Journal of Applied Biomechanics, 2014, 30, 697-706 http://dx.doi.org/10.1123/jab.2013-0256 © 2014 Human Kinetics, Inc.
An Official Journal of ISB www.JAB-Journal.com ORIGINAL RESEARCH
Tai Chi Intervention Improves Dynamic Postural Control During Gait Initiation in Older Adults: A Pilot Study Srikant Vallabhajosula,1 Beverly L. Roberts,2 and Chris J. Hass2 1Elon
University; 2University of Florida
Tai Chi intervention has been shown to be beneficial for balance improvement. The current study examined the effectiveness of Tai Chi to improve the dynamic postural control among older adults with mobility disability. Six sedentary older adults with mobility disability participated in a 16-week Tai Chi intervention consisting of one hour sessions three times a week. Dynamic postural control was assessed pre- and post intervention as participants initiated gait in four stepping conditions: forward; 45° medially, with the stepping leg crossing over the other leg; 45° and 90° laterally. The center of pressure (CoP) displacement, velocity, and its maximum separation distance from the center of mass in the anteroposterior, mediolateral, and resultant directions were analyzed. Results showed that in the postural phase, Tai Chi increased the CoP mediolateral excursions in the medial (13%) and forward (28%) conditions, and resultant CoP center of mass distance in the medial (9%) and forward (19%) conditions. In the locomotion phase, the CoP mediolateral displacement and velocity significantly increased after the Tai Chi intervention (both by > 100% in the two lateral conditions). These results suggest that through alteration in CoP movement characteristics, Tai Chi intervention might improve the dynamic postural control during gait initiation among older adults. Keywords: multidirectional gait initiation, center of pressure, mobility disability, difficulty climbing stairs Several therapeutic programs have been designed to help the geriatric population deal with postural instability and falls. One of them is Tai Chi, a traditional Chinese medicine technique and martial art form that incorporates breath, multidirectional body movement, and attentional training to improve posture and overall well-being.1 Research has consistently shown that Tai Chi interventions are successful at improving balance, reducing falls,2–5 and altering the mechanisms of postural control in older adults.6,7 Tai Chi has also been shown to improve the mechanism of forward momentum generation during gait initiation.6 However, it is currently unknown if Tai Chi exercise can improve the postural control mechanisms during multidirectional gait initiation among older adults. Why study multidirectional gait initiation? Age-related decline in postural control has been well documented.8 Researchers have shown that the elderly often fall when they are walking short distances and when their center of mass is displaced away from the base of support.9,10 These conditions are very challenging and may account for the falls. Among these conditions is gait initiation, or the beginning of walking, which involves transitioning from a stationary stable double leg support to a dynamic unstable single leg support. One characteristic of gait initiation is the ability to separate the center of pressure from the center of mass to initiate and continue movement.6,11–14 These researchers showed that at the start of gait initiation, the center of pressure moves posteriorly and toward the leg used to initiate gait (henceforth referred to as the Srikant Vallabhajosula is with the Department of Physical Therapy Education, Elon University, Elon, NC. Beverly L. Roberts is with the Department of Adult and Elderly Nursing, University of Florida, Gainesville, FL. Chris J. Hass is with the Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL. Address author correspondence to Srikant Vallabhajosula at [email protected].
swing leg). It was also reported that this posterolateral movement of center of pressure was responsible for an efficient way to generate momentum during gait initiation as it causes the center of mass to move anteriorly and toward the other (stance) leg.15 However, older adults experience a decreased posterolateral movement of the center of pressure during the beginning stages of gait initiation.6,13,15,16 Further, the separation distance between the center of pressure and center of mass is directly proportional to the horizontal acceleration of the body based on the inverted pendulum model.17 Indeed, multiple studies have revealed a reduction in momentum generation in older adults by observing a reduced distance between the center of pressure and center of mass, especially during the stance leg toe-off event.14,18 Because these problems are pervasive in older adults, therapies are needed that can help older adults improve their mobility. In addition to walking, turning is another motor task that is often more challenging in the geriatric population. Older adults frequently exhibit more steps and time to turn,19 and alternate strategies20 during turning while walking.21 To date, only a few studies have investigated the problems associated with turning while initiating walk.16,22 These studies involved assessing the mechanisms behind center of pressure movement during lateral (90°) gait initiation16 and kinematics during multidirectional gait initiation22 in older adults who were transitioning to frailty and with Parkinson’s disease. However, the lack of additional research is surprising because initiating stepping motions in different directions is a common activity that is required in mundane tasks such as closing the refrigerator door or choosing an aisle in the supermarket. Because older adults often find these tasks challenging, it is essential to determine whether therapies such as Tai Chi may improve them. The purpose of the current pilot study was to investigate the effect of Tai Chi on the postural control mechanisms during multidirectional gait initiation among older adults. We hypothesized that there would be an overall improvement in the postural control 697
698 Vallabhajosula, Roberts, and Hass
mechanisms in participants during multidirectional gait initiation after the Tai Chi intervention was completed.
Methods
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Participants Eight females and one male (mean ± SD: age, 76.00 ± 3.93 years; height, 1.62 ± 0.06 m; and mass, 74.97 ± 17.62 kg) with a mobility disability were recruited to participate in the study, but data from only six participants (five females and one male; mean ± SD: age, 77.33 ± 3.98 years; height, 1.63 ± 0.07 m; and mass, 72.38 ± 18.37 kg) was used (see Experimental Protocol and Procedures section). Mobility disability included difficulty walking 200 m or climbing 10 steps and being sedentary with no systematic exercise in the three months before recruiting for 30 minutes or more, three or more times per week. Screening for the study was done by communicating with those enrolled in a registry with an interest to participate in research. Recruitment was also done through advertisements in newspapers, newsletters of organizations targeting older adults, and brief lectures to civic groups at churches, geriatric clinics, and senior centers. Flyers about the study were also placed in these places. Eligible participants were then screened through an interview for cognitive status, exercise history, and brief cardiac and respiratory physical exams. An age limit of 70 years or above was also used as an inclusion criterion. Participants were screened for exclusionary criteria including depression, mild cognitive impairment, recent myocardial infarction, implanted defibrillator, severe neurologic disease, and use of an assistive walking device. All participants signed an informed consent form that was approved by the University’s institutional review board.
Tai Chi Training Participants for the 16-week Tai Chi intervention met for one hour three times a week. The instructor leading the classes had more than 25 years of teaching experience that occasionally included students with severe neurologic mobility disorders. Class consisted of a five minute warm-up followed by Tai Chi. During Tai Chi, they focused on physical and mental relaxation, breathing, and visualization, and also used kinesthetic awareness to monitor and adjust their movements. During the Tai Chi training, the participants learned two types of movements. The warm-up movements comprised the first part of class every day. The focus of the warm-up movements was mainly on physical relaxation and kinesthetic awareness of the body in space. This was done using a slow and relaxed rotation of the torso with shifting of the body weight from one leg to the other. Also, the flexors and extensors of both the hip and knee were trained during the warm-up phase. The participants were also taught the developmental movements which represent the building blocks for the Yang form practice itself. These developmental exercises were taught in the first weeks of the study and were referred to throughout the course of the study to reinforce specific aspects of Tai Chi movement. Some of the developmental movements focused on a coordinated movement of the hand or arm with the body and weight shifting and body rotation. The first eight movements of the Chen Man-Ching Yang style short form23—a form (commencement, stroking birds tail left, stroking birds tail right, rolling back, pressing, pushing, and single whip) that emphasizes slow, continuous, and uniform pacing of movements—were used. The movements included rotation of the torso, turning with stepping, and shifting of weight from one leg to another. Tai Chi walking and Tai Chi ruler
were used to teach and practice the principles of weight transfers and stepping that are integral to the Tai Chi movements.
Experimental Protocol and Procedures Testing was done before and immediately after the Tai Chi intervention was completed. Kinetic data were collected at 900 Hz with two force platforms (Bertec Corporation, Columbus, OH). Kinematic data were collected at 60 Hz with a seven-camera motion capture system (Motion Analysis Corp., Santa Rosa, CA) using 25 retroreflective markers. The markers were placed at the following anatomical locations bilaterally: acromion process, olecranon process, wrist center, anterior superior iliac spine, lateral thigh, lateral knee center, shank, lateral malleolus, second meta-tarsal head, and heel. In addition, markers were also placed on the head (top, rear and front), upper back, and sacrum. Participants wore their own shoes and tight-fitting shorts and shirts to maximize their ability to move while minimizing artifacts due to movement of clothing. Gait initiation was evaluated in four different conditions: stepping 45° medially by crossing the swing leg over the stance leg (M45); stepping forward (FWD); stepping laterally 45° (L45); and stepping 90° laterally (L90) as shown in Figure 1. The forward stepping condition was performed first and the other conditions were performed in a random order. After sufficient practice, participants performed three experimental gait initiation trials for each condition at a self-selected pace. The average of the three trials was taken for data analyses. Each trial began with the participants standing quietly with one foot on each force platform about shoulder-width apart. To maintain consistency across conditions, they began each trial with the same initial stance and began stepping with the same self-selected leg. Data collection began while the participants stood with toes pointed forward in a relaxed position. After being given a verbal signal, the participants paused momentarily before initiating stepping toward a target placed at eye level. In spite of demonstrating understanding of the protocols, two female participants for the M45 condition and one female participant for the L45 condition failed
Figure 1 — A seven-camera motion capture system representing gait initiation in four experimental conditions: stepping 45° medially (M45), forward (FWD), stepping 45° laterally (L45), and stepping 90° laterally (L90) with the first stepping (swing) leg represented in gray and the second stepping (stance) leg represented in white.
