老人的機械耗能與步行速度

Abstract

背景 人類步行耗氧量已被廣泛的討論和研究，但人類步行之機械耗能確是較少被討論。 文獻中指出在相同步行速度時，老年人明顯的會較年輕人有更高的耗氧量，過去的研究亦發現老年人和年輕人在步行時的自選速度並無顯著差異，但卻有各關節所產生的功率重新分佈的現象。 目的 本研究的目的在於討論老年人步行策略的改變，因此導致各關節功率之重新分佈是否為老年人在相同步行速度下有較高的耗能表現之原因。機械耗能及能量流的分析會用於此次研究，以探索其耗能背後的生物力學機制。 受試者 十五位健康老年人及十五位健康年輕人。 方法 每位受試者在十公尺的步態分析實驗室中，經過三分鐘的練習後，分別以慢速、自選速度和快速進行實驗。同時以逆向動力學方法以高速攝影機和力板收集所標記運動軌跡及力板反力資訊以獲得力動學及動力學資料。 每位受試者須在各種速度下至少成功收得三筆資料。 結果 老年人和年輕人在自選速度並無顯著差異，在各種步行速度下，老年人都較年輕人有著更高的機械耗能，尤其是在快速時，老年人有相當高的機械耗能。而進一步分析其各關節及肢段的能量表現會發現老年人雖在各肢段的動能及位能表現並無顯著差異，卻在所有關節及肢段幾乎都有較高的能量流進和流出，且進一步分析線性和轉動的分量，再由能量流去分析時會發現老年人的能量儲存機制明顯不如年輕人有效率。 總論 老年人在相同的步行速度下卻有較高的機械耗能表現，其生物力學的原因應是雖然在步行時老年人雖有相同的步行速度，但因年齡而導致步行策略的改變進而影響其各關節在步行時分配的比例，而導致其能量儲及轉換存效率不如年輕人，使個關節需做出額外的功，進而產生較高耗能的最終整體表現。

Background: While metabolic energy cost ambulation has been extensively investigated, mechanical energy cost is relatively unexplored which will be discussed . There were evidences to show that under the same walking speed the older consume higher metabolic energy than the younger. Research literatures also support that the self-selected walking speeds are not much different between the two groups but the cadence of the elders is higher. Furthermore, the aged group showed a redistribution of joint torques and powers during gaits. Purpose: The study is designed to answer the prominent research question: Would the redistribution of joint powers in elders change the segmental energy distribution and cause the high mechanical energy cost during level walking and how? Energy flow analysis would be conducted to look into biomechanical reasons that cause higher energy cost in elders. Materials and Methods : 15 male young (24.2 ± 0.77yrs) and 15 male older adults(71 ± 3.46yrs) participated in the study. Their anthropometric characteristics were: Young: Height (1.76 ± 0.02m), Mass (70 ± 9.37kg), BMI (22 ± 2.92). Elders: Height (1.64 ± 0.01m), Mass (65 ± 3.76kg), BMI (24 ± 1.28). All subjects walked along a 10-meter walkway with shoes at slower speed, self-selected speed and faster speed, respectively. There were 24 segmental landmarks tracked at 100 Hz by two optoelectric sensors (Optotrak Certus, Northern Digital Inc., Waterloo, Canada) for capturing body motions. The kinetic data will be synchronously collected via three force platforms (Accugait, Advanced Mechanical Technology Inc., Massachusetts, USA) embedded in the walkway. Each subject completed at least three successful gait trails after 3-minute practice. Results: For walking speed, it is not significantly different between young men group and elders group. However, a t-test analysis indicated a significant difference between the means of mechanical energy cost of the two groups. We focus on second double limb support(50%-62%), initial swing(62%-75), mid swing(75%-85%), and terminal swing(85%-100%). An independent t-test was conducted evaluated the means of potential and kinetic energy of the two groups. Especially during fast walking, the walking speed is not significantly different, and the segmental kinetic energy is also not significantly different. In analyzing the energy rate of segments and joints by discussing linear and angular flow individually. For linear energy flow of joints, the linear energy rate for proximal and distal are almost symmetrical to the x-axis, it means that the energy rate of the opposite ends of hip joint are with the same value but different signs. The physical meaning is that the linear energy flow is through the joint, but it does not appear on the overall joint power. Conclusions: The cost for fast walking is pretty higher in elders compared to it of young men. A partial explanation for this may lie in the fact that during walking, elders could not store energy effectively, so they change their strategy of walking and joints should generate additional power, and cause higher mechanical energy cost.