exertion

n. 努力,发挥,运用

Now that I'm 90, I find the exertions of travelling too great.

我已经年届90，出远门已力不从心。

Physical or mental exertion, especially when difficult or exhausting; work.

劳动体力或脑力的运用，尤指出现困难或精疲力尽时；工作