HEALTH ISSUES OF the aging population including the

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1 ORIGINAL ARTICLE Stability Limits, Single-Leg Jump, and Body Awareness in Older Tai Chi Practitioners Amanda L. Gyllensten, PhD, Christina W.Y. Hui-Chan, PhD, William W.N. Tsang, PhD ABSTRACT. Gyllensten AL, Hui-Chan CWY, Tsang WWN. Stability limits, single-leg jump, and body awareness in older Tai Chi practitioners. Arch Phys Med Rehabil 2010;91: Objective: To compare stability limits, single-leg jumping, and body awareness in older Tai Chi practitioners and healthy older controls and to determine possible interrelationships among these variables. Design: Cross-sectional study. Setting: University-based rehabilitation center. Participants: Tai Chi practitioners (n 24; age SD, y) and control subjects (n 20; age, y) were recruited. Interventions: Not applicable. Main Outcome Measures: Measures included the following: (1) subjects intentional weight shifting to 8 different spatial positions within their base of support using the limits of stability test, (2) the ability to leave the floor in single-leg jumping and to maintain balance on landing using force platform measurements, and (3) body awareness and movement behaviors using the Body Awareness Scale-Health (BAS-H). Results: The findings showed that Tai Chi practitioners had a significantly better ability to lean further without losing stability and better directional control (P 0.01). They had a better ability to jump off the floor (P 0.05) and to maintain a longer single-leg stance after landing (P.05) and better overall body awareness (P.001). The single-leg jumps also correlated significantly with limits of stability measures of movement velocity, endpoint excursions, and maximum excursions but not with directional control. The BAS-H scores correlated significantly with the limits of stability measures except directional control. They also correlated significantly with the ability to jump off the floor and maintain stability after landing. Conclusions: When compared with healthy controls, Tai Chi practitioners had better stability limits, increased ability to perform a single-leg jump, and more stability in landing on 1 leg as well as better body awareness. Significant correlations among limits of stability measures, single-leg jumping tests, and the BAS-H scores indicate the importance of body awareness in limits of stability, single-leg jumping, and landing. Key Words: Accidental falls; Aging; Exercise; Rehabilitation by the American Congress of Rehabilitation Medicine From the Section of Physiotherapy, Department of Health Sciences, Lund University, Lund, Sweden (Gyllensten); Department of Physical Therapy, University of Illinois at Chicago, Chicago, IL (Hui-Chan); and Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong (SAR), China (Tsang). Supported by The Hong Kong Polytechnic University through an Area of Strategic Development (grant no A102) to C.W.Y. Hui-Chan and W.W.N. Tsang No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprint requests to William W.N. Tsang, PhD, Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, william.tsang@inet.polyu.edu.hk /10/ $36.00/0 doi: /j.apmr HEALTH ISSUES OF the aging population including the causes of injury and death and the resulting cost for society have gained increasing attention. For older adults, falls have been identified as the major cause of injury and death. 1 Previous studies 2-5 have examined the effectiveness of Tai Chi practice on balance performance in an attempt to identify possible contributing factors. Standing with bent knees and the shifting of weight from 2 legs to 1 leg in a smooth and controlled way are believed to improve lower-limb strength and balance performance in Tai Chi practitioners. 2-5 The precision of joint positions and movements is thought to improve their lower-limb joint proprioception and the performance of limits of stability. 5,6 Daily activities do not just involve tasks like walking on level ground. Going up and down stairs is regarded as a difficult task for the elderly, and falls while negotiating stairs are a leading cause of accidental death. 7,8 Aside from the demands on the cardiopulmonary and neuromuscular systems, sensory inputs from somatosensory, visual, and vestibular systems are required for up-thrusting and landing during stair climbing and descent. Will the better physical capabilities of Tai Chi practitioners 4,9-11 enhance the balance control when jumping and landing? Such investigation has not been found in the literature. Body awareness is the attentiveness toward the body in both stillness and motion. This implies an awareness of both the sensory inputs and motor control, which are related to the integration of breathing and movements, coordination, and balance to functional tasks. 12 Previous research studies 13 have shown that patients suffering from musculoskeletal disorders, anxiety, and depression showed decreased body awareness. As a mind-body exercise, Tai Chi practice requires the tranquility of the mind during body movements. The coordination of upper and lower parts of the body in a continuous and harmonious manner is required. 