strengthening of scapular stabilizer muscles plays a crucial role in the treatment of 
 various shoulder pathologies , such as scapular dyskinesia , multidirectional instability , 
 secondary impingement syndrome and postoperative conditions1 .
the serratus anterior is one of the most important muscles responsible for scapular 
 stabilization2 , 3 .
weakness of this muscle causes the scapula to rest in a downwardly 
 rotated position , causing scapular winging3 .
scapular winging may contribute to persistent symptoms in patients 
 with secondary impingement or scapulothoracic dyskinesia4 ; thus , an exercise program to restore the serratus anterior muscle 
 tone is an important item of rehabilitation5 .
the trapezius muscle is also of substantial importance in the 
 painful shoulder condition , contributing to abnormal rotation of the scapula6 , 7 . in 
 patients with painful shoulder ,
the loss of scapular muscles coordination and balance has 
 been described in the literature7,8,9,10 .
push - up exercise is known to be one of the most effective and popular exercises for the 
 strengthening of scapular stabilizer muscles11 , 12 .
push - ups can be performed either on a 
 stable support such as floor or wall , or on an unstable support , such as a swiss ball . 

however , it is not known which exercise is beneficial for specific scapular stabilizer 
 muscles .
previous studies have failed to address and compare which phases of push - up plus 
 exercise contribute to muscle activation , or which specific muscles are activated on stable 
 and unstable bases of support .
the purpose of this study was to measure the differences between two types of push - up plus 
 exercises in terms muscle activities measured by surface emg in order to suggest the best 
 scapular stabilizer strengthening exercise program , and provide clinicians with insight on 
 clinically relevant scapular stabilizer exercise program for the treatment of various 
 shoulder pathologic conditions .
they were evaluated clinically by one 
 orthopedic consultant to confirm the absence of alterations to upper limb structures . 

volunteers with a history of shoulder , elbow , wrist , hand disease or previous operation , 
 cervical spine injury or sustained pain were excluded .
details of their physical constitution are as follows : height , 176.2  
 3.67  cm ; weight , 75.7  5.16  kg ; chest circumference , 91.8  5.99  cm ; shoulder width , 35.4  
 1.71  cm ( mean  sd ) . first , maximum voluntary isometric contraction ( mvic ) was measured . to 
 isolate the activation of the five muscles ( upper trapezius , middle trapezius , lower 
 trapezius , serratus anterior , and latissimus dorsi ) , specific positions for mvic were 
 selected based on mclean and kendal13 , 14 .
the upper trapezius was tested with the volunteer seated , the shoulder abducted to 90 , and 
 the head in a neutral position .
the middle trapezius was tested with the 
 subjects lying prone on a treatment table , and the shoulder externally rotated and 
 horizontally abducted to 90. resistance was applied distal to the elbow14 .
the lower trapezius was tested with the 
 shoulder in external rotation and the arm abducted to 125. resistance was applied distal to 
 the elbow14 .
the mvic of the serratus 
 anterior was tested with the subjects seated on a table , the shoulder internally rotated and 
 abducted to 125 in the scapular plane .
lastly , the mvic of the latissimus dorsi 
 was conducted by resisting subjects as they attempted a pull - down maneuver with the upper 
 arms abducted to 9015 . resting time of 
 at least 1 minute was provided between mvic tests to avoid fatigue . the chair height and
the swiss ball ( 55  cm diameter ) height were standardized and identical 
 in all trials .
a minimum of 3 minutes of rest was given between exercises to prevent the 
 influence of fatigue on electromyographic amplitude changes .
all subjects were educated about the exercise program for this study and performed 
 standardized supervised practice before the test .
after mvic measurement , the subjects were 
 given an educational session about the exercise program and performed the standardized 
 push - up plus exercise three times .
in actual measurement , the subjects were asked to follow 
 the exercises two times in random order and we collected and calculated the average value 
 for final data12 .
surface emg was recorded over the five important scapular stabilizers ; the upper trapezius , 
 middle trapezius , lower trapezius , serratus anterior , latissimus dorsi muscles .
the 
 electrode locations were as follows : upper trapezius electrode was placed slightly lateral 
 to and halfway between the cervical spine at c-7 and the acromion16 ; the middle trapezius electrode was centered vertically 
 between the medial border of the scapula and the spines of the thoracic vertebrae ( t-1 to 
 t-6)5 ; the lower trapezius electrode was 
 placed approximately 5  cm down from the scapular spine ; the serratus anterior electrode was 
 placed just below the axillary area , at the level of the inferior tip of the scapula16 ; and the latissimus dorsi electrode was 
 placed three fingerbreadths distal to and along the posterior axillary fold , parallel to the 
 lateral border of the scapula12 .  
a , the standard push - up 
 plus on a stable chair support ( sp - c ) .
b , knee push - up plus on a stable chair support 
 ( kp - c ) .
c , the standard push - up plus on an unstable swiss ball support ( sp - s ) .
d , knee 
 push - up plus on an unstable swiss ball support ( kp - s ) .
all 
 movements were completed in a standardized position with the hands placed at shoulder width 
 apart with the subjects ' middle fingers under the acromioclavicular joint on the floor . we asked each participant to maintain four postures .
the standard push - up plus ( feet on the 
 ground ) was carried out utilizing a chair as a stable support , as was the knee push - up plus 
 ( knees on the ground ) .
the standard and knee push - up plus were executed utilizing a swiss 
 ball as an unstable support ( fig .
1 ) . a. standard push up plus on stable chair support ( sp - c ) .
c. standard push up plus on unstable swiss ball support ( sp - s ) .
d. knee push up plus on unstable swiss ball support ( kp - s ) .
( scapular retraction ) and  up position  ( scapular protraction ) lasted 
 for 5 seconds in each repetition .
an electrical trigger was used to mark the beginning of the first descent and the finish of 
 the last repetition12 .
the standard push up plus started in the push up position . the volunteer rolled the 
 shoulders forward ( scapular protraction ) and continued to rise up by protracting the 
 scapula , and then lowered his body while approximating shoulder blades ( scapular 
 retraction)17 .
the knee push up plus , a 
 modification of a standard push - up plus , was performed exactly like the standard push up 
 plus except the body weight was supported by the hands and knees , rather than the hands and 
 feet ( fig .
1)5 . to measure surface emg ( semg ) of the muscles , an mp150 ( biopac system inc .
the surface emg signal was recorded at a 1000  hz sampling frequency , and was filtered 
 using a band pass filter between 10  hz and 500  hz .
active electrode ag - agcl discs ( biopac , 
 diameter 2  cm ) were adhered to the skin over each target muscle group following the 
 description of lehman et al.12 , 18 , 19 .
the ground 
 electrode was attached to the cervical spine at c7 . before application of the surface 
 electrodes ,
the subjects ' skin was shaved if necessary , and wiped with alcohol to reduce 
 skin impedance20 .
electrodes were positioned above the midpoint of the muscle 
 belly , parallel to the direction of the muscle fibers .
they were further secured to the skin 
 with adhesive tape together with the preamplifier to reduce motion artefacts21 .
standard descriptive statistical methods were used to calculate normalized root mean 
 squares ( rms ) using percentages of muscle activities of mvic , and means and standard 
 deviations ( sd ) of each muscle , during each exercise .
differences among exercises ( kp - c , 
 sp - c , kp - s and sp - s ) and muscles ( upper trapezius , middle trapezius , lower trapezius , 
 serratus anterior and latissimus dorsi ) were analyzed using repeated measures anova .
spss 12.0 for windows was used throughout , and 
 statistical significance was accepted for values of p<0.05 .
 : kp - c and kp - s showed 
 a statistically significant difference .
+ : sp - c and kp - c showed a statistically 
 significant difference .  : sp - s and kp - s showed a statistically significant difference . 