Tai-Chi Improves Postural Control in Older Adults 699
to perform the task adequately. Instead of facing forward, they had their feet oriented in the direction of stepping or started with their nonpreferred leg. The data for these women were not analyzed for any of the tests. From the data analyzed, four participants began stepping with their right leg and two participants began stepping with their left leg.
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Data Processing Data were processed using the EvaRT 4.6 software (Motion Analysis Corporation, Santa Rosa, CA). Ground reaction force data were filtered with a fourth-order Butterworth low-pass filter with a cutoff frequency of 10Hz.24–26 Similarly, kinematics data were filtered at 6Hz. These cut-off frequencies were chosen as it has been shown that the highest frequency of human locomotion occurs below 10Hz.27,28 The whole-body center of mass location was computed as the weighted sum of each body segment’s center of mass from a 15 segment biomechanical model using Dempster’s anthropometric tables29 and OrthoTrak 6.0 (Motion Analysis Corporation, Santa Rosa, CA). Ground reaction forces and moments were used to calculate the instantaneous location of the center of pressure. All the trials were analyzed from the start of gait initiation to the first heel strike of the stance leg. The start of gait initiation was marked manually for all the trials as the time point from where the vertical ground reaction forces for both legs started to deviate. During this static standing phase, the separate force curves under each leg are fairly flat representing the weight distribution under each leg. Once the participant initiates gait, the force under the first stepping leg increases (representing a shift in weight) before the leg starts to take off and the force value under it starts approaching zero. The force under the other leg (second stepping leg) displays contrasting characteristics (first decreases and then increases) during this whole process. This shift in weight can be better captured using visual inspection of the vertical ground reaction forces. This visual inspection of vertical ground reaction force data was performed by the same investigator (SV) for all the participants to keep it consistent. For estimating the center of pressure characteristics, the gait initiation cycle was divided into three phases (S1, S2, S3) based on the center of pressure trace.6 The S1 phase (anticipatory response) began at the start of gait initiation to the time point where the center of pressure underwent maximum posterior and lateral displacement toward the swing leg. The S2 phase began at the end of the S1 phase and concluded with the toe-off of the swing leg. The S3 phase (locomotor) started from the end of the S2 phase to the toe-off of the stance leg. The characteristics of the center of pressure and center of mass are assumed to be the most important in S1 and S3 phases; hence, the S2 phase was not analyzed. The displacement and mean velocity of the center of pressure in the mediolateral and anteroposterior directions in the S1 and S3 phases were calculated. The maximum separation distance between the center of pressure and center of mass (referred as the center of pressure–center of mass moment arm) was calculated for the mediolateral and anteroposterior directions and the resultant between the two directions. The stance width was calculated as the distance between the two heel markers at the start of gait initiation. The horizontal speed of the center of mass was also calculated. All the dependent variable values were computed using custom MATLAB code (MathWorks Inc., Natick, MA).
Statistical Analysis The one-sample Kolmogorov-Smirnov test was used to confirm normality of the data. To assess for the effects of Tai Chi, a 2 × 4
(time × condition) repeated-measures ANOVA was used. If the time by condition interaction was significant, post hoc comparisons with Bonferroni adjustment were used to determine the significance of the differences between pre- and posttests. SPSS 13.0 for Windows was used for all the statistical analyses (International Business Machines, Armonk, NY). An α-level of .05 was used for all the statistical analyses.
Results To assess the effects of Tai Chi on gait initiation, the main effect of time (pretest vs posttest) and its interaction with condition (direction of stepping) are presented. Condition main effects are presented in Tables 1 and 2. Stance width was not significantly different among the study conditions and time (mean [SE] of stance width in cm: pre-M45, 18.7 [1.3]; pre-FWD, 19.6 [1.3]; pre-L45, 19.0 [1.2]; pre-L90, 19.1 [1.6]; post-M45, 18.3 [2.1]; post-FWD, 18.6 [1.3]; post-L45, 18.2 [1.9]; post-L90, 18.0 [1.9]). In addition, there was no significant main effect of time or time × condition interaction for center of mass’ horizontal speed (mean [SE] of gait initiation speed in m/s: pre-M45, 1.01 [0.05]; pre-FWD, 1.09 [0.03]; pre-L45, 1.10 [0.06]; pre-L90, 0.97 [0.05]; post-M45, 1.01 [0.04]; post-FWD, 1.08 [0.03]; post-L45, 1.04 [0.04]; post-L90, 1.02 [0.04]). Hence, the differences in the study dependent variables of interest were not susceptible to differences in baseline stance width and gait initiation speed. The values and statistical test results for all the dependent variables in S1 and S3 phases are shown in Tables 1 and 2, respectively. Additional statistical test results for all the variables in S1 and S3 phases are shown in Tables 3 and 4, respectively. In the anticipatory postural phase (S1 phase), a significant condition by time interaction for the displacement of the mediolateral center of pressure was found (P = .02). During this phase, the center of pressure always moves in the lateral direction (toward the swing leg). After Tai Chi training, lateral center of pressure displacement was greater toward the swing leg when gait was initiated in the medial and forward conditions. In contrast, the displacement was lesser in the L45 and L90 conditions. A trend toward significance was observed for the L90 condition (Figure 2A; P = .06). Significant interactions for the center of pressure–center of mass moment arms in mediolateral (P = .01) and resultant directions (P = .01) were found. After Tai Chi, participants reduced the mediolateral moment arm significantly only in the L90 condition (P = .03; Figure 2B). Participants also showed a trend toward significance to reduce their resultant center of pressure–center of mass moment arm after Tai Chi (P = .06). No other significant results were observed in this phase. In the locomotor phase, significant time by condition interactions were found for the center of pressure mediolateral displacement (P = .001) and velocity (P = .002). During both the lateral conditions after Tai Chi, participants significantly increased and reversed the direction of the center of pressure displacement (L45, P = .001; L90, P = .003; Figure 3A) and velocity (L45, P < .001; L90, P = .001; Figure 3B). No significant results were observed for the anteroposterior center of pressure displacement and velocity and the center of pressure–center of mass moment arms in the other two gait initiation conditions.
Discussion Tai Chi improved postural and locomotor control among the older adults in the present pilot study in several significant ways. Momentum generation improved in the medial and forward gait initiation
700 –12.09 (1.36) 4.7 (0.3) 4.1 (0.6) 6.3 (0.6)
6.8 (0.6) 2.4 (0.5) 7.3 (0.7)
L45
3.5 (0.5)
2.2 (0.4)
2.7 (0.4)
–8.11 (1.17)
11.87 (1.90)
–2.08 (0.34)
2.95 (0.34)
L90
2.7 (0.5)
0.6 (0.2)
2.6 (0.5)
–0.95 (1.51)
13.49 (1.67)
–0.12 (0.31)
2.90 (0.40)
M45
7.9 (0.6)
2.7 (0.5)
7.4 (0.5)
–7.37 (2.87)
24.31 (1.94)
–2.17 (0.81)
7.52 (0.46)
FWD
7.4 (0.5)
4.8 (0.5)
5.4 (0.5)
–13.73 (2.10)
20.78 (2.51)
–3.85 (0.54)
5.67 (0.54)
Post L45
2.6 (0.5)
1.7 (0.3)
1.8 (0.4)
–9.24 (1.12)
11.63 (1.53)
–1.81 (0.25)
2.45 (0.19)
L90
2.0 (0.7)
0.7 (0.3)
1.9 (0.6)
–3.20 (2.35)
12.01 (2.60)
–0.67 (0.49)
2.49 (0.59)
12.5 (0.7) 9.6 (1.3)
13.0 (0.9) 9.7 (2.2) 16.4 (1.5)
CoP–CoM AP moment arm (cm)
CoP–CoM+ resultant moment arm (cm)
15.3 (0.9)
Pre
14.4 (1.1)
9.6 (1.4)
11.3 (0.7)
27.50 (5.50)
4.97 (1.19)
16.61 (3.09)
3.08 (0.84)
L45
17.1 (2.0)
13 (2.6)
11.6 (1.0)
25.14 (6.72)
2.57 (1.79)
15.35 (3.62)
1.80 (1.13)
L90
16.6 (1.2)
9.7 (2.5)
13.1 (1.5)
27.68 (7.10)
3.62 (2.39)
16.47 (4.55)
2.31 (1.31)
M45
19.6 (2.3)
17.3 (2.7)
10.0 (0.7)
53.86 (7.61)
0.87 (5.10)
31.05 (4.47)
–4.09 (2.34)
FWD
28.17 (3.36)
–6.80 (2.19)
L45
18.6 (2.0)
16.5 (2.5)
9.8 (1.1)
45.54 (6.78)
–10.48 (3.10)
Post
22.7 (3.2)
21.7 (3.4)
8.9 (0.8)
42.33 (7.16)
–11.29 (2.76)
27.95 (4.54)
–7.57 (1.93)
L90
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass. Negative sign indicates medial side movement (for ML-based measures) and posterior movement (for AP-based measures). *Significant interaction; +significant condition main effect. Post hoc showed significant difference between FWD and L90.
