Busa Michael A, Lim Jongil, van Emmerik Richard E A, Hamill Joseph
Biomechanics Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America.
Motor Control Laboratory, Department of Kinesiology, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America.
PLoS One. 2016 Jun 7;11(6):e0157297. doi: 10.1371/journal.pone.0157297. eCollection 2016.
Individuals regulate the transmission of shock to the head during running at different stride frequencies although the consequences of this on head-gaze stability remain unclear. The purpose of this study was to examine if providing individuals with visual feedback of their head-gaze orientation impacts tibial and head accelerations, shock attenuation and head-gaze motion during preferred speed running at different stride frequencies. Fifteen strides from twelve recreational runners running on a treadmill at their preferred speed were collected during five stride frequencies (preferred, ±10% and ±20% of preferred) in two visual task conditions (with and without real-time visual feedback of head-gaze orientation). The main outcome measures were tibial and head peak accelerations assessed in the time and frequency domains, shock attenuation from tibia to head, and the magnitude and velocity of head-gaze motion. Decreasing stride frequency resulted in greater vertical accelerations of the tibia (p<0.01) during early stance and at the head (p<0.01) during early and late stance; however, for the impact portion the increase in head acceleration was only observed for the slowest stride frequency condition. Visual feedback resulted in reduced head acceleration magnitude (p<0.01) and integrated power spectral density in the frequency domain (p<0.01) in late stance, as well as overall of head-gaze motion (p<0.01). When running at preferred speed individuals were able to stabilize head acceleration within a wide range of stride frequencies; only at a stride frequency 20% below preferred did head acceleration increase. Furthermore, impact accelerations of the head and tibia appear to be solely a function of stride frequency as no differences were observed between feedback conditions. Increased visual task demands through head gaze feedback resulted in reductions in head accelerations in the active portion of stance and increased head-gaze stability.
尽管在不同步频跑步时个体对头部所受冲击的传递调节情况尚不清楚，但其对头部注视稳定性的影响仍不明确。本研究的目的是检验在不同步频下以偏好速度跑步时，为个体提供其头部注视方向的视觉反馈是否会影响胫骨和头部加速度、冲击衰减以及头部注视运动。在两种视觉任务条件下（有和没有头部注视方向的实时视觉反馈），在五个步频（偏好步频、偏好步频±10%和±20%）下收集了12名休闲跑步者在跑步机上以其偏好速度跑步时的15步数据。主要测量指标包括在时域和频域评估的胫骨和头部峰值加速度、从胫骨到头部的冲击衰减以及头部注视运动的幅度和速度。步频降低会导致早期站立时胫骨垂直加速度更大（p<0.01），以及早期和晚期站立时头部垂直加速度更大（p<0.01）；然而，对于冲击部分，仅在最慢步频条件下观察到头部加速度增加。视觉反馈导致晚期站立时头部加速度幅度降低（p<0.01）以及频域中积分功率谱密度降低（p<0.01），以及头部注视运动总体降低（p<0.01）。当以偏好速度跑步时，个体能够在很宽的步频范围内稳定头部加速度；仅在步频比偏好步频低20%时头部加速度才会增加。此外，头部和胫骨的冲击加速度似乎仅取决于步频，因为在反馈条件之间未观察到差异。通过头部注视反馈增加视觉任务需求导致站立活动部分头部加速度降低，并提高了头部注视稳定性。
