Reliability and Validity of the Equilibrate System for Balance Measurement

Transcription

1 Reliability and Validity of the Equilibrate System for Balance Measurement A Capstone Project for PTY 769 Presented to the Faculty of the Physical Therapy Department The Sage Colleges School of Health Sciences In Partial Fulfillment of the Requirements for the Degree of Doctor of Physical Therapy Michael D. Witter Kathryn A. Baird August 2011 Approved: Esther M. Haskvitz, PT, PhD, ATC Research Advisor Patricia Pohl, PT, PhD Program Director and Chair, Doctor of Physical Therapy Program

2 SAGE GRADUATE SCHOOLS I hereby give permission to Sage Graduate Schools to use my work, Reliability and Validity of the Equilibrate System for Balance Measurement For the following purposes: - Place in the Sage Colleges Library collection and reproduce for Interlibrary Loan. - Keep in the Program office or library for use by students, faculty, or staff. - Reproduce for distribution to other students, faculty, or staff. - Show to other students, faculty or outside individuals, such as accreditors or licensing agencies, as an example of student work. - Use as a resource for professional or academic work by faculty or staff. Michael D. Witter Date 8/19/2011 Kathryn A. Baird Date 8/19/2011

3 We represent to The Sage Colleges that this project and abstract are the original work of the authors, and do not infringe on the copyright or other rights of others. Reliability and Validity of the Equilibrate System for Balance Measurement Michael D. Witter Date 8/19/2011 Kathryn A. Baird Date 8/19/2011

4 THE SAGE COLLEGES Reliability and Validity of the Equilibrate System for Balance Measurement Capstone PTY 769 Michael D. Witter and Kathryn A. Baird 8/19/2011

5 Abstract Background and Purpose: Balance is the ability to maintain one's center of gravity within a base of support to remain upright and prevent falling. Poor balance may result in an increased risk for falls, which may result in serious injury. In order to minimize the risk of falls and the consequent negative effects associated with them, valid and reliable balance assessment tools are needed. Two pieces of equipment capable of quantifying the measure of standing balance using static posturography are the Equitest and the Equilibrate System. The reliability and validity of the Equitest to measure aspects of standing balance has been established, however, the reliability and validity of the Equilibrate System have yet to be determined. Therefore, the purpose of this study was to determine the concurrent validity and test-retest reliability of the Equilibrate System in a healthy population. Methods: Thirty one healthy subjects with a mean age of 31.1 years (SD = 11.3), 15 males (29.7 yr; SD = 9.2) and 16 females (32.4 yr; SD = 13.2) were recruited and tested. Balance was measured using 2 pieces of balance equipment, the Equitest and the Equilibrate System. Subjects were randomly tested twice on the Equilibrate System to determine the test re-test reliability and once on the Equitest to determine concurrent validity. Results: The Equilibrate System has poor to excellent test-retest reliability for measurement of postural sway and alignment with ICC values ranging from and showed moderate concurrent validity as compared to the Equitest, with significant correlations ranging from Conclusion: The Equilibrate System may be used to provide a valid and reliable measure of postural sway and alignment in a younger healthy population. Key Words: balance measurement, computerized dynamic posturography, static posturography, validity, reliability

6 3 Introduction Balance, or postural control, is the ability to maintain one s center of gravity within a base of support to remain upright and prevent falling. 1-4 This ability plays a critical role in how individuals function in their everyday lives. Poor balance, therefore, not only restricts the ability to perform certain activities of daily living, but is also related to an increased risk of falls that can result in a serious injury. 1-5 According to the Center for Disease Control (CDC), each year more than one third of all adults over 65 fall as a result of poor balance. 5-7 In 2008, these falls accounted for more than 2.1 million visits to the emergency room and more than 559,000 hospitalizations. 5,8 The research on the consequences of falls, especially in the elderly, has found there is a negative impact on all aspects of health: physical, mental and social. 3,8-10 Falls are the main cause of non-fatal injuries. 5,7-9 Non-fatal injuries associated with falls include fractures to the hip, spine, forearm, leg, ankle, pelvis, upper arm and hand; traumatic brain injuries; assistance or dependence in performing activities of daily living (ADL) due to impaired functioning and mobility; and fear of falling which can lead to social isolation, inactivity and depression. 5,7-10 According to the CDC, falls are also the leading cause of death due to hospitalizations from an injury incurred from a fall for adults over 65. 5,8 Due to the serious consequences associated with falls, further research and development of accurate, portable, and affordable balance assessment tools would be beneficial. Balance and postural control involve the integration of 3 sensory systems: the vestibular, proprioceptive and visual systems, in coordination with the neuromuscular and musculoskeletal systems. 2,11-13 Integration of the 3 sensory systems allows for determination of the body s center of gravity (COG) relative to the base of support (BOS) and environment. 2,11-13 The neuromuscular system, by way of the cerebellum, then processes this

