Santello M, McDonagh M J
Applied Physiology Research Unit, School of Sport & Exercise Sciences, University of Birmingham, Birmingham B15 2TT, UK.
Exp Physiol. 1998 Nov;83(6):857-74. doi: 10.1113/expphysiol.1998.sp004165.
The control of self-initiated falls from different heights was studied. The objective of the study was to investigate in a quantitative manner the modulation of EMG timing (i.e. onset from take-off and duration from onset to touch-down) and amplitude (before and after foot contact) as a function of fall height. The muscles studied were m. soleus and m. tibialis anterior. Kinematic (ankle joint angle) and kinetic (ground reaction force) variables were also measured. Six subjects took part in the experiments that consisted of ten landings from each of five heights (0.2, 0.4, 0.6, 0.8 and 1 m) onto a force platform. We found a consistent pattern of co-contraction before and after touch-down across the fall heights studied. In both muscles, the onset of pre-landing EMG activity occurred at a longer latency following take-off when landing from greater heights. The absolute EMG duration was affected to a lesser extent by increasing fall height. These findings suggest that the onset of muscle activity of the muscles studied prior to foot contact is timed relative to the expected time of foot contact. Pre- and post-landing EMG amplitude tended to increase with height. Despite a doubling in the magnitude of ground reaction force, the amplitude of ankle joint rotation caused by the impact remained constant across heights. These findings suggest that the observed pattern of co-contraction is responsible for increasing ankle joint stiffness as fall height is increased. The attainment of an appropriate level of EMG amplitude seems to be controlled by (a) timing muscle activation at a latency timed from the expected instant of foot contact and (b) varying the rate at which EMG builds up.
对从不同高度自行跌倒的控制进行了研究。该研究的目的是以定量方式研究肌电图（EMG）时间调制（即从起跳开始到着地持续时间）和幅度（足部接触前后）作为跌落高度的函数。所研究的肌肉为比目鱼肌和胫骨前肌。还测量了运动学（踝关节角度）和动力学（地面反作用力）变量。六名受试者参与了实验，实验包括从五个高度（0.2、0.4、0.6、0.8和1米）中的每个高度向测力平台进行十次着陆。我们发现在所研究的跌落高度范围内，着地前后存在一致的共同收缩模式。在这两块肌肉中，从较高高度着陆时，着陆前肌电图活动的起始在起跳后出现的潜伏期更长。绝对肌电图持续时间受跌落高度增加的影响较小。这些发现表明，在所研究的肌肉中，足部接触前肌肉活动的起始是相对于预期的足部接触时间进行计时的。着陆前和着陆后肌电图幅度倾向于随高度增加。尽管地面反作用力的大小增加了一倍，但撞击引起的踝关节旋转幅度在不同高度上保持恒定。这些发现表明，观察到的共同收缩模式导致随着跌落高度增加踝关节刚度增加。肌电图幅度达到适当水平似乎受以下因素控制：（a）在从预期足部接触瞬间计时的潜伏期激活肌肉；（b）改变肌电图增强的速率。
