The sport's rules require that a race walker's knees stay straight through most of the leg swing and one foot remain in contact with the ground at all times.
这项运动的规则要求竞走运动员的膝盖在大部分的腿部摆动过程中保持笔直，一只脚始终与地面保持接触。
2
There is one thing I need to estimate first –the area of contact between the ground and the bubble wrap.
当然，还有一件东西是我们必须首先考虑的——那就是地面与汽泡纸接触面的大小。
3
The direct groundcontact protects the Juggernaut from electromagnetic attacks and shield discharges.