7 4 information and coordinates the muscles and joints of the musculoskeletal system to move in the way needed to maintain balance The most common causes of balance deficits are impairments, damage, and/or degeneration in 1 or all 3 of the sensory systems that result in a decreased ability to integrate and/or coordinate these systems. 2,13-14 This decreased or inability can be a result of disease, trauma or normal age related neural and physical degeneration. 11,14-15 Common balance deficits of the 3 sensory systems include dysfunction of the otolith organs (e.g. benign paroxysmal positional vertigo), loss of sensation (e.g. peripheral neuropathy), and loss of vision (e.g. blindness). 1-4 Other impairments not related to the 3 sensory systems that can cause poor balance include pain, weakness, reduced range of motion, impaired mental status (e.g. traumatic brain injury) and reduced coordination due to damage or degeneration of the cerebellum (e.g. ataxia). 12,14 Other factors not related to these impairments that can have a negative effect on balance include the use of medications (e.g. prescription, over the counter, recreational, or illegal), sedentary lifestyle or prolonged inactivity and the environment. 12,14 Poor balance can be caused by any of these impairments or factors alone, but often it is due to a combination of impairments and factors, which can complicate the diagnosis process. 12,14 A complete and thorough balance examination should be performed to assure that an accurate and timely diagnosis of the root cause/causes of impaired balance is made. An accurate and timely diagnosis can help to prevent and/or minimize the negative consequences associated with poor balance. This examination should include a complete medical history as well as tests and procedures that examine all 3 of the sensory systems and the neuromuscular and musculoskeletal systems. 12

8 5 If balance is found to be impaired during the initial part of the examination, further testing would be needed. Common tests used in the clinic to assess balance and to determine fall risk include the Romberg stance, the timed-up-and-go (TUG), the Berg balance scale (BBS), the functional reach test (FRT), and the single limb stance test (SLST). These tests are needed to give a more complete picture of the individual s balance as well as to establish a baseline of balance performance to aid in the establishment of a plan of care. 12 The balance assessment tool chosen should be simple, robust, and ecologically valid, without being redundant with the information obtained in the clinical examination. 11,13 Perell et al 3 also recommend choosing a test that is specific to the setting; has high sensitivity, specificity, and inter-rater reliability; is used on a population similar to one that was used when it was developed; has written standardized instructions that are easy to follow; is not time consuming to administer and has a cut-off score. The cut-off score determines individuals who may be at risk for falls. It is useful in helping to determine when interventions should be initiated as well as determining if the chosen interventions have helped progress the person into a non-risk state. A good balance assessment tool can also help in the diagnosis of the balance deficit, help to develop the plan of care and determine the effectiveness of the intervention chosen based on progress made. 13 The classic Romberg stance has been an integral part of the neurologic exam since the early 19 th century. 16 It was initially developed as a way to detect loss of proprioceptive sensation. The test is performed by instructing the individual to stand with the feet together and both hands clasped against the chest. This is done first with eyes open to rule out other balance issues like possible vestibular dysfunction, and then with eyes closed. Testing is done for 30 seconds for both eyes opened and eyes closed. Loss of postural control when the

