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The Effect of Tai Chi Chuan on Obstacle Crossing Strategy in Older Adults a
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Yao-Ting Chang , Chen-Fu Huang & Jia-Hao Chang
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Department of Physical Education, National Taiwan Normal University, Taiwan Published online: 26 Jun 2015.
Click for updates To cite this article: Yao-Ting Chang, Chen-Fu Huang & Jia-Hao Chang (2015): The Effect of Tai Chi Chuan on Obstacle Crossing Strategy in Older Adults, Research in Sports Medicine: An International Journal, DOI: 10.1080/15438627.2015.1040920 To link to this article: http://dx.doi.org/10.1080/15438627.2015.1040920
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Research in Sports Medicine, 1–15, 2015 © 2015 Taylor & Francis ISSN: 1543-8627 print/1543-8635 online DOI: 10.1080/15438627.2015.1040920
The Effect of Tai Chi Chuan on Obstacle Crossing Strategy in Older Adults YAO-TING CHANG, CHEN-FU HUANG, and JIA-HAO CHANG
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Department of Physical Education, National Taiwan Normal University, Taiwan
The purpose of this study was to determine the effect of Tai Chi Chuan on the strategies of obstacle-crossing behavior in older adults aged over 65 years. Fifteen Tai Chi group (TCG) participants were compared with 15 general group (GG) participants. Kinematic parameters (by Vicon motion analysis system) and ground reaction forces (by Kistler force plates) were synchronously recorded. A twoway mixed-design ANOVA (α = 0.05) was used to test the effects of the group and the obstacle height. The TCG performed significantly faster stride velocities, longer stride lengths, and shorter stride times than GG while crossing the obstacles. TCG could also produce significantly larger forward ground reaction forces to propel the body and were able to make a significantly greater flexion angle of the hip of the leading leg compared with the GG. It was concluded that the TCG adopted a different strategy with GG to cross the obstacles and completed the crossing behavior more effectively. KEYWORDS Tai Chi, aging, biomechanics, gait analysis, martial arts
INTRODUCTION Tripping during obstacle crossing is one of the most frequent causes of falls for older adults (aged over 65 years) with degenerating physiology (Di Fabio, Kurszewski, Jorgenson, & Kunz, 2004; McFadyen & Prince, 2002). Gait Received 18 August 2014; accepted 6 April 2015. This study was supported by ‘Aim for the Top University Plan’ of the National Taiwan Normal University, the Ministry of Education, Taiwan, R.O.C., and Ministry of Science and Technology, Taiwan (NSC 97-2410-H-003-095-MY2). Address correspondence to Jia-Hao Chang, Department of Physical Education, National Taiwan Normal University, No. 88, Sec. 4, Tingjhou Rd., Wunshan Distinct, Taipei City 116, Taiwan. E-mail: [email protected] 1
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performance during obstacle crossing indicates that older adults use slower step velocity and closely approach the trailing edge to cross the obstacle (Lowrey, Watson, & Vallis, 2007). The step length of older adults during obstacle crossing is shorter than that of young adults. Moreover, the crossing time of older adults is longer than that of young adults (Bovonsunthonchai, Hiengkaew, & Vachalathiti, 2012). When the walking speed is the same, the gait stability of healthy older adults is worse than that of healthy young adults (Kang & Dingwell, 2008). When the horizontal distance between the trailing foot and the obstacle is small prior to crossing, the flexion of the hip and knee and the dorsiflexion of the ankle of the trailing leg is reduced as the trailing foot moves above the obstacle. This approach would shorten the toe-obstacle clearance and increase the probability of tripping (Chou & Draganich, 1998). Previous studies indicated that Tai Chi Chuan exercise effectively improved ankle kinesthesia (Zhang, Sun, Yu, Song, & Mao, 2015) and may reduce the risk of falls among older adults (Low, Ang, Goh, & Chew, 2009; Li, Harmer, Fisher, & Mcauley, 2004; Li et al., 2005; Ramachandran, Rosengren, Yang, & Hsiao-Wecksler, 2007). Although Tai Chi Chuan exercise is considered to be a suitable exercise to reduce the risks of falls for older adults, the direct effect on obstacle crossing has rarely been studied. Because of their comfort with a single leg stance due to constant practice in this posture, the effect of Tai Chi Chuan exercise on obstacle crossing behavior in middle-aged adults revealed that Tai Chi Chuan practitioners spent significantly longer periods being supported by a single leg while crossing obstacles (Ramachandran et al., 2007). Older practitioners of Tai Chi Chuan (i.e., the Tai Chi group) performed at a faster crossing velocity during obstacle crossing than the older adults of a control walking group and showed a different plantar pressure distribution in the trailing foot (Zhang, Mao, Riskowski, & Song, 2011). However, these past studies did not focus on the ground reaction force exerted during obstacle crossing. More studies are needed on the effects of Tai Chi Chuan exercise on obstacle crossing in older adults. In the present study, older adults aged over 65 years of a Tai Chi group were compared with the older adults of a general group. The position of the leading foot relative to the obstacle is an important indicator that determines a successful obstacle crossing. The joint angle of the lower limbs when the toe is directly above the obstacle, i.e., the crossing angle, was introduced in a previous study (Lu, Chen, & Chen, 2006) and is also considered in the comparison of the two groups. Additional studies of this crossing position are warranted. Many other spatial and temporal variables determine the vertical clearance between the foot and the obstacle. In this study, the ground reaction force, the joint angle of the lower limbs, and the gait performance of the obstacle crossing when the toe of the foot was vertically above the obstacle were analyzed. Subsequently, the different crossing strategies between the Tai Chi group and the general group were addressed. The differences between the strategies may account for the differences in obstacle crossing performance in older adults. Thus, the
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purpose of this study was to determine the effect of Tai Chi Chuan on the strategies of obstacle crossing in older adults.
METHODS
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Participants Fifteen healthy older adults (nine males and six females, 71.7 ± 4.7 years old, 160.1 ± 7.2 cm, 58.3 ± 6.9 kg) who practiced Yang style Tai Chi Chuan of 108 postures (the duration of the routine is 26 minutes) three days a week for five or more years (the Tai Chi group, henceforth TCG) and 15 normal healthy older adults (nine males and six females, 72.6 ± 5.6 years old, 163.1 ± 8.5 cm, 60.8 ± 8.5 kg) who do leisure exercises (walking or jogging) for the same time period (the general group, henceforth GG) participated in this study. Participants in the TCG who met the experimental requirements were recruited from a Tai Chi Chuan club at the National Taiwan Normal University. Participants in the GG were selected by questionnaires and interviews to ensure that they met the experimental requirements. Independent t-tests showed no significant differences in age (p = 0.051), height (p = 0.093), and body mass (p = 0.325) between the two groups. However, significant differences in leg lengths between the two groups were observed (TCG: 77.9 ± 4.2 cm, GG: 83.8 ± 5.4 cm, p = 0.002). All participants had been free of lower limb neuro-musculoskeletal pathology for at least six months. All participants expressed that they had normal or corrected vision; however, we did not test their vision. This eyesight factor was a limitation of this study. This study was approved by a full board review process of the local Joint Institutional Review Board. The informed consent was explained to the participants, and all of the participants signed approved informed consent forms prior to testing.
