ONE OF THE CHALLENGES that elderly people face is a. The Effects on Sensorimotor Performance and Balance With Tai Chi Training ORIGINAL ARTICLE

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1 82 ORIGINAL ARTICLE The Effects on Sensorimotor Performance and Balance With Tai Chi Training Siu-Ming Fong, MSc, Gabriel Y. Ng, PhD ABSTRACT. Fong S-M, Ng GY. The effects on sensorimotor performance and balance with Tai Chi training. Arch Phys Med Rehabil 2006;87:82-7. Objectives: To compare the effects of short-term and longterm Tai Chi training on the sensorimotor and balance performance of able-bodied subjects. Design: A nonrandomized cross-sectional controlled trial. Setting: Sport laboratory. Participants: Forty-eight healthy subjects, 16 with 3 months of experience in Tai Chi training, 16 with 1 to 3 years of experience in Tai Chi training, and 16 with no experience in Tai Chi training. Intervention: Experimental. Main Outcome Measures: The reflex contraction latencies (reaction time) of medial hamstrings and gastrocnemius after perturbation, the active knee joint angle repositioning error, and the balance time on a tilt board were measured and analyzed with 1-way analysis of covariance. Significant results were further analyzed with post hoc linear contrasts. Results: Long-term Tai Chi practitioners had a significantly faster reflex reaction time in hamstrings (P.000) and gastrocnemius (P.043) muscles and a longer balance time on a tilt board (P.000) than short-term Tai Chi practitioners and nonpractitioners. Both long- and short-term Tai Chi practitioners had significantly less knee joint angle repositioning error than nonpractitioners (P.001 and P.027, respectively). Conclusions: Tai Chi training of more than 1 year might have the benefits of faster hamstrings and gastrocnemius reflex reaction and improved knee joint position sense (JPS). These changes might be associated with an improved dynamic standing balance. Better knee JPS was shown in subjects with 3 months of Tai Chi practice, but this had not led to a significant improvement in balance. Key Words: Aging; Exercise; Muscles; Posture; Reaction time; Rehabilitation by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ONE OF THE CHALLENGES that elderly people face is a decrease in postural stability and an increased risk of falling. There has been growing interest in using Tai Chi training, which is a traditional Chinese exercise characterized by slow and graceful movements, to improve postural balance From the Department of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Hong Kong, China. No commercial party having a direct financial interest in the research findings reported here has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Gabriel Ng, PhD, Dept of Rehabilitation Sciences, Hong Kong Polytechnic University, Hung Hom, Hong Kong, China (HKSAR), rsgng@inet.polyu.edu.hk /06/ $32.00/0 doi: /j.apmr and prevent falls in older people. 1 During the performance of Tai Chi, the shifting of one s body weight, rotations, and standing on a single leg are repeatedly practiced. All of these actions require accurate joint control, muscle coordination, and good balance performance. 2 Although many studies have investigated the effects of Tai Chi on balance and the prevention of falls, the results have been inconsistent. Tse and Bailey 3 compared a group of long-term Tai Chi practitioners with some age-matched nonpractitioners and found that Tai Chi practitioners were able to stand on a single leg longer with their eyes open. Although this finding was supported by Schaller, 4 Hong et al 5 reported the opposite. They found a significant difference between Tai Chi practitioners and nonpractitioners in single-leg stance time with eyes closed only. The discrepancies could be because of the different Tai Chi experiences of their subjects. The subjects of Hong et al 5 had a minimum of 10 years of Tai Chi experience, whereas the subjects of Tse and Bailey 3 had less Tai Chi experience. For studies performed by using laboratory-based measures of balance, the findings were also inconsistent. Forrest 6 measured the center of pressure (COP) while standing on an unstable supporting surface and reported that displacements of the COP in the anteroposterior (AP) and mediolateral (ML) directions were significantly reduced after 16 weeks of Tai Chi training. However, Wolf et al 7 reported negative results with COP displacement in the ML and AP directions after 15 weeks of Tai Chi training. Tsang and Hui-Chan 8 also showed that there was no significant difference in the AP and ML body sway during the static stance of the long-term Tai Chi practitioners when compared with the age-matched control subjects. When tested with computerized balance systems, Tai Chi practitioners did not differ from the control group in simple testing conditions. 1 However, in the more complex Sensory Organization Test (table 1), which involved the simultaneous disturbance of vision and proprioception, the Tai Chi practitioners showed significantly better performance than the control subjects. 1 This implies that Tai Chi practitioners have better sensory organization ability as a result of using their vestibular inputs to mediate postural control than their non Tai Chi counterparts. Studies 8-11 have shown that subjects trained in Tai Chi have a better vestibular ratio in the sensory organization tests and rely more on their visual and vestibular systems during stances. Because visual, somatosensory, and vestibular inputs all contribute to the function of balance, very few studies have examined the proprioception of the lower limbs in Tai Chi subjects. Only recently have Tsang and Hui-Chan, 8-10 by using the passive knee joint repositioning test, reported that Tai Chi practitioners have better knee joint proprioceptive accuracy than control subjects. Because Tai Chi training emphasizes the active reproduction of joint positions and directions of movements, it is reasonable to expect Tai Chi practitioners to have good active knee joint angle reproducing ability because this is an integral part of the proprioceptive circuitry and balance reaction. It is therefore necessary to investigate the effect of Tai Chi on the active joint repositioning of the lower limbs for the function of balance.