tu , upper trapezius ; tm , middle trapezius ; tl , lower trapezius ; ld , latissimus dorsi ; 
 sa , serratus anterior normalized rms values for each muscle studied during each exercise are presented in table 1 .
the rms value of the trapezius during 
 push - ups was always greater than those of the other muscles tested .
table 1 showed the average muscle activity and 
 standard deviations of the two exercise studied on the two different surface bases .
the 
 upper trapezius activity was increased on the unstable support during the  down position  . 
 when subjects performed the  up position  , the muscle activity of the upper trapezius during 
 sp - s was greater than that measured during sp - c .
each exercise showed statistically 
 significant increases in muscle activity on the unstable swiss ball support compared to the 
 stable support .
when sp - c , kp - c and kp - s were compared , the maximum activity level was 
 recorded in sp - c , followed by kp - s and kp - c , although there were no statistically 
 significant differences in muscle activities .
the upper trapezius and latissimus dorsi 
 showed significant increases in muscle activities during sp - s and sp - c , compared to kp - c and 
 kp - s .
the serratus anterior showed the maximum level of muscle activity in sp - s , followed by 
 kp - s , sp - c and kp - c .
there was a tendency for every muscle activities of the scapular stabilizers to be greater 
 on the unstable support than on the stable support .
the middle trapezius and lower trapezius 
 during performance of the standard push - up plus showed significantly increased activities 
 and the same was true of the lower trapezius during performance of the knee push up plus . in 
 addition , the activities of the upper trapezius , middle trapezius and latissimus dorsi 
 during the  down position 
increased noticeably ( p<0.05 ) the muscle activity of the serratus anterior was greater during the  up position  and the 
 activities of the upper trapezius , middle trapezius and lower trapezius were greater in the 
  down position  than in the  up position  . for the latissimus dorsi ,
however , there was no 
 statistically significant difference between the  up  and  down  positions .
also , the muscle 
 activities on the unstable support were greater in the  down position  than in the  up 
 position  ( p<0.05 ) generally ,
the recorded muscle activities were lower in the knee flexion state , however , 
 higher activity levels were measured in the middle trapezius and latissimus dorsi during 
 knee flexion . a statistically significant difference
was observed in the upper trapezius , 
 lower trapezius , serratus anterior , and latissimus dorsi in the  down position  on the 
 stable support and similarly the upper trapezius and lower trapezius during  down position  
 on the unstable support .
the activity of the  up position  was lower than that in the  down 
 position  , but the difference was not significant .
the push up exercise is important for strengthening muscles around the scapula . a medical 
 ball or
swiss ball has been routinely used in the clinical setting , however , few studies 
 have focused on the scapular stabilizer muscles .
this study showed that performance of the 
 knee push - up plus exercise reduced muscle activities compared to the standard push - up plus . 