14 Also, the practice puts great emphasis on the exact joint position and direction. Better performance in joint proprioception 5,6 leads us to postulate that Tai Chi practitioners could have improved body awareness. 15 To answer these questions, the objectives of the study were to compare 2 healthy groups of elderly subjects: 1 group had practiced Tai Chi, and 1 group had been equally physically active in other ways with regard to (1) the ability to initiate voluntary weight shifting to different spatial positions within the base of support without losing their stability (limits of stability), (2) the ability to land after a single-leg jump, and (3) body awareness and movement behaviors in different body positions. If the answers from these questions were in favor of the Tai Chi group, we also wanted to examine if there was a relation- BAS-H COP LOS List of Abbreviations Body Awareness Scale-Health center of pressure limits of stability 215

2 216 TAI CHI IMPROVES BALANCE AND BODY AWARENESS, Gyllensten ship between (1) voluntary body leaning and the ability to jump and maintain balance after landing, (2) voluntary body leaning and body awareness, and (3) the ability to jump and maintain balance after landing and body awareness. METHODS Participants For this cross-sectional study, a total of 44 subjects were recruited into 2 groups. One group consisted of 24 Chinese, community-dwelling, older healthy subjects (average age, y) who had practiced Tai Chi (mainly Yang style, 24 forms) at least 3 times a week and approximately 1 hour per session for at least 3 years. The control group consisted of 20 healthy, elderly Chinese subjects (age, y) who had never practiced Tai Chi. Both groups were recruited from a social center for the elderly in Hong Kong. To be included in the study, the participants had to be independent in the activities of daily living, be able to walk without a walking aid, and have no cognitive impairments. All subjects were screened for cognitive impairments by using a Chinese version of the Mini- Mental Status Examination, which has been validated. 16,17 Recruits who scored below 24 were excluded from the study. Additional exclusion criteria were the presence of symptomatic cardiovascular disease at moderate exertion levels; poorly controlled hypertension; symptomatic orthostatic hypotension; diagnosed stroke, Parkinson s disease, or other neurologic disorder; peripheral neuropathy of the lower extremities; crippling arthritis; and metastatic cancer. Each subject s physical activity level was measured by using the modified version of the Minnesota Leisure-time Physical Activities Scale. 18,19 This scale was designed to evaluate the subject s energy expenditure in leisure-time physical activities such as performing household tasks or sports. Activities were categorized into 3 levels according to their metabolic equivalent status (table 1). The University Ethics Committee approved the project, and written informed consent was obtained from all subjects. The LOS assessment quantified several movement characteristics associated with each subject s ability to voluntarily sway to 8 locations in space and briefly maintain stability at those positions. The LOS was measured by the EquiTest Computerized Dynamic Posturography unit. 20,a The COP trajectory Table 1: Comparison of Age, Sex, Body Weight, Height, MMSE Score, and Physical Activity Level Between Control and Tai Chi Subjects Control (n 20) Tai Chi (n 24) P Age (y) Sex (male/female) 2/18 6/18.26 Body weight (kg) Height (cm) * MMSE score Physical activity levels (n).13 Light 4 METS 7 4 Moderate 5.5 METS Heavy 5.5 METS 1 3 Abbreviations: METS, metabolic equivalents; MMSE, Mini-Mental Status Examination. *Significant difference at the P.05 level when using an independent t test. with respect to height, termed normalized COP, was used to estimate the sway angle of the center of mass. The posturography unit consisted of dual force plates and a video screen on which the subject s current normalized COP was displayed in real time. There were 8 target positions on the screen with the normalized COP during quiet stance displayed in the center. The subject was instructed to shift his/her weight to move the normalized COP trace to 1 of the 8 target positions as quickly and smoothly as possible without moving his/her feet. For each target position, 1 trial was performed. The average value from the 8 target positions was used to compare among the participating subjects. Familiarization trials were allowed before the assessment started. Subjects wore a safety vest to ensure that no falls occurred. The movement velocity, endpoint excursion and maximum excursion, and directional control were recorded to compare balance performance between the 2 groups. The movement velocity was the average speed of COP movement in degrees per second. The endpoint excursion was the distance traveled by the COP on the primary attempt to reach the target expressed in a percent of limits of stability. The endpoint was considered to be the point at which the initial movement toward the target stopped and subsequent corrective movements began. It was determined when the initial COP movement speed reached 0 or when the COP deviated from the target. The maximum excursion was the farthest distance traveled by the COP without falling. 