The effect of histamine on changes in mental energy and fatigue after a single bout of exercise

• Histamine H1 binding was tested as a mechanism of post-exercise fatigue reduction.
• H1 receptor antagonism blocked exercise reductions in feelings of mental fatigue.
• Physical energy increased after exercise for both H1 antagonism and placebo.
• Histamine influences exercise-induced fatigue reductions but not energy increases.

The purpose of this research was to determine if histamine, acting on brain H1 receptors, influences changes in feelings of energy and fatigue or cognitive test performance after acute exercise. Women (n = 20) with low vigor and high fatigue were administered the H1 antagonist drug doxepin hydrocholoride (6 mg) in tomato juice and tomato juice alone (placebo) in a randomized, double-blinded, cross-over experiment before performing 30 min of light intensity cycling exercise and completing energy, fatigue, sleepiness, and motivation scales, and cognitive tasks. After exercise, mental fatigue increased for the doxepin condition (p = 0.014) but not placebo (p = 0.700), while mental energy decreased for both PLA and DOX (p < 0.001) and cognitive task performance was unaffected. It is inferred that histamine binding to H1 receptors in the brain has a role in exercise-induced reductions in mental fatigue, but not increases in energy.