CoP–CoM ML moment arm
24.67 (6.09)
(cm)+
0.57 (2.33) 32.72 (6.03)
–4.69 (2.11)
CoP ML velocity (cm/s)*
CoP AP velocity (cm/s)+
0.18 (1.31) 17.97 (3.09)
–3.12 (1.35) 15.63 (4.00)
FWD
CoP ML displacement (cm)*
M45
CoP AP displacement (cm)
Dependent Measure
Table 2 Mean (SE) of the dependent measures in the S3 phase for both pre and post testing across all the conditions (M45, FWD, L45, L90)
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior, CoM, center of mass. Negative sign indicates medial side movement (for ML-based measures) and posterior movement (for AP-based measures). *Significant interaction; +significant condition main effect; a–e, post hoc results for significant condition main effect. a Significant difference between M45 and FWD. b Significant difference between M45 and L45. c Significant difference between M45 and L90. d Significant difference between FWD and L45. e Significant difference between FWD and L90. f Significant difference between L45 and L90.
CoP–CoM resultant moment arm
(cm)*+(b,c,d,e)
CoP–CoM AP moment arm (cm)+(a,d,e,f)
CoP–CoM ML moment arm
(cm)*+(a,b,c,d,e)
–5.81 (1.27)
CoP AP velocity
15.97 (1.19)
21.23 (2.73)
CoP ML velocity (cm/s)+(a,b,c)
(cm/s)+(e,f)
–3.38 (0.41)
–1.84 (0.40)
CoP AP displacement (cm)+(d,e,f)
FWD 4.42 (0.27)
M45 6.63 (0.73)
CoP ML displacement (cm)*+(a,b,c,d,e)
Dependent Measure
Pre
Table 1 Mean (SE) of the dependent measures in the S1 phase for both pre and post testing across all the conditions (M45, FWD, L45, L90)
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701
F(1,5) = 0.022; P = .888; η2 = .004
η2 = .517
η2 = .044
η2 = .251
F(3,15) = 5.350; P = .011;
F(1,5) = 0.231; P = .651;
F(3,15) = 1.679; P = .214;
= .004
η2
η2 = .515
F(1,5) = 0.018; P = .899;
F(3,15) = 5.309; P = .011;
= .264
η2
η2 = .009
F(1,4) = 1.433; P = .297;
F(3,12) = 0.035; P = .991;
= . 425
η2
η2 = .224
F(1,4) = 2.962; P = .160;
F(3,12) = 1.152; P = .368;
= .113
η2
η2 = .095
F(1,4) = 0.510; P = .515;
F(3,12) = 0.418; P = .743; = .821 = .870 = .801 = .936
η2 = .898
F(3,15) = 43.822; P < .001*;
η2 = .820
F(3,15) = 22.805; P < .001*;
η2
F(3,15) = 72.632; P < .001;
η2
F(3,12) = 16.150; P < .001*;
η2
F(3,12) = 26.671; P < .001*;
η2
F(3,12) = 18.327; P < .001*;
η2 = .932
η2 = .164
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass. *Significant difference (P < .05).
CoP–CoM resultant moment arm
CoP–CoM AP moment arm
CoP–CoM ML moment arm
CoP AP velocity
CoP ML velocity
CoP AP displacement
F(3,12) = 54.959; P < .001*;
F(1,4) = 0.785; P = .426;
η2 = .542
CoP ML displacement
F(3,12) = 4.725; P = .021*;
Dependent Measure
Condition Main Effect (M45 vs FWD vs L45 vs L90)
Time Main Effect (Pre vs Post)
Time (Pre, Post) × Condition (M45, FWD, L45, L90) Interaction
Table 3 Statistical test results for all the dependent measures in the S1 phase
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M45 > L45 (P = .003); M45 > L90 (P = .002); FWD > L45 (P = .010); FWD > L90 (P = .012)
M45 < FWD (P = .019); FWD > L45 (P = .045); FWD > L90 (P = .008); L45 > L90 (P = .011)
M45 > FWD (P = .008); M45 > L45 (P = .001); M45 > L90 (P = .001); FWD > L45 (P = .001); FWD > L90 (P = .009)
FWD > L90 (P = .010); L45 > L90 (P = .003)
M45 > FWD (P = .022); M45 > L45 (P = .016); M45 > L90 (P = .025)
FWD > L45 (P = .048); FWD > L90 (P = .011); L45 > L90 (P = .007)
M45 > FWD (P = .030); M45 > L45 (P = .005); M45 > L90 (P = .006); FWD > L45 (P = .003); FWD > L90 (P = .042)
Post Hoc Test Results for Condition Main Effect (M45 vs FWD vs L45 vs L90)
702 F(1,5) = 2.502; P = .175; η2 = .334
η2 = .204
η2 = .449
F(3,15) = 1.285; P = .316;
F(1,5) = 4.070; P = .100;
η2 = .302
= .329
F(3,15) = 2.168; P = .134;
= .207
η2
η2
= .402
F(1,5) = 2.455; P = .178;
F(3,15) = 1.308; P = .308;
= .217
η2
η2
= .414
F(1,5) = 3.360; P = .126;
F(3,15) = 1.384; P = .286;
= .720
η2
η2
= .446
F(1,5) = 3.532; P = .119;
F(3,15) = 12.881; P = .002*;
= .286
η2
η2
= .449
F(1,5) = 4.024; P = .101;
F(3,15) = 2.005; P = .157;
= .797 = .328 = .222 = .416 = .472
η2 = .348
F(3,15) = 2.666; P = .085;
η2 = .489
F(3,15) = 4.780; P = .016*;
η2
F(3,15) = 4.467; P = .020*;
η2
F(3,15) = 3.560; P = .040*;
η2
F(3,15) = 1.427; P = .274;
η2
F(3,15) = 2.444; P = .104;
= .240
η2
η2
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass; N/A, not applicable. *Significant difference (P < .05).
CoP–CoM resultant moment arm
CoP–CoM AP moment arm
CoP–CoM ML moment arm
CoP AP velocity
CoP ML velocity
CoP AP displacement
F(3,15) = 1.580; P = .236;
F(1,5) = 4.073; P = .100;
η2
CoP ML displacement
F(3,15) = 19.573; P = .001*;
Dependent Measure
Condition Main Effect (M45 vs FWD vs L45 vs L90)
Time Main Effect (Pre vs Post)
Time (Pre, Post) × Condition (M45, FWD, L45, L90) Interaction
Table 4 Statistical test results for all the dependent measures in the S3 phase
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N/A
L45 < L90 (P = .004)
None
FWD > L90 (P = .002)
N/A
N/A
N/A
Post Hoc Test Results for Condition Main Effect (M45 vs FWD vs L45 vs L90)
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Tai-Chi Improves Postural Control in Older Adults 703
Figure 2 — Mean (SE) of A) mediolateral (ML) center of pressure (CoP) displacement, B) maximum (Max) mediolateral center of pressure–center of mass (CoM) separation distance, and C) maximum resultant center of pressure–center of mass separation distance observed for pre- (white column) and post-Tai chi intervention (black column) testing during the S1 phase of the center of pressure trace for gait initiation directed medially (M45), forward (FWD), 45° laterally (L45), and 90° laterally (L90). These three dependent measures showed significant condition × time interaction. *P < .05, significant difference between the pre- and postintervention tests (post hoc). †P < .07, statistical trend between the pre- and postintervention tests (post hoc). Displacements toward lateral side were designated as positive.
tasks. During the postural phase (S1), participants restricted the center of mass displacement toward the stance leg, indicating lower risk of losing stability in the two lateral conditions. During the locomotion phase (S3), Tai Chi increased and reversed the direction of the displacement in the center of pressure toward the stance leg. The significant increase in the center of pressure–center of mass moment arm, an indicator of better dynamic postural control, may have been due to the changes in displacement of the center of pressure. Before completing the Tai Chi intervention, the participants had levels of mobility that are commonly seen in older adults. For example, in the anticipatory postural phase (S1 phase) participants’ lateral6,13,14,30 and posterior center of pressure displacement for the FWD and L90 condition6,13,16 were similar to those seen in frail older adults. The value of the center of pressure’s lateral displacement for the FWD condition in our study during pre-Tai Chi testing (4.42 cm) fell in the range (2.90–4.50 cm) reported by previous researchers. Similarly, the value for the posterior displacement during the FWD condition in the current study (3.38 cm) is comparable to the values obtained in earlier studies (range: 2.81–3.54 cm). In addition, the values of the resultant CoP–CoM moment arm in the S1 phase obtained in our study before the Tai Chi intervention (6.27
cm) were similar to the value obtained by Martin and colleagues (6.05 cm) for a similar population.14 After 16 weeks of Tai Chi, significant changes in postural control occurred during the anticipatory postural phase (S1 phase) based on the condition of gait initiation. The center of pressure mediolateral displacement increased for the M45 and FWD conditions but decreased for the lateral stepping conditions (Figure 2A). These changes in the M45, FWD, and L45 conditions were not significant from pre to post. The change in the L90 condition showed a statistical trend. Although it was not significant, there was a trend for the center of pressure displacement to increase toward the swing leg, which may account for the subsequent increases in the mediolateral center of pressure–center of mass moment arm. It is also possible that after Tai Chi, participants may have been more confident maintaining single leg support and thus more comfortable positioning their center of mass closer to their swing leg. In contrast to the lateral conditions (L45 and L90), participants altered their strategy by restricting the movement of the center of mass toward the stance leg before toe-off of the swing leg. When stepping laterally, their initial movement was toward the swing leg. However, if the center of mass moved to the stance leg instead, the
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704 Vallabhajosula, Roberts, and Hass
Figure 3 — Mean (SE) of A) mediolateral (ML) center of pressure (CoP) displacement and B) mediolateral center of pressure velocity observed for pre- (white column) and post-Tai Chi intervention (black column) testing during the S3 phase of the center of pressure trace for gait initiation directed medially (M45), forward (FWD), 45° laterally (L45), and 90° laterally (L90). These two dependent measures showed significant condition × time interaction. Negative values indicate the center of pressure on stance-leg side moved medially and positive values indicate lateral movement. *P < .05, significant difference between the pre and post tests (post hoc).
