A college student deep into studying for a big exam might do well to give his brain a break.

Just what he does during that break will determine how helpful that pause will be, a growing body of research shows. A stroll in the park could do wonders, for instance, while downing coffee could leave him just as stressed and depleted as before the break. And, sometimes, forcing oneself to simply power through mental fatigue can be more effective than pausing.

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