20 Directional control measured the smoothness of the displacement of the normalized COP to each target position. It compared the amount of on-target movement of the normalized COP with the amount of off-target movement. 21 Measures of the limits of the stability test were also used to study the relationship with single-leg jumping performance and body awareness scores. This test involved the subject jumping on 1 leg high enough to leave the floor from a standardized starting position of a single-leg stance. The subject was asked to maintain the same position after landing. The test was intended to measure both strength and balance control, which may be needed in negotiating stairs. Subjects stood with the dominant leg on a force platform b with their eyes open and arms by their side. The leg used to kick a ball was defined as the dominant leg. Subjects kept the foot of their nondominant leg off the ground and their knee flexed approximately 90 with the hip in a neutral position. Each subject was instructed to jump up just enough to leave the force platform. The ability to actually jump off the floor on 1 leg was determined by using the vertical force component as captured by the force platform. After landing, subjects were required to maintain the single-leg stance for as long as possible up to a maximum of 30 seconds. The time period that subjects could maintain single-leg stance after landing was captured by using another force platform with sampling at 100Hz. Three trials were conducted with a 1-minute rest in between. The average of the 3 trials was used to compare balance performance between the 2 groups. If subjects could not jump to leave the floor, a value of 0 second was allocated to them. Before this study, studies of intrareliability of the jumping test had been performed to assess test-retest reliability in another 7 subjects (1 man and 6 women). The intraclass correlation coefficient for the time period of maintaining the single-leg stance was 0.88 (confidence interval,.43.98), which indicated satisfactory reliability. Body Awareness Scale-Health The BAS-H is applied in the clinical assessment of body awareness and the quality of movements with respect to move-

3 TAI CHI IMPROVES BALANCE AND BODY AWARENESS, Gyllensten 217 Table 2: Comparisons of the and Single-Leg Jumping Tests Measurements Between Control and Tai Chi Subjects Control (n 20) Tai Chi (n 24) Limits of stability Movement velocity (deg/s) Endpoint excursion (%) * Maximum excursion (%) * Directional control (%) * Single-leg jumping test Ability to leave the floor 11/9 21/ (yes/no) Maintaining balance (s) *Significant difference at the P.05/5 or P.01 level when using univariate tests with a Bonferroni adjustment after a multivariate test showed an overall statistically significant difference for the limits of stability test. Significant difference at the P.05 level when using a chi-square test. Significant difference at the P 0.05 level when using an independent t test with height as a covariate. ment behaviors, functional ability, and control. Each participant was assessed by a trained physical therapist who instructed the subject both verbally and by showing the movements according to a standardized testing manual. 13 The assessment involved movements used in everyday activities. The rating was based on clinical observation and the movement definitions provided in the testing manual. 13 The BAS-H assessment includes 25 items each scored on a scale of 0 to 4. The lowest score 0 indicates that the subject performs the movement in a stable, harmonious, relaxed way; the highest score 4 indicates a pattern of malfunction observed in the movement. Items are summarized into a BAS-H total score (25 items), and 4 different subindexes including grounding/center line index (10 items), centering/breathing index (5 items), flow index (6 items), and relational index (4 items) are computed by measuring different aspects of body awareness and the ability to control movements (appendix 1). Statistical Analysis Independent t tests were conducted to compare the age, weight, and height of the 2 groups. Chi-square tests were applied to compare the categoric variables, namely sex, physical activity level, and the ability to leave the floor in jumps. A multivariate analysis of variance was used to compare the outcome measures between the groups for the LOS test. If statistically significant differences were found in the multivariate tests, univariate tests were conducted with Bonferroni adjustment for each outcome measure. An independent t test was used to compare the amount of time subjects could