Wilson Taylor J, Mangalam Madhur, Stergiou Nick, Likens Aaron D
Division of Biomechanics and Research Development, Department of Biomechanics, Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE, United States.
Department of Physical Education and Sport Science, Aristotle University, Thessaloniki, Greece.
Front Netw Physiol. 2023 Oct 19;3:1294545. doi: 10.3389/fnetp.2023.1294545. eCollection 2023.
The seemingly periodic human gait exhibits stride-to-stride variations as it adapts to the changing task constraints. The optimal movement variability hypothesis (OMVH) states that healthy stride-to-stride variations exhibit "fractality"-a specific temporal structure in consecutive strides that are ordered, stable but also variable, and adaptable. Previous research has primarily focused on a single fractality measure, "monofractality." However, this measure can vary across time; strideto-stride variations can show "multifractality." Greater multifractality in stride-tostride variations would highlight the ability to tune and adjust movements more. We investigated monofractality and multifractality in a cohort of eight healthy adults during self-paced walking and running trials, both on a treadmill and overground. Footfall data were collected through force-sensitive sensors positioned on their heels and feet. We examined the effects of self-paced walking vs. running and treadmill vs. overground locomotion on the measure of monofractality, α-DFA, in addition to the multifractal spectrum width, W, and the asymmetry in the multifractal spectrum, W, of stride interval time series. While the α-DFA was larger than 0.50 for almost all conditions, α-DFA was higher in running and locomoting overground than walking and locomoting on a treadmill. Similarly, W was greater while locomoting overground than on a treadmill, but an opposite trend indicated that W was greater in walking than running. Larger W values in the negative direction suggest that walking exhibits more variation in the persistence of shorter stride intervals than running. However, the ability to tune and adjust movements does not differ between treadmill and overground, although both exhibit more variation in the persistence of shorter stride intervals. Hence, greater heterogeneity in shorter than longer stride intervals contributed to greater multifractality in walking compared to running, indicated by larger negative W values. Our results highlight the need to incorporate multifractal methods to test the predictions of the OMVH.
看似周期性的人类步态在适应不断变化的任务约束时会表现出步幅间的变化。最优运动变异性假说（OMVH）指出，健康的步幅间变化呈现出“分形性”——连续步幅中的一种特定时间结构，这些步幅有序、稳定但也具有可变性和适应性。先前的研究主要集中在单一的分形性度量“单分形性”上。然而，这种度量可能随时间变化；步幅间变化可能表现出“多分形性”。步幅间变化中更大的多分形性将突出更强的调整和调节运动的能力。我们在一组八名健康成年人中，对在跑步机上和户外进行的自定步速行走和跑步试验中的单分形性和多分形性进行了研究。通过放置在他们脚跟和脚底的力敏传感器收集落地数据。除了步幅间隔时间序列的多分形谱宽度W和多分形谱中的不对称性ΔW之外，我们还研究了自定步速行走与跑步以及跑步机与户外运动对单分形性度量α-DFA的影响。虽然在几乎所有条件下α-DFA都大于0.50，但在户外跑步和运动时的α-DFA高于在跑步机上行走和运动时的α-DFA。同样，在户外运动时的W大于在跑步机上运动时的W，但相反的趋势表明，行走时的W大于跑步时的W。负方向上更大的W值表明，与跑步相比，行走在较短步幅间隔的持续性方面表现出更多变化。然而，尽管在较短步幅间隔的持续性方面两者都表现出更多变化，但在跑步机和户外之间调整和调节运动的能力并无差异。因此，与跑步相比，较短步幅间隔比较长步幅间隔更大的异质性导致行走中出现更大的多分形性，这由更大的负W值表明。我们的结果强调了纳入多分形方法以检验OMVH预测的必要性。
