the pelvic floor muscle ( pfm ) is known to support the pelvic organs and contribute to the 
 locking mechanism of the urethra and anus , adjusting incontinence , and it has recently been 
 found to perform diverse functions , such as stabilization of the lumbopelvic girdle and 
 spine , and postural adjustment . they also support the ventilation and adjustment of 
 incontinence in the urinary bladder1,2,3,4,5 . the 
 pfm supports trunk stabilization by adjusting or responding to abdominal pressure in 
 cooperation with the muscles surrounding the abdominal cavity1 , 2 , 6 . abdominal hollowing training for stabilizing the lumbo - pelvic region , pulls the abdominal 
 wall toward the inside of the lower abdomen , contracting the transversus abdominis ( tra ) , 
 and it provides effective stabilization training7 . neumann and gill6 reported that 
 contraction of the pfm prompted activation of the tra and internal oblique muscle ( io ) , and 
 also raised the abdominal pressure by 6 mmhg . kim ha - ru8 reported that there were significant changes in the thickness of the 
 tra and io during contraction of the pfm , but electromyography showed there was a 
 significant difference only in the io when the was pfm contracted . kim bo - in1 noted that when the vaginal pressure 
 increased , there was a significant difference in the thickness of the tra . critchley9 observed that there was a more 
 significant difference in the thickness of the tra when contraction of the pfm was made 
 together with the abdominal hollowing motion than when only the abdominal hollowing motion 
 was conducted . these study results show that contraction of the pfm promotes activation of 
 the tra , a deep muscle . however , the pfm is not often used in daily life , and therefore 
 performance of appropriate exercises and precise contraction of the muscle is very 
 difficult . as a measure to resolve such problems for women with urinary incontinence and 
 cystocele , biofeedback using ultrasound is being used to visualize the contraction of the 
 pfm , to provide precise and immediate visual feedback to subjects10 . nevertheless , no research has analyzed the effects of 
 precise pfm contraction on abdominal muscles . therefore , the purpose of this study was to 
 verify whether precise contraction of the pfm using visual feedback actually affects the 
 thickness of the abdominal muscles . the subjects were 29 adults in their 20s who consented to participate in this study . they 
 had no history of neurological or muscle lesions within the previous six months . this study 
 was approved by the ethics committee of the catholic university of pusan . first , the thicknesses of the external oblique muscle ( eo ) , io , and tra were measured with 
 the subjects lying in a supine position at rest . after a 10-minute rest , the subjects were 
 instructed to contract the pfm in an ordinary way during the hollowing motion , and then the 
 thicknesses of their abdominal muscles were measured . in order to exclude a carry - over 
 effect , the thicknesses of the abdominal muscles were measured as the subjects contracted 
 the pfm while watching a visual feedback video the next day . the subjects were instructed to tighten the internal muscles of the pelvis , as if to hold 
 in urine , and slowly pull and raise them internally . however , they were not instructed to induce or prevent the 
 utilization of the abdominal muscles6 . to provide subjects with accurate visual feedback , a convex ultrasound probe was 
 positioned , with the angle between the abdomen and the probe at 10 ( esaote europe b.v . , 
 netherland ) , from 5  cm above the symphysis pubis , and visual feedback was given by casting 
 the probe on the perineum . changes in imaging during the contraction of the pfm were 
 explained , and the subjects were taught how to contract the pfm . for the abdominal hollowing motion , a stabilizer ( chattanooga group inc . , usa ) was used in 
 order to minimize the contraction of the io and eo and to trigger selective contraction of 
 the tra . ultrasonic diagnostic equipment ( sonoace x4 , korea ) was used to measure the thickness of 
 the abdominal muscles . the thicknesses of the external oblique abdominal , the internal 
 oblique abdominal , and the transversus abdominis muscles were measured at the end point of 
 expiration3 . they were measured in an 
 anteromedial direction using a linear probe ( 7.5  mhz ) at the middle , between the iliac crest 
 and the eleventh rib on the right side of the subjects12 , 13 . one - way analysis of 
 variance was employed in order to compare the thicknesses of the abdominal muscles under the 
 three different conditions . general characteristics of subjects ( n=29)mean  sdgender ( m / f)29 ( 13/16)age ( yrs)23.22.7heights ( cm)167.27.6weights ( kg)61.011.3 . there were no statistically significant differences in the eo and io between the 
 measurements taken at rest and during the contraction of the pfm , and between those taken at 
 rest and during the contraction of the pfm with visual feedback ( table 2table 2 . comparison of abdominal muscle thicknesses under the different conditions 
 ( n=29)musclerestpfmc + ahfeedback pfmc + ahexternal oblique0.680.200.650.160.620.11internal oblique0.530.150.630.090.580.25transverse abdominis*0.310.090.510.150.480.21pfmc : pelvic floor muscle contraction , ah : abdominal hollowing . : rest 
 vs. pfmc , : pfmc vs. feedback pfmc , : feedback pfmc vs. 
