The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, GTMI Room 455, 813 Ferst Drive NW, Atlanta, GA, 30332, USA.
The School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA.
Eur J Appl Physiol. 2018 Oct;118(10):2147-2154. doi: 10.1007/s00421-018-3939-3. Epub 2018 Jul 19.
To improve locomotor performance, coaches and clinicians encourage individuals with unilateral physical impairments to minimize biomechanical asymmetries. Yet, it is unknown if biomechanical asymmetries per se, affect metabolic energy expenditure in individuals with or without unilateral impairments during running. Thus, inter-leg biomechanical asymmetries may or may not influence distance-running performance.
We sought to determine whether running with asymmetric step times affects metabolic rate in unimpaired individuals.
Ten unimpaired individuals were instructed to run on a force-measuring treadmill at 2.8 m/s and contact the ground simultaneously to the beat of an audible metronome. The metronome either played at time intervals equal to the respective participant's preferred step times (0% asymmetry), or at time intervals that elicited asymmetric step times between legs (7, 14, and 21% step time asymmetry); stride time remained constant across all trials. We measured ground reaction forces and metabolic rates during each trial.
Every 10% increase in step time and stance average vertical ground reaction force asymmetry increased net metabolic power by 3.5%. Every 10% increase in ground contact time asymmetry increased net metabolic power by 7.8%. More asymmetric peak braking and peak propulsive ground reaction forces, leg stiffness, as well as positive and negative external mechanical work, but not peak vertical ground reaction force, increased net metabolic power during running. Step time asymmetry increases the net metabolic power of unimpaired individuals during running. Therefore, unimpaired individuals likely optimize distance-running performance by using symmetric step times and overall symmetric biomechanics.
我们旨在确定不对称的步时是否会影响正常个体的代谢率。
10 名正常个体被要求在测力跑步机上以 2.8m/s 的速度跑步，并同时按照可听见节拍器的节拍触地。节拍器的时间间隔要么与相应个体的最佳步时相等（0%的不对称），要么在两腿之间产生不同的步时（7%、14%和 21%的步时不对称）；在所有试验中，步长保持不变。我们在每次试验中测量地面反作用力和代谢率。
每增加 10%的步时和站立平均垂直地面反作用力不对称性，净代谢功率增加 3.5%。每增加 10%的着地时间不对称性，净代谢功率增加 7.8%。更大的峰值制动和峰值推进地面反作用力、腿部刚度以及正、负外力功不对称性，但不是峰值垂直地面反作用力增加了跑步时的净代谢功率。步时不对称性增加了正常个体跑步时的净代谢功率。因此，正常个体可能通过使用对称的步时和整体对称的生物力学来优化长跑表现。