9 6 eyes are closed, or in the darkness, is an indicator of proprioceptive sensory loss and a positive Romberg sign. The principle behind the Romberg stance test is that balance requires constant monitoring of body sway, alignment and other information that is supplied by the 3 sensory systems involved in balance. The body is capable of maintaining balance with the loss of 1 sensory system, such as loss of vision when the eyes are closed, as long as the other 2 systems, proprioceptive and vestibular, are still intact. In cases where proprioception may be lost or impaired, removal of 1 of the senses, like vision, will decrease the ability to maintain postural control due to an increase in postural sway, most often in the anterior/posterior direction. 16 The BBS was initially developed and validated by Berg et al 1,17 to measure risk of multiple falls and was found to be strongly correlated with functional and motor performance tasks in patients who sustained a stroke. Since then the BBS has been validated to evaluate the effectiveness of balance interventions, provide quantitative description of function in clinical practice and research, and to predict falls in multiple populations. 1,17,18 The BBS is made up of 14 functional tasks that are graded from 0 (unable to perform item) to 4 (performed item safely) on a 56 point scale. 17 A score less than 46 on the BBS indicates the individual is at risk for falls. Both the intra-rater and inter-rater reliability of the BBS was shown to be high (ICC=.97) in a study by Conradsson et al. 18 The same study found that a change of 8 points is needed to show a clinically significant change in function among the elderly who are dependent in ADL and reside in a residential care facility. The BBS is efficient as it can be performed in approximately 15 minutes, it requires no equipment, can be performed anywhere with open space and has a valid cut-off score.

10 7 The TUG is commonly used because of its simplicity and because it requires minimal time to administer The TUG, which is mainly used in the geriatric population, measures how long it takes the individual to go from sit to stand in a chair, walk 3 meters (10 ft.), turn around, walk back, and sit back down. An individual with normal balance should be able to complete the TUG within 10 sec. A person dependent in ADL and mobility and at risk for falls will take more than 30 sec. 22 In a study by Schoppen et al 23 the inter-rater (ICC=.96) and intra-rater (ICC=.93) test-retest reliability was found to be high. The SLST, like the TUG, is easily and quickly administered. The patient is instructed to stand on each leg independently, first with the eyes open and then with the eyes closed for a specified period of time, usually 30 sec. Hurvitz et al 24 found in an older ambulatory outpatient population that SLST time is associated with a history of falls when it could not be performed for 30 seconds or more. Subjects in the study who fell were found to have a significantly lower SLST time (9.6 sec) as compared with subjects who did not fall (31.3 sec). 24 This study also found the SLST to have 91% sensitivity and 75% specificity for predicting falls. 24 This study found that decreased SLST time in older individuals defined as being in the 7th decade or greater, was a sensitive marker of peripheral neuropathy. 24 The SLST was also found to be able to predict falls in patients with peripheral neuropathy when compared with patients with peripheral neuropathy who have not fallen. Hurvitz et al 24 suggested that the findings in their research show the SLST might actually be a more effective means of identifying people at risk for falls than a detailed peripheral neurologic exam. Verreck et al 11 also found the SLST test to be a good predictor of poor balance and falls in individuals age 40 or younger if they are unable to hold the single limb stance

11 8 position for 10 seconds. The 10 sec cut-off time was also found, in a study by Jacobs et al, 25 to provide the highest combination of sensitivity (75%) and specificity (75%) in patients with Parkinson s disease for a history of one or more falls. This 10 second cut-off time also has the added benefit of detecting frailty in an older population. 25 While these tests are effective in helping the clinician assess fall risk and how well someone is progressing in therapy, they are not capable of quantifying certain aspects of standing balance such as sway, alignment and limits of stability (LOS). 2,13 Quantification of standing balance using computerized dynamic posturography (CDP), which is also known as static posturography, is beneficial in that it can help a clinician with differential diagnosis of a balance disorder, determine the extent of the balance impairment and to determine the efficacy of a balance retraining program. 13 Two pieces of equipment that are capable of quantifying the measurement of standing balance using static posturography are the Equitest and the Equilibrate System. Static posturography is performed by standing on a force plate that contains strain gauges that measure the vertical force placed on it by the individual s feet. 2,27-31 Postural control and balance is assessed by measuring the anterior-posterior and lateral deviations within an individual s LOS, as well as the angular velocity of the center of gravity detected by the force-plates. 2,27-31 The research done by Jeka et al 27 validates the use of angular velocity in the measurement of the COG to assess balance and risk for falls. This assessment is made with the assumption that the body moves as an inverted pendulum. 28 An increase in the velocity of anterior/posterior sway during stance, with both eyes open and eyes closed, is associated with falls. 28 Falls, though, rarely occur during standing. Falls more often occur during dynamic tasks (e.g. ambulation, reaching for an object) due to the increase in the