Equipment An 8 m walkway and a height-adjustable obstacle comprising a thin, light, and soft rod placed across a metal frame were set up in the laboratory (Figure 1). The obstacle was placed at the middle of the walkway. To prevent falls, the rod would drop when the participants made contact with it. Three-dimensional marker trajectories were recorded at 250 Hz using a Vicon Ten Cameras MX13 + motion system (Vicon, Oxford Metrics Ltd., Oxford, UK). For the Vicon system, the spatial unit length (millimeter) was dynamically calibrated (via a calibration wand with reflective markers to determine length scales), and the spatial axial coordinates were statically calibrated (via an L-frame with reflective markers to indicate direction). The error of each camera was less than 0.2 mm. Thirty-nine reflective markers were used to track the motion of the body segments, including the head (left front of the head, left back of the head, right
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FIGURE 1 Top view of the laboratory setting.
front of the head, and right back of the head), hands (ulna styloid processes and second metacarpals), forearms (lateral epicondyle of the humerus, ulna styloid processes, and one tracking marker for each forearm), upper arms (lateral epicondyle of the humerus, acromion, and one tracking marker for each upper arm), torso (acromion, seventh cervical vertebrae, tenth thoracic vertebrae, clavicle, sternum, left and right anterior superior iliac spine (ASIS), left and right posterior superior iliac spine (PSIS), and one tracking marker), pelvis (left and right ASIS and left and right PSIS), thighs (left and right ASIS, left and right PSIS, lateral epicondyle of the femur, and one tracking marker for each thigh), shanks (lateral epicondyle of the femur, lateral malleolus, and one tracking marker for each shank) and feet (second metatarsal head, calcaneus, and lateral malleolus). Two Kistler force plates (9281, 60 × 40 cm2, 9287, 90 × 60 cm2, Kistler, Winterthur, Switzerland) were placed on either side of the obstacle to measure the ground reaction force at 1000 Hz. The force plates system was connected to the Vicon system by a capture card to synchronously record the motion system and force plate data.
Data Collection Participants were asked to walk on the walkway and cross three different obstacle heights (10%, 20%, and 30% of the leg length, in random order), i.e., to walk 4 m, cross the obstacle, and walk an additional 4 m. They were allowed
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to familiarize themselves with the walkway before experimental data were collected. In each crossing condition, participants were instructed to walk along the walkway barefoot at their preferred speed and to step over the obstacle. The average of three successful trials for each condition was reported.
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Data Analysis Human dynamic data were calculated by Visual3D software (C-Motion, Inc.). The whole-body was modeled as a 15-link (limb segment) system; each link was embedded with a local coordinate system (three non-collinear markers defined the coordinate system of a segment) with the positive x-axis to the right, the positive y-axis forward, and the positive z-axis upward. The joint angle was calculated by the rotation (i.e., a Cardan rotation sequence (X–Y–Z)) of the coordinate system of the distal segment relative to the coordinate system of the proximal segment.
Gait Parameters and Foot-obstacle Clearance The stride length, stride time, and stride velocity of a crossing stride (from the trailing foot touch-down before crossing to the next trailing foot touchdown after crossing) were computed for each trial based on heel strike events (Figure 2(a)). The stride length was the distance from the heel position of the trailing foot touch-down (i.e., before crossing) to the heel position of the next trailing foot touch-down (i.e., after crossing) normalized to the leg length (LL). The stride velocity was defined as the ratio of the stride length to the stride time during a crossing stride. The vertical and horizontal clearance values of the leading and trailing feet during obstacle crossing were calculated (Figure 2(b)). The vertical clearance of the leading foot (VCL) and the vertical clearance of the trailing foot (VCT) were defined as the minimum distances when the toe markers were vertically above the obstacle. The horizontal clearance between the obstacle and the heel marker on the leading foot (HCL) was calculated at the instant the leading foot was horizontally flat. The horizontal clearance between the obstacle and the toe marker on the trailing foot (HCT) was calculated at the instant the trailing foot was horizontally flat. The horizontal clearance was normalized to the LL.
Kinematics of the Lower Limbs When the toe marker of the leading foot was vertically above the obstacle, the joint angles on the sagittal plane of the hips, knees and ankles of the leading leg and the trailing leg were calculated. The joint angles of the lower limbs during a natural pose were defined as 0°. As shown in Figure 2(c), the hip
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FIGURE 2 (a) Three step positions were defined as a crossing stride and were used in gait parameter calculations, including stride length, stride time and stride velocity. (b) Definitions of foot-obstacle clearances. VCL and VCT were determined from the minimum of clearances between the toe and the obstacle. HCL and HCT were calculated at heel strike and toe strike, respectively. (c) Definitions of the flexion angle of the hip, knee, and ankle. 0° was defined as along thin lines.
flexion angle was defined as the angle between the extending lines of the trunk (i.e., a vertical, z-axial direction) and of the thigh (i.e., directionally from the hip to the knee). The knee flexion angle was defined as the angle between the extending lines of the thigh (i.e., directionally from the hip to the knee) and the shank (i.e., directionally from the knee to the ankle).
Ground Reaction Force When the toe marker of the leading foot was vertically above the obstacle, the anterior-posterior and vertical ground reaction forces on the trailing foot were analyzed. Additionally, when the toe marker of the trailing foot was vertically above the obstacle, the anterior-posterior and vertical ground reaction force on the leading foot were analyzed. The data were normalized to body weight.
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Statistical Analysis IBM SPSS Statistic 20 was used for all statistical analyses. A two-way mixeddesign ANOVA was used to test the differences between the two groups (TCG and GG) and between the different heights of the obstacle (10%, 20%, and 30% of LL). The effect of the obstacle height was examined by Scheffe’s posthoc comparisons. The differences were considered to be significant for p less than 0.05.
RESULTS
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Gait Parameters and Foot-obstacle Clearance The interactions between the groups and heights were observed in the stride length (p = 0.000) and the stride velocity (p = 0.000). And no interaction but the main effects of group (p = 0.017) and height (p = 0.000) were observed in stride time. The TCG had a significantly shorter stride time (p = 0.017), longer stride length (p = 0.000), and faster stride velocity (p = 0.002) than the GG (Table 1). The height of the obstacle differently affected the stride velocities for the two groups (TCG: 10% > 20% > 30% LL; CG: 10% > 30% LL and 20% > 30% LL). The obstacle height was observed to have an effect on the stride length in the TCG (10% > 20% LL and 10% > 30% LL). In addition, there were no interactions observed in the VCL, VCT, HCL, and HCT. The main effect of the group was observed in VCL, HCL, and HCT. The TCG showed higher VCL (p = 0.034), longer HCL (p = 0.047), and longer HCT (p = 0.003) than the GG (Table 1). The main effect of the obstacle height was observed in VCL (10% > 20% LL, 10% > 30% LL, p = 0.000) and VCT (10% > 20% LL, 10% > 30% LL, p = 0.002).
Kinematics of the Lower Limbs in the Sagittal Plane The joint angles of the leading leg and the trailing leg when the toe marker of the leading foot was vertically above the obstacle are shown in Table 2. There were no interactions between group and height. The TCG showed significantly larger hip flexion of the leading leg than the GG (p = 0.011). In addition, the main effect of the height of the obstacle was found in hip flexion (p = 0.000) and knee flexion (p = 0.000) of the leading leg (10% < 20% LL, 10% < 30% LL).
Ground Reaction Force No significant interactions between group and obstacle height were found. Table 3 shows the ground reaction force on the trailing (or leading) foot when the toe marker of the leading (or trailing) foot was vertically above the obstacle. The main effect of the group was observed in the anterior-posterior
‡
‡
0.21(0.06) 0.21(0.06) 0.29(0.10) 0.34(0.07)
1.68(0.13) 1.26(0.12) 1.05(0.16)
TCG
0.18(0.05) 0.20(0.05) 0.22(0.05) 0.28(0.04)
1.39(0.13) 1.47(0.25) 0.81(0.14)
GG
0.19(0.05) 0.20(0.06) 0.28(0.08) 0.33(0.05)
1.64(0.12) 1.36(0.12) 0.95(0.15)
TCG
20%
Significant interaction between group and height SL [F(2,56) = 10.547, p = 0.00013]. ST [F(2,56) = 1.211, p = 0.306]. SV [F(2,56) = 9.635, p = 0.00025]. VCL [F(2,56) = 0.963, p = 0.388]. VCT [F(2,56) = 0.94, p = 0.397]. HCL [F(2,56) = 2.541, p = 0.088]. HCT [F(2,56) = 0.293, p = 0.747]. * Main effect of groups SL [F(1,28) = 29.456, p = 0.00000086]. ST [F(1,28) = 6.505, p = 0.017]. SV [F(1,28) = 11.968, p = 0.002]. VCL [F(1,28) = 4.974, p = 0.034]. VCT [F(1,28) = 1.474, p = 0.235]. HCL [F(1,28) = 4.301, p = 0.047]. HCT [F(1,28) = 10.778, p = 0.003]. ‡ Main effect of heights SL [F(2,56) = 1.881, p = 0.162]. ST [F(2,56) = 66.418, p = 0.0000000000000017]. SV [F(2,56) = 43.663, p = 0.0000000000037]. VCL [F(2,56) = 11.12, p = 0.000086]. VCT [F(2,56) = 7.128, p = 0.002]. HCL [F(2,56) = 2.196, p = 0.121]. HCT [F(2,56) = 0.482, p = 0.62].
†
VCL (m)* ‡ VCT (m) ‡ HCL (LL)* HCT (LL)*
SL (LL) * ST (sec)* ‡ SV (m/sec)† *
†
Obstacle height (LL)
10%
0.15(0.04) 0.17(0.05) 0.23(0.07) 0.29(0.05)
1.41(0.11) 1.52(0.26) 0.80(0.15)
GG
0.18(0.05) 0.19(0.05) 0.25(0.05) 0.34(0.05)
1.62(0.12) 1.44(0.13) 0.88(0.13)
TCG
30%
0.15(0.04) 0.17(0.05) 0.23(0.08) 0.30(0.07)
1.42(0.13) 1.63(0.27) 0.75(0.13)
GG
TCG: 10% > 20%, 10% > 30% 10% < 20% < 30% TCG: 10% > 20% > 30% GG: 10% > 30%, 20% > 30% 10% > 20%, 10% > 30% 10% > 20%, 10% > 30% No No
Effect of the height of obstacle
TABLE 1 Mean (SD) of Stride Length (SL), Stride Time (ST), Stride Velocity (SV), and Foot-obstacle Clearance for both Groups when Crossing Obstacles with Three Different Heights. The Units of SL, HCL, and HCT were LL (Leg Length). α = 0.05
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61 (9) 87 (13) 13 (5) 1 (10) 8 (6) 7 (3)
7 (6) 8 (5) 10 (3)
GG
73 (9) 91 (9) 15 (6)
TCG
7 (5) 8 (5) 8 (3)
79 (7) 101 (10) 16 (7)
TCG
20%
2 (9) 9 (6) 7 (4)
67 (9) 95 (12) 9 (21)
GG
Significant interaction between group and height Leading hip [F(2,56) = 1.196, p = 0.31]. Leading knee [F(2,56) = 2.293, p = 0.11]. Leading ankle [F(2,56) = 1.504, p = 0.231]. Trailing hip [F(2,56) = 0.254, p = 0.777]. Trailing knee [F(2,56) = 1.940, p = 0.153]. Trailing ankle [F(2,56) = 1.142, p = 0.327]. * Main effect due to groups Leading hip [F(1,28) = 7.515, p = 0.011]. Leading knee [F(1,28) = 0.038, p = 0.846]. Leading ankle [F(1,28) = 1.816, p = 0.189]. Trailing hip [F(1,28) = 3.405, p = 0.076]. Trailing knee [F(1,28) = 0.004, p = 0.951]. Trailing ankle [F(1,28) = 1.816, p = 0.819]. ‡ Main effect due to heights Leading hip [F(2,56) = 12.193, p = 0.00004]. Leading knee [F(2,56) = 9.641, p = 0.00025]. Leading ankle [F(2,56) = 2.684, p = 0.077]. Trailing hip [F(2,56) = 0.397, p = 0.674]. Trailing knee [F(2,56) = 2.735, p = 0.074]. Trailing ankle [F(2,56) = 2.684, p = 0.077].
†
Leading leg (°) Hip flex * ‡ Knee flex ‡ Ankle dorsi-flex Trailing leg (°) Hip flex Knee flex Ankle dorsi-flex
Obstacle height (LL)
10%
7 (7) 10 (7) 8 (5)
81 (21) 100 (30) 15 (9)
TCG
30%
2 (10) 9 (7) 7 (3)
75 (10) 107 (12) 15 (6)
GG
No No No
10% < 20%, 10% < 30% 10% < 20%, 10% < 30% No
Effect of the height of obstacle
TABLE 2 Mean (SD) of Joint Angles of Leading Leg and Trailing Leg for both Groups when the Toe Marker of the Leading Foot was Vertically Above the Obstacle with Three Different Heights. α = 0.05
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0.838 (0.069)
0.845 (0.072)
−0.033 (0.020)
−0.016 (0.010) 0.836 (0.047)
GG
0.823 (0.059)
−0.027 (0.025)
0.011 (0.013) 0.718 (0.058)
TCG
GG
0.839 (0.102)
−0.025 (0.022)
−0.017 (0.021) 0.813 (0.045)
20%
Significant interaction between group and height Trailing foot GRFA-P [F(2,56) = 1.359, p = 0.265]. Trailing foot vGRF [F(2,56) = 1.048, p = 0.357]. Leading foot GRFA-P [F(2,56) = 0.256, p = 0.775]. Leading foot vGRF [F(2,56) = 0.804, p = 0.453]. * Main effect due to groups Trailing foot GRFA-P [F(1,28) = 48.546, p = 0.00000014]. Trailing foot vGRF [F(1,28) = 17.561, p = 0.00025]. Leading foot GRFA-P [F(1,28) = 0.439, p = 0.513]. Leading foot vGRF [F(1,28) = 0.012, p = 0.913] ‡ Main effect due to heights Trailing foot GRFA-P [F(2,56) = 4.137, p = 0.021]. Trailing foot vGRF [F(2,56) = 8.622, p = 0.001]. Leading foot GRFA-P [F(2,56) = 4.816, p = 0.012]. Leading foot vGRF [F(2,56) = 0.972, p = 0.385].
