Letter to the Editor Kinematics and Energy Expenditure of Sitting T’ai Chi Ken Y.T. Lee, MSc, Alice Y.M. Jones, PhD, Christina W.Y. Hui-Chan, PhD, and William W.N. Tsang, PhD Dear Editor: The positive effects of t’ai chi exercise on various physical and psychologic dimensions including muscle strength, balance control, fall risk, functional status, and aerobic ca- pacity have been thoroughly documented. 1–6 However, tra- ditional t’ai chi forms are difficult for older adults with poor standing balance or who are physically dependent, and may increase the risk of falling or injuries. This study was therefore designed to analyze the kine- matics of a newly designed 12-form sitting t’ai chi and compare them with conventional t’ai chi forms. Oxygen costs in (1) sitting, (2) sitting with sandbags restraining the limbs (1 kg at each extremity), (3) standing without lower limb movement, and (4) traditional standing were quantified. Ethics approval was obtained from the Hong Kong Poly- technic University. A healthy t’ai chi master (age 63 years; body weight, 55 kg; height, 1.68 m; body–mass index, 19.58 kg/m 2 ) who had 30 years of practicing t’ai chi experi- ence and 3 years of practicing sitting t’ai chi was invited to participate in the study. Her informed consent was obtained prior to the measurements. A 12-form sitting t’ai chi routine designed by the investi- gators with an experienced t’ai chi master was tested. This routine was derived from Yang’s style of the classic long- form t’ai chi. Its components were selected to encourage trunk, upper limb, and some lower limb movements. The sitting forms aimed to enhance control in weight shifting in different directions, and promote sensorimotor coordination involving the eyes, head, hands, and trunk in a smooth and coordinated manner. The 12 forms of the sitting t’ai chi routine can be completed in about 3 minutes. Center of mass (COM) displacements were captured and cal- culated using a Vicon motion analysis system (Oxford Metrics Ltd., UK). Oxygen consumption during the t’ai chi routines in different positions was measured using a portable cardiopulmo- nary exercise testing device (K4b 2 , Cosmed S.R.L., Rome, Italy). The maximum displacements in the anteroposterior (AP), mediolateral (ML), and vertical directions were normalized using the subject’s standing height. The corresponding tradi- tional 12 forms of standing t’ai chi were also captured for comparison. Oxygen consumption (VO 2 ) was measured for 5 minutes at rest in either standing or sitting position according to the starting position, and measurement was then continued during 10 minutes of t’ai chi practice. 7 The VO 2 during the 10 minutes of t’ai chi movements was then averaged. For the results, the maximal displacement of the COM in the AP direction of each form ranged from 1.5% to 10.3% of the subject’s standing height, 0.4%–5.7% of the subject’s standing height in ML direction, and 2.3%–7.5% of the sub- ject’s standing height in vertical direction (Fig. 1A–C). The comparisons of COM displacements between sitting and traditional standing t’ai chi are also shown in Figure 1. For the energy expenditure performing t’ai chi in different positions, the results confirm that sitting t’ai chi was indeed the lightest exercise (1.9 metabolic equivalents [METs]), followed by sitting t’ai chi with the restraints (2.5 METs), standing without lower limb movement (2.7 METs), and traditional standing (4.6 METs). Knowledge of the kinematic characteristics of each sitting t’ai chi form provides information useful for selecting forms for individuals with different capabilities, and it provides general guidelines for progression. For instance, balance training can be progressed from forms with smaller dis- placements to larger excursions, depending on the degree of fragility. To further progress, various forms can be performed in a less stable sitting condition, such as on a cushion or even a wobble board if balance training is the therapeutic objective. 8 The energy expenditure results indicate that sitting t’ai chi is a low-intensity exercise, which is in line with the findings of other studies. 9 As expected, energy expenditure increased from the sitting to the standing position. Also, the sitting t’ai chi with sandbags, which are commonly used in rehabilita- tion therapy, demands more energy expenditure. These data provide a guideline for clinicians or practitioners selecting conditions/positions to suit different functional and aerobic needs in the rehabilitation process. This has been the first study investigating a newly de- signed sitting t’ai chi routine that targets improving the bal- ance control and cardiopulmonary function of subjects who have difficulty performing traditional standing t’ai chi. However, only 1 t’ai chi master was involved. Further studies recruiting a larger sample and different degrees of frailty or disability will be necessary to ascertain the kinematics and determine the precise energy costs. Acknowledgments The authors thank The Hong Kong Polytechnic University for financial support of this study through the Areas of Excellence Scheme. Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hong Kong, China. THE JOURNAL OF ALTERNATIVE AND COMPLEMENTARY MEDICINE Volume 17, Number 8, 2011, pp. 665–668 ª Mary Ann Liebert, Inc. DOI: 10.1089/acm.2011.0147 665