Mechanical power and efficiency of level walking with different stride rates
Mechanical power and efficiency of level walking with different stride rates
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DOI：
10.1242/jeb.000950
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发表时间：
2007-09-15
影响因子：
2.8
通讯作者：
Martin, Philip E.
中科院分区：
文献类型：
--
作者：
Umberger, Brian R.;Martin, Philip E.
步行的人更喜欢使用代谢能量消耗率最低的步幅。机械功率需求被认为是新陈代谢反应的基础，但据报道，在步幅比首选值低 20-30% 时，机械功率是最小的。这可能是由于总机械功率计算方式的限制，以及未能考虑肌肉工作的效率。我们研究了步行时机械功率和效率如何取决于步幅，这两个量都是根据髋关节、膝关节和踝关节力矩所做的功计算得出的。我们的假设是，机械功率和效率均在首选步速下得到优化，这可以解释为什么代谢能量消耗在此步速下最小化。与我们的假设相反，机械功率曲线表现出跨步率低于首选的平台（预测最佳值：比首选低 11-12%），而净机械效率则表现出跨步率高于首选的平台（预测最佳值：比首选高 8%）。正如预期的那样，首选步速（54.3 步数分钟（-1））与最小化净代谢能量消耗的步速（预测最佳值：比首选高 0.2%）没有什么不同。鉴于机械功率和机械效率在首选步速的两侧表现出稳定状态，步行的首选步速可能代表这两个因素之间的折衷。这也可以解释代谢率曲线在首选步幅附近的相对平坦度。
Walking humans prefer to use the stride rate that results in the lowest rate of metabolic energy expenditure. Mechanical power requirements have been suggested to underlie the metabolic response, but mechanical power is consistently reported to be minimal at stride rates 20-30% lower than preferred. This may be due to limitations in how total mechanical power has been computed, as well as a failure to account for the efficiency with which muscular work is done. We investigated how mechanical power and efficiency depend on stride rate in walking, with both quantities computed from the work done by the hip, knee and ankle joint moments. Our hypotheses were that mechanical power and efficiency are both optimized at the preferred stride rate, which would explain why metabolic energy expenditure is minimized at this rate. Contrary to our hypotheses, mechanical power curves exhibited plateaus that spanned stride rates lower than preferred ( predicted optima: 11-12% below preferred), while net mechanical efficiency exhibited a plateau that spanned stride rates higher than preferred ( predicted optimum: 8% above preferred). As expected, preferred stride rate (54.3 strides min(-1)) was not different from the stride rate that minimized net metabolic energy expenditure ( predicted optimum: 0.2% above preferred). Given that mechanical power and mechanical efficiency exhibited plateaus on opposite sides of the preferred stride rate, the preferred rate in walking likely represents a compromise between these two factors. This may also explain the relative flatness of the curve for metabolic rate in the vicinity of the preferred stride rate.