"mental labor" is correct and usable in written English.
You can use it to describe the mental effort that someone has to put into an activity or task. For example, "It took a lot of mental labor to come up with this solution."
There is no strenuous mental labor here.
Of course, that extra mental labor isn't always pleasant.
Do we really need a break from the "hard mental labor" of reading books?
(The name is a slang term for crystal methamphetamine, the most potent in a class of drugs that ease tedious mental labor, dangerously).
So the mental labor of monotheism prepared the Jews — as it would eventually prepare others in the West — to achieve distinction in law, in mathematics, in science and in literary art.
The same is true about the vexing problem of sexual violence at universities — the mental labor of sorting through the obvious right of women to be safe from casual sexual assault, and that of the accused to be free from unsupported accusations — is only now underway.
It meant that the world could be altered by its inhabitants, and that mental labors could have extraordinary consequences.
For anyone who is paid for the publication of their mental labors, the significance of her will is plain: the artist creates an image (virtual or actual) of herself that's out there in the world and that substitutes, in some way, for her actual self.
A beautifully surreal new profile series uses breathtaking visual effects to portray the physical and mental labors of the working creator.
A higher rate of physical labors and a lower rate of mental labors in female patients probably contribute to prevent them from AMI.
In the ≥ 75 years group, the rate of physical labors was significantly higher in female patients (P < 0.01); the rate of mental labors was significantly lower in female patients (P < 0.01).
