according to the biomechanical etiologic model of chronic low back pain ( clbp ) , the 
 suffering of patients with back pain may be due to aberrant patterns of paraspinal muscle 
 activity during movement1,2,3 , these aberrant 
 muscle patterns are caused by dysfunction in the spinal biomechanical system and may 
 compensate for a loss of spinal stability2 .
thus , analyzing abnormal trunk 
 and pelvic movement patterns in various environments and during various tasks , would help 
 improve the treatment and rehabilitation of lbp4 .
anterior load carriage tasks are mainly used to transfer loads in some industries , such as 
 agriculture and construction5 , 6 .
they result in increased muscular activity of the anterior 
 deltoid as well as thoracic and lumbar erector spinae muscles .
increased muscle contraction 
 intensity can increase the degree of muscle - generated spinal compression and abnormal 
 movement patterns , which are reported to be factors for the development of lbp7 .
transverse trunk and pelvic coordination is important during gait - including anterior load 
 carriage tasks5 .
studies of horse gait 
 show that as walking speed increases , the characteristics of quadruped locomotion change 
 with different coordination patterns ( e.g. , walk , trot , canter , gallop .
therefore , in order 
 to adapt to environmental changes , each segment finds a form of efficient coordination8 .
healthy subjects use transverse pelvic 
 rotation during unloaded gait in order to increase stride length at an increased walking 
 speed9 .
anti - phase coordination , in 
 which the trunk and pelvic segments simultaneously move in opposite directions , in 
 transverse plane is increased to decrease total body angular momentum and improve movement 
 efficiency10 .
however , while running 
 during unloaded gait , patients with clbp exhibit more in - phase coordination , in which the 
 trunk and pelvic segments simultaneously move in the same direction than healthy individuals 
 because of their difficulty moving toward anti - phase coordination at an increased walking 
 speed11 .
when carrying a backpack weighing ( 40% of body weight ) , healthy subjects decrease their 
 transverse pelvic rotation and in - phase coordination of the trunk and pelvis in the 
 transverse plane in order to maintain gait speed as their walking speed increases . in order 
 to compensate for decreased transverse pelvic rotation ,
healthy subjects increase hip 
 excursion , decrease stride length , and increase stride frequency12 .
trunk - pelvis coordination during back - pack and anterior load carriage tasks has been 
 evaluated in healthy subjects . however , no studies have investigated patients with clbp . as 
 walking speed increases
, the segments of the trunk and pelvis can be differentially 
 coordinated in order to achieve overall stability13 .
in other words , individuals with clbp who have reduced stability 
 during an anterior carriage task involving walking are likely to exhibit the opposite 
 changes in the characteristics of trunk - pelvis coordination in the transverse plane compared 
 to healthy individuals11 .
therefore , the 
 present study compared trunk - pelvis coordination with respect to walking speed during an 
 anterior load carriage task in subjects with and without clbp .
we hypothesized that patients 
 with clbp would exhibit more anti - phase coordination during changes of walking speed during 
 the anterior load carriage task than healthy individual .
twenty participants who expressed interest in the study and met the inclusion criteria 
 received information regarding the purpose and methods of this study ; all participants 
 signed a copy of the consent form approved by industry - academic cooperation foundation , 
 hanseo university in accordance with the ethical standards of the declaration of 
 helsinki .
the clbp group contained subjects who had experienced impairments or abnormalities in low 
 back function for more than two months .
lbp was defined as pain under the scapulae and above 
 the cleft of the buttocks .
the inclusion criteria were age 20  years , history of lbp for 
 more than two months without pain referral into the lower extremities .
subjects were excluded if they had been diagnosed with a psychological illness that might 
 interfere with the study protocol , had neurological signs ( i.e. , sensory deficits or motor 
 paralysis ) , or were pregnant .
the 
 control group include age - and sex - matched volunteers to minimize confounding effects during 
 the study period and increase the internal validity of the data14 .
kinematic data in the transverse plane were collected using the vicon motion system ( vicon 
 motion systems , oxford metrics ltd . ,
oxford , uk ) with six infrared cameras ( vicon mx - f20 , 
 oxford metrics ltd . ) at a sampling frequency of 150  hz .
the woltering filter method was 
 used , and the mean squared error was set to 15 .
the centers of rotation of the body were 
 measured in order to obtain height as well as shoulder , elbow , wrist , knee , ankle and leg 
 widths and lengths .
spherical reflective markers ( 14 mm ) from the plug - in gait marker set 
 were used for three - dimensional data collection .
the positions of the markers were c7 , t10 , 
 the right - upper back ( i.e. , mid - scapular spine ) , between the clavicles , the xiphoid process 
 of the trunk , the bilateral anterior and posterior superior iliac spines , thigh , knee joint , 
 tibia , ankle joint , heel , and toe .
the trunk segment was defined according to calibration markers 
 placed on c7 , t10 , the right - upper back , between the clavicles , and the xiphoid process . 

meanwhile , the pelvic segment was defined according to calibration markers placed on the 
 bilateral anterior superior and posterior superior iliac spines .
the participants completed a 10-minute warm - up period by waking repeatedly on a 10  m line . 

they were asked to carry a load anteriorly that was equivalent to 10% of their body weight . 

