regaining balance ability is a fundamental component of the clinician s goals for patients 
 with a variety of disorders1 , 2 . although controlling distal segments such as the ankle , 
 knee , and hip is known to be a major component of balance ability , co - contraction of the 
 abdominal and paraspinal muscles also contributes to maintaining the center of mass within 
 the base of support1,2,3,4 . therefore , facilitating trunk musculature is one of the exercise 
 assessments for enhancing balance ability3 , 4 . previous findings have suggested that impairments in postural control during walking are a 
 major risk factors for falling5 , 6 . kim et al . also suggested that spine stabilization exercise 
 protocols could be helpful for improving overall postural stability in a standing 
 posture6 . although various trunk 
 stabilization exercises have been suggested in the clinical literature and studies , however , 
 there still remains a question regarding which exercise form is effective for enhancing 
 balance ability through trunk exercises7 , 8 . proprioceptive neuromuscular facilitation ( pnf ) interventions classically suggest two 
 stabilizing exercise techniques , which are referred to as stabilizing reversal ( sr ) and 
 rhythmic stabilization ( rs)9 . sr is 
 characterized by alternating isotonic contractions opposed by resistance to prevent motion , 
 which allowing small movements . rs is characterized by isometric contractions against the 
 resistance provided by the therapist , with the subject trying to maintain their position as 
 the therapist changes the direction of resistance9 . the primary purpose of the present study was to investigate whether the sr and rs 
 techniques are effective for enhancing balance ability . the secondary purpose was to 
 determine which exercise is effective for improving trunk stability . thirty - four asymptomatic subjects were recruited from a local university . they were 20 to 
 26 ( 21.9  2.8 ) years old , their mean height and weight were 174.9  5.6 and 66.5  5.3  kg 
 respectively . participants were excluded if they had any history of musculoskeletal problems 
 within the last 6 months . this study was approved by the choonhae university faculty of health sciences human 
 ethics committee . the center of pressure ( cop ) data for under the feet were collected by 
 using a pedoscan ( international gmbh , schlangenbad , germany ) . for the pre - exercise balance 
 test , each subject stood on the pedoscan plate under the following conditions : double - leg 
 stance with the eyes open ( dls - o ) , double - leg stance with the eyes closed ( dls - c ) , one - leg 
 stance with the eyes open ( sls - o ) , and one - leg stance with the eyes closed ( sls - c ) . measurement was performed under each balance test condition during an 11  s period , and the 
 data for the first and last three second seconds of the period were eliminated . the primary 
 researcher performed stabilizing reversal and rhythmic stabilization for each subject to 
 facilitate trunk musculature in a randomized order . the period was 3  min for each exercise , 
 and the period between exercise conditions was one day . immediately after the sr and rs 
 exercise , the cop was measured again under the during four balance test conditions using the 
 pedoscan . significance was accepted for values of p<0.05 , and pasw statistics 
 18.0 was used for statistical analyses . descriptive statics of the balance test and total cop movement are represented in table 1table 1.the average and standard deviation ( sd ) of total anterior - posterior center of 
 pressure ( a - p cop ) movement values before and after stabilizing reversal ( sr ) , and 
 post rhythmic stabilization exercisestrialtotal a - p cop movement ( mean  sd , mm)dls with eyes opendls with eyes closedsls with eyes opensls with eyes closedbefore exercise ( mm)43.4  17.253.9  22.692.8  49.6158.9  58.7*after sr ( mm)44.5  13.757.0  31.981.4  27.9132.6  48.9*after rs ( mm)38.2  9.645.4  17.876.9  29.8149.7  53.1*dls : double - leg stance , sls : one - leg stance . * significant difference between 
 conditions .. there were significant difference in movement of cop when compared according 
 to both exercise and balance test conditions ( p<0.05 ) . subsequent post hoc testing 
 revealed that rs significantly reduced total cop movement compared with the pre - exercise 
 values ( p<0.05 ) . in factor of the balance test , the total cop displacements were 
 gradually altered in serial conditions of double leg stance with eyes - open , double - leg 
 stance of eyes - closed , one - leg stance with eyes - open , one - leg stance with eyes - closed 
 ( p>0.05 ) . evaluation of balance ability in a standing posture is clinically well evidenced , and this 
 includes evaluation under one - leg and double - leg stance and presence of vision1 , 6 , 8 . our data suggested that the double - leg 
 stance with eyes open and double - leg stance with eyes closed , one - leg stance with eyes open 
 and one - leg stance with eyes closed were well differentiated between conditions according to 
 difficulty of conditions . mitchell et al . reported that the presence of vision critically 
 affects standing balance10 , but the 
 present results indicated that a narrow base of support has a major effect on the balance 
 ability of young subjects . rs significantly reduced anterior - posterior cop displacement , compared with the values 
 after sr and those before exercise . some previous studies have reported that rs increased 
 co - contraction , which is necessary for enhancing upright trunk posture11 . theoretically , balance is defined as the ability to 
 maintain the center of mass ( com ) within the base of support12 . furthermore , the com is positioned approximately anterior to the 
 sacrum in a standing position12 . 
 therefore , co - contraction of the trunk muscle could reduce com displacement through the rs 
 technique . although the results of the present study showed significant decreases in cop displacement 
 with the rs technique , the present study could not affirm that sr is less useful than rs . in 
 elderly subjects or patients with insufficient muscle strength , sr , which induces the 
 present study suggests that standing balance could be improved with the rhythmic 
 stabilization technique in asymptomatic subjects . and balance tests with variations of 
 vision and support surface could be well differentiated and could be applied for stepwise 
 assessment .