2 EFFECTS OF TAI CHI TRAINING, Fong 83 Table 1: The Testing Conditions of the Sensory Organization Test 12 Testing Conditions Descriptions 1 Eyes open, fixed support 2 Eyes closed, fixed support 3 Sway-referenced vision, fixed support 4 Eyes open, sway-referenced support 5 Eyes closed, sway-referenced support 6 Sway-referenced vision and support The synchronized timing of muscular activations in a reactive balance response is an important aspect of postural control. 8 Shumway-Cook and McCollum 12 reported that in controlling a forward sway, it is necessary to make ankle, hip, and stepping movements, depending on the extent and location of the perturbation. Reflex muscle activation begins from the distal to the proximal direction on a mobile supporting surface. However, no previous studies had examined the onset latencies of selected lower-limb muscles in response to perturbation in Tai Chi practitioners. This study therefore investigated the muscle reflex contraction latencies and balance with Tai Chi training to explore the effects of Tai Chi on postural control and balance. The objectives of this study were to compare (1) the muscle reflex latency of lower limbs among long- and short-term Tai Chi practitioners and nonpractitioners, (2) active knee joint repositioning accuracy among long- and short-term Tai Chi practitioners and nonpractitioners, and (3) balance performance among long- and short-term Tai Chi practitioners and nonpractitioners. METHODS Forty-eight subjects (24 men, 24 women; age range, 40 78y) were recruited on a voluntary basis for this study. Sixteen were long-term Tai Chi practitioners (mean age standard deviation [SD], y) who had practiced Tai Chi for 1 to 3 years, 3 times a week for 1 to 2 hours a session. Another 16 were short-term Tai Chi practitioners (mean age, y) who had practiced Tai Chi for 3 months, 3 times a week for 1 to 2 hours a session. The rest were normative sedentary control subjects (mean age, y) who had no previous experience in Tai Chi or the martial arts. No significant difference was noted in sex and age among the 3 groups (table 2). All of the subjects were independent in their activities of daily living and required no walking aids. The exclusion criteria were the presence of severe cognitive impairment; vestibular problems; and cardiovascular, pulmonary, metabolic, or neurologic diseases. The study was approved by the ethics review board of the administering institution. The procedures were fully explained to the subjects, and they all gave their written consent before testing. Reflex Latency of Hamstrings and Medial Gastrocnemius Muscles The reflex latency (reaction time) of the hamstrings and medial gastrocnemius muscles was measured with surface electromyography. The activities of the medial hamstrings and the medial gastrocnemius of the dominant leg, defined as the one used to kick a ball, were recorded with active surface electrodes. Skin preparation included shaving, cleansing with alcohol, and lightly abrading with fine sandpaper to reduce the skin impedance. Afterward, 2 active electrodes a positioned approximately 1cm apart were placed over the midpoint of the medial hamstrings, and 2 other active electrodes were placed over the medial gastrocnemius. The electrodes were placed in a line parallel with the longitudinal axis of the lower extremity. A reference electrode was placed on the ipsilateral tibial tuberosity. 13 An accelerometer b was strapped to the chest over the xiphoid process. The electrodes with an in-built gain of 330 times and bandpass filter of 10 to 312Hz were connected to an input box. The common mode rejection ratio of the amplifier was 95dB, and the signals were full-wave rectified. The amplified electromyographic signals together with those of the accelerometer were inputted to a data acquisition unit, c which sampled at 500Hz. The digitized signals were outputted to a personal computer with WinDaq pro software c for recording. The posteroanterior (PA) perturbation test was modified from the study of Ng. 14 A 3-kg medicine ball was suspended with a 1.5-m sling from the ceiling behind the subject. During the test, the subject stood with bare feet apart at shoulder width, arms resting at his/her side, and with eyes and ears shielded. A pile of pillows was placed in front of the subjects as a safety measure. The subject was instructed to stand still and not to take any corrective steps during the test. The examiner pulled the medicine ball back so that the sling suspending it made an angle of 45 with the vertical. On the release of the medicine ball, the medicine ball would exhibit a pendulum motion and strike the back (T12 level) of the subject, thus producing an angular translation of the trunk and disturb the subject s balance (fig 1). The impact energy was calculated to be around 23J. This would trigger a reflex contraction of the hamstrings and medial gastrocnemius to allow the subject to maintain an upright position. No stepping or falling occurred during the test. The means and SDs of the resting electromyographic signals of the hamstrings and gastrocnemius were calculated. The instant of hamstrings and gastrocnemius contraction was defined as the starting point of the electromyographic activity of each muscle that lasted for more than 25ms with 2 SDs away from the mean of the resting value. 13 The reflex hamstrings and gastrocnemius muscle contraction latency was defined as the time interval between the trunk perturbation, which was denoted by the onset of the accelerometer signal, to the first discernible electromyographic activities of the hamstrings and gastrocnemius muscle. Three trials were recorded, and the mean value was used for analysis. Active Knee Joint Angle Repositioning Test Subjects were blindfolded and positioned lying on their nondominant side on a plinth. The dominant leg of the subject was suspended horizontally by slings to counterbalance gravity, 15 and the hips were kept at 45 of flexion. To minimize the Table 2: Comparison of Age and Sex Among Long-Term Tai Chi, Short-Term Tai Chi, and Control Subjects Variables Long-Term Tai Chi (1 3y) Group Short-Term Tai Chi ( 3mo) Group Control Group (normative sedentary subjects) N Mean age SD (range) (y) (41 78) (40 75) (44 77) Sex (n) Men Women

3 84 EFFECTS OF TAI CHI TRAINING, Fong Blindfolded and ear shielded 45 Accelerometer on xiphoid process T12 level Medicine ball Reference EMG electrode on tibial tuberosity EMG medial hamstrings EMG medial gastrocnemius Fig 1. Setup for the PA perturbation test. Abbreviation: EMG, electromyographic. influence of the cutaneous stimulation of the calf, an air splint was applied to the subject s foot and ankle. 15,16 An electrogoniometer d was attached on the lateral side of the knee joint along the femur and fibula. Because the midrange of knee flexion has been shown to be most reliable for joint repositioning measurements, 9,17 the starting position of the knee was taken at 35 of flexion. 16 The knee was randomly moved by the examiner to a new position within the range of 20 to 75 and remained in that position for 3 seconds and then returned to the starting position. Five seconds later, the subject was asked to actively move the knee to the previous position. 13,18 The angle that the subject reproduced was recorded, and the absolute error was calculated. Three trials were conducted at different angles with 30 seconds of rest between each trial, and the mean of the absolute error of each trial was recorded. 13 Dynamic Balance Test The dynamic balance test was modified from that used in Jacobson et al. 19 Subjects stood blindfolded and in bare feet on an AP tilt board (surface area, 46 46cm 2 ; height, 13cm) with their feet apart at shoulder width. Sensors were mounted under the tilt board so that each time the board tilted by 5 or more on the sagittal plane, the sensors would be triggered. Before the test, the examiner supported the subject on the tilt board to maintain it horizontally level. On a start signal, the examiner would remove the support so that the subject had to maintain an active balance. The test was stopped if the deviations on the sagittal plane were more than 5, which was defined as out of balance. The 2 sensors were interfaced with a computer programmed to record the run time of the test. No feedback on the balance status was given to the participants during the test. The procedure was repeated 3 times for each subject, and the average time that a subject could maintain his/her balance on the tilt board was analyzed. Statistical Analysis The intraclass correlation coefficient model 3,3 (ICC 3,3 ) was calculated to assess the test-retest reliability of the hamstrings and gastrocnemius reaction time test, the active knee joint repositioning test, and the tilt board balance test. Each outcome measure was tested 3 times by using 8 subjects during the pilot test. The absolute values in the 3 trials were used to calculate the ICC. For between-group comparisons of the 4 outcome measures, 1-way analysis of covariance with sex and age as covariates was performed. Significant results were further analyzed with post hoc linear contrast. A significance level of.05 was adopted for all of the statistical comparisons. RESULTS The ICC values for the hamstrings and gastrocnemius reflex reaction time, knee joint angle repositioning error, and balance time on the tilt board ranged from.775 to.884. These indicated good reliability for all of the tests. 20 For the hamstrings reflex reaction time, the analysis of covariance result was significant (P.001). A post hoc analysis revealed that the long-term Tai Chi practitioners had significantly faster reaction times than the other 2 groups (fig 2). For the gastrocnemius reflex reaction time, the result also indicated a difference among the 3 groups (P.043). A post hoc analysis revealed that long-term Tai Chi practitioners had faster reaction Fig 2. Reflex latency (reaction time) of medial hamstrings and medial gastrocnemius of the 3 groups of subjects. *Significant difference (P<.05) compared with the control group. Abbreviation: TC, Tai Chi.

4 EFFECTS OF TAI CHI TRAINING, Fong 85 Fig 3. Knee joint repositioning error. NOTE. Values are mean and SD. *Significant difference (P<.05) compared with the control group. times than short-term Tai Chi practitioners and nonpractitioners (see fig 2). For the knee joint angle repositioning test, both long- and short-term Tai Chi practitioners had significantly better knee joint reposition accuracy. Their degree of error was 50% less than that of the control group (P.001 and P.027, respectively) (fig 3). For the balance time on the tilt board, there were significant differences among the 3 groups (P.001). A post hoc analysis revealed that long-term Tai Chi practitioners had significantly longer stand times on the tilt board than the other 2 groups (fig 4). DISCUSSION No previous studies had examined the muscle reflex reaction time to perturbation in Tai Chi. Our finding that long-term Tai Chi practitioners have faster medial hamstrings and gastrocnemius reflex reaction times than non Tai Chi practitioners of a similar age is important in the evaluation of the effects of Tai Chi. A PA perturbation of the trunk would cause an angular translation of the body, thus stretching the hamstrings and gastrocnemius muscles. These muscles responded with reflex contraction to check the forward trunk motion. Our findings revealed that muscle reflex reaction time was faster in the subjects who had practiced Tai Chi for 1 year or more but not for those with only 3 months of Tai Chi practice (see fig 2). This indicated that there might be a time-dependent training effect in achieving faster postural correction. However, because this was a cross-sectional study, the longitudinal effect of Tai Chi training was still uncertain. Proprioception can be defined as static awareness of joint position in space mediated by Ruffini s end organ and Golgi tendon like organs or kinesthetic awareness (ie, the detection of movement and acceleration mediated by the Pacinian corpuscles). It may also affect the closed-loop efferent activity required for the reflex response of joint musculature and the regulation of muscle stiffness. 13,21 The perturbation test examined the closed-loop efferent muscle reflex activity, whereas the static joint repositioning test examined the joint proprioception. Previous studies had shown that the age-related decline in proprioception can be attenuated by regular physical activity. 17,22 Our study further showed that with 3 months of Tai Chi practice, the subjects might have a better sense of knee joint position, which was comparable with the 1-year Tai Chi group. This finding was similar to that of Tsang and Hui- Chan, 8,10 who found that the knee joint angle repositioning error of long-term Tai Chi practitioners was 2 times less than that of the control group. There could be 2 explanations for improvements in joint sense among Tai Chi practitioners. First, Tai Chi exercise involves slow continuous movements that require the body and limbs to be placed in specific positions relative to each other; the need for awareness of the body and limbs and the repeated repositioning of the body parts in space during the exercise could have increased cortical representation of the joints and hence improved their position sense Second, the repeated practice of Tai Chi might increase muscle spindle output through the gamma route, thus inducing plastic changes in the central nervous system (CNS) such as an increase in the strength of synaptic connections and structural changes in the organization and numbers of connections among neurons Balance can be of a static or dynamic nature depending on whether the base is stationary or moving. In static balance, the base of support (BOS) remains stationary and only the body s center of mass (COM) moves; thus, one needs to maintain the COM within the BOS. In dynamic balance, however, both the BOS and COM move, whereas the COM is not always kept above the BOS. 23 Dynamic balance relies more than static balance on sensorimotor information. 1 An examination of dynamic balance can highlight the differences between Tai Chi practitioners and nonpractitioners. 1 Only 2 longitudinal studies 1,19 have been conducted investigating the dynamic balance of Tai Chi practitioners with tilt boards. Both studies showed that Tai Chi practitioners with 8 and 12 weeks of Tai Chi training had significantly improved their balance time on a tilt board. In our study, however, we found that only long-term practitioners had better control of dynamic balance. No significant differences were observed between short-term practitioners and nonpractitioners. The differences between the studies might be because there was no control over the training of the short-term Tai Chi practitioners in our cross-sectional study. It could also be because of the methodologic differences between our study and the previous studies. The subjects in our study were blindfolded during the test, whereas those in the previous studies were not. This might imply that vision might play a more important role in maintaining dynamic balance in short-term Tai Chi practitioners than in long-term Tai Chi practitioners. The importance of vision in maintaining static balance in Tai Chi practitioners has already been shown by Tse and Bailey 3 and Schaller. 