next step with the stance leg would have been more difficult and required a different gait initiation strategy in the mediolateral shift of the center of pressure, a movement that is controlled by the hip abductors of the swing leg or the hip adductors of the stance leg. Another change that resulted from the Tai Chi intervention was a significantly increased resultant center of pressure–center of mass moment arm, which could reflect better momentum generation capabilities during the S1 phase. Changes in the center of pressure and resultant center of pressure–center of mass moment arms were similar for the mediolateral position but not the anterior–posterior directions. This may be due to the fact that the resultant center of pressure–center of mass moment arm and the center of pressure movement are more dependent on each other in the mediolateral direction than in the anterior–posterior direction during the postural phase. The locomotor phase (S3 phase), which is the most challenging phase during gait initiation, consists of the body being supported on a single leg. As the stance leg prepares for push-off, the center of pressure traverses forward under this leg and requires more dynamic postural control. Gatts and Woollacott observed older adults walking and found that their anteroposterior center of mass path significantly increased after Tai Chi training, which suggested an enhanced ability to tolerate unsteadiness or greater and finer control of the center of mass.31 Previous studies have shown that older adults who practice Tai Chi exhibit better postural control characteristics.3,32–34 Tai Chi exercises incorporate slow and continuous movement, focusing on using intrinsic feedback particularly from the proprioceptive sensory system to control center of mass and joint motion.34–37 In the current study, participants were instructed to emphasize physical and mental relaxation, breathing, and visualization, as well as use kinesthetic awareness to monitor and adjust their movements during
Tai Chi training and Tai Chi walking. These movements included coordination of the hand and arm with the body and weight shifting and body rotation. The improvements observed in the current study could be attributed to some of these factors. Since each of the first eight movements of the Yang style short form incorporate weightshifting in some form, it is possible that each of them could have contributed to the improved dynamic postural control seen in the current study. It may be worthwhile using future studies to examine which of these movements play a dominant role in improving postural control in older adults. The results of the present pilot study partially confirm that Tai Chi positively affects the finer dynamic control during the locomotor phase of stepping. Although Tai Chi had no effects on the anteroposterior movement of the center of pressure in the current study, the mediolateral displacement and velocity of the center of pressure did increase. After participants completed Tai Chi, their center of pressure shifted medially toward the stance leg in the two lateral conditions. This may have occurred because compared with walking on a level surface, people performing Tai Chi must maintain a more medial and anterior center of pressure location before toe-off.38 Another consequence of the center of pressure’s medial shift to the stance leg may have been a maximal shift of the center of pressure–center of mass moment arm in the same direction. Though the increase in the center of pressure–center of mass moment arm was not statistically significant in any of the experimental conditions, overall they did increase about 23%. It is possible that this increase resulted from participants’ greater confidence in executing the swing leg step while support remained on the stance leg during turning. Similar findings of the effects of Tai Chi on gait initiation in multiple directions were found for the center of pressure and center of mass separation. It has been reported that compared with level
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Tai-Chi Improves Postural Control in Older Adults 705
walking, Tai Chi movements necessitated experienced Tai Chi practitioners to exhibit a more medial and anterior center of pressure location before toe-off.28 Participants in the present pilot study seemed to have carried forward such mediolateral plantar pressure redistributions after Tai Chi training while performing multidirectional gait initiation. It is possible that more experience with Tai Chi could help the participants to exhibit better anteroposterior plantar pressure distributions while performing multidirectional gait initiation. Enhanced body awareness and stability limits may also account for these findings because they have been found to be increased in older adults who practice Tai Chi.39 The results of the present pilot study should be interpreted with caution because of the lack of a control or comparison group. In spite of the small sample size, significant changes in center of pressure and center of mass during multidirectional gait initiation were found after 16 weeks of Tai Chi. Whether greater changes can be found with a larger sample and longer intervention requires more research. Changes in the movement and displacement in the center of pressure with respect to the center of mass may be mechanisms by which Tai Chi improves dynamic postural control during gait initiation. Enhanced body awareness and confidence in postural control associated with Tai Chi may also contribute to the strategies older adults use during gait initiation. Acknowledgments The authors thank Debra McDonald for her help with editing the manuscript. This study was supported by the University of Florida Opportunity and the National Institutes of Health (Grant No. 5R03HD054594-02).
References 1. Wahbeh H, Elsas SM, Oken BS. Mind-body interventions: applications in neurology. Neurology. 2008;70(24):2321–2328. PubMed doi:10.1212/01.wnl.0000314667.16386.5e 2. Adler PA, Roberts BL. The use of Tai Chi to improve health in older adults. Orthop Nurs. 2006;25(2):122–126. PubMed doi:10.1097/00006416-200603000-00009 3. Wolf SL, Barnhart HX, Kutner NG, et al. Selected as the best paper in the 1990s: Reducing frailty and falls in older persons: an investigation of tai chi and computerized balance training. J Am Geriatr Soc. 2003;51(12):1794–1803. PubMed doi:10.1046/j.15325415.2003.51566.x 4. Zeeuwe PE, Verhagen AP, Bierma-Zeinstra SM, van Rossum E, Faber MJ, Koes BW. The effect of Tai Chi Chuan in reducing falls among elderly people: design of a randomized clinical trial in the Netherlands. [ISRCTN98840266] BMC Geriatr. 2006;6:6. PubMed doi:10.1186/1471-2318-6-6 5. 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(4):546–553. PubMed doi:10.1016/j. apmr.2005.12.040 6. Hass CJ, Gregor RJ, Waddell DE, et al. The influence of Tai Chi training on the center of pressure trajectory during gait initiation in older adults. Arch Phys Med Rehabil. 2004;85(10):1593–1598. PubMed doi:10.1016/j.apmr.2004.01.020 7. Gatts S. Neural mechanisms underlying balance control in Tai Chi. Med Sport Sci. 2008;52:87–103. PubMed doi:10.1159/000134289 8. Cromwell RL, Newton RA. Relationship between balance and gait stability in healthy older adults. J Aging Phys Act. 2004;12(1):90–100. PubMed
9. Ashley MJ, Gryfe CI, Amies A. A longitudinal study of falls in an elderly population II. Some circumstances of falling. Age Ageing. 1977;6(4):211–220. PubMed doi:10.1093/ageing/6.4.211 10. Tinetti ME, Doucette JT, Claus EB. The contribution of predisposing and situational risk factors to serious fall injuries. J Am Geriatr Soc. 1995;43(11):1207–1213. PubMed 11. Jian Y, Winter DA, Ishac MG, Gilchrist L. Trajectory of the body COG and COP during initiation and termination of gait. Gait Posture. 1993;1:9–22. doi:10.1016/0966-6362(93)90038-3 12. Hass CJ, Waddell DE, Fleming RP, Juncos JL, Gregor RJ. Gait initiation and dynamic balance control in Parkinson’s disease. Arch Phys Med Rehabil. 2005;86(11):2172–2176. PubMed doi:10.1016/j. apmr.2005.05.013 13. Halliday SE, Winter DA, Frank JS, Patla AE, Prince F. The initiation of gait in young, elderly, and Parkinson’s disease subjects. Gait Posture. 1998;8(1):8–14. PubMed doi:10.1016/S0966-6362(98)00020-4 14. Martin M, Shinberg M, Kuchibhatla M, Ray L, Carollo JJ, Schenkman ML. Gait initiation in community-dwelling adults with Parkinson disease: comparison with older and younger adults without the disease. Phys Ther. 2002;82(6):566–577. PubMed 15. Polcyn AF, Lipsitz LA, Kerrigan DC, Collins JJ. Age-related changes in the initiation of gait: degradation of central mechanisms for momentum generation. Arch Phys Med Rehabil. 1998;79(12):1582–1589. PubMed doi:10.1016/S0003-9993(98)90425-7 16. Hass CJ, Waddell DE, Wolf SL, Juncos JL, Gregor RJ. Gait initiation in older adults with postural instability. Clin Biomech (Bristol, Avon). 2008;23(6):743–753. PubMed doi:10.1016/j.clinbiomech.2008.02.012 17. Winter DAABC. (Anatomy, Biomechanics, Control) of Balance during Standing and Walking. Waterloo, Canada: Waterloo Biomechanics; 1995. 18. Chang H, Krebs DE. Dynamic balance control in elders: gait initiation assessment as a screening tool. Arch Phys Med Rehabil. 1999;80(5):490–494. PubMed doi:10.1016/S0003-9993(99)90187-9 19. Paquette MR, Fuller JR, Adkin AL, Vallis LA. Age-related modifications in steering behaviour: effects of base-of-support constraints at the turn point. Exp Brain Res. 2008;190(1):1–9. PubMed doi:10.1007/ s00221-008-1448-z 20. Fuller JR, Adkin AL, Vallis LA. Strategies used by older adults to change travel direction. Gait Posture. 2007;25(3):393–400. PubMed doi:10.1016/j.gaitpost.2006.05.013 21. Thigpen MT, Light KE, Creel GL, Flynn SM. Turning difficulty characteristics of adults aged 65 years or older. Phys Ther. 2000;80(12):1174–1187. PubMed 22. Vallabhajosula S, Buckley TA, Tillman MD, Hass CJ. Age and Parkinson’s disease related kinematic alterations during multi-directional gait initiation. Gait Posture. 2013;37(2):280–286. PubMed doi:10.1016/j. gaitpost.2012.07.018 23. China Sports. Simplified, “Taijiquan. 2nd ed. Beijing, China: China Publications Center; 1983:1–5. 24. Tseng SC, Stanhope SJ, Morton SM. Impaired reactive stepping adjustments in older adults. J Gerontol A Biol Sci Med Sci. 2009;64(7):807– 815. PubMed doi:10.1093/gerona/glp027 25. Corbeil P, Anaka E. Combined effects of speed and directional change on postural adjustments during gait initiation. J Electromyogr Kinesiol. 2011;21(5):734–741. PubMed doi:10.1016/j.jelekin.2011.05.005 26. Caderby T, Yiou E, Peyrot N, Bonazzi B, Dalleau G. Detection of swing heel-off event in gait initiation using force-plate data. Gait Posture. 2013;37(3):463–466. PubMed doi:10.1016/j.gaitpost.2012.08.011 27. Winter DA. Biomechanics and Motor Control of Human Movement. 4th ed. New York, NY: John Wiley & Sons; 2009. 28. Robertson DGE, Caldwell GE, Hamill J, Kamen G, Whittlesey SN. Research Methods in Biomechanics. 2nd ed. Champaign, IL: Human Kinetics; 2014.