they subsequently began walking at 3.5 , 4.5 , or 5.5  km / h selected at random .
the tasks were 
 always performed between 10 a.m. and 5 p.m. to account for the diurnal variation in spinal 
 disc fluid content and its effect on the lumbar spine15 . the continuous relative phase ( crp ) during the third right stride ( i.e. , heel strike to 
 heel strike ) of five strides was calculated .
the profile was calculated as the ensemble mean 
 of the relative phase ( rp ) of the control and clbp groups as follows : rp(t)= 
 t(t )  p(t ) , where t(t ) is the phase 
 angle of the trunk , and p(t ) is the phase angle of the pelvis at time t. 
 the rp between the trunk and pelvis was calculated on the basis of the angular 
 displacements16 , 17 .
mean crp was used to calculate the cross - correlation 
 coefficients of crp patterns18 .
the baseline characteristics of the two groups are shown in table 1table 1.subject characteristicscontrol groupclbp groupn ( male / female)10 ( 5/5)10 ( 5/5)age ( years)21.51.821.41.5height ( cm)167.46.2169.95.6mass ( kg)65.77.466.38.3pain scores ( vas)04.50.8disability scores ( odi , % ) 015.52.8clbp : chronic low back pain ; vas : visual analog scale ; odi : oswestry disability 
 index . the crp is presented in fig . 1fig .
1.continuous relative phase during the anterior load carriage task at 3.3  km / h ( a ) , 
 4.4  km / h ( b ) , and 5.5  km / h ( c ) .
the crp differed significantly between groups at all three walking speeds 
 ( p<0.05 ) .
the mean cross - correlation coefficients of the crp between groups 3.5 , 4.5 and 
 5.5  km / h were 0.97 , 0.96 and 0.72 , respectively ( table 
 2table 2.mean cross - correlation coefficients of the continuous relative phase between 
 groupsinter - group coordination3.5  km / h4.5  km / h5.5  km / hcontrol vs. clbp0.970.960.72clbp : chronic low back pain ) .
clbp : chronic low back pain ; vas : visual analog scale ; odi : oswestry disability 
 index continuous relative phase during the anterior load carriage task at 3.3  km / h ( a ) , 
 4.4  km / h ( b ) , and 5.5  km / h ( c ) .
clbp : chronic low back pain ; 
 * p<0.05 clbp : chronic low back pain
this study compared the coordination pattern of the pelvis and trunk in healthy people and 
 patients with clbp carrying an anterior load at various walking speeds .
we hypothesized that 
 patients with clbp would exhibit more anti - phase coordination with walking speed changes 
 during the anterior load carriage task ; our findings support this hypothesis . in humans , increasing walking speed during unloaded walking necessitates achieving proper 
 stability , which also changes from more in - phase to more anti - phase trunk and pelvic 
 transverse rotation9 .
the transition of runners with lbp 
 from walking to running without a load involves more in - phase trunk and pelvic transverse 
 rotation than healthy controls11 .
studies using back - pack conditions demonstrate another transition from more anti - phase to 
 more in - phase trunk and pelvic transverse rotation12 .
gait studies report that patients with lbp have decreased walking speed , step length , swing 
 time , and maximal endurance .
moreover , the transitions of trunk - pelvic transverse rotation 
 are more in - phase as walking speed increases without a load19 .
ipsilateral arm and leg reciprocal swings in unloaded conditions may assist 
 counterbalancing the angular momentum of the lower body20 .
however , unlike backpack 
 conditions , an anterior carriage task does not involve arm swinging but instead only uses 
 the lower body and an upright posture .
this suggests the existence of some level of 
 counterbalancing between the upper and lower body during anterior carriage tasks . 
 accordingly , walking faster than 3.5  km / h during an anterior carriage task may result in a 
 need for counter - rotation between the pelvis and trunk to achieve optimal stability .
the present results indicate the locomotive problems of the clbp group predominantly 
 involve the coordination of pelvic and trunk transverse rotation .
the clbp group showed a 
 lower crp throughout the gait cycle at 3.5 and 4.5  km / h , and from 090% of the gait cycle at 
 5.5  km / h .
this indicates that patients with clbp move the trunk and pelvis as one unit and 
 in - phase , suggesting they can not control the pelvis to maintain a consistent walking speed 
 during an anterior carriage task .
the mean cross - correlation coefficients for crp between groups were close to 1.0 at 3.5 and 
 4.5  km / h but closer to 1.0 at 5.5  km / h , indicating a different coordination pattern at 
 higher walking speeds ; this may be a method for reducing energy consumption at higher 
 walking speeds18 .
the main limitation of this study is the small number of participants , making it difficult 
 to generalize the results .
moreover , clbp was a certain level , and its effects on muscles 
 and in other planes were not analyzed at different walking speeds .
therefore , further 
 research is required to clarify the three - dimensional motions of the pelvis and trunk , and 
 gait parameters as well as focus on the changes in kinematic parameters and muscle activity 
 patterns associated with the changes in trunk and pelvis coordination . in conclusion , patients with clbp use different coordination patterns of trunk and pelvic 
 transverse rotation during an anterior carriage task .
 [ purpose ] this study compared the coordination patterns of the trunk and pelvis in the 
 transverse plane between healthy subjects and patients with chronic low back pain during 
 an anterior load carriage task at various walking speeds . 
 [ subjects ] ten healthy subjects 
 and 10 patients with chronic low back pain performed an anterior carriage task with a load 
 of 10% body weight at walking speeds of 3.5 , 4.5 , or 5.5  km / h . [ methods ] the trunk and 
 pelvic kinematics were measured by using a motion analysis system . during the anterior 
 carriage task , 
 the continuous relative phase differed significantly between groups with 
 respect to walking speed . 
 [ results ] the continuous relative phase was more anti - phase in 
 the chronic low back pain group than the control group . 
 the inter - group continuous 
 relative phase pattern was affected by walking at 5.5  km / h . 
 [ conclusion ] compared to 
 controls , subjects with chronic low back pain are unable to establish an in - phase between 
 the trunk and pelvis from walking at 3.5 to 5.5  km / h during an anterior carriage task . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION