If you twist your legs or feet, pointing away from the rest of the body in a position known as plantar flexion, your calf muscles can become shortened.

【分析】句子总体是一个含有条件从句的复合句。

1. pointing away from the rest of the body in a position known as plantar flexion，是现在分词短语，作 twist 的结果状语。

2. known as plantar flexion，是过去分词短语，作 position 的定语。= which is known as plantar flexion

【翻译】如果你扭曲你的腿或脚，指向远离身体其他部位的一个被称为跖屈的位置，那么，你的小腿肌肉就会缩短。