previous studies focused on retraining muscle coordination patterns in which the optimal 
 ratios between the gluteus maximus ( gm ) and the erector spinae ( es ) are assumed to be 
 essential1,2,3 .
bridging exercises are 
 associated with a risk of dominant hamstring ( ham ) and es activities as compensation for gm 
 weakness3 .
various studies have 
 indicated that specific lumbar stabilizing exercises combined with other therapies can 
 prevent unwanted movement error1 , 4 .
the practice of pointing or positioning 
 tasks improves performance of trunk movement in persons with back pathologies2 .
thus , to prevent excessive movement of the lumbar and thoracic 
 spine , therapists often ask patients to stabilize the spine via therapist hands or abdominal 
 drawing - in maneuver ( adim)5 .
no previous 
 studies have used visual biofeedback with a laser pointer on the pelvic belt for lumbar 
 stabilization exercises as therapy for individuals with low back pain . to our knowledge
, 
 this study is the first to evaluate the effect of trajectory exercises using a laser pointer 
 on gm muscle activity during a bridging exercise .
we created an instrument that enabled 
 trajectory exercises with a laser pointer on a pelvic strap to prevent unwanted movement of 
 the lumbar spine .
in addition , this instrument can aid repositioning accuracy of the trunk 
 during selfbridging exercises .
the purpose of this study was to investigate activities of 
 the hip extensors and es during bridging exercises by using a raiser pointer on the pelvic 
 belt .
twelve non - specific subjects with low back pain ( age , 23 to 33  years ) volunteered for this 
 study .
the inclusion criteria were patients with non - specific low back pain for > 3 months 
 and the willingness and ability to participate in the task safely . the study purpose and 
 methods
were explained to all the subjects , who provided their informed consent according to 
 the principles of the declaration of helsinki before participation .
subjects performed the 
 same bridging exercise twice and maintained each position for 5-s under two conditions : 
 using instruments a laser pointer ( lpt ) and without an lpt .
bridging exercise performed 
 without ilp was followed by bridging exercises with lpt to minimize the carry over or 
 learning effect4 .
both knees were flexed at 90 , the feet were placed hip - width apart 
 while resting on the floor , and the toes were faced forward . the arms were crossed over the 
 chest to minimize arm support .
each subject was instructed to lift the pelvis comfortably at a self - selected 
 speed while maintaining the trunk , pelvis , and thigh in a straight line and holding the 
 bridging position for 5 s. bridging with lpt followed the same procedure as bridging without 
 lpt , with the exception of the application of laser pointer trajectory for visual 
 biofeedback .
a white board and laser pointer attached on the pelvic strap were prepared for 
 visual biofeedback .
the white board , which was 50  cm long and 70  cm wide , was attached to 
 both parallel bar .
a vertical line of 30-cm length through the cranial direction was drawn 
 in the center of the board .
further , the start and end markers of the vertical line were 
 displayed in both ends . a plastic cylinder , 7.5  cm long and 2.5  cm in diameter , designed to 
 focus a 0.5  cm diameter laser pointer was attached to a pelvic strap .
kinematic data from 
 the hip and knee joints were acquired using video analysis system control .
a strap with a 
 laser attached for visual biofeedback was worn on each subject s lower back ( positioned 
 above the asis ) .
subjects performed bridging exercises while attempting to control the red 
 ray from the laser - pointer such that it moved along the vertical line ( length 30  cm ) to the 
 cranial direction until the end marker was drawn on the board .
emg data were collected using 
 biopac mp100wsw ( biopac systems , inc , goleta , ca ) . for normalization ,
two surface electrodes with an 
 interelectrode distance of 2  cm were positioned on the gm , medial ham , and es bilaterally . 

trunk muscles ( es , gm , and ham ) activities with and without trajectory exercises using a 
 laser pointer were analyzed using spss statistics ver .
the 
 significance between the two conditions was tested using paired t - tests , with significance 
 at p<0.05 .
compared to the group with the laser pointer , the emg signal amplitude was significantly 
 higher for the gm in the group that performed bridging exercises with visual biofeedback 
 using a laser pointer ( 28.6  18.0% versus 21.3  12.9% ) , and was significantly lower in the 
 es ( 26.8  15.1% versus 43.1  16.8% ) ( p < 0.05 ) .
however , there were no significant 
 differences in the activities of the ham between the groups with ( 53.3  52.3% ) and without 
 ( 41.7  32.3% ) laser pointer use ( p > 0.05 ) . for bridging exercise with visual 
 biofeedback using laser pointer ,
the gm / es ratios were significantly higher in the group 
 with laser pointer use than in the group without ( p<0.05 ) .
this study is the first to evaluate the effect of trajectory exercise using the laser beam 
 on gm activity during bridging exercises .
gm activity increased significantly during 
 bridging with visual biofeedback using the laser pointer , supporting the research 
 hypothesis . on the other hand
a possible explanation is that performing trajectory exercises with the 
 laser beam during bridging exercises can prevent excessive anterior pelvic tilt .
weakness of 
 the gm and dominant activity of the es due to low back pain may contribute to excessive back 
 spine hyperextension during bridging exercises7 .
thus , moving a raiser pointer on the pelvic strap along the 
 quantified cranial direction during bridging exercises could be a good strategy for clbp 
 when anterior pelvic tilt and lumbar lordosis motion are minimized . in terms of muscle 
 ratios ,
gm / es ratios were significantly higher when a laser pointer was used than when one 
 was not used . based on these studies , synergistic trunk extensors such as
the gm and es can 
 affect one another during bridging , increasing gm activity and reducing es activity .
these 
 results also suggest that using a raiser pointer during bridging exercise promotes 
 activation of the hip extensors , while reducing activation of the es .
previous evidence suggests that patients 
 with chronic low back pain exhibit deficits in trunk proprioception and motor control2 , 7 . 
 these deficits can affect and compromise segmental spinal stability and eventually lead to 
 articular damage and subsequent chronic pain2 .
we consider that applying visual biofeedback using a laser pointer 
 during bridging facilitated gm activity in advance before the initiation of the bridging 
 movement , consequently increasing gm activity .
 [ purpose ] the purpose of this study was to investigate activities of the hip extensors 
 and erector spinae during bridging exercise by using instruments with a laser pointer on 
 the pelvic belt . 
 [ subjects ] twelve subjects ( age , 23 to 33  years ) with non - specific low 
 back pain volunteered for this study . [ methods ] subjects performed bridging exercises with 
 and without trajectory exercises by using a laser pointer fixed to a pelvic strap . 
 the 
 erector spinae , gluteus maximus and hamstring activities with and without trajectory 
 exercises using a laser pointer were recorded on using electromyography . 
 [ results ] 
 compared to the without laser pointer group , the group that underwent bridging with 
 trajectory exercises using a laser pointer had significantly higher gluteus maximus 
 activity and significantly lower erector spinae activity . 
 significantly higher gluteus 
 maximus / erector spinae activity ratios were observed when performing trajectory exercises 
 using a laser pointer during bridging exercises . [ conclusion ] 
 this result suggests that 
 trajectory exercises using a laser pointer during a bridging exercise would be effective 
 for improving gluteus maximus activity . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION