NORMATIVE VALUES OF STAR EXCURSION BALANCE TEST IN YOUNG ADULTS: A CROSS SECTIONAL STUDY.

Background: Star Excursion Balance Test (SEBT) is a simple, reliable, cost effective screening test which is used to evaluate the dynamic balance of lower limbs in 8 selective directions to determine potential risk of injury. Reach distance values of SEBT can be used as an index of dynamic postural control. However, despite its global use, there are currently no normative values available for the SEBT in healthy young adults. In this test volunteer has to maintain balance on one lower extremity and performed 3 trials of the SEBT in each of the 8 directions while balancing with other lower extremity. Materials & Methods: Normative values of star excursion balance test were measured on 240 young adults (114 males and 114 females) from 18 -30 years with different height and BMI. Results: Total 228 number of volunteers (114 male and 114 female) with mean age of male 21.45 ±2.37 and mean age of female 21.19 ± 2.02 were selected for the study and according to height and BMI normative values were recorded in both gender. Conclusion: The normative values of star excursion balance test can be used by physical therapists, coaches and athletic trainers in order to interpret and compare with the normal values which will help to find out the risk of injury. Individual data generated from this test which will help to find out the risk of injury. The possible explanation for reduced excursion reach distance in posterolateral, lateral and posterior direction could be that the subjects got reduced visual feedback in these direction particularly in posterior and posterolateraldirection thus increasing demand on somatosensory system and joints .This findings are supported by Coughlan et al (2012) who found that in SEBT and Y-balance test the reach distance in posterolateral directions is decreased because in the posterolateral directions, visual awareness is reduced, thus it places an increased demand on the somatosensory system and therefore, the inability of the participants to see their scores may limit their reach. In the anterior reach direction, participants received visual feedback from the reach leg as they move and can observe the scored reach distance on each trial, so the excursion distance in this direction are more. 14 This study revealed that SEBT excursion reach increases with increase in height. Excursion reach scores of individuals with 131-140 centimetre height is lower as compared to excursion reach scores of individuals with 171-180 centimetre in both right and left lower extremity. The possible cause may be due to the co-relation between height and leg length which was supported by the study done by Gribble et al (2003) who found that there is a significant co-relation between height, leg length & excursion distance. Height and leg length were found to be strongly correlated with each other as increase in height leads to increase in leg length 15 . The present study showed that SEBT excursion reach is more in volunteers with underweight and normal population and reduced in obese. In obese individuals more torque falls on lower extremity as a result of which excursion reach may reduce and in individual with normal BMI loading decreases significantly which increases the excursion reach. This finding is in accordance with the findings of study by Delporto et al (2012) on biomechanical effects of obesity on balance. They stated that obese individuals show higher knee joint torque compared to hip joint torque (maximal 0.75 Nm·kg -1 ) while this is reversed in normal weight persons (maximal 0.38 Nm·kg -1 ) 16, 17 . Subjects with normal BMI maximize forward trunk flexion in order to avoid high torque at the knee joint.


Introduction:-
Balance is the key to all functional movement. Th is is an integral co mponent of almost every activity of daily liv ing. Fro m standing on toes to reach something on the top shelf, walking up and down the stairs or walking on an irregular surface, running, swimming, b ike riding and in many other daily ac t ivities balance is essential. Any impairment in balance will lead to decrease in performance and increases the risk of injury and fractures a s a result of which daily activ ities may be impaired. Thus balance is of key clinical relevance to any rehabilitation/prophylactic physiotherapy program. 1,2 There are many outcome measures to assess the balance but number of tests for evaluating the dynamic balance is very less. The standardized test that are present for examin ing balance clin ically, mostly put emp hasis on the static balance, whereas many activity of daily living required dynamic balance. 2 The majority of dynamic balance assessment tools e.g. functional reach tests and the berg balance scale, were developed specifically for paediatrics 4 , geriatrics 5 and neurological patients 6 . There are very few practical methods like force plate analysis, modified bass test etc. for evaluating dynamic balance but due to the space and cost requirements associated with these devices, they are not affordable or practical for many clinical settings. Thus, a simple, reliable and valid method is needed to assess lower extremity functional performance 1 .
The Star Excursion Balance Test (SEBT) is a simple, reliab le and cost effective test which is quick to administer and typically accessible in clinical and field settings to assess dynamic balance of lo wer limb 1, 7 monitor rehabilitation progress, assess deficits following injury and identify athletes at high risk for lower ext remity inju ry. SEBT requires neuromuscular characteristics such as lower ext remity coordination, balance, flexib ility and strength. 8 In this test the volunteer has to maintain balance on one lower limb and with other lower limb the volunteer has to reach along a previously marked lines in eight different directions that challenges the subject´s postural control, strength, range of motion and proprioceptive abilit ies. The distance reached in each direction is measured separately and interpreted as a representation of dynamic balance which offers the clinicians a practical alternative for assessing dynamic balance 2 . More is the reach by the subject with one leg while balancing on the opposite leg, the better functional performance they have 9 .
The body of literature that exists suggests that normative values of SEBT can provide objective measures to differentiate deficits and improvements in dynamic postural control related to lower limb injury or fatigue and it has the potential to predict the likelihood of injury to the lower extremity. 3 There is insufficient literature reviews for the normative values of star excursion balance test in young adults.Only one study was conducted in Pennsylvania, United States for normative values of SEBT in athletic individuals with 19-27 years of age. In their geographical zone, standard height is 161.8 to 175.7 cm but considering our country the standard heigh t in this age group is 152.6-166.3 cm according to which the results of normative values may vary. So, the purpose of this cross -sectional study was to find out the normat ive values of star excursion balance test in young adults which will help the therapist to establish a more precise levels of neuro muscular function for the purposes of injury prevention and rehabilitation.

Methodology:-
This prospective cross sectional study measured the excursion values of SEBT fro m students, staffs and volunteers of NILD/nearby institution/locality of Kolkata, India between March, 2017 to February, 2018. Ethical approval was taken fro m the Institute Ethical Co mmittee (IEC) before co mmencing the study. A stratified purposive sample design was used to select the volunteers.
The volunteers included were young healthy adults from 18years to 30years of age with normal range of motion at hip, knee and ankle. The volunteers excluded were the individuals with history of ankle trauma requiring med ical attention within past 2 years, history of any dizziness and vertigo, pre-diagnosed inner ear disorder, pre-d iagnosed nervous system problems like stroke, pre-diagnosed bone or joint abnormality, pre-diagnosed cardiovascular disease like hypertension, volunteers with visual loss and any other disorders that might adversely affect the control of balance.
Total 240 young adults were approached with the proposal of study out of which 12 were excluded and 228 volunteers were agreed to participate and signed the Informed consent form (which includes permission to use their 208 data and photograph for presentation and publication purpose) written in their preferred language (English/ Hindi/ Bengali). Out of those, 114 were male and 114 were female.
Procedure: Vo lunteers were approached with proposal of the study. Aim and procedure of the study were explained to each subject in the most communicable language. Demographic data including age, sex, height, Body Mass Index (BM I) was collected. Prior to the test pre-test precautions and instructions were explained, light weight loose fitting clothes was provided for avoiding any hindrance to movement. The volunteers were supervised to perform warm up exercises in the form of 5 min walk at a self-determined pace around research venue in presence of the evaluator therapist.

Procedure of the test
The evaluator demonstrated the test to all volunteers. The volunteers were asked to place one foot in the middle of the star pattern and with another foot volunteer were asked to reach as far as possible and lightly touch the line with their big toe before returning back to the starting position. With a marker, the researcher marked the spot at which the volunteer touched the line. Data was collected by measuring the length of reach (linear distance) with a measuring tape in all eight directions as shown in the figure 1. The linear distance was measured from the centre spot after the test to calculate the reach distance of each reach direction. When using the right foot as the reaching foot and the left leg to balance, the volunteer co mpleted the circu it in a clockwise fashion and when balancing on the right leg, the volunteer performed the circuit in an anti-clockwise fashion. The volunteers were instructed to repeat this process for a total of 3 times in each direction by both feet. They were given 15 seconds of rest between the reaches. The average of the 3 reaches for each leg in each of the 8 directions was calculated. Trial was discarded and repeated when the volunteera) Does not touch the line with the reach foot wh ile maintaining weight bearing on the stance leg. b) Lifted the stance foot from the centre grid. c) Lost balance at any point in the trial. d) Could not maintain start and return positions for one full second. e) If a volunteer was judged by the examiner to have touched the gro und with the reach foot in a manner that caused the reach leg to considerably support the body 1 .
After comp letion of the test all reach distance of SEBT perfo rmance were measured for both the right and left leg and average reach distance was calculated by using the follo wing simp le equation:

