Wang Y, Pascoe D D, Weimar W
Department of Physical Therapy, Georgia State University, Atlanta 30303, USA.
Ergonomics. 2001 Jul 15;44(9):858-69. doi: 10.1080/00140130118572.
This investigation evaluated accumulated mean and peak impact forces per stride and per metre associated with two book backpack loads and two cadences during single and double support phases of walking. Thirty college participants randomly performed three trials while either walking a self-selected cadence or fixed cadence without (empty pack) or with a load (15% body mass) carried in a bookbag. The fixed cadence (55.5 steps/min) was regulated by a metronome. A computerized Kistler force platform system (phase-locked timing device) recorded (200 Hz) three-dimensional reaction forces, impulses, and time in single and double support phases. A Panasonic video camera AG-450 was set perpendicular to the plane of walking motion to film (60 Hz) the walking pattern from which stride length and selected kinematic data were determined. Repeated measure ANOVA (p<0.05) determined differences of loads and cadences in walking. Accumulated force was evaluated as impulses per stride and impulses per metre (stress index). When carrying the 15% load, there was a decrease in speed, a decrease in single support time (SST), and an increase in double support time (DST). The impulses per stride significantly increased in DST, and significantly decrease in SST. When impulses were analysed per metre, the stress index signficantly increased in DST, but not during SST. These differences in SST may be important when load stress is applied to the single support leg/foot in any given distance of walking. While stride analysis identifies accumulative forces resulting from varying stride lengths, the stress index provides a standardized measure per metre of the accumulative forces that negate the variances of individual stride lengths, and the index measure can easily represent data for any given distance traversed.
本研究评估了在步行的单支撑和双支撑阶段，与两种书包负荷及两种步频相关的每一步幅和每一米的累积平均冲击力和峰值冲击力。30名大学生参与者随机进行了三项试验，分别是以自我选择的步频或固定步频（55.5步/分钟，由节拍器调节）行走，且行走时不背负书包（空背包）或背负相当于体重15%的负荷。一个计算机化的奇石乐测力平台系统（锁相计时装置）以200赫兹的频率记录单支撑和双支撑阶段的三维反作用力、冲量和时间。一台松下AG-450摄像机垂直于行走运动平面设置，以60赫兹的频率拍摄行走模式，从中确定步幅长度和选定的运动学数据。重复测量方差分析（p<0.05）确定了行走中负荷和步频的差异。累积力被评估为每步幅的冲量和每米的冲量（应力指数）。背负15%的负荷时，速度降低，单支撑时间（SST）减少，双支撑时间（DST）增加。双支撑阶段每步幅的冲量显著增加，单支撑阶段则显著减少。当按每米分析冲量时，双支撑阶段应力指数显著增加，但单支撑阶段未增加。在任何给定步行距离内，当负荷应力施加于单支撑腿/脚时，单支撑时间的这些差异可能很重要。虽然步幅分析可识别因步幅长度变化产生的累积力，但应力指数提供了每米累积力的标准化测量值，消除了个体步幅长度差异的影响，且该指数测量值可轻松表示任何给定行走距离的数据。