maintain a singleleg stance after landing. To adjust for potential confounding arising from height differences, body height was treated as a covariate for the single-leg jumping test. To compare ordinal variables (BAS-H scores), the Mann-Whitney U test was used. Linear regression analyses performed in a previous study 12 has shown that height does not confound the BAS-H outcome measures. Spearman rank correlation was used to study correlations among the LOS, the single-leg jumping tests, and the BAS-H scores. The SPSS 14.0 for Windows c and P a significance level of 0.05 were chosen for the statistical comparisons. RESULTS Subjects Table 1 summarizes the demographic results and shows that there were no significant differences between the groups in terms of age, sex, body weight, cognitive function (Mini- Mental Status Examination), and physical activity level (P.05) (see table 1). However, there was a significant difference in height. Balance Control Multivariate analysis of the limits of stability revealed that the Tai Chi subjects performed the tasks significantly better than the control group overall (P.017). Univariate analysis showed that the Tai Chi subjects were significantly better than the control group in terms of their endpoint excursions, maximum excursions, and directional control (P.002, P.001, and P.008, respectively), but there were no significant differences between the 2 groups in terms of movement velocity (P.13) (table 2). The Tai Chi practitioners were significantly better than the controls in the ability to leave the floor when jumping on 1 leg and in their ability to maintain their balance on 1 leg after landing (P.05) (see table 2). Body Awareness The Tai Chi practitioners had significantly better BAS-H total scores than control subjects (P.001). They also scored better than the control subjects on the subindexes of grounding/ centre line, flow, and centering/breathing (P ranged between.009 and.001) (table 3). There was no significant difference between the groups for the subindex relation because subjects in both groups could achieve the full score of 0 in the assessment items (P 1.000). Correlations Among, Single-Leg Jumping, and Body Awareness The correlation between the limits of stability and single-leg jumping revealed significant correlations for movement velocity, endpoint excursions and maximum excursions, and ability to leave the floor (r ranging from.30 to.41, P between.006 and.046) and for movement velocity, endpoint excursions and maximum excursions, and being able to maintain balance after landing (r ranging from.41 to.46, P between.002 and.006) (table 4). Table 3: Comparison of Median and Interquartile Range (Q1, Q3) of the BAS-H Total and Subindex Scores Between Control and Tai Chi Subjects Control (n 20) Tai Chi (n 24) Median Q1 Q3 Median Q1 Q3 BAS-H total * Grounding/centre line * Centering/breathing * Flow * Relational *Significant differences at the P.05/5 or P.01 when using the Mann-Whitney U test with the Bonferroni adjustment. P

4 218 TAI CHI IMPROVES BALANCE AND BODY AWARENESS, Gyllensten Table 4: Correlations Between and There were significant correlations between the BAS-H total score; the grounding/center line, centering/breathing, and flow index scores; and the LOS measurements of movement velocity, endpoint excursions, and maximum excursions (r ranging from.60 to.41, P between.001 and.005) but not in the directional control (table 5). There were also significant correlations between the BAS-H total scores; the scores for grounding/center line, centering/breathing, and flow; and the single-leg jumping test with regard to the ability to leave the floor (r ranging from.44 to.32, P between.005 and.035) and to maintain balance after landing (r ranging from.79 to.47, P between.001 and.002) (see table 5). For the BAS-H subindex relation, there was no correlation with any of the other measures. DISCUSSION Ability to Leave Floor (Yes/No) Maintaining Balance (s) r P r P Limits of stability Movement velocity.30* Endpoint excursions.37* Maximum excursions Directional control NOTE. n 44. *Significant differences at the P.05 level when using the Spearman rank correlation coefficient. Significant differences at the P.01 level when using the Spearman rank correlation coefficient. The Tai Chi group showed significantly better stability in the LOS measures than the control group. This is in line with our previous findings that Tai Chi practitioners can lean further without losing stability (maximum excursion) and showed better control of their leaning trajectory (directional control). 5 In addition, we also showed that Tai Chi practitioners perform significantly better in the endpoint excursion (66.2% vs 55.0% for control subjects) (see table 2). The endpoint excursion represents the ability to preplan the magnitude of the movement (endpoint) (ie, feedforward control). The maximum excursion represents the corrective (feedback) movement control after the endpoint excursion has been reached. 