vGRF
−0.041 (0.027)
Leading foot (when trailing foot crossing) GRFA (+)/P (-) ‡
†
0.018 (0.014) 0.727 (0.079)
TCG
Trailing foot (when leading foot crossing) GRFA (+)/P (-)* ‡ vGRF* ‡
Obstacle height (LL)
10%
0.858 (0.093)
−0.029 (0.033)
0.009 (0.012) 0.707 (0.096)
TCG
GG
Effect of the height of obstacle
−0.024 (0.027) 10% > 20%, 10% > 30% 0.842 (0.140) No
−0.025 (0.016) 10% ≠ 30% 0.799 (0.046) 10% > 20%, 10% > 30%
30%
TABLE 3 Mean (SD) of Anterior-Posterior GRF and Vertical GRF (vGRF) of the Trailing (Leading) Foot for Both Groups when the Toe Markers of the Leading (Trailing) Foot was Vertically above the Obstacle with Three Different Heights. The Unit was Body Weight (BW). α = 0.05
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ground reaction force (p = 0.000) and vertical ground reaction force (p = 0.000) on the trailing foot (supporting). When the toe marker of the leading foot (swinging) was above the obstacle, the ground reaction force on the trailing foot was positive (forward) in the TCG, but it was negative (backward) in the GG. The TCG also showed a significantly smaller vertical ground reaction force (p = 0.000) on the trailing foot than the GG when the toe marker of the swinging leading foot was above the obstacle. Furthermore, the main effect of the obstacle height was found in the anterior-posterior ground reaction force on the trailing foot (10%≠30%, p = 0.021) and the leading foot (10% > 20% LL, 10% > 30% LL, p = 0.012) and the vertical ground reaction force on the trailing foot (10% > 20% LL, 10% > 30% LL, p = 0.001).
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DISCUSSION The height of the leading foot relative to the obstacle is important for a successful obstacle crossing. Here, we address the situation at the instant the toe of the leading foot was directly above the obstacle. On the trailing foot, a forward ground reaction force was observed in the TCG, but a backward ground reaction force was observed in the GG. During the stance phase in a gait cycle, the forward ground reaction force occurred in the push-off period. Normally, the backward ground reaction force occurs within the first half of the stance phase (Ren, Jones, & Howard, 2007). The trailing foot pushed off, and the leading foot crossed the obstacle in the same period of a gait cycle for the TCG. However, for the GG, the leading foot crossed the obstacle before the trailing foot pushed off. A previous study indicated that Tai Chi training significantly increased the COManterior-posterior path in gait (Strawberry, Gatts, & Woollacott, 2007). In the current study, the ground reaction force on the trailing foot of the GG was backward when the leading foot was directly above the obstacle. This outcome may be due to the GG having a longer crossing cycle or a shorter HCT than the TCG. The older adults of the GG were observed to pay more attention to the obstacle crossing prior to walking forward. The older adults of the GG used a longer stride time to make a successful obstacle crossing. The shorter HCT and the slower stride velocity in this study also revealed that the older adults of the GG really adopted a more cautious strategy to cross the obstacle (Lowrey et al., 2007). As the height of the obstacle increased, the variation of the anterior-posterior ground reaction force increasingly reflected this cautious strategy. Compared with the TCG, the older adults of the GG seemed to focus more on the obstacle crossing; however, they still showed a smaller VCL than the older adults of the TCG. In prior studies, older adults showed larger hip flexion angles in the crossing leg than younger adults, which resulted in a larger VCL (Galna, Peters, Murphy, & Morris, 2009, Lu et al., 2006; McFadyen & Prince, 2002). This strategy can reduce the risk of tripping (Lu et al., 2010). In the current
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study, when the leading foot was directly above the obstacle, the TCG flexed the hip of the leading leg more than the GG. This result implied that the TCG adopted a different cautious strategy than the GG to safely cross the obstacle, i.e., to increase the VCL by flexing the hip of the leading leg to a greater degree. Even if the VCL decreased as the height of obstacle increased, both groups of older adults tended to increase the flexion of the leading hip to avoid tripping. The larger hip flexion of the leading leg (swing) also resulted in the faster stride velocity for the older adults of the TCG (Yang, Larsen, Alkjær, Lynnerup, & Simonsen, 2014). In this study, the older adults of the TCG had a longer stride length, less stride time, and faster stride velocity than the older adults of the GG in crossing the obstacles. This result was similar to previous studies (Zhang et al., 2011). Other studies also revealed that younger adults had a shorter stride time than older adults (Bovonsunthonchai et al., 2012; Uchiyama, Demura, & Sugiura, 2012) and that healthy people showed longer stride lengths and faster stride velocities than people with Parkinson’s or cerebellar diseases (Kim et al., 2013; Vitório, Pieruccini-Faria, Stella, Gobbi, & Gobbi, 2010). McFadyen & Prince (2002) revealed that the longer stride time, shorter stride length and slower stride velocity in crossing obstacles may be positively related to a diminishing physical capacity in older adults. Gait speed was associated with survival in older adults (Studenski et al., 2011). Gait speed was found to be a consistent risk factor for disability, cognitive impairment, institutionalization, falls, and mortality (Van Kan et al., 2009). This finding implies that gait speed is correlated with physical capacity for older adults. Moreover, Rosengren, McAuley, & Mihalko (1998) revealed that sedentary older adults adopted a more cautious walking style than active older adults and exhibited shorter step lengths and slower step velocities in walking with or without obstacles. Shorter step lengths and slower step velocities were associated with cautious strategies. The older adults of the TCG were observed to have better physical capabilities and adopted a different strategy that resulted in a longer HCT, faster stride velocity, longer stride length, and lower stride time compared with the older adults of the GG. During Tai Chi Chuan exercise, the body smoothly shifts from foot to foot in a semi-squatting posture. Different parts of the body take turns playing the role of stabilizer and mover, allowing smooth movements to be executed (Wong, Lin, Chou, Tang, & Wong, 2001). The duration of single-limb support is much longer in Tai Chi Chuan exercises than in normal walking (Wu, Liu, Hitt, & Millon, 2004). The increased contraction duration of the muscles due to weight bearing on the supporting limbs may improve muscle strength (Mao, Hong, & Li, 2006). Tai Chi Chuan movements include combinations of stepping forward, backward, sideways, up, and down, turning, and fixing. Diversified stepping patterns could improve the balance control ability, even for instantaneous changes in the stepping pattern (Mao et al., 2006). Therefore, Tai Chi Chuan training could improve balance, postural control (Law & Li, 2014; Lelard, Doutrellot, David, & Ahmaidi, 2010; Li et al., 2012), muscular strength, and flexibility for older adults
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(Hong, Li, & Robinson, 2000, Law & Li, 2014). According to past studies, Tai Chi training improved some abilities, such as single foot support, postural control, and the range of joint motion. The benefits of these improvements were indicated in the older adults of the TCG with increased hip flexing of the leading leg (when the leading leg was swinging) on a single support phase, faster stride velocity and longer step length (Strawberry et al., 2007) in obstacle-crossing behavior. These results correlated with the results of the current study. The effect of Tai Chi Chuan training was made by long-term practice. This study adopted a cross-sectional study design. Although this study was not a random controlled study and could not precisely point out that all the benefits were from Tai Chi Chuan training only, differences between the TCG and GG in obstacle-crossing behavior were observed. Through a discussion and comparisons with other studies, we believe that the older adults of the TCG executed different patterns from general older adults in crossing obstacles due to long-term Tai Chi Chuan training.
CONCLUSIONS The results from this study revealed that the TCG had more efficient performance than the GG in obstacle-crossing behavior. With regular Tai Chi Chuan training, older adults may improve their physical capabilities and can adopt a more efficient strategy, i.e., paying less attention to crossing the obstacle and increasing the VCL by flexing the hip of the leading leg more, which enables them to cross the obstacle safely at a faster speed. Therefore, this study suggested that long-term, regular Tai Chi Chuan training is beneficial for older adults in obstacle-crossing behavior.
