the sit - to - stand ( sts ) movement is a movement people frequently perform as they change from 
 a sitting to standing position , and the ability of an individual to rise from a chair has 
 been considered an important indicator of an elderly person s functional independence ; if 
 impaired , it increases the risk of falling1 . among community - dwelling older adults , one in three experience at 
 least one fall each year , with more than 30% requiring medical treatment after falling2 . compared with young adults , healthy people 
 65  years of age or older exhibit moderate to high age - associated reductions in strength and 
 functional limitations for tasks such as the sts task3 .
additionally , particularly in the frontal plane , older adults have 
 greater difficulty maintaining and recovering postural stability caused by weak lower 
 extremity muscles4 .
a previous study 
 examined the functional role of hip adduction ( add ) and abduction ( abd ) during squat 
 exercise .
coqueiro et al.5 reported 
 increased activity of the medial and lateral portions of the quadriceps during squats with 
 isometric hip add .
felcio et al.6 
 reported the squat exercise was associated with hip add producing higher activation of the 
 vastus medialis oblique muscle and an increase in the activity of the gluteus medius muscle . 

hip abd during the squat exercise stimulated activation of the gluteus medius and produced 
 higher activity in the vastus lateralis longus muscle .
pereira et al.7 showed that displacement from 60 to 90 knee flexion 
 increased myoelectric activity during a squat with hip abd .
although the sts movement is 
 necessary for older adults to live independently , no study of the sts task with hip add and 
 abd has been performed . furthermore , in contrast to hip and knee muscle activity , relatively 
 few studies have documented ankle muscle activity , such as the activities of the tibialis 
 anterior ( ta ) and soleus ( sol ) muscles during the sts task . therefore , in the present study 
 we compared the activation of the ankle joint muscles during the sts movement with hip add 
 and hip abd in elderly females .
sixteen healthy elderly subjects ( 67.75  1.61  years of age , range , 6570 years ) 
 participated in this study . the mean height and weight of the subjects were 153.5  6.61  cm 
 and 54.46  7.22  kg , respectively .
subjects were included in the study if they were able to follow directions , 
 had no lower - extremity amputations , and had no restrictions on lower - extremity movement or 
 weight bearing ordered by a physician .
the study participants had no muscular pathology or 
 gait or balance disorders , no chronic deficiencies associated with a neurological , 
 rheumatologic or orthopedic affections ; and no chronic or acute illness leading to an 
 inflammatory syndrome .
this study was approved by the inje university faculty of health 
 science human ethics committee , and all subjects provided written informed consent prior to 
 participating in the study .
the activities of the dominant lower extremity muscles were 
 measured using a wireless electromyography ( emg ) system ( delsys , inc . ,
boston , ma , usa ) with 
 surface electrodes fixed at an interelectrode distance of 10  mm .
emg surface electrodes were 
 placed over muscle bellies of the dominant side tibialis anterior ( ta ) and soleus ( sol ) 
 muscles . for normalization ,
maximal emg signals were acquired during a maximum voluntary 
 isometric contraction ( mvic ) maneuver , which was performed for 5 s. the emg data expressed 
 the entire sts task as a percentage of the mvic . the starting position for the subjects was 
 standardized .
sitting posture and movement pattern during the sts task were explained to the 
 subjects before measurement . in a sitting posture
, the subjects were positioned on an 
 adjustable height chair without armrests or a backrest .
the subjects were barefoot , placed 
 both their legs symmetrically with their feet shoulder - width apart , and stretched their 
 trunk in a straight line .
the seat height for each subject was 100% of the lower leg length 
 ( lll ) measured from the center of the knee joint to the floor with the subject standing 
 barefoot . to minimize any influence of the upper extremities ,
subjects were instructed to 
 cross their arms lightly against their chest to minimize movement during observation . 

 they 
 then performed a total of nine sts trials , including three trials each for hip add , hip abd 
 and natural sts ( n ) tasks , with the ordering of the conditions randomized .
subjects were 
 instructed to face forward and stand up from the seat at their own speed .
the emg data 
 during the sts tasks were collected from frontal and transversal planes with the 
 participants feet apart and hips in a neutral position .
the sts tasks with the mivc of hip 
 add were performed in the same position as for n , a supportive position with the legs bent 
 at the medial femoral epicondyle level .
the sts tasks with hip abd were performed in the 
 same position as for n but with the mivc of hip abd resisted by a nonelastic band , 
 adjustable with velcro , positioned at the lateral femoral epicondyle level . 
 following the sts movement ,
the subjects were instructed to stand still for 5 s. subjects 
 were allowed to practice the sts movement before the actual data collection started . due to 

