一字步不是一字线，是一足跟着地，再接另一足足尖提起行走．
http://www.daifumd.com/_daifumd/dochome/html/40/articles/art...
2)Mann征：嘱患者足跟接另一足足尖，呈"一"字步站立或行走，共济失调者站立或行走不能，称Mann征阳性。
4)直线步态试验：嘱患者沿某一方向直线行走，共济失调患者行走路径不呈直线。

http://www.mastersofpediatrics.com/cme/cme2005/lecture30_1.a...
＇Normal Heel-Toe Gait

As you can see here, a normal gait is called a heel-toe gait and that means that as one leg swings forward, it lands with the heel on the ground first. Then the body proceeds over that stance phase limb and finally the foot raises up on tip-toe right before it swings forward again. As you can see, when the leg is on tip-toe, the other leg is on heel strike so in normal gait there is never a time when a child should be on tippy-toes bilaterally. ＇