12 9 amplitudes of the anterior/posterior and lateral directions that can surpass one s LOS. 28 Tandem stance and unilateral stance are 2 static stance positions that are used during a dynamic task, such as ambulation, that can be assessed using a force plate. The data provided from these stance positions can provide information that may indicate an increased risk for falls. An increase in medial/lateral deviations is usually associated with falls during ambulation, while an increase in anterior-posterior deviations is associated with falls during standing tasks. 28 One of the main balance assessment tests on the Equitest is the sensory organization test (SOT). The SOT is a modified version of the Romberg stance test and has been found to be a valid and reliable test It consists of 6 conditions, each designed to challenge and isolate the 3 sensory systems and is performed on a moveable force plate encased in a movable visual enclosure. 2,13-14,27-31 The 6 conditions are (1) eyes open, surrounding and platform stable; (2) eyes closed, surrounding and platform stable; (3) eyes open, swayreferenced surrounding; (4) eyes open, sway referenced platform; (5) eyes closed, swayreferenced platform; and (6) eyes open, sway-referenced surrounding and platform The SOT was initially developed by Nasher in the 1960 s and 1970 s to assess astronauts returning from space with balance impairments. 13 According to Nasher 2 gravity is required for the otholith organs to function properly and to supply the vestibular system with appropriate sensory information. The absence of gravity, and therefore lack of appropriate vestibular input, for an extended period of time temporarily affected the way the vestibular system functioned once gravity was reintroduced. The proprioceptive and visual systems are also dependent on this vestibular information to react appropriately and maintain balance. Thus, as Black 13 described in his review on static posturography and vestibular function, the

13 10 vestibular system and gravity are the most important aspects of balance and postural control. This principle is what makes the SOT so useful because this system is able to isolate each of the 3 sensory systems involved with balance to determine the best interventions. Computerized dynamic posturography using the SOT on the Equitest is currently the gold standard of balance assessment. 13 The Equitest is the only device that is capable of isolating 2, 13 and quantifying the contribution of the different sensory systems used to control balance. The usefulness of the SOT is that it assesses the ability to integrate the 3 different sensory systems that are used to maintain standing balance when sensory information is either absent or manipulated. 2,14,29 While the SOT on Equitest cannot alone diagnose a balance pathology or site of lesion, it has been found to provide complementary information that aids in the plan of care of an individual with impaired balance. 13,31 The SOT on the Equitest is sensitive enough to detect vestibular recovery after medication or surgery is put in place to disrupt it, sensitive enough to document postural control, and capable of detecting exaggerated balance such as in some injured workers cases. 13 The Equilibrate System is similar to the Equitest in that it uses force plates to measure COG. Unlike the Equitest it does not have a movable visual enclosure and the force platforms used are also not movable. Instead, it has a motion analysis system that records light-reflecting markers attached to a vest that is mounted to specific anatomical landmarks. The motion analysis system attempts to measure the 3-dimensional movement of the upper body movements with the measurements of the COG of the force plates. This is in contrast to the Equitest which, as mentioned earlier, calculates the upper body movements with the assumption that the body moves as an inverted pendulum.

14 11 The reliability and validity of the of the balance measurements and assessment of fall risk using the Equitest has been established. 2, 13 Its expense and large size, though, makes it impractical for some clinics to own and because of its size is non-transportable. The Equilibrate System is less expensive, more compact and is easily transported. Unlike the Equitest, the validity and reliability of balance measurement on the Equilibrate System has not been established. Therefore, the purpose of this study was to determine the concurrent validity and test-retest reliability of the Equilibrate System when measuring balance in a healthy population. Methods Subjects Thirty one healthy subjects with a mean age of 31.1 years (SD = 11.3), 15 males (29.7 yr; SD = 9.2) and 16 females (32.4 yr; SD= 13.2) were recruited from The Sage Colleges and surrounding community. In order to be included in the study the healthy individuals had to be between the ages of 18-55, free of any balance deficits, able to follow simple instructions, and able to answer health related questions prior to testing. The health related questions were: 1) Do you currently or have you ever had any diagnosed balance disorders? 2) Do you currently or have you ever had any diagnosed conditions that affect/affected your balance? 3) Do you have a history of falls? 4) Are you currently taking any medication that may affect your balance? If the subjects answered yes to any of these questions they were excluded from the study. Subjects were also excluded if they had any disorders or impairments of the vestibular,

