Moore Isabel S, Ashford Kelly J, Cross Charlotte, Hope Jack, Jones Holly S R, McCarthy-Ryan Molly
Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom.
Front Sports Act Living. 2019 Nov 4;1:53. doi: 10.3389/fspor.2019.00053. eCollection 2019.
Trained endurance runners appear to fine-tune running mechanics to minimize metabolic cost. Referred to as self-optimization, the support for this concept has primarily been collated from only a few gait (e.g., stride frequency, length) and physiological (e.g., oxygen consumption, heart rate) characteristics. To extend our understanding, the aim of this study was to examine the effect of manipulating ground contact time on the metabolic cost of running in trained endurance runners. Additionally, the relationships between metabolic cost, and leg stiffness and perceived effort were examined. Ten participants completed 5 × 6-min treadmill running conditions. Self-selected ground contact time and step frequency were determined during habitual running, which was followed by ground contact times being increased or decreased in four subsequent conditions whilst maintaining step frequency (2.67 ± 0.15 Hz). The same self-selected running velocity was used across all conditions for each participant (12.7 ± 1.6 km · h). Oxygen consumption was used to compute the metabolic cost of running and ratings of perceived exertion (RPE) were recorded for each run. Ground contact time and step frequency were used to estimate leg stiffness. Identifiable minimums and a curvilinear relationship between ground contact time and metabolic cost was found for all runners ( = 0.84). A similar relationship was observed between leg stiffness and metabolic cost ( = 0.83). Most (90%) runners self-selected a ground contact time and leg stiffness that produced metabolic costs within 5% of their mathematical optimal. The majority ( = 6) of self-selected ground contact times were shorter than mathematical optimals, whilst the majority ( = 7) of self-selected leg stiffness' were higher than mathematical optimals. Metabolic cost and RPE were moderately associated ( = 0.358 = 0.011), but controlling for condition (habitual/manipulated) weakened this relationship ( = 0.302, = 0.035). Both ground contact time and leg stiffness appear to be self-optimized characteristics, as trained runners were operating at or close to their mathematical optimal. The majority of runners favored a self-selected gait that may rely on elastic energy storage and release due to shorter ground contact times and higher leg stiffness's than optimal. Using RPE as a surrogate measure of metabolic cost during manipulated running gait is not recommended.
训练有素的耐力跑者似乎会微调跑步机制，以将代谢成本降至最低。这种被称为自我优化的概念，其支持证据主要来自少数几个步态特征（如步频、步长）和生理特征（如耗氧量、心率）。为了拓展我们的理解，本研究的目的是考察在训练有素的耐力跑者中，改变地面接触时间对跑步代谢成本的影响。此外，还研究了代谢成本与腿部僵硬度以及主观用力感觉之间的关系。10名参与者完成了5组6分钟的跑步机跑步测试。在习惯跑步过程中确定自选的地面接触时间和步频，随后在接下来的四种情况下，在保持步频（2.67±0.15赫兹）的同时增加或减少地面接触时间。每位参与者在所有测试条件下均采用相同的自选跑步速度（12.7±1.6千米·小时）。用耗氧量来计算跑步的代谢成本，并记录每次跑步的主观用力感觉评分（RPE）。用地面接触时间和步频来估计腿部僵硬度。所有跑者均呈现出可识别的最小值以及地面接触时间与代谢成本之间的曲线关系（R² = 0.84）。在腿部僵硬度与代谢成本之间也观察到类似的关系（R² = 0.83）。大多数（90%）跑者自选的地面接触时间和腿部僵硬度所产生的代谢成本在其数学最优值的5%以内。大多数（n = 6）自选的地面接触时间短于数学最优值，而大多数（n = 7）自选的腿部僵硬度高于数学最优值。代谢成本与主观用力感觉评分呈中度相关（R = 0.358，P = 0.011），但控制测试条件（习惯/改变）后这种关系有所减弱（R = 0.302，P = 0.035）。地面接触时间和腿部僵硬度似乎都是自我优化的特征，因为训练有素的跑者的运行状态处于或接近其数学最优值。大多数跑者倾向于自选的步态，由于地面接触时间比最优值短且腿部僵硬度比最优值高，这种步态可能依赖于弹性储能和释放。不建议在改变跑步步态期间使用主观用力感觉评分作为代谢成本的替代指标。
