他的衣服后背在大火中烧掉了。

The clothing on his back got burnt away in the fire.

《牛津词典》

她的长发瀑布般地倾泻在后背上。

Her hair tumbled in a cascade down her back.

《牛津词典》

转过身去让我看看你的后背。

Turn around and let me look at your back.

《牛津词典》

If possible, your back relaxing against the back rest.

如果可以，后背在靠背上放松。

哈佛公开课 - 幸福课课程节选

It's already been one day and I'm really, really hungry.

现在已经过去一天了，我真是饿得前胸贴后背了。

I'm frustrated 实战 - SpeakingMax英语口语达人

You can see this region here is going to develop into one of the upper limbs, the arms here and the back is different from the front, the spinal cord is developing in the back, whereas, the structures that become our intestinal tract is developing on the other surface.

你能看到这个区域,将会发育成为上肢,这里是手臂,而且身体前后也有不同,脊椎正在后背发育,另外,会成为我们肠管的结构,也在另一个表面发育着

耶鲁公开课 - 生物医学工程探索课程节选