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29. Dempster WT. Space Requirements of the Seated Operator. 1955. Wright Patterson-Air Force Base, Ohio. WADC-TR-55-159. 30. Dibble LE, Nicolson DE, Shultz B, MacWilliams BA, Marcus RL, Moncur C. Sensory cueing effects on maximal speed gait initiation in persons with Parkinson’s disease and healthy elders. Gait Posture. 2004;19(3):215–225. PubMed doi:10.1016/S0966-6362(03)00065-1 31. Gatts SK, Woollacott MH. How Tai Chi improves balance: biomechanics of recovery to a walking slip in impaired seniors. Gait Posture. 2007;25(2):205–214. PubMed doi:10.1016/j.gaitpost.2006.03.011 32. Tse SK, Bailey DM. Tai Chi and postural control in the well elderly. Am J Occup Ther. 1992;46:295–300. PubMed doi:10.5014/ajot.46.4.295 33. Wolfson L, Whipple R, Derby C, et al. Balance and strength training in older adults: intervention gains and Tai Chi maintenance. J Am Geriatr Soc. 1996;44:498–506. PubMed 34. Jacobson BH, Chen HC, Cashel C, et al. The effect of Tai Chi Chuan training on balance, kinesthetic sense, and strength. Percept Mot Skills. 1997;84:27–33. PubMed doi:10.2466/pms.1997.84.1.27
35. Li JX, Xu DQ, Hong Y. Effects of 16-week Tai Chi intervention on postural stability and proprioception of knee and ankle in older people. Age Ageing. 2008;37:575–578. PubMed doi:10.1093/ageing/afn109 36. Wayne PM, Kiel DP, Krebs DE, et al. The effects of Tai Chi on bone mineral density in postmenopausal women: a systematic review. Arch Phys Med Rehabil. 2007;88:673–680. PubMed doi:10.1016/j. apmr.2007.02.012 37. Hong Y, Li JX, Robinson PD. Balance control, flexibility, and cardiorespiratory fitness among older Tai Chi practitioners. Br J Sports Med. 2000;34(1):29–34. PubMed doi:10.1136/bjsm.34.1.29 38. Mao de W, Li JX, Hong Y. Plantar pressure distribution during Tai Chi exercise. Arch Phys Med Rehabil. 2006;87(6):814–820. PubMed doi:10.1016/j.apmr.2006.02.035 39. Gyllensten AL, Hui-Chan CW, Tsang WW. Stability limits, singleleg jump, and body awareness in older Tai Chi practitioners. Arch Phys Med Rehabil. 2010;91(2):215–220. PubMed doi:10.1016/j. apmr.2009.10.009
An Official Journal of ISB www.JAB-Journal.com ORIGINAL RESEARCH
Tai Chi Intervention Improves Dynamic Postural Control During Gait Initiation in Older Adults: A Pilot Study Srikant Vallabhajosula,1 Beverly L. Roberts,2 and Chris J. Hass2 1Elon
University; 2University of Florida
Tai Chi intervention has been shown to be beneficial for balance improvement. The current study examined the effectiveness of Tai Chi to improve the dynamic postural control among older adults with mobility disability. Six sedentary older adults with mobility disability participated in a 16-week Tai Chi intervention consisting of one hour sessions three times a week. Dynamic postural control was assessed pre- and post intervention as participants initiated gait in four stepping conditions: forward; 45° medially, with the stepping leg crossing over the other leg; 45° and 90° laterally. The center of pressure (CoP) displacement, velocity, and its maximum separation distance from the center of mass in the anteroposterior, mediolateral, and resultant directions were analyzed. Results showed that in the postural phase, Tai Chi increased the CoP mediolateral excursions in the medial (13%) and forward (28%) conditions, and resultant CoP center of mass distance in the medial (9%) and forward (19%) conditions. In the locomotion phase, the CoP mediolateral displacement and velocity significantly increased after the Tai Chi intervention (both by > 100% in the two lateral conditions). These results suggest that through alteration in CoP movement characteristics, Tai Chi intervention might improve the dynamic postural control during gait initiation among older adults. Keywords: multidirectional gait initiation, center of pressure, mobility disability, difficulty climbing stairs Several therapeutic programs have been designed to help the geriatric population deal with postural instability and falls. One of them is Tai Chi, a traditional Chinese medicine technique and martial art form that incorporates breath, multidirectional body movement, and attentional training to improve posture and overall well-being.1 Research has consistently shown that Tai Chi interventions are successful at improving balance, reducing falls,2–5 and altering the mechanisms of postural control in older adults.6,7 Tai Chi has also been shown to improve the mechanism of forward momentum generation during gait initiation.6 However, it is currently unknown if Tai Chi exercise can improve the postural control mechanisms during multidirectional gait initiation among older adults. Why study multidirectional gait initiation? Age-related decline in postural control has been well documented.8 Researchers have shown that the elderly often fall when they are walking short distances and when their center of mass is displaced away from the base of support.9,10 These conditions are very challenging and may account for the falls. Among these conditions is gait initiation, or the beginning of walking, which involves transitioning from a stationary stable double leg support to a dynamic unstable single leg support. One characteristic of gait initiation is the ability to separate the center of pressure from the center of mass to initiate and continue movement.6,11–14 These researchers showed that at the start of gait initiation, the center of pressure moves posteriorly and toward the leg used to initiate gait (henceforth referred to as the Srikant Vallabhajosula is with the Department of Physical Therapy Education, Elon University, Elon, NC. Beverly L. Roberts is with the Department of Adult and Elderly Nursing, University of Florida, Gainesville, FL. Chris J. Hass is with the Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL. Address author correspondence to Srikant Vallabhajosula at [email protected].
swing leg). It was also reported that this posterolateral movement of center of pressure was responsible for an efficient way to generate momentum during gait initiation as it causes the center of mass to move anteriorly and toward the other (stance) leg.15 However, older adults experience a decreased posterolateral movement of the center of pressure during the beginning stages of gait initiation.6,13,15,16 Further, the separation distance between the center of pressure and center of mass is directly proportional to the horizontal acceleration of the body based on the inverted pendulum model.17 Indeed, multiple studies have revealed a reduction in momentum generation in older adults by observing a reduced distance between the center of pressure and center of mass, especially during the stance leg toe-off event.14,18 Because these problems are pervasive in older adults, therapies are needed that can help older adults improve their mobility. In addition to walking, turning is another motor task that is often more challenging in the geriatric population. Older adults frequently exhibit more steps and time to turn,19 and alternate strategies20 during turning while walking.21 To date, only a few studies have investigated the problems associated with turning while initiating walk.16,22 These studies involved assessing the mechanisms behind center of pressure movement during lateral (90°) gait initiation16 and kinematics during multidirectional gait initiation22 in older adults who were transitioning to frailty and with Parkinson’s disease. However, the lack of additional research is surprising because initiating stepping motions in different directions is a common activity that is required in mundane tasks such as closing the refrigerator door or choosing an aisle in the supermarket. Because older adults often find these tasks challenging, it is essential to determine whether therapies such as Tai Chi may improve them. The purpose of the current pilot study was to investigate the effect of Tai Chi on the postural control mechanisms during multidirectional gait initiation among older adults. We hypothesized that there would be an overall improvement in the postural control 697
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mechanisms in participants during multidirectional gait initiation after the Tai Chi intervention was completed.
Methods
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Participants Eight females and one male (mean ± SD: age, 76.00 ± 3.93 years; height, 1.62 ± 0.06 m; and mass, 74.97 ± 17.62 kg) with a mobility disability were recruited to participate in the study, but data from only six participants (five females and one male; mean ± SD: age, 77.33 ± 3.98 years; height, 1.63 ± 0.07 m; and mass, 72.38 ± 18.37 kg) was used (see Experimental Protocol and Procedures section). Mobility disability included difficulty walking 200 m or climbing 10 steps and being sedentary with no systematic exercise in the three months before recruiting for 30 minutes or more, three or more times per week. Screening for the study was done by communicating with those enrolled in a registry with an interest to participate in research. Recruitment was also done through advertisements in newspapers, newsletters of organizations targeting older adults, and brief lectures to civic groups at churches, geriatric clinics, and senior centers. Flyers about the study were also placed in these places. Eligible participants were then screened through an interview for cognitive status, exercise history, and brief cardiac and respiratory physical exams. An age limit of 70 years or above was also used as an inclusion criterion. Participants were screened for exclusionary criteria including depression, mild cognitive impairment, recent myocardial infarction, implanted defibrillator, severe neurologic disease, and use of an assistive walking device. All participants signed an informed consent form that was approved by the University’s institutional review board.
Tai Chi Training Participants for the 16-week Tai Chi intervention met for one hour three times a week. The instructor leading the classes had more than 25 years of teaching experience that occasionally included students with severe neurologic mobility disorders. Class consisted of a five minute warm-up followed by Tai Chi. During Tai Chi, they focused on physical and mental relaxation, breathing, and visualization, and also used kinesthetic awareness to monitor and adjust their movements. During the Tai Chi training, the participants learned two types of movements. The warm-up movements comprised the first part of class every day. The focus of the warm-up movements was mainly on physical relaxation and kinesthetic awareness of the body in space. This was done using a slow and relaxed rotation of the torso with shifting of the body weight from one leg to the other. Also, the flexors and extensors of both the hip and knee were trained during the warm-up phase. The participants were also taught the developmental movements which represent the building blocks for the Yang form practice itself. These developmental exercises were taught in the first weeks of the study and were referred to throughout the course of the study to reinforce specific aspects of Tai Chi movement. Some of the developmental movements focused on a coordinated movement of the hand or arm with the body and weight shifting and body rotation. The first eight movements of the Chen Man-Ching Yang style short form23—a form (commencement, stroking birds tail left, stroking birds tail right, rolling back, pressing, pushing, and single whip) that emphasizes slow, continuous, and uniform pacing of movements—were used. The movements included rotation of the torso, turning with stepping, and shifting of weight from one leg to another. Tai Chi walking and Tai Chi ruler
were used to teach and practice the principles of weight transfers and stepping that are integral to the Tai Chi movements.
Experimental Protocol and Procedures Testing was done before and immediately after the Tai Chi intervention was completed. Kinetic data were collected at 900 Hz with two force platforms (Bertec Corporation, Columbus, OH). Kinematic data were collected at 60 Hz with a seven-camera motion capture system (Motion Analysis Corp., Santa Rosa, CA) using 25 retroreflective markers. The markers were placed at the following anatomical locations bilaterally: acromion process, olecranon process, wrist center, anterior superior iliac spine, lateral thigh, lateral knee center, shank, lateral malleolus, second meta-tarsal head, and heel. In addition, markers were also placed on the head (top, rear and front), upper back, and sacrum. Participants wore their own shoes and tight-fitting shorts and shirts to maximize their ability to move while minimizing artifacts due to movement of clothing. Gait initiation was evaluated in four different conditions: stepping 45° medially by crossing the swing leg over the stance leg (M45); stepping forward (FWD); stepping laterally 45° (L45); and stepping 90° laterally (L90) as shown in Figure 1. The forward stepping condition was performed first and the other conditions were performed in a random order. After sufficient practice, participants performed three experimental gait initiation trials for each condition at a self-selected pace. The average of the three trials was taken for data analyses. Each trial began with the participants standing quietly with one foot on each force platform about shoulder-width apart. To maintain consistency across conditions, they began each trial with the same initial stance and began stepping with the same self-selected leg. Data collection began while the participants stood with toes pointed forward in a relaxed position. After being given a verbal signal, the participants paused momentarily before initiating stepping toward a target placed at eye level. In spite of demonstrating understanding of the protocols, two female participants for the M45 condition and one female participant for the L45 condition failed
Figure 1 — A seven-camera motion capture system representing gait initiation in four experimental conditions: stepping 45° medially (M45), forward (FWD), stepping 45° laterally (L45), and stepping 90° laterally (L90) with the first stepping (swing) leg represented in gray and the second stepping (stance) leg represented in white.
Tai-Chi Improves Postural Control in Older Adults 699
to perform the task adequately. Instead of facing forward, they had their feet oriented in the direction of stepping or started with their nonpreferred leg. The data for these women were not analyzed for any of the tests. From the data analyzed, four participants began stepping with their right leg and two participants began stepping with their left leg.
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Data Processing Data were processed using the EvaRT 4.6 software (Motion Analysis Corporation, Santa Rosa, CA). Ground reaction force data were filtered with a fourth-order Butterworth low-pass filter with a cutoff frequency of 10Hz.24–26 Similarly, kinematics data were filtered at 6Hz. These cut-off frequencies were chosen as it has been shown that the highest frequency of human locomotion occurs below 10Hz.27,28 The whole-body center of mass location was computed as the weighted sum of each body segment’s center of mass from a 15 segment biomechanical model using Dempster’s anthropometric tables29 and OrthoTrak 6.0 (Motion Analysis Corporation, Santa Rosa, CA). Ground reaction forces and moments were used to calculate the instantaneous location of the center of pressure. All the trials were analyzed from the start of gait initiation to the first heel strike of the stance leg. The start of gait initiation was marked manually for all the trials as the time point from where the vertical ground reaction forces for both legs started to deviate. During this static standing phase, the separate force curves under each leg are fairly flat representing the weight distribution under each leg. Once the participant initiates gait, the force under the first stepping leg increases (representing a shift in weight) before the leg starts to take off and the force value under it starts approaching zero. The force under the other leg (second stepping leg) displays contrasting characteristics (first decreases and then increases) during this whole process. This shift in weight can be better captured using visual inspection of the vertical ground reaction forces. This visual inspection of vertical ground reaction force data was performed by the same investigator (SV) for all the participants to keep it consistent. For estimating the center of pressure characteristics, the gait initiation cycle was divided into three phases (S1, S2, S3) based on the center of pressure trace.6 The S1 phase (anticipatory response) began at the start of gait initiation to the time point where the center of pressure underwent maximum posterior and lateral displacement toward the swing leg. The S2 phase began at the end of the S1 phase and concluded with the toe-off of the swing leg. The S3 phase (locomotor) started from the end of the S2 phase to the toe-off of the stance leg. The characteristics of the center of pressure and center of mass are assumed to be the most important in S1 and S3 phases; hence, the S2 phase was not analyzed. The displacement and mean velocity of the center of pressure in the mediolateral and anteroposterior directions in the S1 and S3 phases were calculated. The maximum separation distance between the center of pressure and center of mass (referred as the center of pressure–center of mass moment arm) was calculated for the mediolateral and anteroposterior directions and the resultant between the two directions. The stance width was calculated as the distance between the two heel markers at the start of gait initiation. The horizontal speed of the center of mass was also calculated. All the dependent variable values were computed using custom MATLAB code (MathWorks Inc., Natick, MA).
Statistical Analysis The one-sample Kolmogorov-Smirnov test was used to confirm normality of the data. To assess for the effects of Tai Chi, a 2 × 4
(time × condition) repeated-measures ANOVA was used. If the time by condition interaction was significant, post hoc comparisons with Bonferroni adjustment were used to determine the significance of the differences between pre- and posttests. SPSS 13.0 for Windows was used for all the statistical analyses (International Business Machines, Armonk, NY). An α-level of .05 was used for all the statistical analyses.
Results To assess the effects of Tai Chi on gait initiation, the main effect of time (pretest vs posttest) and its interaction with condition (direction of stepping) are presented. Condition main effects are presented in Tables 1 and 2. Stance width was not significantly different among the study conditions and time (mean [SE] of stance width in cm: pre-M45, 18.7 [1.3]; pre-FWD, 19.6 [1.3]; pre-L45, 19.0 [1.2]; pre-L90, 19.1 [1.6]; post-M45, 18.3 [2.1]; post-FWD, 18.6 [1.3]; post-L45, 18.2 [1.9]; post-L90, 18.0 [1.9]). In addition, there was no significant main effect of time or time × condition interaction for center of mass’ horizontal speed (mean [SE] of gait initiation speed in m/s: pre-M45, 1.01 [0.05]; pre-FWD, 1.09 [0.03]; pre-L45, 1.10 [0.06]; pre-L90, 0.97 [0.05]; post-M45, 1.01 [0.04]; post-FWD, 1.08 [0.03]; post-L45, 1.04 [0.04]; post-L90, 1.02 [0.04]). Hence, the differences in the study dependent variables of interest were not susceptible to differences in baseline stance width and gait initiation speed. The values and statistical test results for all the dependent variables in S1 and S3 phases are shown in Tables 1 and 2, respectively. Additional statistical test results for all the variables in S1 and S3 phases are shown in Tables 3 and 4, respectively. In the anticipatory postural phase (S1 phase), a significant condition by time interaction for the displacement of the mediolateral center of pressure was found (P = .02). During this phase, the center of pressure always moves in the lateral direction (toward the swing leg). After Tai Chi training, lateral center of pressure displacement was greater toward the swing leg when gait was initiated in the medial and forward conditions. In contrast, the displacement was lesser in the L45 and L90 conditions. A trend toward significance was observed for the L90 condition (Figure 2A; P = .06). Significant interactions for the center of pressure–center of mass moment arms in mediolateral (P = .01) and resultant directions (P = .01) were found. After Tai Chi, participants reduced the mediolateral moment arm significantly only in the L90 condition (P = .03; Figure 2B). Participants also showed a trend toward significance to reduce their resultant center of pressure–center of mass moment arm after Tai Chi (P = .06). No other significant results were observed in this phase. In the locomotor phase, significant time by condition interactions were found for the center of pressure mediolateral displacement (P = .001) and velocity (P = .002). During both the lateral conditions after Tai Chi, participants significantly increased and reversed the direction of the center of pressure displacement (L45, P = .001; L90, P = .003; Figure 3A) and velocity (L45, P < .001; L90, P = .001; Figure 3B). No significant results were observed for the anteroposterior center of pressure displacement and velocity and the center of pressure–center of mass moment arms in the other two gait initiation conditions.
