Kiernan Dovin, Miller Ross H, Baum Brian S, Kwon Hyun Joon, Shim Jae Kun
Department of Kinesiology, University of Maryland College Park, 4200 Valley Dr., College Park, MD 20742, United States; Biomedical Engineering Graduate Group, University of California Davis, 350 Howard Way, Davis, CA 95616, United States.
Department of Kinesiology, University of Maryland College Park, 4200 Valley Dr., College Park, MD 20742, United States.
J Biomech. 2017 Jul 26;60:248-252. doi: 10.1016/j.jbiomech.2017.06.019. Epub 2017 Jun 21.
Compared to intact limbs, running-specific prostheses have high resonance non-biologic materials and lack active tissues to damp high frequencies. These differences may lead to ground reaction forces (GRFs) with high frequency content. If so, ubiquitously applying low-pass filters to prosthetic and intact limb GRFs may attenuate veridical high frequency content and mask important and ecologically valid data from prostheses. To explore differences in frequency content between prosthetic and intact limbs we divided signal power from transtibial unilateral amputees and controls running at 2.5, 3.0, and 3.5m/s into Low (<10Hz), High (10-25Hz), and Non-biologic (>25Hz) frequency bandwidths. Faster speeds tended to reduce the proportion of signal power in the Low bandwidth while increasing it in the High and Non-biologic bandwidths. Further, prostheses had lower proportions of signal power at the High frequency bandwidth but greater proportions at the Non-biologic bandwidth. To evaluate whether these differences in frequency content interact with filter cut-offs and alter results, we filtered GRFs with cut-offs from 1 to 100Hz and calculated vertical impact peak (VIP). Changing cut-off had inconsistent effects on VIP across speeds and limbs: Faster speeds had significantly larger changes in VIP per change in cut-off while, compared to controls, prosthetic limbs had significantly smaller changes in VIP per change in cut-off. These findings reveal differences in GRF frequency content between prosthetic and intact limbs and suggest that a cut-off frequency that is appropriate for one limb or speed may be inappropriate for another.
与完整肢体相比，跑步专用假肢具有高共振的非生物材料，且缺乏能衰减高频的活性组织。这些差异可能导致地面反作用力（GRFs）含有高频成分。如果是这样，对假肢和完整肢体的GRFs普遍应用低通滤波器可能会衰减真实的高频成分，并掩盖来自假肢的重要且具有生态效度的数据。为了探究假肢和完整肢体在频率成分上的差异，我们将经胫单肢截肢者和对照组以2.5、3.0和3.5米/秒的速度跑步时的信号功率划分为低（<10Hz）、高（10 - 25Hz）和非生物（>25Hz）频率带宽。更快的速度往往会降低低带宽中信号功率的比例，同时增加高带宽和非生物带宽中的信号功率比例。此外，假肢在高频带宽中的信号功率比例较低，但在非生物带宽中的比例较高。为了评估这些频率成分上的差异是否与滤波器截止频率相互作用并改变结果，我们用1至100Hz的截止频率对GRFs进行滤波，并计算垂直冲击峰值（VIP）。改变截止频率对不同速度和肢体的VIP产生的影响并不一致：更快的速度下，截止频率每变化一次，VIP的变化显著更大，而与对照组相比，假肢肢体截止频率每变化一次，VIP的变化显著更小。这些发现揭示了假肢和完整肢体在GRF频率成分上的差异，并表明适合一个肢体或速度的截止频率可能不适用于另一个。