20,21 In this study, the Tai Chi practitioners showed significantly better endpoint and maximum excursions. This may indicate that they know better where to go in space, know better how to get there (feedforward), and also know how to reach the target on a subsequent attempt (feedback). 22 Each Tai Chi form has a spatial requirement for practitioners to achieve, and Tai Chi practitioners have to practice to get there. Repeated practice with either self-corrections using mirror or external corrections from peers or a Tai Chi master may improve feedforward and/or feedback controls. 23 This may explain why Tai Chi practitioners showed better performance in endpoint and maximum excursions. Also, the demand to shift their body weight during practice to different target positions in a smooth and coordinated manner may improve directional control as shown in the present study. Despite the improved performance, movement velocity did not differ between the groups. This is not surprising considering that Tai Chi subjects practiced slow and controlled movements and were not trained to be fast in any special way. Single-Leg Jumping Interestingly, 73% of the subjects had the ability to leave the floor in a slight jump although there was a significant difference in favor of the Tai Chi group (88% vs 55% for controls). Jumping off the floor is not something that one needs to do in everyday life, but it is an interesting functional test of muscle work demanding both strength and balance control. Even more interesting is the ability to maintain balance when subjects land again. This action demands contractions of a number of the muscles of the foot, knee, and hip. It is a rather complicated functional activity that demands muscle strength, body awareness, and stability and balance control. 24 These elements would enable the practitioners to perform jumping and landing better. Body Awareness Tai Chi practitioners also revealed a better body awareness than the healthy controls. The overall body awareness was significantly better although the control participants were physically active on the same energy level (see table 1). The subindexes of grounding/centre line, centering/breathing, and flow were all significantly better in the Tai Chi group (see table 3). It seems that Tai Chi trains awareness of the use of the body. The Western view toward the essentials of Tai Chi practice have been summarized as 3 basic principles in the work of Wolf et al. 25 The first principle requires the practitioners to extend and relax their bodies. They should be aware of trunk alignment and focus on deep breathing. The second principle of Tai Chi focuses on the mind. During practice, it requires the practitioners to have a calm but alert mind, leading Table 5: Correlations Between the BAS-H Scores and and Results Movement Velocity Endpoint Excursions Maximum Excursions Directional Control Ability to Leave the Floor Maintaining Balance r P r P r P r P r P r P BAS-H scores total.49* * * * *.000 Grounding/center line.49* * * * *.000 Centering/breathing.42* * * * *.002 Flow.47* * * *.001 Relational *Significant differences at the P.01 level when using the Spearman rank correlation coefficient. Significant differences at the P.05 level when using the Spearman rank correlation coefficient.

5 TAI CHI IMPROVES BALANCE AND BODY AWARENESS, Gyllensten 219 to better awareness of body movement and their environment. The third principle requires the practitioners to have a wellcoordinated sequencing of body segments, and this originates from the waist and pelvis. Improved body awareness in Tai Chi practitioners may reflect the training essentials as explained previously. 26 In this study, subjects in both groups achieved a full score in items of the subindex relational (denoted as 0 ) (see table 3) because all the participants could relate well to the assessor and to themselves. This subindex is able to differentiate persons with a history of psychologic or psychiatric problems from healthy subjects. 12 Correlation of, Single-Leg Jumping, and Body Awareness Significant correlations were found between limits of stability and single-leg jumping and landing except for the directional control (see table 4). The question arises as to why the leaning of COP to reach one s limits of stability in a horizontal plane would correlate with the ability to lift oneself off the floor and to maintain balance control after landing in a vertical plane. Note that, first, the correlation values between the 2 measures were only fair. Second, both tasks require the subjects to maneuver their trajectory of COP, which could involve similar neural control mechanisms. For example, in the limits of stability, subjects have to shift their weight to 8 different spatial locations, and it was found that the maximum excursion is inversely correlated to the proprioceptive acuity of knee joint. 