DISCLOSURE STATEMENT No potential conflict of interest was reported by the author(s).
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The Effect of Tai Chi Chuan on Obstacle Crossing Strategy in Older Adults a
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Yao-Ting Chang , Chen-Fu Huang & Jia-Hao Chang
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Department of Physical Education, National Taiwan Normal University, Taiwan Published online: 26 Jun 2015.
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The Effect of Tai Chi Chuan on Obstacle Crossing Strategy in Older Adults YAO-TING CHANG, CHEN-FU HUANG, and JIA-HAO CHANG
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Department of Physical Education, National Taiwan Normal University, Taiwan
The purpose of this study was to determine the effect of Tai Chi Chuan on the strategies of obstacle-crossing behavior in older adults aged over 65 years. Fifteen Tai Chi group (TCG) participants were compared with 15 general group (GG) participants. Kinematic parameters (by Vicon motion analysis system) and ground reaction forces (by Kistler force plates) were synchronously recorded. A twoway mixed-design ANOVA (α = 0.05) was used to test the effects of the group and the obstacle height. The TCG performed significantly faster stride velocities, longer stride lengths, and shorter stride times than GG while crossing the obstacles. TCG could also produce significantly larger forward ground reaction forces to propel the body and were able to make a significantly greater flexion angle of the hip of the leading leg compared with the GG. It was concluded that the TCG adopted a different strategy with GG to cross the obstacles and completed the crossing behavior more effectively. KEYWORDS Tai Chi, aging, biomechanics, gait analysis, martial arts
INTRODUCTION Tripping during obstacle crossing is one of the most frequent causes of falls for older adults (aged over 65 years) with degenerating physiology (Di Fabio, Kurszewski, Jorgenson, & Kunz, 2004; McFadyen & Prince, 2002). Gait Received 18 August 2014; accepted 6 April 2015. This study was supported by ‘Aim for the Top University Plan’ of the National Taiwan Normal University, the Ministry of Education, Taiwan, R.O.C., and Ministry of Science and Technology, Taiwan (NSC 97-2410-H-003-095-MY2). Address correspondence to Jia-Hao Chang, Department of Physical Education, National Taiwan Normal University, No. 88, Sec. 4, Tingjhou Rd., Wunshan Distinct, Taipei City 116, Taiwan. E-mail: [email protected] 1
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performance during obstacle crossing indicates that older adults use slower step velocity and closely approach the trailing edge to cross the obstacle (Lowrey, Watson, & Vallis, 2007). The step length of older adults during obstacle crossing is shorter than that of young adults. Moreover, the crossing time of older adults is longer than that of young adults (Bovonsunthonchai, Hiengkaew, & Vachalathiti, 2012). When the walking speed is the same, the gait stability of healthy older adults is worse than that of healthy young adults (Kang & Dingwell, 2008). When the horizontal distance between the trailing foot and the obstacle is small prior to crossing, the flexion of the hip and knee and the dorsiflexion of the ankle of the trailing leg is reduced as the trailing foot moves above the obstacle. This approach would shorten the toe-obstacle clearance and increase the probability of tripping (Chou & Draganich, 1998). Previous studies indicated that Tai Chi Chuan exercise effectively improved ankle kinesthesia (Zhang, Sun, Yu, Song, & Mao, 2015) and may reduce the risk of falls among older adults (Low, Ang, Goh, & Chew, 2009; Li, Harmer, Fisher, & Mcauley, 2004; Li et al., 2005; Ramachandran, Rosengren, Yang, & Hsiao-Wecksler, 2007). Although Tai Chi Chuan exercise is considered to be a suitable exercise to reduce the risks of falls for older adults, the direct effect on obstacle crossing has rarely been studied. Because of their comfort with a single leg stance due to constant practice in this posture, the effect of Tai Chi Chuan exercise on obstacle crossing behavior in middle-aged adults revealed that Tai Chi Chuan practitioners spent significantly longer periods being supported by a single leg while crossing obstacles (Ramachandran et al., 2007). Older practitioners of Tai Chi Chuan (i.e., the Tai Chi group) performed at a faster crossing velocity during obstacle crossing than the older adults of a control walking group and showed a different plantar pressure distribution in the trailing foot (Zhang, Mao, Riskowski, & Song, 2011). However, these past studies did not focus on the ground reaction force exerted during obstacle crossing. More studies are needed on the effects of Tai Chi Chuan exercise on obstacle crossing in older adults. In the present study, older adults aged over 65 years of a Tai Chi group were compared with the older adults of a general group. The position of the leading foot relative to the obstacle is an important indicator that determines a successful obstacle crossing. The joint angle of the lower limbs when the toe is directly above the obstacle, i.e., the crossing angle, was introduced in a previous study (Lu, Chen, & Chen, 2006) and is also considered in the comparison of the two groups. Additional studies of this crossing position are warranted. Many other spatial and temporal variables determine the vertical clearance between the foot and the obstacle. In this study, the ground reaction force, the joint angle of the lower limbs, and the gait performance of the obstacle crossing when the toe of the foot was vertically above the obstacle were analyzed. Subsequently, the different crossing strategies between the Tai Chi group and the general group were addressed. The differences between the strategies may account for the differences in obstacle crossing performance in older adults. Thus, the
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purpose of this study was to determine the effect of Tai Chi Chuan on the strategies of obstacle crossing in older adults.
METHODS
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Participants Fifteen healthy older adults (nine males and six females, 71.7 ± 4.7 years old, 160.1 ± 7.2 cm, 58.3 ± 6.9 kg) who practiced Yang style Tai Chi Chuan of 108 postures (the duration of the routine is 26 minutes) three days a week for five or more years (the Tai Chi group, henceforth TCG) and 15 normal healthy older adults (nine males and six females, 72.6 ± 5.6 years old, 163.1 ± 8.5 cm, 60.8 ± 8.5 kg) who do leisure exercises (walking or jogging) for the same time period (the general group, henceforth GG) participated in this study. Participants in the TCG who met the experimental requirements were recruited from a Tai Chi Chuan club at the National Taiwan Normal University. Participants in the GG were selected by questionnaires and interviews to ensure that they met the experimental requirements. Independent t-tests showed no significant differences in age (p = 0.051), height (p = 0.093), and body mass (p = 0.325) between the two groups. However, significant differences in leg lengths between the two groups were observed (TCG: 77.9 ± 4.2 cm, GG: 83.8 ± 5.4 cm, p = 0.002). All participants had been free of lower limb neuro-musculoskeletal pathology for at least six months. All participants expressed that they had normal or corrected vision; however, we did not test their vision. This eyesight factor was a limitation of this study. This study was approved by a full board review process of the local Joint Institutional Review Board. The informed consent was explained to the participants, and all of the participants signed approved informed consent forms prior to testing.
