緒論：下階梯轉換是下階梯到最後一階、緊接著轉換往前行走的過程，隨著老化造 成的身體機能衰退，這類具挑戰的日常生活行動具有更高的跌倒風險。藉由運動的方式 減緩老化所造成的運動能力退化，甚而提升運動能力實為積極有效的作法。在眾多運動 中，太極拳的運動形式更是適合老年人從事的項目之一。許多研究指出太極拳可以增進 下肢肌力並增加平衡能力，因此本研究目的在比較長期規律太極拳運動老年人與一般運 動老年人，在下階梯轉換階段質心運動的差異。方法：以每組16 名，共32 位老年人為 研究對象，在一年內皆無影響下肢活動之病史。使用10 台Vicon Motion System 紅外線攝 影機 (250Hz) 與1 塊Kistler 測力板 (1000Hz) 同步擷取、並使用Visual 3D 軟體進行計 算下階梯轉換動作之質心運動學與壓力中心 (center of pressure, COP) 參數，所得資料使 用獨立樣本t 檢定進行統計分析，顯著水準為α = .05。結果：太極拳組在下階梯轉換、 下階梯期與著地前行期皆有較快之質心 (center of mass, COM) 合速度與較短之時間。在 著地前行期，太極拳組有較大之第一著地步長、前後COM-COP 水平距離與踝關節最大 背屈、蹠屈角速度。結論：長期規律從事太極拳運動的老年人，由於太極拳的運動型態 與下肢肌群訓練的效果，在下階梯轉換時有較佳的速度表現與動態平衡能力，而踝關節 最大關節角速度也許與太極拳組較佳表現息息相關。與下階梯相比，兩組受試者在下階 梯轉換過程皆著重於往前的質心運動，太極拳組則有更明顯往前之質心運動。

The stair-to-floor transition strides were constituted two discrete walking patterns, and as such were inherently variable and unstable. Increased falls were occurred during the stair-to-floor transition with aging. Regular exercise is a recommendation often used to resist the progressive decline in muscular abilities that are often associated with aging. Due to its qualities, Tai Chi has been promoted as a good choice of exercise for the elderly. Many studies indicated improvement in lower extremities strength and dynamic balance after long-term practicing Tai Chi exercise. The purpose of the study was to investigate the effects on center of mass (COM) motion during stair-to-floor transition between regular Tai Chi practice and normal exercise older people. Methods: Sixteen regular Tai-Chi practitioners (Tai-Chi group) and sixteen healthy elderly (control group) participated. Exclusion criteria were any known neurological or orthopedic disease and any current difficulties impeding their typical locomotion. COM was obtained from ten Vicon high-speed cameras (250Hz), and center of pressure (COP) was simultaneously obtained using one Kistler force plate (1000Hz). The COM kinematics and COM-COP separation were calculated by Visual 3D software. Independent samples t-test was assessed the variables and set α = .05. Results: Tai Chi group presented faster COM velocity and shorter duration while descending and following-walk phase. During following-walk phase, Tai Chi group demonstrated greater 1st step length, antero-posterior COM-COP separation, peak ankle plantarflexion and dorsiflexion angular velocity. Conclusion: From the improvement in muscular abilities of lower limbs by long-term Tai Chi practice, Tai Chi group had faster COM velocity and better abilities of body control during stair-to-floor transition. And ankle angular velocity might be related to the better performance in Tai Chi group during stair-to-floor transition. Compared with stair descent, both groups would present more forward instead of downward COM motion during stair-to-floor transition. Therefore, elders were recommended to engage in long-term Tai Chi exercise.