Heels not only have to be the right height but in the right position: not too far back, but under the centre of the heel so they support your weight properly, following the natural line of your body.

鞋跟不仅要有一个合适的高度，也需要在正确的位置上：不能太靠后，要在脚后跟的中心，这样的鞋跟才能沿着你的身体曲线有效地支持你的体重。

youdao

If your foot points down, you need to measure the distance between the top of your big toe and an imaginary line from the bottom of your heel.

如果你的脚底朝下，那么你需要测量你的脚后跟到你大脚趾所在垂线的最短距离。

youdao

With your leg stretched out in front of you and the knee supported, make an imaginary line from the heel to the ground.

将你的腿前向伸展，膝盖绷紧，作一条从脚后跟到地面的垂线。

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Wales became penned back in their own half because of their other Achilles' heel - the line-out.

BBC: Wales fail to buck losing trend against Boks

Cameron Jerome twice came close to pulling one back for Birmingham but first he saw an effort hit the bar and then a back heel cleared off the line by Keogh.

BBC: Birmingham 0-2 Wolves

Melchiot was denied a 25th-minute opener when Giles Barnes appeared to clear the defender's five-yard back-heel from behind the goal-line.

BBC: Wigan 2-0 Derby