however , it was noteworthy that the muscle activities of the middle trapezius and latissimus 
 dorsi were exceptionally high during in the knee push - up plus stage . for developing the strength of the serratus anterior muscle , isometric contraction
, so that the muscle activity of the serratus anterior can 
 be sustained at a high level . holding the pose in the  down position  can strengthen the 
 muscle activity of the upper trapezius , middle trapezius and lower trapezius .
we compared the two types of exercises in terms of muscle activity measured by surface emg . 

the upper trapezius showed greater mean electric activation amplitude during scapular 
 retraction than during scapular protraction , and the serratus anterior showed greater mean 
 electric activation amplitude during scapular protraction than during scapular retraction . 

the rms normalized values of the muscles were greater during exercise on the unstable swiss 
 ball support than on the stable base of support . during scapular retraction ,
the activation 
 amplitude of the upper trapezius was greater than those of the majority of the muscles 
 studied . during the scapular protraction position ,
the activation amplitude of the serratus 
 anterior was greater than those of the other muscles studied . moreover , the anterior action 
 of the serratus anterior has been associated with assisting the centralization of the 
 humeral head in the glenoid fossa22 . the present contribute to the basic data of the levels of muscular activation during 
 exercises that are common in the clinical practice of shoulder and scapula rehabilitation , 
 and clarify the differences in terms of the type of base support used .
further study is 
 required to identify the levels of muscular activation under different conditions utilizing 
 an unstable base support for patients with sick scapular syndrome and scapular dyskinesia . 

the exercises used in the present study promoted varying levels of activity within the 
 studied muscles ; thus , exercises must be chosen according to patients ' individual needs .
for 
 example , a patient with a weak upper trapezius and latissimus dorsi should perform the 
 push - up plus exercise with scapular retraction as this would provide the best effect . in 
 addition , the most effective exercise for the improvement of the serratus anterior would be 
 performance of the push - up plus with a round back .
a limitation of this study is the small number of healthy participants and the lack of a 
 control group .
the exercise was performed two times , and there may be concern about the 
 results ' reproducibility ; however we found the results were consistent with the findings of 
 a pilot study .
surface emg to monitor shoulder muscles is less accurate than invasive needle 
 emg ; however , it does not provoke pain . in summary
, we found greater scapular stabilizer muscle activities on the unstable support 
 than on the stable support , suggesting that push - up plus on the knees , especially on a 
 stable support is recommended as an initial program , when a patient or athlete has not fully 
 recovered after an injury or operation .
the results contribute to the basic data of the levels of muscular activation during 
 exercises that are common in the clinical practice of shoulder and scapula rehabilitation , 
 and clarify differences in terms of the types of base support used .
   [ purpose ] scapular stabilizer strengthening exercise is crucial for shoulder 
 rehabilitation . the purpose of this study was to compare two types of push - up plus 
 exercises , on a stable and unstable bases of support , using surface electromyography 
 ( emg ) , to suggest an effective shoulder rehabilitation program . 
 [ subjects and methods ] ten 
 healthy men volunteered for this study . 
 all volunteers performed two sets of push - up plus 
 exercise ( standard push up and knee push up ) on stable and unstable bases of support . the 
 muscle activities of five important scapular stabilizer muscles ( upper trapezius , middle 
 trapezius , lower trapezius , serratus anterior , latissimus dorsi ) were recorded during the 
 exercise . [ results ] the upper trapezius showed greater mean electric activation amplitude 
 in the scapular retraction posture than in the scapular protraction posture , and the 
 serratus anterior showed greater mean electric activation amplitude in the scapular 
 protraction posture than in the scapular retraction posture . 
 the root - mean - square 
 normalized emg values of the muscles were greater during the exercise performed on the 
 unstable support than those on the stable support . 
 [ conclusion ] the standard push - up plus 
 exercise on an unstable base of support helps to increase muscle activity , especially 
 those of the upper / middle trapezius and serratus anterior . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION