a pulley system is a useful tool for facilitating articular rehabilitation and muscle 
 strengthening . especially , the pulley with weight is relatively easy to standardize , and 
 readily available in places like hospitals and fitness centers for improving muscle strength 
 and muscle endurance1 . the pulley with 
 weight is an exercise in which weights are lifted using a pulley system . this fitness 
 equipment can be used to create a variety of joint angles and muscle lengths . kapandji et 
 al.2 noted that the angle of the joint 
 was related to muscle length , so muscle strength would vary according to the angle of the 
 joint . also , norkin3 reported that the 
 moment of force was affected by the angle of the joint and muscle length , and kim et 
 al.4 reported that angular variation of 
 the joint changes muscle activation . thus , to heighten the effect of pulley exercise with 
 change in the joint angle and muscle length , the weights of the pulley system or the 
 subject 's joint angle need to be changed . nevertheless , there is little guidance and 
 research regarding the joint angle and the method for exercise using the pulley system . from the aspect of biomechanics , change in the joint angle results from periarticular 
 muscle contraction5 . the change in the 
 joint angle leads to change in the lever arm length and muscle length , and this accompanies 
 variation in muscle contraction6 . therefore , there should be a joint angle which has an optimal mechanical advantage in each 
 joint5 , and the optimal muscle length 
 would be at the angle which exercises maximal strength3 . consequently , the muscular strength would be determined by the 
 length - tension relationship and the mechanical characteristics of the lever . in order to 
 perform an exercise for muscle strength improvement , it is important to know the 
 relationship between the muscle strength and the joint angle of the muscle7 . it has been reported that when the muscle 
 length increases , the muscle activation begins to decrease8,9,10 . it has also been reported that the muscle length is unrelated to 
 muscle activation11 . however , recently , 
 deusen12 showed that the muscle length 
 affects muscle contraction , and reported that there was a relationship between the muscle 
 length and muscle activation . thus , it can be assumed that there must be a muscle length 
 that generates optimal strength , and it seems meaningful to study the joint angle and muscle 
 activation because of the close connection between muscle length and joint angle . 
 particularly , considering this aspect , an exercise program needs to be developed for the 
 pulley exercise with changes in joint angle and muscle length , because knowing the joint 
 angle that creates maximal strength increases the effect of the pulley exercise . therefore , 
 this study was conducted in order to find out the joint angle which creates maximal muscle 
 activation using a pulley system , based on the premise that the joint angle is related to 
 muscle activation . also , this research offers basic data for the development of an effective 
 exercise program for muscle strength improvement . the research subjects were 24 healthy male students attending s university in busan , 
 republic of korea , who gave their prior written consent to participation . they were 
 right - handed , had no congenital deformity in upper extremity which would have affected the 
 results of this study , no surgical or neurological disorders , and no pain in the neck , back , 
 or shoulder . their average age was 30.38  years , their average height was 175.8  cm , and their 
 average weight was 75.09  kg . surface electromyography ( keypoint , medtronic , usa ) was used to 
 measure muscle activations of the brachioradialis and biceps brachii at different elbow 
 joint angles with the shoulder joint in the resting position . the angle between the shoulder joint and 
 elbow joint was measured using a goniometer ( anymedi , korea ) . to trigger the contraction of 
 elbow flexor , a special the 
 pulley system could control the load amount in one - hundred - gram units according to the 
 muscle strength , and could provide the merit of maintaining the load regardless of the 
 length of the rope in a pulley system . to show the effect of angular variation of the elbow 
 joint on the muscle activation of elbow flexor muscles , the non - dominant hand , the left 
 hand , was used . the subjects were made to stand with their feet shoulder width apart , and 
 their shoulder joints and elbow joints were placed in a resting position . for the resting 
 position , the shoulder joint was abducted at 55 , and horizontally abducted at 30 ; and the 
 elbow joint was flexed at 70 , and supinated at 1013 . during the pulley exercise , the resting position of the shoulder 
 joint was maintained , while the angle of the elbow joint was positioned at 3 different 
 angles . sohn et al.14 reported the 
 maximum tension was likely to be developed at 1.2 times the length of the muscle in the 
 resting position . thus , the flexion angle of the elbow joint was positioned at 55 in the 
 first step ; at 70 , the same as the resting position of the elbow joint , in the second step ; 
 and at 90 , the angle usually used during exercise , in the third step . a 90 angle was made 
 between the pulley system and the forearm . when the muscle contracts , the change in muscle 
 strength is proportionate to the change in the electromyogram value , because the action 
 potential occurs in the muscle4 . 
 consequently , to detect the change in the muscle strength due to the angular variation at 
 the elbow joint in the resting position of the shoulder joint , isometric contraction was 
 induced , and then the muscle activation was measured using surface electromyography . isometric contraction was performed for 5 seconds , and the electromyogram of the 4 seconds , 
 excluding the first second , was recorded . three measurement trials at each elbow angle were 
 made , and two minutes rest was given before changing the angle of the elbow joint , based on 
 the preceding studies , to prevent the muscle fatigue15 . the flexion of the elbow joint is induced by the brachialis , 
 biceps brachii , brachioradialis , pronator teres16 , but we only recorded the electromyograms of the biceps brachii and 
 brachioradialis due to the ease of their measurability . the electrodes were attached 2 
 centimeters apart at the thickest part of the muscle belly after muscle contraction17 . before the electrodes were attached , hair 
 on the attachment site was removed by shaving to reduce the skin resistance , and then the 
 site was cleaned with an alcohol swab for exfoliation . the ground electrode was attached to 
 the non - dominant left triceps brachii . to determine the significance of the changes in 
 muscle strength due to the angular variation of the elbow , repeated measures anova was 
 conducted . to find the joint angle which showed differences in the muscle activation , wilcoxon 's signed rank test , a nonparametric method , was performed , because the 
 shapiro - wilk 's test showed the data were not normally distributed . for the analysis , we used 
 spss for windows ( ver . a : 55>90 ( p<0.05 ) , b : 
 70>90 ( p<0.05 ) , c : 55>70 ( p<0.05 ) , d : 55>90 ( p<0.05 ) , e : 
 70>90 ( p<0.05 ) by wilcoxon 's signed rank test the muscle activations of the biceps brachii and brachioradialis showed statistically 
 significant changes with changes of the elbow joint . the muscle activities of the biceps 
 brachii were 366.5  mv at 55 , 295.3  mv at 70 , and 159.9  mv at 90 ( p<0.05 ) . the muscle 
 activities of the brachioradialis were 1678.1  mv at 55 , 1043.3  mv at 70 , and 362.4  mv at 
 90 ( p<0.05 ) . the muscle activation of the biceps brachii was not significantly different 
 between the elbow angles of 55 and 70 ; however , between 55 and 90 , the muscle activation 
 was significantly higher at 55 ( p<0.05 ) , and between 70 and 90 , the muscle activation 
 was significantly higher at 70 ( p<0.05 ) . for the brachioradialis , between elbow angles 
 of 55 and 70 , the muscle activation was significantly higher at 55 ( p<0.05 ) , between 
 55 and 90 , the muscle activation was significantly higher at 55 ( p<0.05 ) , and between 
 70 and 90 , the muscle activation was significantly higher at 70 ( p<0.05 ) ( table 1 ) . the bones of the human body are connected through joints18 , and the human body can adopt various postures due to angular 
 movement of the joints19 . the movements 
 of the joints are developed through muscle contraction , which is closely connected with 
 muscle length20 . in other words , changes 
 in muscle length lead to changes in joint angles , affecting the muscle 's strength21 . the change in the muscle strength 
 depending on the angular variation of the elbow joint can be explained through the lever 
 principle and the length - tension curve of the muscle . in explaining the movement of the 
 human body using the lever principle , the fulcrum is the joint , the force generating the 
 effect is the muscle , and the weight or resistance is the human body22 . in this respect , change in the joint angle accompanies 
 the change in the length of the lever arm and muscle , leading to change in the muscle 
 activation and contraction4 , 6 . also , the biggest tension is developed at a specific range 
 of musle length in the length - tension curve , which is why the change in the muscle strength 
 induced by angular variation of the elbow joint can affect the muscle activation23 . in this context , eloranta and komi11 and bobbert and harlaar24 confirmed that isokinetic contraction of 
 extensor muscles and electromyogram values of maximum voluntary isometric contraction were 
 the biggest at the middle range of angles , and that is why correlation exists between the 
 joint angles and muscle activation . kim et al.25 argued that during specific movements , the muscle length and joint 
 position changes constantly , causing change in the moment of force . consequently , they said 
 that when a muscle contracts , the muscle strength will differ depending on the angular 
 variation . lee et al.26 also reported 
 that during movement , if proper muscle length and joint position were set , a subject would 
 display the maximum power in the easiest way , and perform exercise properly . thus , if the 
 exercise were done with a pulley system , consideration of the joint angles would be an 
 important factor for the maximum effect of the exercise . nevertheless , there are few studies 
 which have scientifically investigated the optimal joint angle , which can improve the effect 
 of the exercise when using a pulley system . thus , the object of this study was to provide 