5 To our knowledge, there is no direct study on the relationship between single-leg jumping and landing and joint proprioception, but we purport that proprioception is needed to sense the lifting of the foot off the ground and the moment when the subject lands on the floor and the subsequent maintenance of balance. In a previous study, 15 we have verified the reliability of the BAS-H. Also, the scale has been validated by using subjective measurement methods such as the Nottingham Health Profile, Sense of Coherence, and Symptom Checklist 90-R. 12 In this study, we used objective balance control tests such as LOS and single-leg jumping and landing to correlate with the BAS-H scores. LOS and BAS-H achieved significant negative correlations except with directional and relational scores (see table 5). This indicated that those who are able to lean faster and further (denoted by higher values) when instructed to shift their weight to 8 different spatial limits of stability within the base of support had better scores in the grounding/center line, centering/breathing, and flow indexes of the BAS-H (denoted by lower scores). It suggests that both tests require balance and movement control. However, the correlations were not high and ranged from fair to moderate probably because of the fact that the BAS-H incorporated more assessments such as sitting down on the floor and standing up. The directional control of LOS measures the smoothness of the leaning trajectory to the target positions. The degrees of smoothness might not be picked up by the BAS-H because the measurement concentrates mainly on gross motor control. 12 Moreover, the subindex relation does not involve balance control ability, and it may explain its insignificant correlation with LOS parameters. The BAS-H scores also have significant negative correlation with the single-leg jumping and landing performance. The correlation between grounding/center line and the ability to maintain balance after landing was relatively high ( 0.79, see table 5). It should be noted that this subindex contains assessments including balance on 1 leg, ability to perform a slight jump, and climbing a chair. The demands of muscle strength and balance control are similar to single-leg jumping and landing. Significant correlations between these measures indicate the importance of body awareness to balance control in elderly subjects. CONCLUSIONS The limitations and conclusions of this study are described as follows. The assessor was not formally blinded as to what group the participant belonged. This might have introduced some bias in the body awareness ratings. Therefore, these results should be interpreted with some caution. Because we used a cross-sectional design in the present study, a causal relation between Tai Chi practice and better performance in the stability limits, ability at landing after single-leg jump, and better body awareness cannot be established. A randomized controlled trial is needed before inference can be made because the self-selection factor plays an important role in the effects of exercise. Only the dominant leg of the participants was examined in the jumping and landing tests in the present study. This might not reflect the demands of Tai Chi practice, which requires practitioners to shift their body weight over 1 leg to the other, thereby benefiting both legs. Furthermore, the nondominant leg is often used interchangeably for a stabilizing purpose in daily life. In future studies, testing both legs might provide more comprehensive understanding of the benefits of Tai Chi practice. Although a subjective questionnaire on physical activity level was conducted and found to show no significant difference between the 2 groups, the study still suffered from lacking an objective measure of physical fitness. Also, the older subjects recruited in this study might suffer from recall bias arising from the questionnaire. The sample size was relatively small and might not be able to detect the difference of the 3 factors, namely, age, body weight, and the physical activity level, which might confound the balance measurements. Bearing these limitations in mind, our results showed superior stability limits, single-leg jumping, landing, and also body awareness in elderly Tai Chi practitioners. Also, significant correlations among these variables were shown. Acknowledgments: The authors thank Bill Purves, MSc, for his English editorial advice. APPENDIX 1: THE BAS-H SUBINDEXES: GROUNDING/CENTER LINE, CENTERING/BREATHING, FLOW AND RELATIONAL, AND ITEMS INCLUDED IN THE RESPECTIVE INDEX Grounding/center line index focuses on the observation of postural balance. This index assesses how the force of gravity is transmitted all the way to the ground (grounding) and the postural response in terms of a posture that is stable and balanced with a minimum of effort (the center line). Postural stability in standing Leg flexibility in springing gait Weight transfer Balance on 1 leg Getting down to sit on the floor Getting down to lie on the floor Jumping/hopping Area of contact between body and the floor Ability to step up onto a chair Centering/breathing index rates the 3-dimensional trunk coordination and the ability to integrate breathing with movement.

