - tolerance test . 
 [ subjects and methods ] the body composition of korea air force students ( n=77 ) was 
 measured by an impedance method . 
 a muscular function test was performed using a humac norm 
 ( usa ) at angular speeds of 60/sec and 240/sec and an isokinetic muscular function test 
 was also conducted . 
 [ results ] in the failed c and passing groups , muscle mass and fat 
 percentages were significantly higher than those of students in the failed a group . 
 the 
 bmi of the failed c and passing groups were significantly higher than that of the failed a 
 group . 
 the group that passed had a significantly higher value of left knee 60/sec flexion 
 peak torque than the failed b group . moreover , the total work of left knee extension of 
 the failed c group and the passing group was significantly higher than that of the failed 
 a group . 
 the c group and the passing group had significantly higher values of the trunk 
 60/sec flexor / extensor ratio than the failed a group , and the total work flexor / extensor 
 ratio of the passing group was significantly higher than that of the failed a group . 
 [ conclusions ] based on these results , balance the right and left knee flexor / extensor 
 ratio , and a high flexor / extensor ratio of the trunk are required to endure a high 
 g - tolerance test ( + 6g/30 sec ) . moreover , 
 an improvement in the maximum muscular strength 
 is necessary to endure a situation of rapidly increasing acceleration in the early 
 stage .