Discussion Tai Chi improved postural and locomotor control among the older adults in the present pilot study in several significant ways. Momentum generation improved in the medial and forward gait initiation
700 –12.09 (1.36) 4.7 (0.3) 4.1 (0.6) 6.3 (0.6)
6.8 (0.6) 2.4 (0.5) 7.3 (0.7)
L45
3.5 (0.5)
2.2 (0.4)
2.7 (0.4)
–8.11 (1.17)
11.87 (1.90)
–2.08 (0.34)
2.95 (0.34)
L90
2.7 (0.5)
0.6 (0.2)
2.6 (0.5)
–0.95 (1.51)
13.49 (1.67)
–0.12 (0.31)
2.90 (0.40)
M45
7.9 (0.6)
2.7 (0.5)
7.4 (0.5)
–7.37 (2.87)
24.31 (1.94)
–2.17 (0.81)
7.52 (0.46)
FWD
7.4 (0.5)
4.8 (0.5)
5.4 (0.5)
–13.73 (2.10)
20.78 (2.51)
–3.85 (0.54)
5.67 (0.54)
Post L45
2.6 (0.5)
1.7 (0.3)
1.8 (0.4)
–9.24 (1.12)
11.63 (1.53)
–1.81 (0.25)
2.45 (0.19)
L90
2.0 (0.7)
0.7 (0.3)
1.9 (0.6)
–3.20 (2.35)
12.01 (2.60)
–0.67 (0.49)
2.49 (0.59)
12.5 (0.7) 9.6 (1.3)
13.0 (0.9) 9.7 (2.2) 16.4 (1.5)
CoP–CoM AP moment arm (cm)
CoP–CoM+ resultant moment arm (cm)
15.3 (0.9)
Pre
14.4 (1.1)
9.6 (1.4)
11.3 (0.7)
27.50 (5.50)
4.97 (1.19)
16.61 (3.09)
3.08 (0.84)
L45
17.1 (2.0)
13 (2.6)
11.6 (1.0)
25.14 (6.72)
2.57 (1.79)
15.35 (3.62)
1.80 (1.13)
L90
16.6 (1.2)
9.7 (2.5)
13.1 (1.5)
27.68 (7.10)
3.62 (2.39)
16.47 (4.55)
2.31 (1.31)
M45
19.6 (2.3)
17.3 (2.7)
10.0 (0.7)
53.86 (7.61)
0.87 (5.10)
31.05 (4.47)
–4.09 (2.34)
FWD
28.17 (3.36)
–6.80 (2.19)
L45
18.6 (2.0)
16.5 (2.5)
9.8 (1.1)
45.54 (6.78)
–10.48 (3.10)
Post
22.7 (3.2)
21.7 (3.4)
8.9 (0.8)
42.33 (7.16)
–11.29 (2.76)
27.95 (4.54)
–7.57 (1.93)
L90
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass. Negative sign indicates medial side movement (for ML-based measures) and posterior movement (for AP-based measures). *Significant interaction; +significant condition main effect. Post hoc showed significant difference between FWD and L90.
CoP–CoM ML moment arm
24.67 (6.09)
(cm)+
0.57 (2.33) 32.72 (6.03)
–4.69 (2.11)
CoP ML velocity (cm/s)*
CoP AP velocity (cm/s)+
0.18 (1.31) 17.97 (3.09)
–3.12 (1.35) 15.63 (4.00)
FWD
CoP ML displacement (cm)*
M45
CoP AP displacement (cm)
Dependent Measure
Table 2 Mean (SE) of the dependent measures in the S3 phase for both pre and post testing across all the conditions (M45, FWD, L45, L90)
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior, CoM, center of mass. Negative sign indicates medial side movement (for ML-based measures) and posterior movement (for AP-based measures). *Significant interaction; +significant condition main effect; a–e, post hoc results for significant condition main effect. a Significant difference between M45 and FWD. b Significant difference between M45 and L45. c Significant difference between M45 and L90. d Significant difference between FWD and L45. e Significant difference between FWD and L90. f Significant difference between L45 and L90.
CoP–CoM resultant moment arm
(cm)*+(b,c,d,e)
CoP–CoM AP moment arm (cm)+(a,d,e,f)
CoP–CoM ML moment arm
(cm)*+(a,b,c,d,e)
–5.81 (1.27)
CoP AP velocity
15.97 (1.19)
21.23 (2.73)
CoP ML velocity (cm/s)+(a,b,c)
(cm/s)+(e,f)
–3.38 (0.41)
–1.84 (0.40)
CoP AP displacement (cm)+(d,e,f)
FWD 4.42 (0.27)
M45 6.63 (0.73)
CoP ML displacement (cm)*+(a,b,c,d,e)
Dependent Measure
Pre
Table 1 Mean (SE) of the dependent measures in the S1 phase for both pre and post testing across all the conditions (M45, FWD, L45, L90)
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701
F(1,5) = 0.022; P = .888; η2 = .004
η2 = .517
η2 = .044
η2 = .251
F(3,15) = 5.350; P = .011;
F(1,5) = 0.231; P = .651;
F(3,15) = 1.679; P = .214;
= .004
η2
η2 = .515
F(1,5) = 0.018; P = .899;
F(3,15) = 5.309; P = .011;
= .264
η2
η2 = .009
F(1,4) = 1.433; P = .297;
F(3,12) = 0.035; P = .991;
= . 425
η2
η2 = .224
F(1,4) = 2.962; P = .160;
F(3,12) = 1.152; P = .368;
= .113
η2
η2 = .095
F(1,4) = 0.510; P = .515;
F(3,12) = 0.418; P = .743; = .821 = .870 = .801 = .936
η2 = .898
F(3,15) = 43.822; P < .001*;
η2 = .820
F(3,15) = 22.805; P < .001*;
η2
F(3,15) = 72.632; P < .001;
η2
F(3,12) = 16.150; P < .001*;
η2
F(3,12) = 26.671; P < .001*;
η2
F(3,12) = 18.327; P < .001*;
η2 = .932
η2 = .164
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass. *Significant difference (P < .05).
CoP–CoM resultant moment arm
CoP–CoM AP moment arm
CoP–CoM ML moment arm
CoP AP velocity
CoP ML velocity
CoP AP displacement
F(3,12) = 54.959; P < .001*;
F(1,4) = 0.785; P = .426;
η2 = .542
CoP ML displacement
F(3,12) = 4.725; P = .021*;
Dependent Measure
Condition Main Effect (M45 vs FWD vs L45 vs L90)
Time Main Effect (Pre vs Post)
Time (Pre, Post) × Condition (M45, FWD, L45, L90) Interaction
Table 3 Statistical test results for all the dependent measures in the S1 phase
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M45 > L45 (P = .003); M45 > L90 (P = .002); FWD > L45 (P = .010); FWD > L90 (P = .012)
M45 < FWD (P = .019); FWD > L45 (P = .045); FWD > L90 (P = .008); L45 > L90 (P = .011)
M45 > FWD (P = .008); M45 > L45 (P = .001); M45 > L90 (P = .001); FWD > L45 (P = .001); FWD > L90 (P = .009)
FWD > L90 (P = .010); L45 > L90 (P = .003)
M45 > FWD (P = .022); M45 > L45 (P = .016); M45 > L90 (P = .025)
FWD > L45 (P = .048); FWD > L90 (P = .011); L45 > L90 (P = .007)
M45 > FWD (P = .030); M45 > L45 (P = .005); M45 > L90 (P = .006); FWD > L45 (P = .003); FWD > L90 (P = .042)
Post Hoc Test Results for Condition Main Effect (M45 vs FWD vs L45 vs L90)
702 F(1,5) = 2.502; P = .175; η2 = .334
η2 = .204
η2 = .449
F(3,15) = 1.285; P = .316;
F(1,5) = 4.070; P = .100;
η2 = .302
= .329
F(3,15) = 2.168; P = .134;
= .207
η2
η2
= .402
F(1,5) = 2.455; P = .178;
F(3,15) = 1.308; P = .308;
= .217
η2
η2
= .414
F(1,5) = 3.360; P = .126;
F(3,15) = 1.384; P = .286;
= .720
η2
η2
= .446
F(1,5) = 3.532; P = .119;
F(3,15) = 12.881; P = .002*;
= .286
η2
η2
= .449
F(1,5) = 4.024; P = .101;
F(3,15) = 2.005; P = .157;
= .797 = .328 = .222 = .416 = .472
η2 = .348
F(3,15) = 2.666; P = .085;
η2 = .489
F(3,15) = 4.780; P = .016*;
η2
F(3,15) = 4.467; P = .020*;
η2
F(3,15) = 3.560; P = .040*;
η2
F(3,15) = 1.427; P = .274;
η2
F(3,15) = 2.444; P = .104;
= .240
η2
η2
Note. CoP, center of pressure; ML, mediolateral; AP, anteroposterior; CoM, center of mass; N/A, not applicable. *Significant difference (P < .05).
