目的：藉由功能性的上下樓梯動作，探討年齡差異 (組間) 及不同任務情境 (組內)，對認知任務表現和步態時間空間參數之影響。方法：16名老年人受試者 (7 男9 女，79.16 ± 6.97 歲，160.49 ± 7.27 公分，62.16 ± 11.26 公斤) 及12 名年輕人受試者 (6 男6 女，23.00 ± 1.21 歲，165.25 ± 4.11 公分，60.25 ± 6.90 公斤)，皆須接受坐姿的認知任務測驗、上下樓梯行走測驗，以及上下樓梯合併認知任務回答測驗。結果：老年人和年輕人在認知任務的組內比較，都達顯著差異。步行時間、步頻及步速，組間和組內效果在樓梯的四個時期都達顯著差異，步長則在上樓期的組間和組內、下樓期的組間和下樓轉換的組間和組內，達顯著差異。上樓期的速度變異交互作用達顯著差異，下樓轉換期的組間速度變異也達顯著差異。結論：老年人和年輕人會根據動作的困難度，選擇是否專注於認知任務上。老年人在上樓期時，因雙重任務情境造成姿勢控制的不穩定，而採取比較保守的動作策略來降低速度變異，避免跌倒的風險，而下樓梯則因和上樓梯動作機制需求的不同及較高困難度，時空參數的差異並非由雙重任務效應所影響。

Purpose: The aim of this study was to investigate the effect of aging (between groups) and different conditions (within group) on cognitive performance and spatiotemporal gait parameters during stair negotiation. Methods: 16 healthy elderly adults (7 males and 9 females, 79.16 ± 6.97 years, 160.49 ± 7.27 cm, 62.16 ± 11.26 kg) and 12 healthy young adults (6 males and 6 females, 23.00 ± 1.21 years, 165.25 ± 4.11 cm, 60.25 ± 6.90 kg) were recruited in this study to perform cognitive task on sitting posture and stair negotiation; they also performed stair negotiation with cognitive task. Results: Significant within group difference were found in cognitive performance for elderly and young adults. Significant between and within group difference were detected on time of gait cycle, cadence and gait velocity during four gait phases. Significant differences were detected for stride length on between and within group of SA phase, between group of SD phase and between and within group of stair to floor transition phase. During SA phase, a significant statistical interaction was found in gait velocity variability. Significant between group differences were detected between young and elderly subjects in gait velocity variability during stair to floor transition phase. Conclusions: Elderly and young subjects alike depended on the degree of difficulty of motor task to determine whether to focus on cognitive task or not. During SA phase, walking with concurrent cognitive task resulted in destabilization of posture control and indicated that elderly subjects were found to be able to adapt a conservative strategy to decrease gait velocity variability in order to prevent the risk of fall. Due to the difference of mechanical demands and levels of hazardous between SA and SD, significant difference of spatiotemporal parameters couldn’t be demonstrated from the dual task effect.