疾病逐渐削弱了他的力气。用英语怎么说？

疾病逐渐削弱了他的力气。

Illness undermined his strength.

illness

n. 疾病，某种具体疾病，不健康；

例句
Although his mental illness had coincided with his war service it had not been caused by it...
虽然他的精神病刚好在他参战期间发作，但并不是由此引起的。

undermined

adj. 潜行的；v. 在某物下挖洞或挖通道( undermine的过去式和过去分词 )，侵蚀…的基础，暗中破坏，逐渐削弱；

例句
The authority of his voice is undermined by the smallness of his build.
瘦小的身形削弱了他声音中的权威感。

his

pron. (he的所有格)他的，(he的物主代词)他的东西；det. 属于他的，用于名词前，自己的，指某人的，上帝的；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

strength

n. 力量，优点，长处，（光、声、色等的）力度，人力[数]；

例句
Roland was taken aback by our strength of feeling...
我们反应如此强烈，令罗兰大吃一惊。