15 12 neuromuscular, or musculoskeletal systems which may affect their balance. Materials Balance was measured using 2 balance assessment tools, the Equitest * and the Equilibrate System. The Equitest consists of force plates on a raised platform within a 3- sided frame (Fig 1). The dual foot force plates detect rotation, translation, and provide a measurement based on the forces exerted vertically through the feet. The Equitest measures balance by calculating an equilibrium score. According to Chaundry et al, 30 the equilibrium score reflects the overall coordination of the visual, proprioceptive, and vestibular systems for maintaining standing posture. The second balance assessment tool, the Equilibrate System, consists of 2 adjacent force plates at ground level and 2 upright, adjustable cameras at 45 degree angles to the force plates. To measure upper body movement, subjects wore a vest with reflective markers that were placed on C7, the spine of each scapula, T12, each posterior superior iliac spine and S1. Upper body movement was recorded by the cameras and fed into the computer system (Fig 2). The numerical measurements obtained by both the force plates and cameras were used to quantify a subject's balance ability. The Equilibrate System determines balance through sway and alignment measurements. Sway, as defined by the manufacturer (M. Compisi, written communication, April 2011), is upper body displacement in 3 axes. The sway score is the variance of the 7 markers in each of the 3 planes of movement, x, y, and z, for each frame of data. Alignment, as defined by the manufacturer (M. Compisi, written communication, April 2011), is the total body displacement with respect to center of force. The alignment score is the sum of the absolute * NeuroCom, 9570 SE Lawnfield Rd, Clackamas, OR Balance Engineering, 999 Lehigh Station Rd, Henrietta, NY 14467

16 13 distance each marker travels from its initial starting point in each of the 3 planes of movement x, y, and z, for each frame of data. Procedures Subjects were each tested twice on the Equilibrate System to determine the test re-test reliability and once on the Equitest to determine concurrent validity of the Equilibrate System. The testing order was randomized and done on the same day with 5 minute rest intervals between each test. Subjects were tested in dark, comfortable clothing and athletic footwear. Subjects were instructed to wear dark colored clothing in order for the Equilibrate System cameras to better sense the reflective markers on the vest. On each piece of equipment subjects were asked to perform these balance tests sequentially: static standing with eyes opened and closed and single limb stance on the left with eyes opened, then left eyes closed followed by single limb stance on the right eyes opened then right eyes closed. Testing on the Equilibrate System was performed using the pre-set protocol of 15 seconds for the bilateral stance test with eyes open, 10 seconds for bilateral stance with eyes closed and single limb stance with eyes open, and 5 seconds for single limb stance with eyes closed. Tests performed on the Equitest were each 20 seconds for normal stance, eyes open and eyes closed and 10 seconds for single limb stance, eyes open and eyes closed; each test was repeated a total of 3 trials. If a subject was unable to complete a single limb stance after 3 attempts, the data for that single limb stance was not collected for that subject. One researcher operated the software associated with each piece of equipment and another provided stand-by guard/assistance for each subject in case of loss of balance. Data Analysis Independent t-tests were used to determine gender differences in balance measures

17 14 between males and females. A mixed model ANOVA was used to calculate the intraclass correlation coefficients (ICC) to determine the test-retest reliability of sway and alignment measurements on the Equilibrate System. Spearman s rho was used to determine the concurrent validity of the Equilibrate System measurements with the Equitest. Data were analyzed using SPSS, version Results There were no significant gender differences in balance measures (Tab. 1); therefore, all further analyses were done with a total of 31 subjects. Fleiss s criteria were used to classify the results of the ICC. Based on these criteria any ICC value for a given condition that was less than.4 was considered to have poor reliability, any ICC values between.4 and.75 were considered to have fair to good reliability and any value greater than.75 was considered to have excellent reliability. 32 As indicated in Table 2, the test-retest reliability for sway measurements on the Equilibrate System shows a range from poor to excellent for normal stance. As indicated in Table 3, the test-retest reliability for alignment measurements on the Equilibrate System ranged from poor to excellent for normal stance. Ten out of the 12 ICCs (Tab. 2 and Tab. 3) indicated at least fair to excellent testretest reliability. Normal stance eyes open had poor reliability for both sway and alignment measurements. As indicated in Tables 2 and 3, all ICC values for the eyes closed conditions were higher when compared to the eyes opened conditions, with the exception of single limb stance on the left. The sway and alignment scores on the Equilibrate System when compared to the SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606

18 15 equilibrium scores on the Equitest are presented in Table 4. The results of the concurrent validity analysis showed a moderate correlation between the measurements on the Equilibrate System and the Equitest. Discussion The results of this study indicate the Equilibrate System has poor to excellent testretest reliability and the Equilibrate System showed moderate concurrent validity with the Equitest. In addition, there were no significant differences in the balance performance between males and females in these normal healthy subjects. This study provides evidence that the Equilibrate System may be used as a means to provide a valid and reliable measure of postural sway and alignment in a younger healthy population. In this study measurement of normal stance eyes opened was found to have poor reliability with ICC values of.34 for sway and.33 for alignment, while measurement of normal stance eyes closed showed excellent reliability for both sway (.78) and alignment (.75). A similar result was also found in a recent study by Clark et al 33 using the Wii Balance Board System. Of the 4 conditions tested, (1) single limb with eyes open, (2) single limb with eyes closed, (3) double limb with eyes open and feet apart and (4) double limb with eyes closed and feet together, only double limb with eyes open and feet apart failed to reach an ICC value that was considered excellent (>.75). 33 All of the ICC values found in the study by Clark et al 33 were also higher for the eyes closed condition when compared to the eyes opened condition, with the exception of single limb stance on the left. The eyes closed condition measurements having greater reliability than the measurements for the eyes opened condition was also found in research by Bauer et al, 34 but the values of both were higher with excellent reliability. In the same research by Bauer et al 34

19 16 they hypothesized that the normal stance and single limb stance conditions are positions with which the subjects had little to no experience. This lack of experience meant that subjects had to adapt to these new test positions. Possibly, it was easier for the subjects to adapt when vision was intact, such as in the normal or single limb stance eyes open conditions, than when it was removed, such as in normal or single limb stance eyes closed conditions, suggesting a learning effect. The order of the testing, therefore, might cause a smaller variability between the first and the consecutive trials for the normal stance eyes closed and the single limb stance eyes closed conditions. Other research, such as that by Grindstaff et al, 35 found similar results. Grindstaff et al 35 recommended performing a practice trial before collecting data to account for any practice effect. In our study participants were able to perform one practice trial for each stance condition before being tested. A study by Wrisely et al 36 examined the learning effect when the SOT is done on the Equitest. This study had participants perform 3 trials of all 6 conditions on the SOT over a period of 6 sessions with varying time between tests. Conditions 1 and 2 on the SOT are 2 of the conditions used in our study, normal stance eyes opened (condition 1) and normal stance eyes closed (condition 2). Their study found a significant difference in the equilibrium scores among all 3 trials in all sessions for conditions 4, 5, and 6 but not for conditions 1 through While the study found that a learning effect does exist in healthy young adults, this effect only occurs when the individual is provided with 5 repetitions of the SOT over a 2-week period and occurs primarily in the composite score in conditions 4 through Therefore, it is unlikely that a learning affect interfered with the findings in our study due to the fact that our study only used conditions 1 (normal stance eyes opened) and condition 2 (normal stance eyes closed) that did not show a learning effect. Wrisley et al 37 concluded that multiple

20 17 baseline measures of the SOT should be administered in order to document change due to rehabilitation. Clinically, it should be noted that improvements of more than 8 points in the composite score indicated recovery beyond the effect of adaptation to the SOT itself. 36 This improvement criterion provides an additional method for assessing outcomes in intervention studies. Wrisley et al 36 also found in the same study that the SOT had fair to good test-retest reliability (ICC =.67) for the SOT composite score from session 1 to session 2 with an average of days in between testing. These results of fair to good test-retest reliability are also similar to what has been found in the literature in other studies of the test-retest reliability of the Equitest and the Balance Master. 14,37 In a study by Brouwer et al 37 on normal variability of balance using the Balance Master, they found that in young, healthy individuals the reliability of standing balance performance was generally found to be poor to fair. They determined in the study that while the mean positions of the COG within the base of support during quiet standing with eyes open was consistent for an individual, the total area of sway and the performance of weight shifts, including the direction and speed, varied both within and across subjects. Brouwer et al 37 concluded that the initial position of the COG within the base of support, the different balance strategies available, and to what extent the postural control system is being challenged all have an impact on balance performance. The ability to voluntarily move the COG within the LOS and control weight shifting is required to safely perform mobility tasks such as ambulation, reaching for objects and transitioning from a seated to standing position. A reduced LOS can affect the safety and quality of one s gait and performance of ADL. Individuals with reduced LOS in the anteriorposterior direction take smaller steps during gait, while individuals with reduced LOS in the