 rest ) . rest 
 vs. pfmc , : pfmc vs. feedback pfmc , : feedback pfmc vs. 
 rest according to the post hoc test result , there were significant differences in the tra 
 between the measurements taken at rest and during the contraction of the pfm , and between 
 those taken at rest and during the contraction of the pfm with visual feedback . in 
 particular , the thickness of the tra was highest during the contraction of the pfm without 
 visual feedback ( table 2 ) . according to the results of the present study , there were no significant differences in the 
 thicknesses of the eo and io during contraction of the pfm between rest and with and without 
 visual feedback when the subjects conducted the abdominal hollowing motion . the tra thickness increased 
 more during the contraction of the pfm without visual feedback than during the precise 
 contraction of the pfm with visual feedback . in a study where subjects were instructed to contract the pfm lightly , at a moderate 
 intensity , and at a strong intensity , reported that the thickness of the tra and io 
 increased as the contraction intensity increased , but that there was no change in the 
 thickness of the eo14 . this result is 
 similar to the results of our present study , in that the contraction rate of the tra was 
 higher during the contraction of the pfm without visual feedback . critchley2 compared subjects that conducted abdominal 
 hollowing only and those that contracted the pfm in a crawling position , and reported that 
 the thicknesses of the eo and io decreased , but that the thickness of the tra increased 
 during abdominal hollowing compared to the at - rest measurements . this result is similar to 
 that of the present study , in that the thickness of the tra showed a statistically 
 significant increase under both contraction conditions . however , critchely2 noted that because precise contraction of 
 the pfm was difficult when subjects conducted the hollowing motion and contracted the pfm at 
 the same time , there was a possibility that movement of the pfm did not occur or that 
 subjects concentrated more on the contraction of the deep abdominal muscles drawing in the 
 lower abdomen than on the contraction of the pfm . this could explain our result , that the 
 thickness of the tra increased less during the precise contraction of the pfm with visual 
 feedback than during the contraction of the pfm without visual feedback . due to the pfm s anatomical location and structure , it is hard to voluntarily conduct 
 precise contraction of the pfm . this may result in the iliacus muscle , the abductor muscle 
 inside the hip joint , and the abdominal muscles , in particular the tra and the io , 
 contracting together , rather than a contraction of the pfm9 , 15 . therefore , we presume 
 that when subjects conduct the hollowing motion without precisely performing the contraction 
 of the pfm , they concentrate on the contraction of the deep abdominal muscles , such as the 
 tra , which affects the thickness of the tra . this study verified that there is an increase in the thickness of the tra during pfm 
 contraction , but that the increase in the thickness of the tra was smaller during the 
 contraction of the pfm with visual feedback . we speculate that this is likely because the 
 precise contraction of the pfm decreases mobilization of the deep muscles reducing the 
 simultaneous contraction rate of the tra . training to strengthen the pfm may be an effective exercise for improving continence . 
 however , if the purpose is to strengthen the tra simply for the stabilization of the 
 lumbopelvic girdle , hollowing with visual feedback is not an efficient exercise method for 
 the pfm .
[ purpose ] the purpose of this study is to verify whether precise contraction of the pelvic 
 floor muscle ( pfm ) using visual feedback actually affects the thickness of abdominal 
 muscles . 
 [ subjects ] the subjects were 29 healthy adults in their 20s who consented to 
 participate in this study . [ methods ] this study provided visual feedback on pfm using one 
 ultrasound device and identified changes in the transversus abdominis ( tra ) using another 
 ultrasound device . 
 abdominal muscle thicknesses were measured by ultrasound under three 
 conditions ( rest , pfm contraction , pfm contraction with visual feedback ) . [ results ] 
 there 
 were no statistically significant differences in the external oblique ( eo ) and internal 
 oblique ( io ) muscles between the measurements taken at rest and during the contraction of 
 the pfm , and between those taken at rest and during the contraction of the pfm with visual 
 feedback . 
 there were significant differences in the tra . 
 in particular , tra thickness was 
 highest in the order of pfm contraction , pfm contraction with visual feedback , and rest . 
 [ conclusion ] hollowing with visual feedback is not an efficient stabilization exercise 
 method for the pfm .