CoP–CoM resultant moment arm
CoP–CoM AP moment arm
CoP–CoM ML moment arm
CoP AP velocity
CoP ML velocity
CoP AP displacement
F(3,15) = 1.580; P = .236;
F(1,5) = 4.073; P = .100;
η2
CoP ML displacement
F(3,15) = 19.573; P = .001*;
Dependent Measure
Condition Main Effect (M45 vs FWD vs L45 vs L90)
Time Main Effect (Pre vs Post)
Time (Pre, Post) × Condition (M45, FWD, L45, L90) Interaction
Table 4 Statistical test results for all the dependent measures in the S3 phase
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N/A
L45 < L90 (P = .004)
None
FWD > L90 (P = .002)
N/A
N/A
N/A
Post Hoc Test Results for Condition Main Effect (M45 vs FWD vs L45 vs L90)
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Tai-Chi Improves Postural Control in Older Adults 703
Figure 2 — Mean (SE) of A) mediolateral (ML) center of pressure (CoP) displacement, B) maximum (Max) mediolateral center of pressure–center of mass (CoM) separation distance, and C) maximum resultant center of pressure–center of mass separation distance observed for pre- (white column) and post-Tai chi intervention (black column) testing during the S1 phase of the center of pressure trace for gait initiation directed medially (M45), forward (FWD), 45° laterally (L45), and 90° laterally (L90). These three dependent measures showed significant condition × time interaction. *P < .05, significant difference between the pre- and postintervention tests (post hoc). †P < .07, statistical trend between the pre- and postintervention tests (post hoc). Displacements toward lateral side were designated as positive.
tasks. During the postural phase (S1), participants restricted the center of mass displacement toward the stance leg, indicating lower risk of losing stability in the two lateral conditions. During the locomotion phase (S3), Tai Chi increased and reversed the direction of the displacement in the center of pressure toward the stance leg. The significant increase in the center of pressure–center of mass moment arm, an indicator of better dynamic postural control, may have been due to the changes in displacement of the center of pressure. Before completing the Tai Chi intervention, the participants had levels of mobility that are commonly seen in older adults. For example, in the anticipatory postural phase (S1 phase) participants’ lateral6,13,14,30 and posterior center of pressure displacement for the FWD and L90 condition6,13,16 were similar to those seen in frail older adults. The value of the center of pressure’s lateral displacement for the FWD condition in our study during pre-Tai Chi testing (4.42 cm) fell in the range (2.90–4.50 cm) reported by previous researchers. Similarly, the value for the posterior displacement during the FWD condition in the current study (3.38 cm) is comparable to the values obtained in earlier studies (range: 2.81–3.54 cm). In addition, the values of the resultant CoP–CoM moment arm in the S1 phase obtained in our study before the Tai Chi intervention (6.27
cm) were similar to the value obtained by Martin and colleagues (6.05 cm) for a similar population.14 After 16 weeks of Tai Chi, significant changes in postural control occurred during the anticipatory postural phase (S1 phase) based on the condition of gait initiation. The center of pressure mediolateral displacement increased for the M45 and FWD conditions but decreased for the lateral stepping conditions (Figure 2A). These changes in the M45, FWD, and L45 conditions were not significant from pre to post. The change in the L90 condition showed a statistical trend. Although it was not significant, there was a trend for the center of pressure displacement to increase toward the swing leg, which may account for the subsequent increases in the mediolateral center of pressure–center of mass moment arm. It is also possible that after Tai Chi, participants may have been more confident maintaining single leg support and thus more comfortable positioning their center of mass closer to their swing leg. In contrast to the lateral conditions (L45 and L90), participants altered their strategy by restricting the movement of the center of mass toward the stance leg before toe-off of the swing leg. When stepping laterally, their initial movement was toward the swing leg. However, if the center of mass moved to the stance leg instead, the
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704 Vallabhajosula, Roberts, and Hass
Figure 3 — Mean (SE) of A) mediolateral (ML) center of pressure (CoP) displacement and B) mediolateral center of pressure velocity observed for pre- (white column) and post-Tai Chi intervention (black column) testing during the S3 phase of the center of pressure trace for gait initiation directed medially (M45), forward (FWD), 45° laterally (L45), and 90° laterally (L90). These two dependent measures showed significant condition × time interaction. Negative values indicate the center of pressure on stance-leg side moved medially and positive values indicate lateral movement. *P < .05, significant difference between the pre and post tests (post hoc).
next step with the stance leg would have been more difficult and required a different gait initiation strategy in the mediolateral shift of the center of pressure, a movement that is controlled by the hip abductors of the swing leg or the hip adductors of the stance leg. Another change that resulted from the Tai Chi intervention was a significantly increased resultant center of pressure–center of mass moment arm, which could reflect better momentum generation capabilities during the S1 phase. Changes in the center of pressure and resultant center of pressure–center of mass moment arms were similar for the mediolateral position but not the anterior–posterior directions. This may be due to the fact that the resultant center of pressure–center of mass moment arm and the center of pressure movement are more dependent on each other in the mediolateral direction than in the anterior–posterior direction during the postural phase. The locomotor phase (S3 phase), which is the most challenging phase during gait initiation, consists of the body being supported on a single leg. As the stance leg prepares for push-off, the center of pressure traverses forward under this leg and requires more dynamic postural control. Gatts and Woollacott observed older adults walking and found that their anteroposterior center of mass path significantly increased after Tai Chi training, which suggested an enhanced ability to tolerate unsteadiness or greater and finer control of the center of mass.31 Previous studies have shown that older adults who practice Tai Chi exhibit better postural control characteristics.3,32–34 Tai Chi exercises incorporate slow and continuous movement, focusing on using intrinsic feedback particularly from the proprioceptive sensory system to control center of mass and joint motion.34–37 In the current study, participants were instructed to emphasize physical and mental relaxation, breathing, and visualization, as well as use kinesthetic awareness to monitor and adjust their movements during
Tai Chi training and Tai Chi walking. These movements included coordination of the hand and arm with the body and weight shifting and body rotation. The improvements observed in the current study could be attributed to some of these factors. Since each of the first eight movements of the Yang style short form incorporate weightshifting in some form, it is possible that each of them could have contributed to the improved dynamic postural control seen in the current study. It may be worthwhile using future studies to examine which of these movements play a dominant role in improving postural control in older adults. The results of the present pilot study partially confirm that Tai Chi positively affects the finer dynamic control during the locomotor phase of stepping. Although Tai Chi had no effects on the anteroposterior movement of the center of pressure in the current study, the mediolateral displacement and velocity of the center of pressure did increase. After participants completed Tai Chi, their center of pressure shifted medially toward the stance leg in the two lateral conditions. This may have occurred because compared with walking on a level surface, people performing Tai Chi must maintain a more medial and anterior center of pressure location before toe-off.38 Another consequence of the center of pressure’s medial shift to the stance leg may have been a maximal shift of the center of pressure–center of mass moment arm in the same direction. Though the increase in the center of pressure–center of mass moment arm was not statistically significant in any of the experimental conditions, overall they did increase about 23%. It is possible that this increase resulted from participants’ greater confidence in executing the swing leg step while support remained on the stance leg during turning. Similar findings of the effects of Tai Chi on gait initiation in multiple directions were found for the center of pressure and center of mass separation. It has been reported that compared with level
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Tai-Chi Improves Postural Control in Older Adults 705
walking, Tai Chi movements necessitated experienced Tai Chi practitioners to exhibit a more medial and anterior center of pressure location before toe-off.28 Participants in the present pilot study seemed to have carried forward such mediolateral plantar pressure redistributions after Tai Chi training while performing multidirectional gait initiation. It is possible that more experience with Tai Chi could help the participants to exhibit better anteroposterior plantar pressure distributions while performing multidirectional gait initiation. Enhanced body awareness and stability limits may also account for these findings because they have been found to be increased in older adults who practice Tai Chi.39 The results of the present pilot study should be interpreted with caution because of the lack of a control or comparison group. In spite of the small sample size, significant changes in center of pressure and center of mass during multidirectional gait initiation were found after 16 weeks of Tai Chi. Whether greater changes can be found with a larger sample and longer intervention requires more research. Changes in the movement and displacement in the center of pressure with respect to the center of mass may be mechanisms by which Tai Chi improves dynamic postural control during gait initiation. Enhanced body awareness and confidence in postural control associated with Tai Chi may also contribute to the strategies older adults use during gait initiation. Acknowledgments The authors thank Debra McDonald for her help with editing the manuscript. This study was supported by the University of Florida Opportunity and the National Institutes of Health (Grant No. 5R03HD054594-02).
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