Equipment An 8 m walkway and a height-adjustable obstacle comprising a thin, light, and soft rod placed across a metal frame were set up in the laboratory (Figure 1). The obstacle was placed at the middle of the walkway. To prevent falls, the rod would drop when the participants made contact with it. Three-dimensional marker trajectories were recorded at 250 Hz using a Vicon Ten Cameras MX13 + motion system (Vicon, Oxford Metrics Ltd., Oxford, UK). For the Vicon system, the spatial unit length (millimeter) was dynamically calibrated (via a calibration wand with reflective markers to determine length scales), and the spatial axial coordinates were statically calibrated (via an L-frame with reflective markers to indicate direction). The error of each camera was less than 0.2 mm. Thirty-nine reflective markers were used to track the motion of the body segments, including the head (left front of the head, left back of the head, right
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FIGURE 1 Top view of the laboratory setting.
front of the head, and right back of the head), hands (ulna styloid processes and second metacarpals), forearms (lateral epicondyle of the humerus, ulna styloid processes, and one tracking marker for each forearm), upper arms (lateral epicondyle of the humerus, acromion, and one tracking marker for each upper arm), torso (acromion, seventh cervical vertebrae, tenth thoracic vertebrae, clavicle, sternum, left and right anterior superior iliac spine (ASIS), left and right posterior superior iliac spine (PSIS), and one tracking marker), pelvis (left and right ASIS and left and right PSIS), thighs (left and right ASIS, left and right PSIS, lateral epicondyle of the femur, and one tracking marker for each thigh), shanks (lateral epicondyle of the femur, lateral malleolus, and one tracking marker for each shank) and feet (second metatarsal head, calcaneus, and lateral malleolus). Two Kistler force plates (9281, 60 × 40 cm2, 9287, 90 × 60 cm2, Kistler, Winterthur, Switzerland) were placed on either side of the obstacle to measure the ground reaction force at 1000 Hz. The force plates system was connected to the Vicon system by a capture card to synchronously record the motion system and force plate data.
Data Collection Participants were asked to walk on the walkway and cross three different obstacle heights (10%, 20%, and 30% of the leg length, in random order), i.e., to walk 4 m, cross the obstacle, and walk an additional 4 m. They were allowed
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to familiarize themselves with the walkway before experimental data were collected. In each crossing condition, participants were instructed to walk along the walkway barefoot at their preferred speed and to step over the obstacle. The average of three successful trials for each condition was reported.
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Data Analysis Human dynamic data were calculated by Visual3D software (C-Motion, Inc.). The whole-body was modeled as a 15-link (limb segment) system; each link was embedded with a local coordinate system (three non-collinear markers defined the coordinate system of a segment) with the positive x-axis to the right, the positive y-axis forward, and the positive z-axis upward. The joint angle was calculated by the rotation (i.e., a Cardan rotation sequence (X–Y–Z)) of the coordinate system of the distal segment relative to the coordinate system of the proximal segment.
Gait Parameters and Foot-obstacle Clearance The stride length, stride time, and stride velocity of a crossing stride (from the trailing foot touch-down before crossing to the next trailing foot touchdown after crossing) were computed for each trial based on heel strike events (Figure 2(a)). The stride length was the distance from the heel position of the trailing foot touch-down (i.e., before crossing) to the heel position of the next trailing foot touch-down (i.e., after crossing) normalized to the leg length (LL). The stride velocity was defined as the ratio of the stride length to the stride time during a crossing stride. The vertical and horizontal clearance values of the leading and trailing feet during obstacle crossing were calculated (Figure 2(b)). The vertical clearance of the leading foot (VCL) and the vertical clearance of the trailing foot (VCT) were defined as the minimum distances when the toe markers were vertically above the obstacle. The horizontal clearance between the obstacle and the heel marker on the leading foot (HCL) was calculated at the instant the leading foot was horizontally flat. The horizontal clearance between the obstacle and the toe marker on the trailing foot (HCT) was calculated at the instant the trailing foot was horizontally flat. The horizontal clearance was normalized to the LL.
Kinematics of the Lower Limbs When the toe marker of the leading foot was vertically above the obstacle, the joint angles on the sagittal plane of the hips, knees and ankles of the leading leg and the trailing leg were calculated. The joint angles of the lower limbs during a natural pose were defined as 0°. As shown in Figure 2(c), the hip
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FIGURE 2 (a) Three step positions were defined as a crossing stride and were used in gait parameter calculations, including stride length, stride time and stride velocity. (b) Definitions of foot-obstacle clearances. VCL and VCT were determined from the minimum of clearances between the toe and the obstacle. HCL and HCT were calculated at heel strike and toe strike, respectively. (c) Definitions of the flexion angle of the hip, knee, and ankle. 0° was defined as along thin lines.
flexion angle was defined as the angle between the extending lines of the trunk (i.e., a vertical, z-axial direction) and of the thigh (i.e., directionally from the hip to the knee). The knee flexion angle was defined as the angle between the extending lines of the thigh (i.e., directionally from the hip to the knee) and the shank (i.e., directionally from the knee to the ankle).
Ground Reaction Force When the toe marker of the leading foot was vertically above the obstacle, the anterior-posterior and vertical ground reaction forces on the trailing foot were analyzed. Additionally, when the toe marker of the trailing foot was vertically above the obstacle, the anterior-posterior and vertical ground reaction force on the leading foot were analyzed. The data were normalized to body weight.
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Statistical Analysis IBM SPSS Statistic 20 was used for all statistical analyses. A two-way mixeddesign ANOVA was used to test the differences between the two groups (TCG and GG) and between the different heights of the obstacle (10%, 20%, and 30% of LL). The effect of the obstacle height was examined by Scheffe’s posthoc comparisons. The differences were considered to be significant for p less than 0.05.
RESULTS
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Gait Parameters and Foot-obstacle Clearance The interactions between the groups and heights were observed in the stride length (p = 0.000) and the stride velocity (p = 0.000). And no interaction but the main effects of group (p = 0.017) and height (p = 0.000) were observed in stride time. The TCG had a significantly shorter stride time (p = 0.017), longer stride length (p = 0.000), and faster stride velocity (p = 0.002) than the GG (Table 1). The height of the obstacle differently affected the stride velocities for the two groups (TCG: 10% > 20% > 30% LL; CG: 10% > 30% LL and 20% > 30% LL). The obstacle height was observed to have an effect on the stride length in the TCG (10% > 20% LL and 10% > 30% LL). In addition, there were no interactions observed in the VCL, VCT, HCL, and HCT. The main effect of the group was observed in VCL, HCL, and HCT. The TCG showed higher VCL (p = 0.034), longer HCL (p = 0.047), and longer HCT (p = 0.003) than the GG (Table 1). The main effect of the obstacle height was observed in VCL (10% > 20% LL, 10% > 30% LL, p = 0.000) and VCT (10% > 20% LL, 10% > 30% LL, p = 0.002).
Kinematics of the Lower Limbs in the Sagittal Plane The joint angles of the leading leg and the trailing leg when the toe marker of the leading foot was vertically above the obstacle are shown in Table 2. There were no interactions between group and height. The TCG showed significantly larger hip flexion of the leading leg than the GG (p = 0.011). In addition, the main effect of the height of the obstacle was found in hip flexion (p = 0.000) and knee flexion (p = 0.000) of the leading leg (10% < 20% LL, 10% < 30% LL).