21 18 lateral direction have a broad-based gait Chaudhry et al 30 found that the functional LOS to be about 7 degrees anteriorly and 5 degrees posteriorly. This range of LOS may be reduced when one s eyes are closed, giving an individual less of an area to sway. Additionally, the lack of vision may decrease the different balance strategies available due to the fact that only 2 out of the 3 sensory systems involved in balance, vestibular and proprioceptive, are intact. This reduced area of sway and decrease in available balance strategies may cause less variability in test results which may have an effect on the test-retest reliability of the measurements. We observed in this study that participants used a variety of balance strategies to maintain their balance when performing the single limb stance conditions. On the Equitest the protocol calls for the arms to be placed on the hips during testing, while on the Equilibrate System the arms are free to move as needed to help maintain balance. Some participants maintained their balance with lower extremity strategies such as flexing the knee of the dependent leg or using the non-dependent leg to control weight shifting. Others used their arms to control their weight shifting to help them maintain their balance. In this study we did not use a standardized position for the arms during testing on either piece of equipment, and participants were allowed to move their arms freely to maintain their balance. Further research should be performed to examine the different strategies individuals use to maintain their balance with the single limb stance condition, as well as to determine whether or not the arms should be fixated in a standardized position, such as with the Equitest or free to move, such as with the Equilibrate System. There were several limitations in our study. The first limitation is that the results found in our study only pertain to a younger healthy population; therefore, more studies

22 19 would need to be done to establish reliability and validity in different patient populations. Another limitation was that the majority of the subjects had difficulty completing all 3 trials of the single limb stance condition with eyes closed. As a result of these individuals not being able to complete all 3 trials we had a smaller sample size and less data for those conditions, which could have biased the ICC values found for those conditions. Finally, the determinants of balance differed between the 2 pieces of equipment. While the sway and alignment scores of the Equilibrate System and the equilibrium scores of the Equitest represent the same thing, risk for falls, they are calculated differently. Therefore the concurrent validity of the two pieces of equipment may not be completely accurate. More research should be conducted to assure the comparison is valid. In conclusion, this study found that the Equilibrate System can be used as a valid and reliable tool to assess balance in a normal healthy population. Further research should be performed to validate its use in various patient populations.

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26 23 Table 1- Balance measurements for sway and alignment on the Equilibrate System Conditions Males Females Eyes Open Sway (2.7) (1.8) Eyes Open Alignment (4.3) (2.8) Eyes Closed Sway (4.5) (3.1) Eyes Closed Alignment (7.0) (5.0) Left Eyes Open Sway (13.1) (11.8) Left Eyes Open Alignment (20.8) (18.9) Left Eyes Closed Sway (15.5) (25.1) Left Eyes Closed Alignment (27.6) (41.4) Right Eyes Open Sway (17.5) (10.9) Right Eyes Open Alignment (28.4) (17.4) Right Eyes Closed Sway (19.4) (22.9) Right Eyes Closed Alignment (31.0) (36.7) All values are means with standard deviation in parentheses. No significant differences between the balance measures of males and females.

27 24 Table 2- The test-retest reliability for sway on the Equilibrate System Normal Stance ICC Eyes Open.34 Eyes Closed.78 Single Limb Stance Left Eyes Open.74 Left Eyes Closed.52 Right Eyes Open.72 Right Eyes Closed.88 ICC = Intraclass Correlation Coefficient

28 25 Table 3- The test-retest reliability for alignment on the Equilibrate System Normal Stance ICC Eyes Open.33 Eyes Closed.75 Single Limb Stance Left Eyes Open.73 Left Eyes Closed.55 Right Eyes Open.73 Right Eyes Closed.88 ICC = Intraclass Correlation Coefficient

29 26 Table 4- Correlation of the sway and alignment scores of the Equilibrate System with the equilibrium scores of the Equitest to determine the concurrent validity Test Condition Sway Alignment 1-Normal Stance Eyes Open.57 (.001).57 (.001) 2-Normal Stance Eyes.58 (.001).57 (.001) Closed 3-Single Limb Stance-Left.53 (.002).53 (.002) Eyes Open 4-Single Limb Stance-Left.54 (.004).52 (.005) Eyes Open 5-Single Limb Stance-Right.41 (.023).39 (.032) Eyes Open 6-Single Limb Stance-Right Eyes Closed.55 (.005).55 (.005)

30 Figure 1- Equitest 27

31 Figure 2- Equilibrate System 28