4 For Tai Chi practitioners of more than 1 year, neurophysiologic and neuromuscular changes might lead to an improvement in dynamic standing balance. According to Horak and Nashner, 24 ankle and hip strategies are usually used in response to unexpected PA perturbations of varying magnitudes. Shumway-Cook and Olmscheid 25 also found that to correct for loss Fig 4. Balance time on the tilt board. NOTE. Values are mean and SD. *Significant difference (P<.05) compared with the control group.

5 86 EFFECTS OF TAI CHI TRAINING, Fong of balance in the forward direction in healthy subjects, reflexactivated muscle activity is initiated at 90ms in the gastrocnemius muscle to produce an ankle torque that reverses the direction of COM movements, allowing recovery of stance stability on a moving platform, which is known as the ankle strategy. Activity in the hamstrings and paraspinal muscles then follows, generating torques at the knees and hips, which minimize the indirect effects of ankle torques in proximal body segments. Therefore, faster hamstrings and gastrocnemius reflex reaction times after postural perturbation in long-term Tai Chi subjects might result in quicker control of movement and hence better balance. Because the postural control system operates as a feedback circuit among the sensory sources, the CNS, and the musculoskeletal system, proprioceptors, visual, and vestibular centers all contribute afferent information to the CNS on body position and balance. If proprioception improved with Tai Chi training, it is logical that balance would be improved. Although subjects in the short-term Tai Chi group showed better knee joint position sense (JPS) than the control group, the overall dynamic balance performance between these 2 groups did not differ. This might indicate that the neurophysiologic changes had not yet occurred in the short-term Tai Chi practitioners. Furthermore, other factors such as lower-limb muscle strength 19,26 and sensory organization ability 1,3 might also affect the dynamic balance ability of Tai Chi practitioners at different periods of time. It has been reported that balance and limb proprioception decrease with age 3,17,27,28 and in some pathologic conditions such as anterior cruciate ligament injury. 13,16,29 The potential benefits of Tai Chi training on dynamic balance and proprioception might have clinical implications for improving the balance of patients and preventing falls. Li et al 30 evaluated the efficacy of a 6-month Tai Chi intervention program in inactive subjects older than 70 years. They found that Tai Chi training 3 times a week for 6 months effectively decreased the number of falls, the risk of falling, and fear of falling in these subjects. It also improved their functional balance and physical performance. Tai Chi training could be a suitable rehabilitation program or fall-prevention program. Despite the fact that there were negative findings by Wolf et al 7 with laboratory-based balance measures, these testing conditions might not be directly applicable to the functional balance performance in daily living. Based on the present findings, long-term Tai Chi training might lead to neurophysiologic changes not observed in 3 months of Tai Chi practice. A long-term prospective study is warranted to examine the balance training effect of Tai Chi. In our study, only a part of the sensorimotor aspect of balance was considered. Further studies should explore other physiologic changes such as kinesthetic senses, vestibular inputs, sensory organization changes, muscle strength, and flexibility, which might affect balance with Tai Chi training. Furthermore, because our study is of a cross-sectional design, it is difficult to draw a causal relation between Tai Chi training and the outcome measures. A longitudinal study will shed light on the training effect and optimal training time of Tai Chi. CONCLUSIONS This study revealed that Tai Chi training of more than 1 year might have the benefits of shortening the hamstrings and the gastrocnemius reflex reaction times and improving knee JPS. These changes might be associated with an improvement in dynamic standing balance. Better knee JPS was shown in subjects with 3 months of Tai Chi practice, but this did not lead to an improvement in their overall balance ability. 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