Part 1. Characteristics of foot movement in Tai Chi exercise. The performance of 16 experienced Tai Chi practitioners demonstrating a whole set of 42-form Tai Chi movements were recorded with two cameras. The APAS motion analysis system was used to identify the foot supporting and stepping characteristics during the practice. Seven foot support patterns and six step directions were identified. The results revealed that compared with normal walking, Tai Chi movement had more double support and less single support total duration. The duration of each support pattern was longer and movement from one pattern to the next was slow. The duration of each step direction was short, and changes of direction were frequent. It was expected that support patterns changed slowly, and combined with various step directions, they were found to be better than those of walking in simulating the gait challenges that may be encountered in daily activities. / Part 2: The plantar pressure distribution during Tai Chi exercise. The purpose of this study is to describe and quantify the plantar pressure distribution characteristics during Tai Chi exercise and to explain the beneficial effects of Tai Chi on balance control and muscle strength as compared with normal walking. Sixteen experienced Tai Chi practitioners participated in this study. Five typical Tai Chi movements represented by stepping forward, backward, sideways, up-down, and fixing could be isolated from the whole set of 42-form Tai Chi. The pressure-time integral, ground reaction force, displacement of center of pressure during the performance of the five typical movements were recorded and analyzed by the Pedar-X insole system (Germany). Results showed that during Tai Chi movements, the loading of the first metatarsal head and the great toe were significantly greater than in other regions (p<0.05). The ground reaction forces varied between the Tai Chi movements and normal walking. Compared with normal walking, the locations of the center of pressure in the Tai Chi movements were significantly more medial and posterior at initial contact (p<0.05), and were significantly more medial and anterior at the end of contact with the ground (p<0.05). The displacements of the center of pressure were significantly wider (p<0.05) in the mediolateral direction in the forward, backward and sideways Tai Chi movements. The displacement was significantly larger (p<0.05) in the anterposterior direction in the forward movement. The plantar pressure characteristics of Tai Chi movements found in this study may be one of the important factors for Tai Chi's improvement of balance control and muscle strength. / Part 3. The duration and plantar pressure distribution during one-leg stance in Tai Chi exercise. The aim of this study is to quantify the one-leg stance duration and plantar pressure distribution during the one-leg stance in Tai Chi and to try to elaborate on its probable effects on the ability to balance on one leg. Sixteen experienced Tai Chi practitioners participated in this study. The Novel Pedar-X insole system (Germany) was used to record the plantar forces during the execution of a set of 42-form Tai Chi movements and during normal walking. The one-leg stance duration and plantar pressure distribution during the one-leg stance were analyzed. Results showed that in Tai Chi, the total duration spent in the one-leg stance was less (p<0.05), the duration of each one-leg stance was longer (p<0.01) and the medial-lateral displacement of the center of pressure was greater (p<0.05) than during normal walking. The peak pressure and pressure-time integral of the second and third metatarsal heads and the fourth and fifth metatarsal heads were significantly greater (p<0.05) than those of other plantar regions during the one-leg stance in normal walking; whereas the peak pressure and pressure-time integral of the first metatarsal head and the great toe were significantly greater (p<0.05) than those of other plantar regions during the one-leg stance in Tai Chi. The longer duration of each one-leg stance and the plantar pressure distribution characteristics during the one-leg stance in Tai Chi may be associated with an improved ability to balance on one leg. / Part 4. The muscle contraction characteristics of the lower extremities during Tai Chi exercise. The objective of this study is to examine the muscle contraction characteristics of the lower extremities during Tai Chi exercise and to explain the beneficial effect of Tai Chi on the improvement of muscle strength. Sixteen experienced Tai Chi practitioners participated in this study. Five typical Tai Chi movements, represented by stepping in forward, backward, sideways, up-down and fixing were selected. The electromyographic activity of the rectus femoris, semitendinosus, gastrocnemius, and anterior tibialis muscles were recorded by Delsys electromyography measurement system (USA) during the performance of five typical Tai Chi movements. (Abstract shortened by UMI.) / Mao Dewei. / "August 2006." / Adviser: Youlian Hong. / Source: Dissertation Abstracts International, Volume: 68-03, Section: B, page: 1598. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (p. 102-112). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.