Introduction

Continuous exercise can produce a transient state of euphoria – an emotional state involving the experience of pleasure and feelings of profound contentment, elation, and well-being – which is colloquially known as a “runner’s high” in distance running or a “rower’s high” in rowing.

Outline

The runner’s high is a transient state of euphoria coupled with lessened feelings of anxiety and a higher pain threshold, which can come either from continuous moderate physical exertion over time or from short bursts of high-intensity exercise. The exact prevalence is unknown, but it seems to be a relatively rare phenomenon that not every athlete experiences. The name comes from distance running, and it is alternatively called “rower’s high” in rowing.

Mechanism of Action

Current medical reviews indicate that several endogenous euphoriants are responsible for producing exercise-related pleasurable feelings, specifically phenethylamine (an endogenous psychostimulant), β-endorphin (an endogenous opioid), and anandamide (an endogenous cannabinoid). However, more recent studies suggest that endorphins have a limited role in the feelings of euphoria specifically related to the runner’s high due to their inability to cross the blood-brain barrier, placing more importance in the endocannabinoids instead, which can cross this barrier.

β-Phenylethylamine

β-Phenylethylamine, commonly referred to as phenethylamine, is a human trace amine and potent catecholaminergic and glutamatergic neuromodulator that has similar psychostimulant and euphoriant effects and a similar chemical structure to amphetamine. Thirty minutes of moderate to high intensity physical exercise has been shown to induce an enormous increase in urinary β-phenylacetic acid, the primary metabolite of phenethylamine. Two reviews noted a study where the average 24 hour urinary β-phenylacetic acid concentration among participants following just 30 minutes of intense exercise increased by 77% relative to baseline concentrations in resting control subjects; the reviews suggest that phenethylamine synthesis sharply increases while an individual is exercising, during which time it is rapidly metabolized due to its short half-life of roughly 30 seconds. In a resting state, phenethylamine is synthesized in catecholamine neurons from L-phenylalanine by aromatic amino acid decarboxylase (AADC) at approximately the same rate at which dopamine is produced.

In light of this observation, the original paper and both reviews suggest that phenethylamine plays a prominent role in mediating the mood-enhancing euphoric effects of a runner’s high, as both phenethylamine and amphetamine are potent euphoriants.

β-Endorphin

β-Endorphin (contracted from “endogenous morphine”) is an endogenous opioid neuropeptide that binds to μ-opioid receptors, in turn producing euphoria and pain relief. A meta-analytic review found that exercise significantly increases the secretion of β-endorphin and that this secretion is correlated with improved mood states. Moderate intensity exercise produces the greatest increase in β-endorphin synthesis, while higher and lower intensity forms of exercise are associated with smaller increases in β-endorphin synthesis. A review on β-endorphin and exercise noted that an individual’s mood improves for the remainder of the day following physical exercise and that one’s mood is positively correlated with overall daily physical activity level.

However, humans studies showed that pharmacological blockade of endogenous endorphins does not inhibit a runner’s high, while blockade of endocannabinoids may have such an effect.

Anandamide

Anandamide is an endogenous cannabinoid and retrograde neurotransmitter that binds to cannabinoid receptors (primarily CB1), in turn producing euphoria. It has been shown that aerobic exercise causes an increase in plasma anandamide levels, where the magnitude of this increase is highest at moderate exercise intensity (i.e. exercising at ~⁠70⁠–-80⁠% maximum heart rate). Increases in plasma anandamide levels are associated with psychoactive effects because anandamide is able to cross the blood-brain barrier and act within the central nervous system. Thus, because anandamide is a euphoriant and aerobic exercise is associated with euphoric effects, it has been proposed that anandamide partly mediates the short-term mood-lifting effects of exercise (e.g. the euphoria of a runner’s high) via exercise-induced increases in its synthesis.

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