6 220 TAI CHI IMPROVES BALANCE AND BODY AWARENESS, Gyllensten APPENDIX 1: THE BAS-H SUBINDEXES: GROUNDING/CENTER LINE, CENTERING/BREATHING, FLOW AND RELATIONAL, AND ITEMS INCLUDED IN THE RESPECTIVE INDEX (Con t) Stamping Trunk coordination in flexion-extension Ability to coordinate arms and legs in movements Ability to stretch throughout the body Breathing distribution in the trunk Breathing integrated in movements Flow index expresses the integration of postural balance with centering and breathing in full movement. Trunk turning Inhibited motor activity Vegetative dysfunctions in movement test Muscle tension Trunk rotation and arm swing during gait Selective movement control Relational index indicates the subject s ability to relate to another (the assessor) or to his/her own body using a mirror. Relation to mirror image The encounter Eye contact Flow of speech (increased/decreased) References 1. Tinetti ME. Preventing falls in elderly persons. N Engl J Med 2003;348: Jacobson BH, Chen HC, Cashel C, Guerrero L. The effect of T ai Chi Chuan training on balance, kinesthetic sense, and strength. Percept Mot Skills 1997;84: Song R, Lee EO, Lam P, Bae S-C. Effects of Tai Chi exercise on pain, balance, muscle strength, and perceived difficulties in physical functioning in older women with osteoarthritis: a randomized clinical trial. J Rheumatol 2003;30: Tsang WW, Hui-Chan CW. Comparison of muscle torque, balance, and confidence in older Tai Chi and healthy adults. Med Sci Sports Exerc 2005;37: Tsang WW, Hui-Chan CW. Effects of Tai Chi on joint proprioception and stability limits in elderly subjects. Med Sci Sports Exerc 2003;35: Xu D, Hong Y, Li J, Chan K. Effect of Tai Chi exercise on proprioception of ankle and knee joints in old people. Br J Sports Med 2004;38: Startzell JK, Owens DA, Mulfinger LM, Cavanagh PR. Stair negotiation in older people: a review. J Am Geriatr Soc 2000;48: Hamel KA, Cavanagh PR. Stair performance in people aged 75 and older. J Am Geriatr Soc 2004;52: Tsang WW, Hui-Chan CW. Standing balance after vestibular stimulation in Tai Chi-practicing and nonpracticing healthy older adults. Arch Phys Med Rehabil 2006;87: Wang C, Collet JP, Lau J. The effect of Tai Chi on health outcomes in patients with chronic conditions: a systematic review. Arch Intern Med 2004;164: Lan C, Lai JS, Chen SY, Wong MK. 12-month Tai Chi training in the elderly: its effect on health fitness. Med Sci Sports Exerc 1998;30: Gyllensten AL, Ekdahl C, Hansson L. Validity of the Body Awareness Scale-Health (BAS-H). Scand J Caring Sci 1999;13: Gyllensten AL. Basic body awareness therapy [dissertation]. Sweden: Lund University; Yu KP. Concise dictionary of Tai Chi Chuan. Taiwan: Hsin Chao She; Gyllensten AL, Ovesson MN, Lindstrom I, Hansson L, Ekdahl C. Reliability of the Body Awareness Scale-Health. Scand J Caring Sci 2004;18: Chiu HF, Lee HC, Chung WS, Kwong PK. Reliability and validity of the Cantonese version of Mini-Mental Status Examination: a preliminary study. J Hong Kong Coll Psychiatr 1994;4: Folstein MF, Folstein SE, McHugh PR. Mini-mental state. A practical method for grading the cognitive status of patients for the clinician. J Psychiatr Res 1975;12: Taylor HL, Jacobs DR Jr, Schucker B, Knudsen J, Leon AS, Debacker G. A questionnaire for the assessment of leisure time physical activities. J Chron Dis 1978;31: Van Heuvelen MJ, Kempen GI, Ormel J, Rispens P. Physical fitness related to age and physical activity in older persons. Med Sci Sports Exerc 1998;30: Nashner LM. Evaluation of postural stability, movement and control. In: Hasson SM, editor. Clinical exercise physiology. St. Louis: Mosby; Ghez C, Krakauer J. The organization of movement. In: Kandel ER, Schwartz JH, Jessell TM, editors. Principles of neural science. New York: McGraw-Hill; NeuroCom. EquiTest System operator s manual (version 8). Clackamas, OR: NeuroCom International, Inc.; Tsang WW, Hui-Chan CW. Effects of exercise on joint sense and balance in elderly men: Tai Chi versus golf. Med Sci Sports Exerc 2004;36: Wolf SL, Barnhart HX, Ellison GL, Coogler CE. The effect of Tai Chi Quan and computerized balance training on postural stability in older subjects. Atlanta FICSIT Group. Frailty and Injuries: Cooperative Studies on Intervention Techniques. Phys Ther 1997; 77: Wolf SL, Coogler CE, Xu T. Exploring the basis for Tai Chi Chuan as a therapeutic exercise approach. Arch Phys Med Rehabil 1997;78: Wayne PM, Kaptchuk TJ. Challenges inherent to t ai chi research: part I T ai chi as a complex multicomponent intervention. J Altern Complement Med 2008;14: Suppliers a. NeuroCom International Inc, 9570 SE Lawnfield Rd, Clackamas, OR b. Advanced Mechanical Technologies Inc, 176 Waltham St, Watertown, MA c. SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL