背景與目的：自主性跨步動作測試是預測老年人跌倒的重要評估工具之一。本研究目的在探討健康年輕人執行向前、側、後三方向快速自主性跨步動作時之動作表現、足底壓力中心相關參數、及動作表現與足底壓力中心相關參數間之相關性。方法：16位健康年輕人（平均年齡23.1±3.7歲）接受雙下肢向前、側、後三方向各六次的跨步測試。動作表現方面量測其反應時間、動作時間、跨步步長及跨步速度；足底壓力中心方面則分析其移動軌跡、與前後向及側向最大位移。結果：側向跨步時的反應時間、動作時間與跨步步長在三方向跨步中最短(p<.017)。前向跨步時之跨步速度顯著高於側向跨步時(p<.017)。前、後向跨步時，足底壓力中心均先移向跨步腳；側向跨步時足底壓力中心則多先移向站立腳。足底壓力中心前後向最大位移在後向跨步時較前向跨步時大(p<.05)；足底壓力中心側向最大位移則在側向跨步時最大(p<.017)。足底壓力中心前後向最大位移在前、後向跨步時皆與跨步步長及步速有中高度相關(r≥.71, p<.05)；但無論跨步方向，足底壓力中心之側向最大位移則與跨步步長及步速均無顯著相關。結論：本研究結果顯示側向跨步與前、後向跨步之力學控制機轉與動作表現顯著不同。而在前、後向跨步動作中，足底壓力中心量化參數與動作表現有中高度相關，顯示足底壓力中心之量化分析有助於瞭解跨步表現好壞之力學成因。未來期能採用本研究結果作為評估老年人執行自主性多方向跨步能力之重要依據。

Background and Purposes: Performance of volitional stepping has been proposed as an importance assessment tool for predicting falls in older adults. The purpose of this study was to investigate movement characteristics and center-of-pressure (COP) related parameters associated with volitional forward, sideways and backward stepping in healthy young adults. Methods: Sixteen healthy young adults (mean age = 23.1±2.7 years) performed 6 trials each of rapid, volitional forward, sideways, and backward stepping with each leg. The movement characteristics investigated included reaction time (RT), movement time (MT), step length (SL), and step velocity (SV). The COP parameters examined included the COP trajectories, and maximum COP displacements in anterior-posterior and medio-Iateral directions (COPap and COOml, respectively). Relationships between COP parameters and movement characteristics were also investigated. Results: Sideways stepping presented the shortest RT, MT, and SL among the three directions of stepping (p<.017). The SV was significantly greater in forward stepping than in sideways stepping (p<.017). In both forward and backward stepping, the COP trajectory initially moved toward the stepping leg, whereas in sideways stepping the trajectory normally firstly moved toward the stance leg. The COPap was significantly greater in backward stepping than in forward stepping (p<.05); the COPml was greatest in sideways stepping (p<.017). The correlations between the COPap and SV and SL were moderate to high (r≥.71, p<.05) for forward and backward stepping, whereas those between COPml and SV and SL were not significant regardless of the step direction. Conclusions: The results indicated a different kinetic mechanism for sideways stepping compared to forward and backward stepping. The moderate to high correlations between the COP measures and movement characteristics suggest that quantitative COP measures could shed light on the kinetic causes that could explain the behavioral outcomes of stepping. These findings can serve as the relevant baseline information for assessing performance of volitional stepping in older adults in future studies.