co - activation of 
 these muscles is necessary in programs aimed at treating and preventing lumbar pain1,2,3 . to stabilize the spine ,
harmonious 
 coordination of all of the trunk muscles is crucial , rather than activation of a particular 
 muscle3 . adjusting the co - ordination of 
 global and local muscles
the global muscles largely 
 generate strength and are involved in overall stabilization of the trunk , and the local 
 muscles are involved in segmental trunk stabilization5 .
the stabilization of the trunk is necessary for the stability of 
 the spine and the pelvis when they are in a functional position , to increase stability 
 during movement , to enhance muscle strength , and to adjust muscle movements and balance6 .
the principal trunk stabilization exercises are pelvic tilt exercises , quadruped exercises , 
 abdominal hollowing exercises , and bridging exercises7 . among these
, the aim of bridging exercises is to make lumbar pain 
 patients feel more comfortable by reducing their pain and retraining their global and local 
 muscles to ensure they are coordinated in an appropriate manner4 .
berkefors et al.8 reported that the use of a deep abdominal muscle training method 
 enhanced the activity of the deep muscles .
akuthota and nadler9 stressed the importance of core strengthening of the lumbar area in 
 different positions .
exercise on an unstable surface increases the co - contraction of the 
 muscles and the stability of the trunk10 , 
 and prompts postural adjustment and balance more than exercise on a stable surface11 .
in addition to methods which gradually 
 increase the intensity of trunk stabilization exercises , there are methods which increase 
 the intensity of the resistance and the intensity of the exercise .
such methods heighten the 
 degree of instability on a support surface using a treatment ball , a vestibular balance 
 plate , or a form roller12 .
bridging exercise is a method which is often used clinically , and much research has been 
 conducted using diverse methods and modifications .
recently , attention has focused on 
 changes in the activities of the trunk muscles during bridging exercises , and many studies 
 have attempted to identify an efficient method of enhancing the activities of the trunk 
 muscles .
the conventional bridging exercise is conducted in a supine position , and most are 
 other exercises are modifications of this exercise . to the best of our knowledge ,
very 
 little research of prone bridging exercises has taken place . accordingly , this study 
 investigated the effect of different types of bridging exercise ( in prone and supine 
 positions ) on the activities of the trunk muscles .
twenty - four subjects participated in this study ( males : 13 , females : 11 ) , and their average 
 age , height , and weight were 21.38  1.64  years , 167.71  7.55  cm , and 60.04  9.22  kg , 
 respectively .
none of the subjects had complained of pain in the musculoskeletal region during 
 the previous six months , and none had orthopedic or neurological disease .
prior to 
 participation , all participants were required to read and sign an informed consent form , in 
 accordance with the ethical standards of the declaration of helsinki .
exercise 1 ( supine bridging ) : in the starting position of the bridging exercise in the 
 supine position , the subjects bent their knee joints at 90 degrees and spread both arms at 
 about 30 degrees , with both hands on the ground .
they kept their head and neck in a straight 
 position , with their eyes looking at the ceiling ( fig . 

supine bridging exercise exercise 2 ( supine bridging on balance pads ) : the subjects adopted the same position as 
 that of exercise 1 , but they placed their feet on togu balance pads ( fig .
supine bridging exercise on togu exercise 3 ( unilateral bridging ) : again , adopting the same position as that of exercise 1 , 
 the subjects raised their dominant - side leg ( fig . 

unilateral bridging exercise ) .   unilateral bridging exercise exercise 4 ( prone bridging on the elbows and toes ) : in a prone position , the subjects bent 
 their elbows at 90 degrees and supported their bodies with their forearms and toes , with 
 their neck slightly extended and their eyes looking to the front ( fig .
prone bridging exercise on the elbows and toes to reduce errors while performing the different exercises , the subjects adopted a neutral 
 position , with the pelvis raised .
the researcher stood at the side to ensure that the 
 subjects adopted the correct position .
prior to the exercises , the subjects were also 
 advised how to conduct the exercises .
a dynamic air cushion ( togu , germany ) was used for the 
 unstable support surface .
the subjects performed the exercises in a random manner by 
 selecting a closed envelope containing the name of the exercise to be performed .
the 
 subjects started each exercise on the command of  start  and took a rest of 5 minutes after 
 each exercise to prevent muscle fatigue .
a surface electromyography system ( telemyo 2400t - g2 , noraxon , usa ) was used to measure the 
 activities of the trunk muscles . to reduce the skin s resistance prior to the application of 
 ag / ag - cl ( biopac , diameter 2  cm ) electrodes to the subjects bodies ,
their skin was shaved 
 to remove hair from the area where the electrodes would be attached .
the surface of their 
 skin was then cleaned with absorbent cotton , which was sterilized by soaking in alcohol , 
 before the electrodes were attached along the direction of the muscle fibers .
the ground 
 electrode was placed on the anterior superior iliac spine ( asis ) of the dominant side . to measure the muscle activities of the subjects in the different exercise positions ,
the 
 electrodes were attached to four muscles : 3  cm lateral to the umbilicus for the rectus 
 abdominis ( ra ) ; midway between the anterior iliac spine and symphysis pubis and above the 
 inguinal ligament for the internal oblique muscle ( io ) ; 15  cm lateral to the umbilicus for 
 the external oblique muscle ( eo ) ; and 2  cm lateral to the l2 spinous process for the erector 
 spinae ( es)13 .
the surface electromyography signals 
 were digitized and processed using the mr - xp program on a personal computer .
signals were band - pass filtered 
 between 20 and 500  hz , and full - wave rectified .
the root mean square ( rms ) of the values was 
 calculated . to standardize
the action potential of each muscle , the maximal voluntary isometric 
 contraction ( mvic ) was used .
each position was held for 7 
 seconds to reduce measurement variation at the start and end points of the exercise .
the 
 activity of the muscles was measured for 5 seconds , excluding the first and last second .
the 
 collected data were statistically processed using spss 18 pasw statistics , and the averages 
 and standard deviation of the general characteristics of the subjects were calculated . 