Ground Reaction Force No significant interactions between group and obstacle height were found. Table 3 shows the ground reaction force on the trailing (or leading) foot when the toe marker of the leading (or trailing) foot was vertically above the obstacle. The main effect of the group was observed in the anterior-posterior
‡
‡
0.21(0.06) 0.21(0.06) 0.29(0.10) 0.34(0.07)
1.68(0.13) 1.26(0.12) 1.05(0.16)
TCG
0.18(0.05) 0.20(0.05) 0.22(0.05) 0.28(0.04)
1.39(0.13) 1.47(0.25) 0.81(0.14)
GG
0.19(0.05) 0.20(0.06) 0.28(0.08) 0.33(0.05)
1.64(0.12) 1.36(0.12) 0.95(0.15)
TCG
20%
Significant interaction between group and height SL [F(2,56) = 10.547, p = 0.00013]. ST [F(2,56) = 1.211, p = 0.306]. SV [F(2,56) = 9.635, p = 0.00025]. VCL [F(2,56) = 0.963, p = 0.388]. VCT [F(2,56) = 0.94, p = 0.397]. HCL [F(2,56) = 2.541, p = 0.088]. HCT [F(2,56) = 0.293, p = 0.747]. * Main effect of groups SL [F(1,28) = 29.456, p = 0.00000086]. ST [F(1,28) = 6.505, p = 0.017]. SV [F(1,28) = 11.968, p = 0.002]. VCL [F(1,28) = 4.974, p = 0.034]. VCT [F(1,28) = 1.474, p = 0.235]. HCL [F(1,28) = 4.301, p = 0.047]. HCT [F(1,28) = 10.778, p = 0.003]. ‡ Main effect of heights SL [F(2,56) = 1.881, p = 0.162]. ST [F(2,56) = 66.418, p = 0.0000000000000017]. SV [F(2,56) = 43.663, p = 0.0000000000037]. VCL [F(2,56) = 11.12, p = 0.000086]. VCT [F(2,56) = 7.128, p = 0.002]. HCL [F(2,56) = 2.196, p = 0.121]. HCT [F(2,56) = 0.482, p = 0.62].
†
VCL (m)* ‡ VCT (m) ‡ HCL (LL)* HCT (LL)*
SL (LL) * ST (sec)* ‡ SV (m/sec)† *
†
Obstacle height (LL)
10%
0.15(0.04) 0.17(0.05) 0.23(0.07) 0.29(0.05)
1.41(0.11) 1.52(0.26) 0.80(0.15)
GG
0.18(0.05) 0.19(0.05) 0.25(0.05) 0.34(0.05)
1.62(0.12) 1.44(0.13) 0.88(0.13)
TCG
30%
0.15(0.04) 0.17(0.05) 0.23(0.08) 0.30(0.07)
1.42(0.13) 1.63(0.27) 0.75(0.13)
GG
TCG: 10% > 20%, 10% > 30% 10% < 20% < 30% TCG: 10% > 20% > 30% GG: 10% > 30%, 20% > 30% 10% > 20%, 10% > 30% 10% > 20%, 10% > 30% No No
Effect of the height of obstacle
TABLE 1 Mean (SD) of Stride Length (SL), Stride Time (ST), Stride Velocity (SV), and Foot-obstacle Clearance for both Groups when Crossing Obstacles with Three Different Heights. The Units of SL, HCL, and HCT were LL (Leg Length). α = 0.05
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8 Y.-T. Chang et al.
61 (9) 87 (13) 13 (5) 1 (10) 8 (6) 7 (3)
7 (6) 8 (5) 10 (3)
GG
73 (9) 91 (9) 15 (6)
TCG
7 (5) 8 (5) 8 (3)
79 (7) 101 (10) 16 (7)
TCG
20%
2 (9) 9 (6) 7 (4)
67 (9) 95 (12) 9 (21)
GG
Significant interaction between group and height Leading hip [F(2,56) = 1.196, p = 0.31]. Leading knee [F(2,56) = 2.293, p = 0.11]. Leading ankle [F(2,56) = 1.504, p = 0.231]. Trailing hip [F(2,56) = 0.254, p = 0.777]. Trailing knee [F(2,56) = 1.940, p = 0.153]. Trailing ankle [F(2,56) = 1.142, p = 0.327]. * Main effect due to groups Leading hip [F(1,28) = 7.515, p = 0.011]. Leading knee [F(1,28) = 0.038, p = 0.846]. Leading ankle [F(1,28) = 1.816, p = 0.189]. Trailing hip [F(1,28) = 3.405, p = 0.076]. Trailing knee [F(1,28) = 0.004, p = 0.951]. Trailing ankle [F(1,28) = 1.816, p = 0.819]. ‡ Main effect due to heights Leading hip [F(2,56) = 12.193, p = 0.00004]. Leading knee [F(2,56) = 9.641, p = 0.00025]. Leading ankle [F(2,56) = 2.684, p = 0.077]. Trailing hip [F(2,56) = 0.397, p = 0.674]. Trailing knee [F(2,56) = 2.735, p = 0.074]. Trailing ankle [F(2,56) = 2.684, p = 0.077].
†
Leading leg (°) Hip flex * ‡ Knee flex ‡ Ankle dorsi-flex Trailing leg (°) Hip flex Knee flex Ankle dorsi-flex
Obstacle height (LL)
10%
7 (7) 10 (7) 8 (5)
81 (21) 100 (30) 15 (9)
TCG
30%
2 (10) 9 (7) 7 (3)
75 (10) 107 (12) 15 (6)
GG
No No No
10% < 20%, 10% < 30% 10% < 20%, 10% < 30% No
Effect of the height of obstacle
TABLE 2 Mean (SD) of Joint Angles of Leading Leg and Trailing Leg for both Groups when the Toe Marker of the Leading Foot was Vertically Above the Obstacle with Three Different Heights. α = 0.05
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The Effect of Tai Chi Chuan on Obstacle Crossing Strategy 9
0.838 (0.069)
0.845 (0.072)
−0.033 (0.020)
−0.016 (0.010) 0.836 (0.047)
GG
0.823 (0.059)
−0.027 (0.025)
0.011 (0.013) 0.718 (0.058)
TCG
GG
0.839 (0.102)
−0.025 (0.022)
−0.017 (0.021) 0.813 (0.045)
20%
Significant interaction between group and height Trailing foot GRFA-P [F(2,56) = 1.359, p = 0.265]. Trailing foot vGRF [F(2,56) = 1.048, p = 0.357]. Leading foot GRFA-P [F(2,56) = 0.256, p = 0.775]. Leading foot vGRF [F(2,56) = 0.804, p = 0.453]. * Main effect due to groups Trailing foot GRFA-P [F(1,28) = 48.546, p = 0.00000014]. Trailing foot vGRF [F(1,28) = 17.561, p = 0.00025]. Leading foot GRFA-P [F(1,28) = 0.439, p = 0.513]. Leading foot vGRF [F(1,28) = 0.012, p = 0.913] ‡ Main effect due to heights Trailing foot GRFA-P [F(2,56) = 4.137, p = 0.021]. Trailing foot vGRF [F(2,56) = 8.622, p = 0.001]. Leading foot GRFA-P [F(2,56) = 4.816, p = 0.012]. Leading foot vGRF [F(2,56) = 0.972, p = 0.385].
vGRF
−0.041 (0.027)
Leading foot (when trailing foot crossing) GRFA (+)/P (-) ‡
†
0.018 (0.014) 0.727 (0.079)
TCG
Trailing foot (when leading foot crossing) GRFA (+)/P (-)* ‡ vGRF* ‡
Obstacle height (LL)
10%
0.858 (0.093)
−0.029 (0.033)
0.009 (0.012) 0.707 (0.096)
TCG
GG
Effect of the height of obstacle
−0.024 (0.027) 10% > 20%, 10% > 30% 0.842 (0.140) No
−0.025 (0.016) 10% ≠ 30% 0.799 (0.046) 10% > 20%, 10% > 30%
30%
TABLE 3 Mean (SD) of Anterior-Posterior GRF and Vertical GRF (vGRF) of the Trailing (Leading) Foot for Both Groups when the Toe Markers of the Leading (Trailing) Foot was Vertically above the Obstacle with Three Different Heights. The Unit was Body Weight (BW). α = 0.05
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The Effect of Tai Chi Chuan on Obstacle Crossing Strategy
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ground reaction force (p = 0.000) and vertical ground reaction force (p = 0.000) on the trailing foot (supporting). When the toe marker of the leading foot (swinging) was above the obstacle, the ground reaction force on the trailing foot was positive (forward) in the TCG, but it was negative (backward) in the GG. The TCG also showed a significantly smaller vertical ground reaction force (p = 0.000) on the trailing foot than the GG when the toe marker of the swinging leading foot was above the obstacle. Furthermore, the main effect of the obstacle height was found in the anterior-posterior ground reaction force on the trailing foot (10%≠30%, p = 0.021) and the leading foot (10% > 20% LL, 10% > 30% LL, p = 0.012) and the vertical ground reaction force on the trailing foot (10% > 20% LL, 10% > 30% LL, p = 0.001).
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DISCUSSION The height of the leading foot relative to the obstacle is important for a successful obstacle crossing. Here, we address the situation at the instant the toe of the leading foot was directly above the obstacle. On the trailing foot, a forward ground reaction force was observed in the TCG, but a backward ground reaction force was observed in the GG. During the stance phase in a gait cycle, the forward ground reaction force occurred in the push-off period. Normally, the backward ground reaction force occurs within the first half of the stance phase (Ren, Jones, & Howard, 2007). The trailing foot pushed off, and the leading foot crossed the obstacle in the same period of a gait cycle for the TCG. However, for the GG, the leading foot crossed the obstacle before the trailing foot pushed off. A previous study indicated that Tai Chi training significantly increased the COManterior-posterior path in gait (Strawberry, Gatts, & Woollacott, 2007). In the current study, the ground reaction force on the trailing foot of the GG was backward when the leading foot was directly above the obstacle. This outcome may be due to the GG having a longer crossing cycle or a shorter HCT than the TCG. The older adults of the GG were observed to pay more attention to the obstacle crossing prior to walking forward. The older adults of the GG used a longer stride time to make a successful obstacle crossing. The shorter HCT and the slower stride velocity in this study also revealed that the older adults of the GG really adopted a more cautious strategy to cross the obstacle (Lowrey et al., 2007). As the height of the obstacle increased, the variation of the anterior-posterior ground reaction force increasingly reflected this cautious strategy. Compared with the TCG, the older adults of the GG seemed to focus more on the obstacle crossing; however, they still showed a smaller VCL than the older adults of the TCG. In prior studies, older adults showed larger hip flexion angles in the crossing leg than younger adults, which resulted in a larger VCL (Galna, Peters, Murphy, & Morris, 2009, Lu et al., 2006; McFadyen & Prince, 2002). This strategy can reduce the risk of tripping (Lu et al., 2010). In the current
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Y.-T. Chang et al.
study, when the leading foot was directly above the obstacle, the TCG flexed the hip of the leading leg more than the GG. This result implied that the TCG adopted a different cautious strategy than the GG to safely cross the obstacle, i.e., to increase the VCL by flexing the hip of the leading leg to a greater degree. Even if the VCL decreased as the height of obstacle increased, both groups of older adults tended to increase the flexion of the leading hip to avoid tripping. The larger hip flexion of the leading leg (swing) also resulted in the faster stride velocity for the older adults of the TCG (Yang, Larsen, Alkjær, Lynnerup, & Simonsen, 2014). In this study, the older adults of the TCG had a longer stride length, less stride time, and faster stride velocity than the older adults of the GG in crossing the obstacles. This result was similar to previous studies (Zhang et al., 2011). Other studies also revealed that younger adults had a shorter stride time than older adults (Bovonsunthonchai et al., 2012; Uchiyama, Demura, & Sugiura, 2012) and that healthy people showed longer stride lengths and faster stride velocities than people with Parkinson’s or cerebellar diseases (Kim et al., 2013; Vitório, Pieruccini-Faria, Stella, Gobbi, & Gobbi, 2010). McFadyen & Prince (2002) revealed that the longer stride time, shorter stride length and slower stride velocity in crossing obstacles may be positively related to a diminishing physical capacity in older adults. Gait speed was associated with survival in older adults (Studenski et al., 2011). Gait speed was found to be a consistent risk factor for disability, cognitive impairment, institutionalization, falls, and mortality (Van Kan et al., 2009). This finding implies that gait speed is correlated with physical capacity for older adults. Moreover, Rosengren, McAuley, & Mihalko (1998) revealed that sedentary older adults adopted a more cautious walking style than active older adults and exhibited shorter step lengths and slower step velocities in walking with or without obstacles. Shorter step lengths and slower step velocities were associated with cautious strategies. The older adults of the TCG were observed to have better physical capabilities and adopted a different strategy that resulted in a longer HCT, faster stride velocity, longer stride length, and lower stride time compared with the older adults of the GG. During Tai Chi Chuan exercise, the body smoothly shifts from foot to foot in a semi-squatting posture. Different parts of the body take turns playing the role of stabilizer and mover, allowing smooth movements to be executed (Wong, Lin, Chou, Tang, & Wong, 2001). The duration of single-limb support is much longer in Tai Chi Chuan exercises than in normal walking (Wu, Liu, Hitt, & Millon, 2004). The increased contraction duration of the muscles due to weight bearing on the supporting limbs may improve muscle strength (Mao, Hong, & Li, 2006). Tai Chi Chuan movements include combinations of stepping forward, backward, sideways, up, and down, turning, and fixing. Diversified stepping patterns could improve the balance control ability, even for instantaneous changes in the stepping pattern (Mao et al., 2006). Therefore, Tai Chi Chuan training could improve balance, postural control (Law & Li, 2014; Lelard, Doutrellot, David, & Ahmaidi, 2010; Li et al., 2012), muscular strength, and flexibility for older adults
The Effect of Tai Chi Chuan on Obstacle Crossing Strategy
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(Hong, Li, & Robinson, 2000, Law & Li, 2014). According to past studies, Tai Chi training improved some abilities, such as single foot support, postural control, and the range of joint motion. The benefits of these improvements were indicated in the older adults of the TCG with increased hip flexing of the leading leg (when the leading leg was swinging) on a single support phase, faster stride velocity and longer step length (Strawberry et al., 2007) in obstacle-crossing behavior. These results correlated with the results of the current study. The effect of Tai Chi Chuan training was made by long-term practice. This study adopted a cross-sectional study design. Although this study was not a random controlled study and could not precisely point out that all the benefits were from Tai Chi Chuan training only, differences between the TCG and GG in obstacle-crossing behavior were observed. Through a discussion and comparisons with other studies, we believe that the older adults of the TCG executed different patterns from general older adults in crossing obstacles due to long-term Tai Chi Chuan training.
CONCLUSIONS The results from this study revealed that the TCG had more efficient performance than the GG in obstacle-crossing behavior. With regular Tai Chi Chuan training, older adults may improve their physical capabilities and can adopt a more efficient strategy, i.e., paying less attention to crossing the obstacle and increasing the VCL by flexing the hip of the leading leg more, which enables them to cross the obstacle safely at a faster speed. Therefore, this study suggested that long-term, regular Tai Chi Chuan training is beneficial for older adults in obstacle-crossing behavior.
DISCLOSURE STATEMENT No potential conflict of interest was reported by the author(s).
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