Results:-
The mean and standard deviation (SD) for demographic data-age, gender, height, BM I are shown in table 1 in the form of descriptive statistics.  We observe that in anterior, posterior, medial & posterior-med ial positions there is no significant difference between the right and left leg.

Discussion:-
One of the most significant step in rehabilitat ion is to evaluate the selective movement patterns to determine potential risk of in jury as any abnormal findings can only be judged on the basis of normal findings. The SEBT is a promising test of postural control that not only used to assess physical p erfo rmance, but also can b e used to screen d eficits in dynamic postural cont ro l du e to muscu los keletal in ju ries (e.g. ch ron ic an kle instab ility ), to ident ify ath letes at g reater ris k fo r lo wer ext remity in ju ry, as well as during the reh ab ilitat ion of orthop aed ic in ju ries in healthy act ive adu lts. 10,11 The volunteers who participated (n=228) in this study were young healthy adults ranged from 18 to 30 years of age. So, the incidence of false negative values had been reduced by excluding volunteers above 30 years of age.
In this study gender, height and BMI specific reference values were obtained for the SEBT in healthy young adults. These gender, height and BMI specific reference values would enhance the interpretation of the SEBT in regular clin ical practice and offer reference values against which the performance of patients could be compared; moreover, these reference values of SEBT could be used as reach targets during the progression of rehabilitation of patients.
The excursion reach of SEBT in accordance with gender shows that male individual's ha s higher normalized excursion reach scores in all 8 directions of the SEBT when co mpared with females because height and leg length of male subjects was comparatively h igher than females. These findings are supported by Egwu et al (1994) where they mentioned that females are generally reported to have shorter legs as compared to males 12 as a result of which SEBT excu rsion reach may reduce in females.
Overstall P et al (1977) found that males possess better balance performance then women because in wo men postural sway increases due to increase in body weight. 13 When body weight is more in comparison to muscle mass then it will fail to maintain balance resulting in less excursion reach distance.
This study revealed that right lower limb o f male have reduced reach distance in posterolateral, lateral, posterior direction and highest excursion reach in anteromedial, anterior and medial direct ion. Left lower limb of male has shown reduced excursion reach distance in posterolateral, lateral, posterior direction and highest excursion reach distance in anteromedial, anterio r and medial direction.

