研究背景和目的：在行走的過程中，人們會利用來自周圍環境的視覺訊息對步態做出適當的調整。除了視覺訊息之外，年齡也是影響行走表現的因素之一，相較於年輕人，老年人更依賴視覺以維持行走時的姿勢控制與平衡。而向後行走是在日常生活中移動所需常見的動作，不同於向前行走，當向後行走時，看不到前進方向的環境，是否會如同向前行走時視覺所扮演的角色，根據視覺訊息調整步態，目前並不清楚，因此，本研究目的為探討健康年輕人和老年人在不同視覺情況下向後行走的表現。
方法：本研究招募20位健康年輕人(22.3 ±1.7歲)與健康老年人(69.2 ± 5.5歲)。所有受試者分別在三種不同視覺情況向後行走，分別是(1)一般視力向後行走、(2)看著置於前方的鏡子向後行走及(3)配戴模糊的眼鏡向後行走。在行走的過程中，使用SIMI MOTION® 動作分析系統及Delsys無線肌電感應系統分別記錄向後行走時的下肢動作及肌肉活動表現，並計算相關之步態參數、下肢關節活動角度及下肢肌肉活動情形。其中空間-時間步態參數包括速度、步長、步寬、跨步時間與步態週期百分比；下肢關節活動角度則包括髖關節、膝關節以及踝關節之角度變化; 與慣用腳之肌肉活動程度及大腿、小腿前後側肌肉同時收縮之時間長度。統計分析使用重複測量二因子變異數分析(Two-way repeated measure ANOVA)，分析兩組受試者在三個不同視覺情況的步態表現差異。p值設小於0.05達到顯著差異。
結果：老年人向後行走的步行速度顯著比年輕人慢，步長也顯著短於年輕人，而老年人髖關節活動角度在腳離地期與站立時期的最大屈曲角度、髖關節活動度顯著比年輕人小。老年人在站立時期的膝關節活動度則是顯著小於年輕人；踝關節最大蹠曲角度在腳離地期與擺盪期與年輕人比起顯著較大。除此之外，老年人之股二頭肌、脛骨前肌和腓腸肌也比年輕人有顯著較大的肌肉活動程度，不論是大腿或小腿在單腳站立期，老年人的慣用側下肢前後側肌肉同時收縮時間皆顯著比年輕人長。比較三種視覺情況，年輕人在一般視力與配戴模糊眼鏡向後行走的跨步時間皆顯著比看著鏡子長，而老年人在則是在一般視力向後走比起其他兩個情況有較長的跨步時間。
結論：年齡與向後行走步態表現有關，除了步態產生改變，關節角度與肌肉活化程度也受到影響; 一般而言老年人比年輕人更小心地向後走，包括行走速度較慢，步長縮短，減少下肢關節活動度以及增加肌肉活動程度。此外當向後行走時，不同的視覺情況對年輕人與老年人的步態表現有些微影響，老年人會使用不同的策略適應不同的視覺情況。本研究提供老年人在向後走時適應不同視覺情況之步態表現，因此為老年人設計向後走運動時須考慮年紀與視覺的影響。

Background and Purpose: Visual information from the surrounding environment is essential during walking. The visual information is usually used to make appropriate modulation to gait pattern. In addition to the visual information, ageing might be another factor associated with changes of gait pattern. Elderly were found to rely more on visual information for postural control and balance than young adults during walking. Different from forward walking, during backward walking, a commonly seen movement in daily life, one could not see the environment of the heading direction. It is unclear whether one would modulate gait pattern during backward walking using visual information from the surrounding environment. No study has reported how visual information would influence backward walking performance. The purpose of this study was to investigate the influence of different visual conditions on backward walking performance in healthy young and older adults.
Methods: Twenty healthy young (22.3 ±1.7 years) and older adults (69.2 ± 5.5 years) were recruited in the study. All subjects were asked to walk backward at self-selected speed on a walkway under three different visual conditions: (i) normal vision, (ii) looking at a mirror placing at the front to provide additional visual information, and (iii) wearing a pair of blurry goggles. SIMI MOTION® and Delsys wireless electromyography system were used to obtain gait parameters, and joint angles and muscle activities of the lower extremities during backward walking. Spatiotemporal gait parameters, including walking speed, stride length, step width, stride time and gait cycle percentage of each phase were measured. Joint angles of hip, knee and ankle joint during backward walking were recorded. Muscle activities of vastus lateralis, biceps femoris, tibialis anterior and gastrocnemius medialis of the dominant leg and muscle co-contraction duration of the dominant thigh and shank were measured. Two-way repeated measures ANOVA was used to compare differences of all the parameters between the two groups and among the three visual conditions. Significance level was set at p<0.05.
Results: The older adults walked backward with significantly slower speed and shorter stride length than the young adults did in all visual conditions. The angular displacement of hip flexion at foot off, and maximal hip flexion and range of motion during stance phase were significantly smaller in the older adults than the young adults. The significantly smaller range of motion of knee joint was found in the older adults than the young adults during stance phase. Ankle plantar flexion at foot off and ankle plantar flexion during swing phase were significantly greater in the older adults compared to the young adults. Muscle activities of the biceps femoris, tibialis anterior and gastrocnemius of the dominant leg during single limb support phase and swing phase showed significant greater activities in the older adults than the young adults. Muscle co-contraction duration of the dominant thigh and shank during single limb support phase was significantly longer in the older adults than the young adults. Comparing different visual conditions, the young adults exhibited longer stride time in normal vision and wearing blurry goggles condition than looking at the mirror condition. The older adults showed significantly longer stride time in normal vision than the other two conditions.
Conclusion: Ageing is associated with altered gait pattern during backward walking. In general, older adults walked backward with more cautious gait pattern than young adults including slower walking speed, shorter stride length and decreased range of motion of lower extremities. In addition, different visual conditions might have a subtle influence on gait pattern during backward walking in both young and older adults. Older adults would use different strategy to adapt to different visual conditions. This study provided important information on how older adults would respond to different visual conditions during backward walking. This information should be considered when designing backward walking related exercise for older adults.

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