可以這麼說但也不完全是。「無法或沒有使出全力」是比較好的解釋。「心有餘而力不足」意謂有心想要做得更好，但是你問的這句英文並沒有這個意涵；也許他們本來就不想要使出全力。也許你會覺得這是雞蛋裡挑骨頭但我回答都盡量精準一點。 The sentence means that they are working with a disadvantage or unable to perform at their best. 心有餘而力不足 implies that they have the intention to perform better; without more context, the sentence you asked about simply says that they are "unable" to perform at their best, and doesn't specify their intention. Splitting hair, I know, but I do think there is a difference. The phrase "one arm tied behind one's back" is more often used say that something is very easy to do, sometimes with a note of contempt. For example, I can bake a cake with one arm tied behind my back means that I can bake a cake very easily. "One's hands are tied" is another similar phrase that you may want to remember together. It means that you can't do anything about a situation because something prevents you from acting freely. For example, I wish I can help you but my hands are tied.