repeated one - way analysis of variance was used to determine changes in the activities of the 
 muscles in the different types of exercises . within - individual analysis and within - subject 
 contrast
were used to detect changes in the activity of the muscles in the various types of 
 exercises .
there were significant differences in % mvics of the io , eo , ra , and es ( p<0.05 ) among 
 the exercises , and the patterns of increase of muscle activities of the muscles , except es , 
 were consistent across the exercises .
the activities of io , eo and ra were the highest in 
 exercise 4 , followed by exercise 3 and exercise 2 .
the activities of io , eo , and ra were the 
 lowest in exercise 1 .
different from other muscles , the activity of es was the highest in 
 exercise 3 followed by exercise 2 and 1 .
the activity of es was the lowest in exercise 4 
 ( table 1table 1 . comparison of the activities of the muscles in different types of bridge 
 exercises ( unit : % mvic)ioeoraesexercise 17.886.01 * 8.277.04 * 4.092.46 * 48.0543.97*exercise 29.267.01 * 9.987.87 * 4.723.01 * 54.6246.80exercise 317.3715.18 * 23.4918.77 * 9.468.04 * 64.5876.73exercise 457.5435.77 * 37.3830.95 * 46.9830.10 * 9.529.13**p<0.05 , io : internal oblique , eo : external oblique , ra : rectus abdominis , es : 
 erector spinae ) . * p<0.05 , io : internal oblique , eo : external oblique , ra : rectus abdominis , es : 
 erector spinae
recent research has focused on the evaluation of the activities of the trunk muscles in 
 bridging exercises .
this study was conducted to determine more efficient methods for 
 increasing the activities of the trunk muscles in different types of exercises .
the results 
 reveal there were significant differences among the four exercise methods in the activities 
 of the io , eo , ra , and es muscles . in exercise 4 , the activities of the ra , eo , and the io 
 muscles were higher than in exercises 1 , 2 , and 3 . overall , the activity of the es was high 
 in exercises 1 , 2 , and 3 , and the activity of the es was the lowest in exercise 4 .
the 
 appropriate activation of local muscles and interactions between local muscles and global 
 muscles are necessary to ensure functional stability15 .
it has also been reported that bridging exercises with the feet on 
 an unstable surface , like a swiss ball , induce higher muscle activities than the same 
 exercises with the feet on a stable surface .
accordingly , bridging exercises with the feet 
 on unstable surface are effective at increasing dynamic balance , especially for the 
 prevention of spinal damage2 .
kavcic et 
 al.16 reported that bridging exercise 
 with the right leg lifted was very closely associated with the activity of the ra in the 
 side bridging exercise when healthy adults performed lumbar stabilization exercise .
the 
 detection of high io , eo , and ra activity in the present study suggests that exercise 4 
 mobilizes more muscle fibers in the trunk than the other exercises .
our results also show 
 that the trunk muscle activity in exercise 4 was the highest followed by exercise 3 , then 
 exercise 2 , while the trunk muscle activity in exercise 1 was the lowest .
exercise 4 is similar to a push - up exercise , but the subjects elbows are used for support 
 rather than their hands .
the push - up 
 motion is a closed - chain exercise , and it has been employed to enhance the balance of the 
 proprioceptors and to increase the activity of the shoulder muscles17 .
it is connected to the serratus anterior muscle through the fascia , and the connection 
 ring causes the eo to contract during push - up motions .
maenhout et al.19 also reported that the connection of the muscles to the 
 fascia affects the activities of the io and the eo , thereby increasing the mobilization of 
 the muscle fibers .
ludewig et al.20 observed that the load 
 on a subject s upper arms may be reduced when the elbows support the subject s weight .
thus , 
 the exercise position may be maintained for a longer time , and it is easier for patients to 
 perform the exercise in rehabilitation .
the results of the present study suggest that the position adopted in exercise 4 is useful 
 for lowering the activity of the es and increasing the activity of the io , eo , and ra . as 
 bridging exercise in a prone position reduces the base of support
, the subject s elbows and 
 feet support the weight in the distal part .
therefore , in the process of overcoming 
 instability , the activities of the muscles increase in response to biophysical demands .
the subjects were healthy young adults in their 20s , 
 making it difficult to generalize the results to the general population . for clinical 
 applications , research with patients who have symptoms and pain is necessary .
   [ purpose ] the purpose of this study was to examine the effects of different types of 
 bridging exercises on the activities of the trunk muscles . 
 [ methods ] twenty - four students 
 participated in this experiment . 
 the activities of the internal oblique ( io ) , external 
 oblique ( eo ) , rectus abdominis ( ra ) , and erector spinae ( es ) muscles were measured in four 
 different bridging exercises . 
 [ results ] there were significant differences in the io , eo , 
 ra , and es among the four kinds of bridging exercise . 
 the activities of io , eo and ra were 
 the highest in prone bridging ( exercise 4 ) , followed by unilateral bridging ( exercise 3 ) , 
 and supine bridging on balance pads ( exercise 2 ) . in conventional bridging 
 ( exercise 1 ) , 
 the activities of io , eo , and ra were the lowest . 
 the activity of es was the highest in 
 exercise 3 followed by exercises 2 and 1 . 
 the activity of es was the lowest than in 
 exercise 1 . 
 [ conclusions ] bridging exercise in the prone position may be a more effective 
 method of enhancing trunk muscle activities exercises in other positions . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION