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
Puppets need the ground only to glance against lightly, like elves, and through this momentary check to renew the swing of their limbs.
木偶只需在地上轻轻一瞥，就像精灵一样，通过这短暂的停顿，就能使它们的四肢重新摆动起来。
3
Sitting on the swing, he gave the ground a push with one foot.