Exertion

The tremendous exertions which I have gone through during the last day or two have worn me out. Not so much bodily exertion, you understand, as the strain upon the mind. You will appreciate that, Mr. Sherlock Holmes, for we are both brain-workers.

Source: tatoeba (6310021)

After much exertion, he was exhausted.

Source: tatoeba (11535887)

Researchers at the University of California San Diego have designed what they’re calling a biobattery in the form of a temporary tattoo. The battery works by “detecting and responding to lactate,” which is found in sweat. When your body needs more energy because of physical exertion, a process called glycolysis occurs. Glycolysis basically turns sugars into usable energy for the body. A byproduct of this process is lactate.

Source: tatoeba (12216195)

Again she felt a return of that utter despondency which had fallen upon her after Guido's death: but then she could indulge in it unmolested, and that was something of relief: now she was forced into exertion, that sort of exertion of all the most tiresome, because the least interesting...

Source: wiktionary