Alleviating mental fatigue: What works? Original paper

Mental fatigue impairs cognitive and physical performance in a number of settings. Although research has investigated means of counteracting these effects, an overview of these countermeasures is needed.

This systematic review analyzed 33 studies on the effects of behavioral, physiological, and psychological countermeasures on mental fatigue. All of the studies induced mental fatigue using tasks of at least 30 minutes and included placebo or control groups. All study participants were between the ages of 18 and 50.

Multiple studies found that caffeine reduced the symptoms of mental fatigue, both alone and in combination with glucose. The authors of this review noted that 33 mg and 38 mg doses of caffeine combined with glucose were less effective than 46 mg of caffeine with glucose. Higher daily caffeine doses of 200 mg/day for 7 days were also effective. A caffeine and maltodextrin mouth rinse subjectively improved the participants’ experience and task performance.

In addition to caffeine’s effect of blocking adenosine receptors, the taste of caffeine may trigger brain activity that mitigates the effects of mental fatigue. Carbohydrate mouth rinses may cause a similar cascade of activity, and bitter taste receptors may also play a role. Intermittent exposure to a variety of odors (e.g., menthol and floral) also produced positive effects in fatigued participants.

Auditory stimuli, such as music and binaural beats, produced positive effects on experience and performance, while mechanical massage, mild steam bathing, and exposure to a natural environment improved recovery from mental fatigue.

Mindfulness training increases the capacity for self-regulation, eventually leading to reduced fatigue from a given task. However, learning the practice of mindfulness requires some self-regulatory resources, as evidenced by a novice mindfulness group performing worse than a control group on cognitive tasks.

Some studies found that naps and rest periods had positive effects, and light aerobic exercise may aid recovery from mental fatigue. Motivation interventions, such as adding a time-based reward, improved performance despite the participants subjectively still feeling fatigued.

The authors of the review note that the variation in methods of inducing and measuring mental fatigue makes comparisons of countermeasures difficult.