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The possible exp lanation for reduced excursion reach distance in posterolateral, lateral and posterior direction could be that the subjects got reduced visual feedback in these direction particularly in posterior and posterolateraldirect ion thus increasing demand on somatosensory system and joints .This findings are supported by Coughlan et al (2012) who found that in SEBT and Y-balance test the reach distance in posterolateral direct ions is decreased because in the posterolateral directions, visual awareness is reduced, thus it places an increased demand on the somatosensory system and therefore, the inability of the participants to see their scores may limit their reach. In the anterior reach direction, participants received visual feedback fro m the reach leg as they move and can observe the scored reach distance on each trial, so the excursion distance in this direction are mo re. 14 This study revealed that SEBT excursion reach increases with increase in height. Excursion reach scores of individuals with 131-140 centimetre height is lower as compared to excursion reach scores of individuals with 171-180 centimetre in both right and left lower extremity. The possible cause may be due to the co-relation between height and leg length which was supported by the study done by Gribble et al (2003) who found that there is a significant co-relation between height, leg length & excursion distance. Height and leg length were foun d to be strongly correlated with each other as increase in height leads to increase in leg length 15 .
The present study showed that SEBT excursion reach is more in volunteers with underweight and normal population and reduced in obese. In obese individuals more torque falls on lo wer extremity as a result of which excursion reach may reduce and in individual with normal BMI loading decreases significantly wh ich increases the excursion reach. This finding is in accordance with the findings of study by Delpo rto et al (2012) on biomechanical effects of obesity on balance. They stated that obese individuals show higher knee joint torque compared to hip joint torque (maximal 0.75 Nm·kg -1 ) while this is reversed in normal weight persons (maximal 0.38 Nm·kg -1 ) 16, 17 . Subjects with normal BMI maximize forward trunk flexion in order to avoid high torque at the knee joint. Obese individuals may avoid this strategy in order to prevent vertebral column torque (which may exacerbate back pain) and as a result of limited capacity to flex the trunk. 18,19.20 Gilleard and Smith (2007) observed that there is a decreased capacity of forward flexion of the thoracolumbar spine in obese adults and thus ROM of trunk was limited due to decreased forward stability thus reducing the excursion reach. It was also observed that increased fatty tissue in the abdominal area may also create a physical barrier to full ROM during some movements. 21 Bro wning and Kram 22 (2007) found that peak vertical ground reaction force were 60% greater for o bese subjects as compared to their normal weight subjects. Obese subjects had a mass of 61% g reater than normal weight subjects but experienced 91% greater ground reaction force. Similarly, Messier et al. 23 in the year 2005 found that joint loading decreases significantly with weight loss. For each step taken, joint load at the knee is reduced 4-fold fo r each one-pound reduction in body weight.
Prasetiowati L et al (2017) found that obese children have decreased postural balance when co mpared overweight and normal children aged 8-10 years. Weight of a person (and weight loss) is a crucial determinant of balance control. External and internal forces acting on the erect body create destabilizing events yielding postural oscillations. The postural control system regulates these oscillations by maintaining the vertical alignment of the body segments. When a person stands on a force platform, the point of application of the ground reaction forces under the feet (centre of foot pressure, COP) is the outcome of t he inert ial forces of the body and the restoring equilibriu m forces of the postural control system. It is generally accepted that the mean speed of the COP displacements is an indicator of postural stability with a greater speed indicating a decrease in postural stability 24, 25. Obese individuals shows greater balance impairment because with increase BMI centre of pressure displacement is higher which leads to balance problems. Thus Obesity could represent an important risk factor for falls; a factor that has been given, up to now, little attention. 26 Obese individuals are less stable than healthy-weight indiv iduals and this decreased stability reduces the SEBT perfo rmance. The literature supports that the weight loss can improve balance. With high levels of weight loss, patients demonstrate significant increase in relative strength and significantly improved measures of postural stability.
In this study it was found that the SEBT excursion reach scores was more on right side as compared to left side because in most of the volunteers right side was dominant side as a result the excursion distance also increased. This findings was supported by Bahamonde R et al (2007) who conducted a study on the effects of leg dominance on the single leg hop functional test in non-injured adults and found that subjects were able to significantly ju mp farther by using dominant leg because dominant leg produces more vertical and horizontal ground reaction forces as compared to non-dominant leg. 27 213

Li mitations Of The Study:-
The normative values of star excursion balance test established in this study may not be generalized to all the Indian population, data was collected fro m a single centre and nearby locality, so the normative values cannot be generalized. Samp le size was relatively small for a cross sectional study and co-relation between bilateral leg length and SEBT value was not established in this study.

Conclusion:-
This study provides the normative values for SEBT of young adults for different gender, height and BMI strata. SEBT excursion values in young adults increases with increase in height in both male and female. It can be also concluded from the result of this study the values of SEBT excu rsion is more on right stance leg as compared to left stance leg in d iffe rent heights in both gender. The SEBT excursion values in underweight volunteers have highest excursion values followed by normal, overweight and obese volunteers respectively. Therefore, it is reco mmended that physical therapists and clinicians should ass ess SEBT values with respect to above mentioned normative values, taking into account the effects of height, BMI and gender variability.