Did you slow down after several lifts because of the ache in the mental muscle?

But he found himself using unfamiliar mental muscles when he thought about 'they'.

Mentally I was stronger than he, for he had been long alone, and mental muscles can be exercised only on another mind.

The shift forced him to exercise some different mental muscles.

My mind developed pockets of resistance, mental muscles, auxiliary storage areas.

The mental, as well as physical, muscles must be exercised.

He hadn't the mental or emotional muscle to sustain extended use of the Power.

Designing and maintaining a city is a task that exercises all the mental muscles.

The cigarette was for practice, to stretch the mental muscles.

"The other side of the argument is that you build mental muscles by struggling and then succeeding," he said.