the sts start and finish times were determined 
 with a marker attached on the right acromion . for the purpose of analysis ,
the sts movement 
 was divided into a pre - thigh - off ( to ) phase and a post - to phase with respect to chair seat 
 support . to assess differences in emg activity in the sts testing ,
standard descriptive statistics were performed , and the data are reported as means 
  standard deviation .
, chicago il , usa ) with the level of statistical significance set at p < 
 0.05 .
in the pre - to phase , the normalized emg data of the ta muscle increased significantly ( p 
 < 0.05 ) when the sts task was performed with hip add ( 17.20  13.21% ) compared with hip 
 abd ( 12.81  9.22% ) , but the normalized emg data of the sol muscle were not significantly 
 different ( p > 0.05 ; add , 10.17  8.06% , abd , 8.98  4.69% ) . in the post - to phase , the 
 normalized emg data of the ta muscle showed a significant increase ( p < 0.05 ) during the 
 sts task with hip add ( 25.27  19.48% ) compared with hip abd ( 20.58  15.53% ) .
additionally , 
 the normalized emg data of the sol muscle increased significantly ( p < 0.05 ) when the sts 
 task was performed with hip add ( 26.55  9.14% ) compared with hip abd ( 23.50  9.11% ) .
in the elderly , a postural control system deficit is caused by greatly decreasing muscle 
 strength and power .
this leads to deterioration of the ability to rise from a chair and can 
 become a critical limiting factor for quality of life3 .
the purpose of this study was to compare the activation of the ta 
 and sol muscles during the sts movement with hip adduction and hip abduction in elderly 
 females . in the pre - to phase
, the normalized emg data of the ta muscle increased 
 significantly when the sts task was performed with hip add compared with hip abd . in the 
 post - to phase , the normalized emg data of the ta muscle showed a significant increase during 
 the sts task with hip add compared with hip abd .
additionally , the normalized emg data of 
 the sol muscle increased significantly when the sts task was performed with hip add compared 
 with hip abd . in the present study , we examined muscle activity during the sts task with hip 
 add and abd movement to create baseline data regarding ankle stability in healthy elderly 
 subjects .
sts motion requires optimal neuromuscular coordination and postural adjustments to 
 control movement changes and to prevent loss of balance8 .
postural adjustments necessary for task modification or in altered 
 environmental conditions must be controlled appropriately to maintain postural balance9 . in the present study ,
the muscle activities 
 of the ta and sol were investigated during sts tasks under hip add and abd conditions .
the 
 emg activities in the ta and sol were greater during the sts task with hip add compared with 
 hip abd movement .
the results showed that in the elderly performing the sts task with hip 
 add , the ta and sol muscles were recruited more to maintain body stability .
moreover , muscle 
 co - contraction has been observed as a task - independent strategy used to stiffen the joint 
 and enhance stability10 .
our results 
 suggest that older adults may employ greater coactivation of the uniarticular ta and sol 
 muscles during the sts movement with hip add in the post - to phase , which may increase ankle 
 stiffness and improve balance .
therefore , the sts movement with hip add poses a greater 
 challenge for balance control , indicating that certain elderly individuals have difficulty 
 in executing an abrupt adjustment in their dynamic postural stability during the sts 
 movement , resulting in an increased risk of falling .
   [ purpose ] the purpose of this study was to compare the activation of the tibialis 
 anterior ( ta ) and soleus ( sol ) muscles during the sit - to - stand ( sts ) task with hip 
 adduction and hip abduction in elderly females . 
 [ subjects ] we recruited 16 healthy elderly 
 females with no pain in the knee joint and no other orthopedic problems of the lower 
 limbs . [ methods ] the activities of the dominant lower extremity muscles were measured 
 using a wireless electromyography ( emg ) system . 
 subjects then performed a total of nine 
 sts trials , including three trials each for hip adduction , hip abduction , and natural sts 
 tasks . 
 [ results ] in the pre- thigh - off ( to ) phase , the normalized emg data of the ta 
 muscle increased significantly when the sts task was performed with hip adduction compared 
 with hip abduction . in the post - to phase , the normalized emg data of the ta muscle showed 
 a significant increase during the sts task with hip adduction compared with hip abduction . 
 
 additionally , the normalized emg data of the sol muscle increased significantly when the 
 sts task was performed with hip adduction compared with hip abduction . 
 [ conclusion ] 
 therefore , the sts movement with hip adduction poses a greater challenge for balance 
 control , indicating that certain elderly individuals would have difficulty in executing an 
 abrupt adjustment in their dynamic postural stability during the sts movement . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION