isokinetic evaluation of the shoulder joint is often used to assess functional dynamic 
 stability and shoulder musculature performance , especially in overhead athletes1,2,3,4 . 
 moreover , it could also help to determine the profile of patients or athletes suffering from 
 shoulder disorders and guide their therapy and rehabilitation5 , 6 . imbalance in the strength of the internal rotators ( irs ) and the external rotators ( ers ) of 
 the shoulder joint is regarded as a possible factor in shoulder dysfunction7 , 8 . the er : ir ratio , the agonist - antagonist strength balance , has been used to identify possible 
 risk factors for shoulder pathology9 , 10 and may help to formulate a suitable 
 muscle - training program10 . the initial 
 value reported for the er : ir ratio in normal subjects was about 0.66 and remained about the 
 same throughout the velocity spectrum11 . however , the rotational joint strength 
 may be affected by the testing joint position14,15,16,17,18 
 due to the muscle length - tension relationship and rotational speed14 , 15 , 18 , 19 , which may 
 cause different er : ir ratios in different exercise positions and at different speed . however , to the authors knowledge , there has been little research investigating the ratio 
 of change in the different positions and rotational speeds in the scapular plane that may be 
 used to minimize the stress on the rotator cuff . shoulder injuries caused by overuse frequently occur in baseball players , who repeatedly 
 perform internal arm rotation with very fast angular velocities ( about 6000/sec ) during the 
 throwing motion20 . the main agonists are 
 the irs being contracted concentrically in the acceleration phase , while the ers have to 
 maintain the stability of the shoulder joint dynamic . therefore , it is important to evaluate 
 the ir and er strengths to develop injury prevention and rehabilitation programs and to 
 design training programs for baseball players . given 
 the high number of times a baseball player throws a ball , it is important to determine which 
 shoulder position is the most stable , and this has not yet been discussed . moreover , 
 soderberg and blaschak ( 1987 ) suggested that by establishing a progression of difficulty 
 according to isokinetic test positions , a rehabilitation program following that progression 
 would be valuable15 . therefore , the purpose of this study was to determine the 
 isokinetic strength profiles and er : ir ratio in baseball players at various shoulder 
 abduction positions in the scapular plane and at different speeds and to compare these 
 values with those of healthy non - players . it was thought that comparing baseball players 
 values to normal values would be helpful in determining the effectiveness of their training 
 program and in preventing risk of injury . the control group comprised 39 subjects including 20 first - level collegiate baseball 
 players and 19 college students of matched ages . all of these subjects were male , and none 
 had experienced a shoulder musculoskeletal injury within six months or any shoulder 
 discomfort or weakness during activity . the average age of the baseball players group was 
 19.50.6  years . the average height was 176.85.1  cm , and the average weight was 73.27.3  kg . the average height was 
 174.44.7  cm , and the average weight was 71.810.2  kg . all subjects were briefed on the 
 study s procedures and its possible risks , and they provided written consent voluntarily 
 before participation . the present study was approved by the institutional review board of 
 kaohsiung medical university chung - ho memorial hospital . a biodex isokinetic dynamometer ( system 3 , biodex medical systems , shirley , ny , usa ) was 
 used in the evaluation of shoulder muscle strength . this system s test velocity ranged from 
 0.25/s to 300/s , and torque could be measured from 0.7 n - m to 680 the subjects 
 were seated , and their trunks were stabilized by anterior straps stretched diagonally from 
 just above the shoulder level to the opposite pelvic side . an additional strap was used to 
 stabilize the pelvis . strength was tested through 
 a 150 range of motion , between 60 of internal rotation and 90 of external rotation , in 
 both the internal and external rotation test . after the test procedure was presented , 
 subjects stretched their shoulders as a warm - up and performed five to ten submaximal trials 
 to familiarize themselves with the testing conditions . each test session comprised three 
 repetitions of external and internal rotation in concentric movement . three testing 
 positions with shoulder abduction of 45 , 70 , and 90 combined with three testing speeds of 
 60/s , 120/s , and 210/s were tested . the order of positions was randomized , as was the order of testing 
 speeds at each position . descriptive statistics ( mean and standard deviation ) including age , height , weight , peak 
 torque of the ers and irs , and er : ir ratio of the subjects are presented . two - way repeated 
 measure anova was used to analyze the effect of the testing positions and the exercise 
 speeds on the peak torques of external rotation and internal rotation and the ratio of the 
 peak torque of the ers to that of the irs within the two groups . a one - way anova test was 
 used to determine whether there was a significant difference in any testing parameter 
 between the two groups . table 1table 1.peak torques of external and internal rotation in baseball players and the 
 control group ( n - m)velocitybaseball players groupcontrol groupposition457090457090external rotation60/s24.423.7031.475.9030.404.7124.124.3029.646.5527.895.85120/s23.683.7230.765.9028.714.8922.173.6528.135.7325.825.55210/s23.283.9428.974.9427.774.6520.362.6125.985.1823.834.65internal rotation60/s39.007.8545.3510.0044.0510.0030.347.6834.279.5634.0110.68120/s39.497.7644.0110.2544.879.4829.407.1832.828.5932.308.57210/s40.188.2045.159.0043.979.2729.536.2934.369.3332.568.73meansd shows the peak torques of the ers and irs in the three testing positions at 
 three different speeds in the baseball players group and the control group . the er peak 
 torque generated in the different positions and speeds revealed significant differences . the 
 maximum er peak torque for the three testing positions was found with shoulder abduction of 
 70 , while the maximum value occurred at the speed of 60/s for both groups . the maximum ir 
 peak torque was also found with shoulder abduction of 70 ; however , there was no significant 
 difference in peak torque according to testing speed . there was a significant difference in 
 ir peak torque among the different positions in both groups . but the testing speed and 
 interaction of the testing positions and speeds showed no significant differences ( table 2table 2.analysis of variance results for the peak torques of external and internal 
 rotation in different positions at various speedsbaseball players groupcontrol groupf - valueremarksf - valueremarksexternal rotationposition * ( deg)20.1170>4531.0170>4590>4590>4570>9070>90velocity * ( /s)5.7560>12029.3660>12060>21060>210120>210120>210angle velocity1.320.16internalrotationposition * ( deg)10.8270>457.4870>4590>4590>45velocity ( /s)0.175.42angle velocity1.440.88*p<0.05 ) . table 3table 3.the ratios of external rotation / internal rotation peak torque in different 
 positions at various speeds ( % ) velocitybaseball players groupcontrol groupposition45709045709060/s64.2711.9271.1312.3471.1612.9781.7112.5989.0614.3186.1618.51120/s61.3311.2671.3310.6565.3710.5077.8613.9488.1415.8382.0114.04210/s59.3110.8765.349.8264.348.8970.9312.6378.3615.2675.7714.66meansd shows the ratios of the two groups for the peak torque er : ir in different 
 testing positions and speeds . the maximum ratio was also found with the shoulder abduction 
 of 70 and at the velocity of 60/s . the ratio varied with the testing positions and also 
 with the testing speeds in both groups ( table 
 4table 4.analysis of variance results for the ratios of external rotation / internal 
 rotation peak torque in different positions at various speedsbaseball players groupcontrol groupf - valueremarksf - valueremarksposition * ( deg)6.2270>454.7470>45velocity * ( /s)4.0760>21012.8460>210120>210position velocity2.520.44 ) . however , there was no interaction between the testing positions and 
 speeds . the er peak torques of the baseball players with shoulder abduction of 45 and a velocity 
 of 210/s and with abduction 90 and a velocity of 210/s were higher than those of the 
 control group . the baseball players ir peak torques were greater than those of the control 
 group under all testing conditions ( 3 angles  3 speeds ) . the results for the er : ir ratio 
 were opposite of those for the ir peak torque ; the ratios of the control group were greater 
 than those of the baseball players under all testing conditions ( table 5table 5.analysis of variance results for comparisons of test parameters between baseball 
 players and the control groupvelocityposition457090external rotation peak torque60/s0.8270.3900.166120/s0.2270.1850.107210/s0.013 * 0.0860.016*internal rotation peak torque60/s0.002 * 0.002 * 0.006 * 120/s0.000 * 0.001 * 0.000 * 210/s0.000 * 0.001 * 0.001*er : ir60/s0.000 * 0.000 * 0.008 * 120/s0.000 * 0.001 * 0.000 * 210/s0.006 * 0.004 * 0.008 * ) . the internal shoulder rotators were found to be significantly stronger than the external 
 rotators under all nine testing conditions ( 3 positions  3 speeds ) in both groups . this is consistent with 
 the muscle - size differences between the two rotator muscle groups . the muscles with a larger 
 cross - section area could produce more muscle force . the large internal rotators such as the 
 latissimus dorsi and pectoralis major are stronger than the external rotators such as the 
 infraspinatus and teres minor . the lever arm of the internal rotators is usually also larger 
 than that of the external rotators24 . previous studies have shown that shoulder joint positions could affect muscle 
 activation25,26,27 around the shoulder and 
 the shoulder s rotational strength14 , 15 , 18 . the present study also found that the er and ir strengths of the 
 shoulder changed with the shoulder abduction angles in the scapular plane . with the arm away 
 from the trunk , the length - tension relationship of the rotator cuff and surrounding 
 musculatures and the tension of the ligament and joint capsule were changed . moreover , the 
 changes in the ligaments and capsule also caused a variable fulcrum point during humeral 
 movement15 . several studies 
 investigated the effect of testing positions on shoulder strength production or testing 
 reliability14,15,16,17,18 . however , few of them 
 focused on the strength changes at various positions in the same plane14 , 15 . soderberg and 
 blaschak ( 1987 ) found that both the er and ir had maximum rotation strength in the neutral 
 position , followed by 90 of abduction and 45 of abduction14 . ( 2011 ) also found that rotational strength was 
 greater at 90 of abduction than at 45 of abduction15 . moreover , the maximum rotational strength was found at 70 of abduction in both 
 groups not tested in the previous study . in brown s study ( 1988 ) , the subjects were often 
 apprehensive of producing full effort at 90 of abduction , since this position is inherently 
 less stable . moreover , a previous study 
 found that a ball was usually thrown at just lower than 90 of abduction during throwing 
 motion20 . this may mean there was less 
 constraint from the soft tissue of the shoulder , resulting in the ability to perform with 
 greater rotational strength . several researchers also suggested modifying the traditional 
 shoulder isokinetic positions by keeping the humerus below 80 abduction to reduce the risk 
 of injury15 , 28 . therefore , application of this position in the athletes training 
 program should be considered to achieve more effective training and to prevent injury . several researchers found that as speed increases , torque decreases during concentric 
 muscle contractions due to the muscle force - velocity relationship14 , 15 , 18 , 19 . however , we 
 did not find a significant difference in shoulder ir strength at various speeds . this 
 conflict in the results may come from the speeds of shoulder internal rotation in the daily 
 throwing motion usually being above 20003000/s and even reaching as high as 6000/sec in 
 the pitching motion , which is far faster than our testing speeds ( 210/s was the maximum ) . moreover , testing in the 
 sitting position may result in trunk compensation during the ir strength test . with respect to examining er : ir strength ratios , the results of this study were similar to 
 those of previous reports describing this ratio as between 0.53 to 0.911 , 15 , 21 , 23 , 29 . the authors found a significantly lower ratio in baseball 
 players than in normal subjects in the present study . the lower ratio is attributed to a greater ir strength without a 
 concomitant increase in er strength1 , 12 . in this study , we also found the strength 
 of the internal rotators in baseball players was greater than in normal subjects , while er 
 strength in baseball players was not significantly greater than that in normal subjects 
 under most testing conditions . a possible explanation for the greater ir strength is that 
 most players do resistance strength training with greater focus on the larger muscles such 
 as the latissimus dorsi and the pectoralis major , which are internal rotators , and ignore 
 the small external rotators . moreover , it is possible that a gain in ir strength may result 
 from the shortened repeated stretch cycle of the throwing motion . the baseball players need 
 to generate a large amount of torque in the irs to pitch or transfer the ball with 
 sufficient velocity . conversely , the external rotators are shortened during the late cocking 
 phase before lengthening rapidly during the acceleration and follow - through phase . in our 
 study , contraction of the external rotators was reduced during the deceleration phase , as 
 the er torque was produced primarily by the elastic elements of the musculature30 . the effect of training on the external 
 rotators may be less than that on the internal rotators . the external rotators had a high activity level during baseball pitching , especially during 
 deceleration of the pitching arm in the follow - through phase . alderink and kuck ( 1986 ) 
 suggested that perhaps training programs should strive to increase the er : ir ratio21 . increasing the concentric er : increasing the 
 external rotation could effectively bias this ratio and add greater stability to the 
 shoulder joint in athletes performing overhead activities and possibly prevent shoulder 
 injuries . moreover , the results of this study further suggest that the physical activity 
 required of baseball players does indeed place special demands on the shoulder as compared 
 with the demands placed on nonplayers shoulders . the results of this study showed that the shoulder abduction position was a significant 
 factor in the generation of ir and er strength . the maximum torque occurred with abduction 
 of 70 , and ir strength showed no significant difference between the testing positions with 
 shoulder abduction of 70 and 90. speed had a significant effect on er strength only . the 
 baseball players had greater ir strengths than the control group ; however , this was not the 
 case with respect to er strength . it was shown that baseball players need to improve the 
 external rotators to improve shoulder joint stability . the er : ir strength ratio was affected 
 by the shoulder abduction positions and rotational speeds . positioning was found to affect torque production , and 
 selecting a position for training or rehabilitation based upon the degree of difficulty 
 could have a positive effect on training .
[ purpose ] this study aimed to investigate the effect of shoulder positions and speeds on 
 internal and external rotation torque of college baseball players and age - matched 
 non - players . 
 [ subjects ] twenty first - level collegiate baseball players and 19 college 
 students were recruited . 
 [ methods ] a dynamometer system was used to evaluate the shoulder 
 rotation strength in sitting postures . 
 three testing positions , namely shoulder abduction 
 of 45 , 70 , and 90 in the scapular plane , were combined with three testing speeds at 
 60/s , 120/s , and 210/s . [ results ] 
 the maximum external and internal rotation torques 
 both occurred at shoulder abduction of 70. however , only external rotation torque was 
 affected by the speed , with the peak value observed at 60/s . 
 the internal rotation torque 
 of baseball players was larger than that of the control group under all testing 
 conditions , but the external rotation did not show any difference . 
 the ratio of external 
 to internal rotation torque changed with the testing positions and speeds in both groups . 
 the ratio in the control group was greater than that in the player group . 
 [ conclusion ] the 
 shoulder position could affect the rotational strength , and the baseball players could 
 strengthen their external rotators for better performance and injury prevention .