 basic data concerning the proper joint angle during pulley exercise . borstad27 researched the relationship 
 between the changes in muscle length relative to the resting position and damage to the 
 shoulder joint . he argued that change of the resting position occurred when the resting 
 length of the muscle involved in the related movement became shorter . therefore , when joint 
 angles were selected for this study , three elbow angles were chosen considering to the 
 resting position of the elbow joint and the length tension relationship of the muscle . while 
 the shoulder joint was placed on the resting position , the elbow joint was flexed at an 
 angle of 70 , which is its resting position , in the first step . in the next step , it was 
 flexed at an angle of 55 , which gives a length 20% greater than the resting position . finally , the elbow was flexed at an angle of 90 , which gives a length 30% less than its 
 resting position . since the change in muscle activation depends on the angular variation of 
 the elbow joint , only the muscle 
 activation of the biceps brachii showed no significant difference between the elbow angles 
 of 55 and 70. the other muscle activities of the biceps brachii and brachioradialis showed 
 angle - related changes in the order of 55 , which showed the biggest value , followed by 70 
 and 90 ( p<0.05 ) . therefore , the results suggest it would be more effective to make an 
 angle of 90 between the pulley with weights and the forearm when the muscle is stretched to 
 a length 20% greater than its resting position . this result and those of other studies ' 
 agree with the study of sohn14 , who 
 reported the smaller the angle of the elbow joint was , the higher the muscle activation was . 
 also , nam and kim28 varied the angle of 
 the flexion of the elbow joint from 110 to 70 at 5 intervals , and investigated the muscle 
 strength . they reported that the smaller the angle of flexion of the elbow joint was , the 
 higher the muscle activation was , and that the rate of increase in the muscle strength was 
 the highest at an angle of 70. this is in consistent with the results of the present study , 
 that the muscle strengths of the biceps brachii and brachioradialis were higher at an angle 
 of 90 than at 70. although , most studies have not provided a scientific basis that is 
 applicable to all joints , the results of the present study can be generalized to all joints 
 because the angles at which the muscle length was stretched by 20% compared to the resting 
 position of each joint were used . the results of this study can be explained through the 
 results of the study by cooke and fay29 . they showed that the active force at the resting length was the greatest , but if the muscle 
 length were stretched by 20 to 30% of its resting length , the bigger the passive force 
 became , and the bigger the total force was . that 's why the results of the present study show 
 that the muscle activation became greater , because active force was added to the passive 
 force at the angle at which the muscle length was stretched by more than 20% of its 
 length . consequently , in order to improve the muscle strength of the elbow flexor using a pulley 
 system , it would be more effective to set an angle of 90 between the pulley with weights 
 and the forearm , and use an angle at which the muscle is stretched to a length 20% greater 
 than its resting position . however , more research is needed to confirm this result through a 
 comparative study of muscle activations at angles at which the muscle length is stretched by 
 more than 20% from its resting length and using joints other than the elbow , which was 
 studied in the present study .
[ purpose ] this research investigated the effect of angular variation of flexion of the 
 elbow joint on the muscle activation of elbow flexor muscles . 
 [ subjects ] the research 
 subjects were 24 male college students with a dominant right hand who had no surgical or 
 neurological disorders and gave their prior written consent to participation with full 
 knowledge of the method and purpose of this study . [ methods ] the subjects ' shoulder joints 
 stayed in the resting position , and the elbow joint was positioned at angles of 55 , 70 , 
 and 90. the angle between the pulley with weights and forearm stayed at 90. surface 
 electromyography was used to measure muscle activities . 
 three measurements were made at 
 each elbow angle , and every time the angle changed , two minutes rest was given . 
 [ result ] 
 the muscle activities of the elbow flexors showed significant changes with change in the 
 elbow joint angle , except for the biceps brachii activities between the angles of 55 and 
 70 of elbow flexion . 
 the muscle activities of the biceps brachii and brachioradialis 
 showed angle - related changes in the order of 55 , which showed the biggest value , followed 
 by 70 and 90. [ conclusion ] in order to improve muscle strength of the elbow flexor using 
 a pulley system , it seems more effective to have a 90 angle between the pulley with 
 weights and the forearm when the muscle is stretched to a length 20% greater than its 
 resting position .